NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

National Research Council (US) Committee on Medical and Biological Effects of Environmental Pollutants. Arsenic: Medical and Biologic Effects of Environmental Pollutants. Washington (DC): National Academies Press (US); 1977.

Cover of Arsenic

Arsenic: Medical and Biologic Effects of Environmental Pollutants.

Show details

3Distribution of Arsenic in the Environment

NATURAL SOURCES

Earth's Crust

Arsenic ranks twentieth among the elements in abundance in the earth's crust. The abundance of arsenic in the continental crust of the earth is generally given as 1.5–2 ppm. Thus, it is relatively scarce. Nevertheless, it is a major constituent of no fewer than 245 mineral species. Arsenic is found in high concentration in sulfide deposits, where it is present as the native element or alloys (four minerals), arsenides (27 minerals), sulfides (13 minerals), sulfosalts (sulfides of arsenic with metals, such as lead, copper, silver, and thallium, 65 minerals), and the oxidation products of the foregoing (two oxides, 11 arsenites, 116 arsenates, and seven silicates). Of these minerals, arsenopyrite is by far the most common. In addition, many sulfides contain appreciable amounts of arsenic in solid solution; the most important of these is pyrite, which has a maximal arsenic content of about 5% (common range, 0.02–0.5%). The arsenic-bearing sulfides and sulfosalts oxidize readily; under surface conditions, oxidation proceeds to arsenic trioxide and to the arsenate stage.

Igneous and Sedimentary Rock

Concentrations of arsenic in igneous rocks are listed in Table 3-1. No trend of concentration is apparent with respect to content of silica or other major elements. The limited data available indicate rather uniform distribution of arsenic among the major constituent minerals, except for slight enrichment in the sulfide minerals of igneous rocks.

TABLE 3-1. Arsenic in Igneous Rocks .

TABLE 3-1

Arsenic in Igneous Rocks .

Data on the concentration of arsenic in sedimentary rocks are summarized in Table 3-2. Shales, clays, phosphate rocks, and sedimentary iron and manganese oxides are notably enriched in arsenic. The data of Tourtelot 794 indicate that most of the arsenic in nonmarine clays and shales is associated with the clay minerals, whereas a considerable proportion of the arsenic in offshore marine samples is present as pyrite. Tourtelot, Schultz, and Gill 795 found a correlation between the arsenic and organic carbon concentrations. A similar correlation was observed by Ruch, Kennedy, and Shimp 689 for unconsolidated sediments of Lake Michigan; they attributed this arsenic to man's activities—the arsenic content in surface sediments (0–6 cm) averaged more than twice that at depths greater than 20 cm (12.4 vs. 5.3 ppm).

TABLE 3-2. Arsenic in Sedimentary Rocks .

TABLE 3-2

Arsenic in Sedimentary Rocks .

It should be noted that a higher than average content of arsenic is commonly found in sandstones, shales, and coals associated with uranium mineralization in Utah, Colorado, Wyoming, and South Dakota; this suggests considerable mobility of arsenic.

High concentrations of arsenic (maximum, 2,100 ppm; average, 115 ppm; median, 60 ppm) have also been noted in sediments from the area of hot brines in the Red Sea. 345 , 408

Most of the analyses for phosphorites 316 , 797 are related to samples from the United States (Table 3-3). There is considerable variation in arsenic content, even from a single area, and no correlations with concentrations of phosphorus pentoxide, organic matter, or other major constituents are proved. Gulbrandsen 316 suggested a correlation of arsenic with organic matter for the phosphorites of the Phosphoria Formation (Montana, Wyoming, and Idaho); Stow 764 found no such correlation for Florida land-pebble phosphate, but found a positive correlation with iron content. The available analyses have been made on whole rock; consequently, correlations of arsenic with other constituents can be made with confidence only if the purified phosphate mineral and associated clay material are determined. It would be especially desirable to conduct such studies on samples of high arsenic content.

TABLE 3-3. Arsenic in Phosphorites.

TABLE 3-3

Arsenic in Phosphorites.

Soil

Arsenic is present in all soils, and the geologic history of a particular soil determines its arsenic content. 308 The natural arsenic content in virgin soils varies from 0.1 to 40 ppm. The average is about 5–6 ppm, but it varies considerably among geographic regions. 159 Soils overlying sulfide ore desposits commonly contain arsenic at several hundred parts per million; the reported maximum is 8,000 ppm. This arsenic may be present in unweathered sulfide minerals or in an inorganic anion state. The most common sulfide is arsenopyrite, although arse nosulfides of almost any metal cation can be found. Inorganic arsenate may be bound to iron and aluminum cations or oxides or to any other cation present (such as calcium, magnesium, lead, and zinc).

Arsenic may also be bound to the organic matter in soils, in which case it is released into the soil solution as the organic matter is oxidized and is then available for plant uptake or fixation by soil cations. 675 Some arsenic from other inorganic forms is also available for plant uptake, inasmuch as the slightly soluble iron and aluminum arsenates and the soil solution are in equilibrium. The amount released for plant uptake is a function of the particular chemical and physical forms of individual arsenic compounds. The amount of available arsenic (extracted with 0.05 N hydrochloric acid and 0.025 N sulfuric acid) is small in virgin soils and averages about one-tenth of the total arsenic present in most cultivated soils. 159,308,311

Water

The cycle of arsenic in natural waters has recently been reviewed by Ferguson and Gavis. 249 Data on the arsenic content of waters and sediments are summarized in Table 3-4 and Table 3-5. Sugawara and Kanamori 768 showed that the ratio of As(V) to total arsenic was close to 0.8 : 1 in ocean water. Braman 97 reported ratios of 0.56 : 1 and 0.81 : 1 for a tidal flat and saline bay water, respectively. He also found that As(III), methanearsonic acid, and cacodylic acid were present. The ratio of As(V) to As(III), based on thermodynamic calculations, should be 1026 : 1 for oxygenated seawater at a pH of 8.1. In reality, it is 0.1 : 1 to 10 : 1. This unexpectedly high As(III) content is caused, at least in part, by biologic reduction in seawater. 393 The content of arsenic in seawater is a small fraction (perhaps 0.1%) of the amount calculated to have been carried into the sea. Nearly all the arsenic has been precipitated or adsorbed on marine clays (probably most important), phosphorite, and hydrous oxides of iron and manganese. The scavenging of arsenic from solution by coprecipitation with hydrous oxides of iron and manganese in laboratory experiments is well known, but its occurrence in natural waters has not been studied in detail. Moenke 551 noted that spring waters (pH, 5.1) of high arsenic content precipitated about 80% of their arsenic in iron-rich sediments within 160 m of the source of entry.

TABLE 3-4. Arsenic in Fresh Waters.

TABLE 3-4

Arsenic in Fresh Waters.

TABLE 3-5. Arsenic in Sediments.

TABLE 3-5

Arsenic in Sediments.

The high content of arsenic in hot springs is notable; fumarolic gases have been reported to contain arsenic at up to 0.7 ppm. Extremely high arsenic concentrations have been reported in some groundwaters from areas of thermal activity, 312 , 448 from areas of rocks with high arsenic content, 86 , 294 , 883 and in some waters of high dissolved-salt content. 478 , 851 Most of the other high values reported in rivers and lakes and in sediments (Table 3-4 and Table 3-5) are probably due to industrial contamination. Angino and others 18 have shown that household detergents (mostly of the high-phosphate type) widely used in the United States contained arsenic at 1–73 ppm; their use probably contributes significant amounts of arsenic to surface waters. Sollins, 751 however, felt that, after dilution during use, the concentration would be well below the recommended maximum and constitute no particular hazard. It has been generally assumed that surface waters, like the ocean, are “self-purifying” with respect to arsenic—i.e., that the arsenic is removed from solution by deposition with sediments; but quantitative studies are lacking. Sediments are always higher in arsenic than the waters with which they are associated.

The data on ground waters are inadequate. About 3% of the analyses show arsenic at more than 50 ppb, the 1962 maximal permissible concentration in drinking water. 808 , 813 In view of recent reports of chronic arsenic poisoning attributed to the use of such waters in Chile 86 and in Oregon, 294 further study is imperative. The volcanic rocks from which the arsenic-rich waters come in Oregon are of a type that is common in the western United States. 262

Plants

Arsenic is ubiquitous in the plant kingdom. Its concentration varies from less than 0.01 to about 5 ppm (dry-weight basis). Appendix A lists the arsenic concentrations of some plants and plant products. Differences in arsenic content probably reflect species differences in plants and, in a larger sense, environmental and edaphic factors in a particular geographic region. Plants growing in arsenic-contaminated soils generally have higher residues than plants grown in normal soils. Arsenic concentrations are less than 5.0 ppm (dry wt) or 0.5 ppm (fresh wt) for untreated vegetation, whereas treated plants may have much higher concentrations. However, values for some nontreated plants are as high as or higher than those for plants that were treated with arsenic or grown in arsenic-contaminated soil. Natural variations among plants, plant species, available soil arsenic, and growing conditions are all responsible in part for these discrepancies. There appears to be little chance that animals would be poisoned by consuming plants that contain arsenic residues from contaminated soils, because plant injury occurs before toxic concentrations could appear.

Marine plants, particularly algae and seaweed, may have extremely high arsenic contents. In 11 varieties of British seaweed examined, a range of 5.2 ppm (in Chondrus crispus) to 94 ppm (in Laminaria digitata) was recorded. 398 In green algae, the amount of arsenic varied inversely with the apparent chlorophyll content, from 0.05 to 5.0 ppm on a dry-weight basis. 519 For brown algae, values of around 30 ppm have been reported.

Animals and Humans

Arsenic is present in all living organisms (Appendix B). Marine fish may contain up to 10 ppm; coelenterates, some mollusks, and crustaceans may contain higher arsenic concentrations. Freshwater fish contain up to about 3 ppm, although most values are less than 1 ppm. Domestic animals and man generally contain less than 0.3 ppm on a wet-weight basis. The total human body content varies between 3 and 4 mg and tends to increase with age. With the exception of hair, nails, and teeth, analyses have revealed that most body tissues contain less than 0.3 ppm.

The median arsenic content in 1,000 samples of human hair was 0.51 ppm, as determined by neutron-activation analysis. 743 The median concentrations for males and females were 0.62 and 0.37 ppm, respec tively. Arsenic content of hair has served as an indicator in incidents of suspected poisoning. Values greater than about 2–3 ppm indicate possible poisoning, although higher concentrations have been recorded in occupational surveys. For example, a survey of workers in a copper processing plant in Czechoslovakia showed mean arsenic contents of 178 ppm in 21 persons exposed to air containing arsenic trioxide at 1.01–5.07 mg/m3 and 56.6 ppm in 18 persons exposed to air containing 0.08–0.18 mg/m3; a control (nonexposed) group had 0.149 ppm. 651 In such occupational surveys, it is important to distinguish between exogenous arsenic from atmospheric pollution and cosmetics and that from ingestion. Nail clippings from a patient with acute polyneuritis from arsenic poisoning contained arsenic at 20–130 ppm. 818 The normal arsenic content of nails is 0.43–1.08 ppm. 380

The arsenic content of urine can vary normally from 0.1 to 1.0 ppm. Great daily variations exist and depend on the amount of arsenic in various foodstuffs. It is generally high after consumption of seafood. When arsenic is ingested, the amount excreted increases over several days to a maximum and then declines to normal.

Some of the highest concentrations of arsenic in biota are encountered in marine organisms. The average arsenic content of freshwater fish—including shad, gar, carp, bullhead, pickerel, bluegill, black bass, white bass, buffalo, and horned dace—varied up to 2.1 ppm. 233 The average oil content of these fish was only 2.49%, but the oil carried 22.8% of the total arsenic present. The arsenic in the liver oil of the large-mouthed black bass averaged 30 ppm. These values are generally lower than those reported for marine fish, which range up to 32.4 ppm for cod. Shrimp contain arsenic at 3.8–128 ppm on a dry-weight basis. 172 A survey of canned seafood showed the following arsenic concentrations: clams, 15.9 ppm; oysters, 16.0 ppm; smoked oysters, 45.8 ppm; lobsters, 22.1 ppm; and shrimp, 19.9 ppm. 203

Air

Trace amounts of arsenic may be present in air. Although no 24-h maximal atmospheric concentration has been set in the United States, 3 µg/m3 has been recommended in the U.S.S.R. and Czechoslovakia. 676 The threshold limit recommended for industrial workers is 500 µg/m3 for arsenic and its compounds and 200 µg/m3 for arsine. 425 Exposure standards for inorganic arsenic have recently been proposed by the Occupational Safety and Health Administration. 809 They limit air concentration to “4 µg As/m3 of air averaged over an eight hour period.” A ceiling limit of 10 µg/m3 is proposed for any 15-min period during a work shift.

Data on emission of arsenic to the atmosphere have been summarized by Sullivan 770 and by Davis and Associates 196 and are discussed at the end of this chapter. Arsenic content in air and dust is summarized in Table 3-6. In areas remote from industrial contamination, air concentrations of arsenic generally are less than 0.02 µg/m3, whereas in urban areas they vary from less than 0.01 to 0.16 µg/m3. Two of the air values reported as “United States, Miscellaneous” were 2.50 µg/m3 in Anaconda, Montana, in 1961–1962 (the maximum) and 1.40 µg/m3 in El Paso, Texas, in 1964. 770

TABLE 3-6. Arsenic in Air and Dust.

TABLE 3-6

Arsenic in Air and Dust.

MAN-MADE SOURCES

Production

Data on domestic and world production, imports, and domestic consumption of arsenic from 1964 to 1973, as shown in Table 3-7, were obtained from the Bureau of Mines, Minerals in the U.S. Economy. 811 Much of the arsenic processed in the United States is imported in copper ore and concentrates. An equal amount is imported as arsenic compounds. Agriculture is the largest user of arsenic, accounting for about 80% of the demand. Figure 3-1 indicates sources of arsenicals by country and type of material in 1973. Table 3-8, Table 3-9, and Table 3-10 show U.S. imports for consumption of white arsenic (arsenic trioxide), U.S. imports of arsenicals by class, and world production of white arsenic. 812

TABLE 3-7. Arsenic Supply–Demand Relationships, 1964-1973 (Short Tons).

TABLE 3-7

Arsenic Supply–Demand Relationships, 1964-1973 (Short Tons).

FIGURE 3-1. Arsenic supply–demand relationship.

FIGURE 3-1

Arsenic supply–demand relationship. Reprinted from Minerals in the U.S. Economy, Bureau of Mines, 1975.

TABLE 3-8. U.S. Imports of Arsenic Trioxide, by Country.

TABLE 3-8

U.S. Imports of Arsenic Trioxide, by Country.

TABLE 3-9. U.S. Imports of Arsenicals, by Class.

TABLE 3-9

U.S. Imports of Arsenicals, by Class.

TABLE 3-10. World Production of Arsenic Trioxide.

TABLE 3-10

World Production of Arsenic Trioxide.

In the United States, arsenic is produced entirely as a by-product of the smelting of nonferrous-metal ores. Domestic production of arsenic has been adversely affected since the 1920's, when very large quantities of imported by-product arsenic became available from a copper mine in Sweden whose ore contained a high proportion of arsenic. The demand for arsenic was reduced after World War II by the advent of organic substances developed during and after the war that were used as pesticides and for other purposes for which arsenic had previously been used. The resulting surplus of by-product arsenic kept the price of white arsenic (77% arsenic metal) at 6.25–6.75 cents/lb (13.8–14.9 cents/kg) from July 1968 through 1973. However, in early 1974, the price increased to 13 cents/lb (28.7 cents/kg).

Arsenic is a troublesome contaminant in ores. Some arsenic compounds volatilize during smelting and must be removed from smelter exhaust gases. Its presence in metals reduces electric conductivity and malleability to below commercial specifications for most uses. The cost of removing arsenic during smelting and refining exceeds its value. Arsenic was last produced for its own value during World War II, when military uses increased demand and supplies from Sweden were interrupted. Substantial resources of high-grade arsenic ore are available in the United States, in case arsenic production again becomes necessary.

Arsenic is present in appreciable amounts in many lead–zinc and copper ores; therefore, emission of arsenic may be a problem at any smelter treating such ores. However, the only U.S. plant recovering arsenic from those ores is a copper smelter in Tacoma, Washington. This facility is equipped to smelt copper ores and concentrates containing a considerable proportion of arsenic and to complete smelting of intermediate products—such as flue dust, speiss, and various residues of high arsenic content—received from other smelters.

At the Tacoma plant, the high-arsenic ores and concentrates treated usually contain 3–15% arsenic, and the speiss and flue dust 5–30% or even more. The charge is first roasted with reducing fluxes to drive off as much arsenic as possible. Fluxing is necessary to ensure vaporization of arsenic, because arsenic pentoxide forms stable arsenates with common metallic oxides. Pyrite, galena, or carbonaceous material added to the charge reduces the pentoxide to trioxide, which sublimes at 193° C. The arsenic compounds are collected in cooling flues or chambers, where the temperatures of the gas and vapor are controlled. They enter the first chamber at approximately 220° C; by the time the gas and vapor reach the last chamber, they have been cooled to 100° C or less. The condensed crude product is 90–95% arsenic trioxide. Exhaust from the cooling flues passes through baghouses and Cottrell precipitators to remove any remaining arsenic trioxide or other dust. The calcine, now low in arsenic, is smelted for copper and other metals. The impure trioxide is resublimed and recondensed to remove impurities, until a product with the required purity is obtained. 746 , 812

The arsenic-containing ore from U.S. mines received at Tacoma originates mainly in the Butte, Montana, and Coeur d'Alene, Idaho, districts. However, most of the arsenic feed material comes as concentrates from foreign mines for treatment at the Tacoma copper smelter or is an intermediate product from the treatment of ores at other U.S. smelters.

Since 1971, federal and state regulations have been adopted that will greatly limit atmospheric discharges of particulate matter and sulfur from metal smelters, power generating stations, and other industrial plants. Large construction programs were in progress during 1974 at nearly all nonferrous smelters and at most coal-fired electric generating plants to install equipment that will remove about 99% of the particulate matter from smelter exhausts and will treat all stack gases in acid plants or other sulfur-removing facilities to lower the sulfur content of the final discharge to a harmless concentration. As larger percentages of particulate matter and sulfur dioxide are removed from effluent gases, so also should the amount of arsenic emitted be lowered.

Uses

Approximately 97% of the arsenic produced enters end-product manufacture in the form of white arsenic, and the remaining 3% as metal for metallurgic additives in special lead and copper alloys. 812

In an expanding agricultural market, agricultural uses accounted for about 81% of total consumption of arsenic in 1973 (Table 3-7). Arsenic trioxide is the raw material for arsenical pesticides, including lead arsenate, calcium arsenate, sodium arsenite, and organic arsenicals. These compounds are used in insecticides, herbicides, fungicides, algicides, sheepdips, wood preservatives, and dyestuffs and for the eradication of tapeworm in sheep and cattle.

Insecticides

The names, uses, and toxic dosages of several important arsenical pesticides are listed in Table 3-11. Compounds like Paris green (copper acetoarsenite) used to be popular insecticides in orchards, but are of minor importance today. 787 Likewise, lead arsenate and calcium arsenate have been used extensively in the United States for insect control on fruits, tobacco, cotton, and some vegetables, but current use is slight. The U.S. Department of Agriculture (USDA) used to be responsible for registering arsenical pesticides; today, all uses of arsenical pesticides for crop protection are registered by the Environmental Protection Agency.

TABLE 3-11. Names and Properties of Some Important Arsenical Pesticides.

TABLE 3-11

Names and Properties of Some Important Arsenical Pesticides.

Lead arsenate was first used about 1892. 787 It has been used chiefly for controlling codling moths, weevils, grasshoppers, Japanese beetles, cankerworms, leaf rollers, tomato fruitworms, bud worms, scale, plum curculio, cabbageworms, potato bugs, and tobacco hornworms. Lead arsenate is a stomach poison, with very little contact activity when used on chewing insects. Calcium arsenate is more effective than lead arsenate in combating the cotton bollworm. 451

Pesticides related to lead arsenate include lead arsenite, used to a limited extent as an insecticide and fungicide; lead m-arsenate; and monolead o-arsenate and trilead arsenate, used as insecticides.

Magnesium arsenate was first used as an insect stomach poison on the Mexican bean beetle around 1920–1930, but its use is now very limited. Zinc arsenate has been used as an insecticide since about 1920 and controls many of the same pests as lead arsenate. It has been used in place of lead arsenate, because it leaves no lead residue. Compounds related to zinc arsenate used as pesticides include zinc fluoroarsenate, to control codling moths, and zinc m-arsenite, used to a limited extent as a wood preservative. Zinc arsenite has been used as an insecticide against chewing insects since about 1900, mainly on potatoes; it is too phytotoxic to use on orchards, bush crops, or other forage crops.

Sodium arsenite came into use as an insecticide between 1920 and 1930, mainly as a bait and as a livestock dip. As an insecticide, it must be used very carefully because of its extreme phytotoxicity; consequently, it is applied around the base of plants to prevent contact with the foliage. As a cattle dip, it is used to control ticks, fleas, and lice. Unfortunately, many children and domestic animals have been harmed accidentally by sodium arsenite.

The USDA took action to reduce the hazards from some arsenical pesticides intended for use in and around homes. In a press release dated November 24, 1967, the USDA proposed to decrease the percent age of sodium arsenite and arsenic trioxide in products for home use. Specifically, the following actions were recommended: products containing more than 2.0% sodium arsenite or 1.5% arsenic trioxide would not be registered for use around the home, and labels for arsenical products registered for agricultural, commercial, or industrial use would be required to display prominently the statements “Do not use or store in or around the home” and “Do not allow domestic animals to graze treated area.” A press release dated July 17, 1969, gave notice that these restrictions were put on arsenical products for home use.

Herbicides

The inorganic arsenicals, primarily sodium arsenite, have been widely used since about 1890 as weedkillers, particularly as nonselective soil sterilants. 178 Consequently, sodium arsenite found use around military and commercial installations—along roadsides and on railroad rights-of-way. Its use for the control of crabgrass (Digitaria sanguinalis) expanded rapidly from only a few hundred tons a year in the early 1950's to 5,000 tons (4,536 tonnes) in 1959.

The use of organic arsenical herbicides—MSMA (monosodium methanearsonate), DSMA (disodium methanearsonate), and cacodylic acid—has grown rapidly in the last decade. MSMA and DSMA have been used as selective herbicides for the postemergence control of crabgrass, Dallisgrass (Paspalum dilatatum), and other weedy grasses in turf. 4 They are currently used extensively as selective postemergence herbicides in cotton and noncrop areas for the control of Johnsongrass (Sorghum halepense), nutsedge (Cyperus spp.), watergrass, sandbur (Cenchrus spp.), foxtail (Echinochloa spp.), cocklebur (Xanthium spp.), pigweed (Amaranthus spp.), and grasses in noncrop areas.844DSMA was first used for cotton weed control in 1961 to enhance the activity of another herbicide, 3′,4′-dichloro-2-methylacrylanilide. 786 In 1963, 71,000 acres (about 29,000 ha) in Mississippi were treated with DSMA as a directed spray, and more than 329,000 acres (about 133,000 ha) were treated in 1964. 534

The need for the selective herbicides for cotton production in the United States is particularly critical. 265 Johnsongrass, a hardy perennial species, is extremely difficult to control 427 , 545 and is estimated to infest approximately 4.3 million acres (about 1.74 million hectares) of cotton-producing soils. The methanearsonates are selective economic herbicides for Johnsongrass control. 321 , 322 , 323 , 324 Unfortunately, no complete estimates are available on the amounts of MSMA and DSMA being used in the United States. In 1969, Baker et al. 46 estimated that the annual use in the United States ranged from 6,000 to 8,000 tons (5,400 to 7,300 tonnes). An informal survey conducted by the National Cotton Council from reports submitted by different state specialists resulted in an estimate of 4.5 million acres (1.82 million hectares) that received MSMA and DSMA salts. 579 Assuming two applications of 2 lb/acre (2.2 kg/ha), an estimate of 9,000 tons (8,200 tonnes) of MSMA and DSMA would appear to be reasonable. It must be emphasized that these are only estimates. Nevertheless, they do indicate that substantial amounts of these organic arsenicals are finding widespread use in major cotton-growing regions. The National Cotton Council's survey also indicated that severe economic repercussions would be felt in the American cotton industry if these substances were lost to the farmer, because of losses in yield due to weed competition. 579 In 1972, it is estimated that 9,500 tons (8,600 tonnes) of MSMA was consumed in the United States. 829

Cacodylic acid is a contact herbicide that will defoliate or desiccate a wide variety of plant species. It has been used as a crop destruction agent (Agent Blue) in South Vietnam. Cacodylic acid is not registered for use on agricultural commodities. It is registered as a silvicide (forest pesticide) and for lawn renovation.

Desiccants

Arsenic acid is used extensively as a cotton desiccant in the Black Prairie of Texas, the rolling plains of Oklahoma and Texas, and the high plains of Texas. The use of arsenic acid as a cotton desiccant began about 1955. The use of desiccants has increased rapidly in these cotton-growing regions, owing to the widespread use of mechanical pickers. About 85% of the treated acreage is in Texas. In 1971, over 98% of the U.S. cotton crop was harvested by machines. There are two types of mechanical harvesters—the cotton picker and the cotton stripper. Desiccants are used to prepare cotton plants for stripper harvesting by depleting the leaves and other plant parts of moisture. The reduction in moisture improves harvesting efficiency and prevents degradation of fiber quality that results from leaf staining. In addition, the earlier harvest results in less insect damage and lower insecticide use. Because of the lower harvesting costs, cotton harvest by stripping is rapidly expanding. In Texas, about 75% of the cotton was machine-stripped and about 25% machine-picked in 1970.

It was reported that 2,500 tons (2,300 tonnes) of arsenic was used as desiccants on 1,222,000 acres (about 495,000 ha) of U.S. cotton in 1964. In 1971, it is estimated that Texas alone treated over 2,000,000 acres (about 810,000 ha) with arsenic acid as a desiccant. Arsenic acid is applied once at a rate equivalent to 1.5 quarts (0.0014 m3) of 75% o-arsenic acid per acre. This rate of application represents a maximum of about 4.5 lb (2.0 kg) of the actual technical chemical per acre during any one season. On the basis of figures for Texas in 1971, this would amount to over 4,500 tons (4,100 tonnes) of arsenic acid used as a desiccant.

Wood Preservatives

Compared quantitatively with the organic liquid wood preservatives (pentachlorophenol and creosote), arsenic is of less importance. The use of the principal wood preservatives in the United States in 1968–1973 is shown in Table 3-12. Use of chromated copper arsenate has increased threefold in that period. Pentavalent arsenic compounds are used alone or mixed with other substances. Lansche has summarized the uses of some of the compounds, including Wolman salts (25% sodium arsenate) and Osmosalts (25% sodium arsenate). 451 There are three “Bolidensalts” (which probably derived their name from the Boliden mining operation in Sweden), including the following tradename products: Bolidensalt BIS, Bolidensalt BIS Copperized, and Bolidensalt K33. The zinc and chromium arsenates are used in a water solution in wood preservative plants and are applied to wood under vacuum and pressure. They are precipitated in the wood fibers, making the treated wood resistant to leaching.

TABLE 3-12. Use of Principal Wood Preservatives, United States.

TABLE 3-12

Use of Principal Wood Preservatives, United States.

Feed Additives

Four organic arsenicals (arsanilic acid, 3-nitro-4-hydroxyphenylarsonic acid, 4-nitrophenylarsonic acid, and 4-ureidophenylarsonic acid, or carbarsone), all substituted phenylarsonic acids, have qualified for feed-additive use under the Food Additive Law of 1958 (see Chapter 5). A food-additive petition demonstrating safety and efficacy of each is on record with the Food and Drug Administration (FDA). Drug combinations that include one of the arsenicals require separate petitions. These are to be found in the Federal Register and in the Feed Additive Compendium, a Miller Publishing Co. adjunct to Feedstuffs, a news journal for the feed industry. 587 Three of the pentavalent organic arsenicals were marketed in the early 1950's and described in an FDA-sponsored symposium. 274 The discussion also included the coccidiostat, arsenosobenzene, a trivalent organic arsenical (later abandoned with the advent of the Food Additive Law). The arsenical feed additives were further discussed in a second symposium on drugs in feeds sponsored by the National Academy of Sciences. 628 The recommended uses and safety considerations are discussed in Chapter 5 of the present report.

Less arsenic is used in feed additives than in pesticides, defoliants, or herbicides. In a typical year, the following are manufactured or sold: arsanilic acid, 1,360 tonnes; carbarsone, 450 tonnes; 3-nitro-4-hydroxyphenylarsonic acid, 900 tonnes; and combinations, 450 tonnes.

Concern was expressed about the fate of the various arsonic acids excreted by animals. Although these have been shown to undergo no degradation or only minor structural alteration before excretion, it is not known to what extent they accumulate in poultry litter or manure. Morrison reported that commercial use of 3-nitro-4-hydroxyphenylarsonic acid yielded arsenic at 15–30 ppm in the litter, but the con centrations of arsenic in the poultry tissues and feathers were not high. 562 Indeed, the tissue concentrations in birds raised on the litter did not appear to differ from those in birds raised on wire. At the recommended fertilization rate for poultry litter, 4–6 tons/acre (0.002–0.003 kg/ha), the addition of arsenic to soil was calculated as 1–2 ppm per year. The arsenic concentrations of soil, cover crops, and alfalfa crops fertilized for up to 20 years with arsenical poultry litter were not increased. Drainage water after 20 years of such fertilization was reported to contain arsenic at 0.29 ppm.

Drugs

Inorganic arsenic compounds have been used in medicine since the dawn of history and have been claimed to be effective in many diseases or where a tonic was indicated. The introduction of Salvarsan (arsphenamine) by Ehrlich at the turn of the century gave rise to intense activity on the part of the organic chemists, and it is estimated that more than 32,000 arsenic compounds were synthesized.

These drugs were active primarily against the parasites causing syphilis, yaws, relapsing fever, trichomonal vaginitis, trypanosomiasis, and amebic dysentery. With the advent of penicillin, the use of these drugs has been largely discontinued, although some are still in common use. (Some of these compounds have been reintroduced for other purposes—e.g., as feed additives and herbicides—and their dosages when used as drugs should be recalled when their toxicity for man and animals is considered.) Sodium cacodylate was used as a tonic and given by injection (because of its poor absorption when given orally) at 0.03–0.10 g every 2–3 days. It often produced the odor of garlic in the urine, breath, and sweat. DSMA (then called Arrhenal) was used for the same purpose and in the same dosage. The phenylarsonate Atoxyl (sodium arsanilate) was once used hypodermically in trypanosomiasis at 0.03–0.06 g/day.

The following drugs are in current use in human and veterinary medicine:

  • Glycobiarsol 278 —used in intestinal amebiasis, trichomoniasis, and moniliasis; toxicity rare, because only 4% is absorbed.
  • Carbarsone—used in intestinal amebiasis in man 278 and blackhead in turkeys 849 and chickens; 623 toxicity rarely reported; lacks effect on optic nerve reported for other p-NH2 arsenobenzenes.
  • Melarsoprol—used in trypanosomiasis 278 , 512 and filariasis; 22 , 518 occasional reactive encephalitis, usually fatal.
  • Tryparsamide—used in syphilis and trypanosomiasis with cerebral involvement;278,512 can cause retinitis with optic atrophy.
  • Neoarsphenamine—used in eperythrozoonosis of swine and Spirillum minus infections (rat-bite fever) in man.512
  • Dichlorophenarsine—used in dirofilariasis (heartworm infection) in dogs.402,442
  • Caparsolate—used in filariasis in dogs214,386,611,612 and lungworm infection in dogs.206,611,612
  • Lead arsenate—used in monieziasis in sheep and goats.512
  • Melarsonyl—used in filariasis in dogs221 and trypanosomiasis.278

War Gases and Riot-Control Agents

The war gas lewisite was used in World War I and was highly effective in producing casualties, because it caused skin lesions that were difficult to heal.

Arsenic compounds are still in use that are less toxic than lewisite but that are highly irritating to the skin, eyes, and respiratory tract, thereby causing dermal pain, lacrimation, sneezing, and vomiting. (The commonly used tear gas and mace apparently are not arsenicals, but alkylating agents related to chloroacetophenone.) Information on these compounds, both chemical and pharmacologic, is difficult to obtain, because research data on them are classified or for other reasons.283 Some such compounds are listed in Table 3-13. Ruchhoft et al.690 were interested in the possibility that the use of these compounds would contaminate city water supplies, and they studied some of them with that possibility in mind. Rothberg680 was interested in the possibility that these compounds could cause sensitization and tested the alkylating agents CS (O-chlorobenzilide malononitrile), CN (α-chloroacetophenone), and BBC (α-bromotolunitrile) and the arsenical compound DM (phenylarsazine chloride) in guinea pigs. He found that CS and CN caused sensitization, but that DM and BBC did not.

TABLE 3-13. Arsenic Compounds Used or Developed for Use as Chemical-Warfare or Riot-Control Agents.

TABLE 3-13

Arsenic Compounds Used or Developed for Use as Chemical-Warfare or Riot-Control Agents.

In summary, several arsenical compounds are available for use as riot-control agents that act as severe irritants to the skin and mucus membranes. Information about their other pharmacologic and toxicologic effects is not available in the literature.

Other Minor Uses

Because of its semimetallic properties, arsenic has metallurgic applications as an additive metal. Addition of 0.5–2% to lead improves the sphericity of lead shot. The addition of up to 3% arsenic to lead-base bearing alloys improves their mechanical properties, particularly at high temperatures. A small amount of arsenic is added to lead-base battery grid metal and cable sheathing to increase their hardness.

Addition of smaller amounts of arsenic improves the corrosion resistance and raises the recrystallization temperature of copper. At 0.15–0.50%, it improves the high-temperature properties of copper parts used for locomotive staybolts, firebox straps, and plates. At 0.02–0.05%, it minimizes or prevents dezincification of brass. It has been claimed that small additions of arsenic to brass minimize “season cracking” (failure of stressed material in a corrosive environment).

High-purity arsenic (exceeding 99.999%) is used in semiconductor technology. This material may be produced from the reduction of purified arsenic compounds, such as arsenic trioxide and arsenic trichloride, with hydrogen or the thermal dissociation of arsine. Specifically, it is used to make gallium arsenide, which is used in such semiconductor devices as diodes, transistors, and lasers. Indium arsenide is used for infrared detectors and in Hall effect applications. Small quantities are also used as a dopant in germanium and silicon devices. High-purity arsenic trichloride and arsine are used in the production of epitaxial gallium arsenide. A series of low-melting-point glasses containing high-purity arsenic have been developed for semiconductor and infrared applications.

Nearly all glass contains arsenic as an additive. It aids in the formation of glass and is a fining agent for removing gases, an oxidizing–reducing agent, and a decolorizing agent. The arsenic content of glass is normally 0.2–1%.

Arsenic is also used as a catalyst in the hydrogenation–cracking of hydrocarbons in the presence of olefins, in the manufacture of paper pulp and chloromethylsilane, in the oxidation of propene to acrolein, and in the ozonization of cyanides. Arsenic finds use in the Giammarco–Vetrocoke hydrogen sulfide removal process for treating coke-oven gas, synthesis gas, and high-pressure gas streams. 510 Alkaline arsenites and arsenates are used to react with hydrogen sulfide and absorb it from gas.

Residues

Arsenic, which occurs ubiquitously in nature, may also enter the biosphere through unintended contamination from industrial activity or through desired use, e.g., as a pesticide, medicine, or feed additive. Some of the arsenic is easily recycled in nature (that from pesticides, medicines, etc.), but other arsenic (such as that used as additives in metal and glass) is not easily recycled. The following sections discuss the residues that occur in the biosphere as a result of man's activity.

Soils

Soils are usually contaminated with arsenic through the use of pesticides, although some contamination occurs from smelting operations, burning of cotton wastes, and fallout from the burning of fuel. An excellent review of arsenic behavior in soil has recently been published. 837 Arsenic in the environment can undergo oxidation, reduction, methylation, and demethylation in soil.

Large residues have been found on orchard soils that received 30–60 lb of lead arsenate per acre (34–67 kg/ha) per year from pesticide applications, which began in the early 1900's. The soils have therefore received 1,800–3,600 lb of lead arsenate per acre (2,020–4,035 kg/ha). This is equivalent to an arsenic concentration of 194–389 ppm, if the arsenate remains in the top 6 in. (15.24 cm) of soil. Arsenic was accumulated at up to 2,500 ppm in a fine soil. 877 It contained high concentrations of hydrous iron and aluminum oxides or their cations. Little arsenic accumulates in sandy soils that are low in available iron and aluminum compounds. Soils removed from orchard production after these concentrations of arsenic are reached are generally phytotoxic, although the toxicity may decrease with time. 822 If a tree is to be replanted in areas with such concentrations, the soil may be excavated and replaced by new soil to promote growth.

High-arsenic soil may be toxic to plant life. 181 However, different soils with the same total arsenic content do not have the same toxicity to plants, 7 unless they have similar contents of iron, aluminum, organic matter, and phosphate and similar pH and unless the plants grown on them are under the same environmental stresses. Woolson et al. 876 have shown that various chemical forms of arsenic have different phytotoxicities. Thus, soils with high concentrations of easily soluble arsenic (soils low in reactive iron and aluminum) will be more toxic to plants than soils with low concentrations of easily soluble arsenic, although the total arsenic contents may be similar. Because plants growing in high-arsenic soils have very little growth, human consumption of high arsenic residues through the plant food chain is unlikely. Plant growth is reduced as arsenic content increases. 28 , 71 For instance, a total arsenic content of about 300 ppm equivalent to extracted available arsenic at about 30 ppm in an average soil will reduce growth of many crops by about 50%. Seedlings shown to contain arsenic at 15 ppm on a dry-weight basis have suffered a 50% reduction in growth; this is equivalent to about 1.5 ppm on a flesh-weight basis, which is below the tolerances set by the FDA for arsenic in fruits. Sensitive crops, such as green beans, are adversely affected by extracted available arsenic at as low as 5 ppm. 873

The use of different fertilizer materials and fertilization practices also influences the soluble arsenic content of soils and the arsenic content of the harvested crop. 757 A high phosphate application to soils receiving arsenicals increases the arsenic content of corn foliage, but apparently not of corn seed. Schweizer 715 showed the effects of phosphate fertilization on DSMA residues with cotton bioassay. The toxicity depended on the amount of phosphate applied and on the soil type. Phosphate fertilizers may contain arsenic at up to 1,200 ppm, but at normal application rates, “it seems highly improbable that the arsenic in domestic phosphate fertilizer exerts any toxic effects, even with very large annual applications of the fertilizer over extended periods of time.” 797

Arsenic may be leached downward in sandy soils. In heavier soils, little leaching is likely. 530 High phosphate contents and excess phosphate fertilization increase the rate of arsenic leaching. Arsenate in solution at saturation follows the order: sodium arsenate > calcium arsenate (10−5 M) > aluminum arsenate (10−7 M) > iron arsenate (10−9 M). 151 , 152 Thus, the more soluble arsenates (sodium and calcium) will leach from a soil more readily than the less soluble (aluminum and iron) forms. When a soil was subjected to leaching conditions with potassium biphosphate, the percentage of aluminum arsenate (extractable with 0.5 N ammonium fluoride) decreased and percentage of the more insoluble iron arsenate (extractable with 0.1 N sodium hydroxide) increased. 878 Thus, the arsenic that remains after phosphate treatment and subsequent leaching is itself less phytotoxic.

Total soil arsenic does not accurately reflect the form that is available to plants. Arsenic phytotoxicity decreases in this order: water-soluble > calcium arsenate ≃ aluminum arsenate > iron arsenate. Toxicity is probably related to the solubility constant of the individual compound. Extractants used to test for available nutrients (Bray P-1, 0.5 N sodium bicarbonate, and a mixed acid—0.05 N hydrochloric acid + 0.025 N sulfuric acid) more accurately reflect amounts of arsenic that are available for uptake at the root surface. Extractable arsenic at 5 ppm is toxic to sensitive species.

The behavior of the organoarsenic herbicides in soil has been reviewed by Hiltbold. 354 The organoarsenic herbicides are used in foliar treatment at lower rates than the inorganic arsenic insecticides. Methanearsonic acid (MAA) and its salts (MSMA and DSMA) are selective herbicides used to control specific weeds. Cacodylic acid is a general contact desiccant used to defoliate or destroy unwanted vegetation.

Organic aliphatic arsenic compounds behave very much like the inorganic arsenic salts in soil. 395 The methanearsonic acids are fixed in soil and are only gradually leached through the soil profile. 204 , 355 Both the amount and rate of leaching are increased when soil is coarse and its reactive iron and aluminum content is low. Cacodylic acid is likewise fixed by iron and aluminum in the soil, although not as strongly as inorganic arsenate or MAA. Metabolism of organic arsenicals occurs in soil with inorganic arsenate as the major metabolite under aerobic conditions. A volatile organoarsenic compound, possibly dimethylarsine (cacodyl hydride), is generated in soil under both aerobic and anaerobic soil conditions from cacodylic acid. 412 , 879 Trimethylarsine has also been isolated above grass. 97 Residue accumulation in cotton soils should be slower than that in orchard soils, because less arsenic is applied with the organic arsenicals (1–2 ppm) than was applied with lead arsenate (3.3–6.6 ppm). In addition, the aliphatic arsenicals are reduced to arsines more readily than is arsenate and will be lost from the site of application as a gas.

Large accumulations occur around smelters. 541 A survey of the Helena Valley indicated that soil samples collected from the upper 10.2 cm within 1.6 km of the smelter stack contained arsenic at up to 150 ppm. The arsenic content decreased with distance from the stack for a distance of 8–16 km. A calculated total of 780 tonnes of arsenic has been added to the soil at a distance of 1.07–16 km from the stack during 80 years of operation. Accumulations up to 380 ppm occurred around the Tacoma smelter. 188

It should be noted that continued additions of arsenicals, regardless of the source, may result in soils that are too toxic to support some forms of plant life. The constant turnover of organic matter and the resulting microbial reduction and volatilization (see Figure 3-2) will tend to reduce high concentrations of arsenicals. This will result in a reduction in toxicity. Arsenicals will accumulate in soil when greater amounts are added than are removed in harvested plants, through volatilization, and through leaching.

FIGURE 3-2. A proposed arsenic cycle.

FIGURE 3-2

A proposed arsenic cycle. 1, the cycle in nature involves organic arsenicals; few identified. 2, marine algae may contain arsenic at up to 9 ppm, land plants generally at less than 0.5 ppm. 3, edible tissues of food animals contain, on average, below (more...)

Water

As noted earlier, arsenic is found in all waters. The U.S. Geological Survey reported that 79% of 727 samples examined from across the United States contained arsenic at less than 10 µg/liter (the 1962 recommended drinking-water concentration), 21% at greater than 10 µg/liter, and 2% at greater than 50 µg/liter (the 1962 maximal allowable arsenic content for drinking water). 224 The highest concentration (1,100 µg/liter) was found in South Carolina in a sample downstream from an industrial complex in North Carolina that contained an arsenical-producing company. At the next sampling station downstream, the concentration was 10 µg/liter. The EPA has recently published primary interim standards for drinking water. The maximal allowable arsenic content remains 50 µg/liter. 811

Arsenic can be removed from industrial waste by several methods before the waste is discharged into the water system. Among the methods reported are precipitation by calcium oxide and ferric chloride, basic anion-exchange resins, passage through lime and ashes, and flocculation with chlorine-saturated water and ferrous sulfate.

Questions have been raised over the arsenic added to the environment through phosphate detergents. Angino found that water treated with cold lime contained arsenic at 0.4 ppb. 18 Water at the intake contained 2.6–3.6 ppb before treatment. The arsenic in water returned to the Kansas River after sewage treatment ranged from 1.5 to 2.1 ppb, which is lower than the concentration at the intake. Angino felt that arsenic in detergents added significant quantities of arsenic to the river system; others have felt that there was little danger. 622 , 751

Most arsenic in water is added through industrial discharges. The highest concentrations, other than those occurring naturally in spring waters, are usually in areas of high industrial activity.

Rivers seem to be self-cleansing relative to soluble arsenic. The arsenic concentration in solution decreases with the distance from the source of pollution. Arsenic decreased to background concentrations in river waters 400–1,300 m from the source of pollution. However, the rate of disappearance was a function of stream characteristics. Arsenates and arsenites presumably form insoluble salts with cations in the water and settle out in the sediments of these rivers. Arsenic was detected at 75 ppm in sediments of polluted waterways, compared with 11 ppm in clean waterways.

Endemic contamination of freshwater supplies has been reported in Argentina, Reichenstein, Silesia, and Antofagasta, Chile. In Silesia, the contamination arose through leaching of arsenic wastes from mining operations into spring water. In Chile, arsenic in drinking water decreased from 800 ppb to 30 ppb after the installation of a water-treatment plant. 86 In New Zealand, dairy cattle have been poisoned by arsenic in mineral springs. Wells in Lane County, Oregon, were contaminated with arsenic naturally and had high pH and high sodium and bicarbonate contents. 294

Concentrations found in water, ice, and oceans are presented in Table 3-4. Waters with known contamination are generally high in arsenic, although many waters not contaminated by man are also high in arsenic. The latter are generally alkaline, with very high sodium and bicarbonate contents. Mud downstream from a source of contamination may also contain high concentrations of arsenic residues.

Plants

Plants are affected by arsenic applied intentionally as pesticides and accidentally from smelter fallout. The effects are usually dose-related, but are strongly modified by a host of variables, including plant species, geographic region, soil type, and climatic conditions. Two important dose-related effects measurable in plants are arsenic residues and phytotoxicity.

The detailed studies have been conducted on paired crop soil residues in tobacco. Arsenicals were removed in 1952 from the list of recommended insecticides for control of hornworms on tobacco (the arsenic insecticide had been added directly to the leaf), and a sharp decrease in the arsenic content of cigarettes was later reported. The concentration of arsenic in the cured leaf of field-grown tobacco was generally less than 2 ppm where no arsenic was applied to soils. In general, there was an increase in arsenic content in tobacco with increasing rates applied to soils, but this response is greatly modified by soil type. The previous use of arsenic pesticides in tobacco had been challenged as a possible health hazard. It was proposed that tobacco can be expected to contain high concentrations of arsenic because of absorption from soil. Results of Small and McCants appeared to refute this hypothesis. 738 In an extensive survey of arsenic residues in soils and in cured leaves collected from major flue-cured tobacco-producing regions of North Carolina, soil arsenic concentrations ranged from 1 to 5 ppm (average, 2.8 ppm), and leaf residues, from 0.5 to 3.5 ppm (average, 1.5 ppm). The arsenic content of these soils appears to be within the natural limits for virgin soils, and that of the resulting leaves, within natural background limits. Apparently, previous arsenic spray applications had not contributed significantly to soil residues. With low concentrations of arsenic in soils, soil type and other variables may be more important in determining plant arsenic content than small increases in soil arsenic concentration.

Vegetables do not have significant arsenic content when grown in soils containing high concentrations of applied arsenic trioxide. 532 Soils in New Jersey were subjected to applications of lead arsenate at 250, 500, and 1,000 lb/acre (280, 560, and 1,121 kg/ha), and vegetables grown in these soils were analyzed for arsenic (Table 3-14). Arsenic uptake varied between plant species and increased with increasing amounts of applied arsenic. No plants exceeded tolerance limits where limits existed. Soils around smelters contain high concentrations of arsenic. 185 , 541 This results in vegetation with increased arsenic content. 357 In the East Helena area, arsenic was found at 0.05 ppm or less in apples, kohlrabi, onions, radishes, and string beans and at up to 3.3 ppm in fresh sunflower leaves. Residues in field crops varied from 0.05 ppm or less in wheat to 14.3 ppm in fresh barley straw. For this type of contamination, the amount of arsenic present decreases in the order of pasture grasses, alfalfa, garden plants, and small grains.

TABLE 3-14. Arsenic Content of Vegetables Grown in Soils Treated with Lead Arsenate.

TABLE 3-14

Arsenic Content of Vegetables Grown in Soils Treated with Lead Arsenate.

There is no correlation between the selenium and arsenic contents of soils and those of plants growing in the soils. 600 The arsenic content of seleniferous soils from South Dakota varied from 7.1 to 18.4 ppm, and the selenium content, from 1.15 to 5.00 ppm. With a few exceptions, however, indigenous plants contained more selenium than arsenic. The selenium content of plants varied from 0 to 266.7 ppm, and the arsenic content, from 1 to 4.2 ppm.

It is important to note the large variability in the relationships among soil arsenic content, plant arsenic content, injury symptoms, and phytotoxicity reported by different investigators. Vandecaveye et al. 817 reported that alfalfa and grasses grown on a soil having soluble arsenic at less than 2.5 ppm contained arsenic at 20–30 ppm on a dry-weight basis. MacPhee et al. 509 analyzed pea and bean plants grown in pesticide-persistence plots at Kentville, Nova Scotia. The soil plots contained arsenic at 126–157 ppm. Most of the arsenic in the plants was found in vines (2.1 ppm) and pods (0.88 ppm), with small amounts in seeds (0.18 ppm). Reed and Sturgis analyzed rice plants grown on arsenic-treated soils. 662 They reported arsenic at up to 5.0 ppm in the rice head and 2.5 ppm in the straw. Woolson 873 correlated extractable arsenic with plant growth and plant residues for six vegetable crops. Available arsenic concentrations of 6.2–48.3 ppm were necessary to reduce growth by 50%. At these concentrations, edible dry plant contained arsenic at 0.7–76.0 ppm.

There is evidence in the literature of beneficial effects on plant growth from relatively high arsenic concentrations in soils. Stewart and Smith 759 found that a concentration of 25 ppm in soils enhanced the growth of peas, radishes, wheat, and potatoes, whereas beans showed a steady decrease in growth when the arsenic content increased. MacPhee et al. 509 reported an increase in turnip yields with a total arsenic content of 150 ppm in soils. This effect was attributed to control of the turnip root maggot. However, there was a yield decrease in other crops tested, including peas and beans. A beneficial effect on several crops was noted when fields were treated with high concentrations of calcium arsenate. The concentrations of total arsenic in soil where yield decreases were first noted for vetch, oats, and barley were 94, 188, and 283 ppm, respectively (calcium arsenate applied at 500, 1,000, and 1,500 lb/acre, or 560, 1,121, and 1,681 kg/ha). 163 When arsenic applied was below these toxic concentrations, the soils treated with calcium arsenate yielded more than the untreated soils. For example, the yields of rye from soil treated with calcium arsenate at 188 ppm (1,000 lb/acre, or 1,121 kg/ha) were greater than the yields from the same soil if untreated. Wheat yields were increased at 1,131 ppm (6,000 lb/acre, or 6,725 kg/ha), the highest concentration used. In another soil type, corn, sorghum, soybeans, and cotton showed yield increases from applications of 188 ppm (1,000 lb of calcium arsenate per acre, or 1,121 kg/ha). 164

The increasing use of the methanearsonate herbicides MSMA and DSMA to control weeds in cotton has led to an extensive survey of cottonseed for arsenic residues. Possible sources of methanearsonates for human consumption, owing to their use in cotton, are cottonseed flour and cottonseed oil and, indirectly, milk, meat, and eggs from cows and chickens fed cottonseed meal. Reports compiled by the National Agricultural Chemicals Association (NACA) Industry Task Force for Agricultural Arsenical Pesticides 270 showed that methanearsonates cause no significant arsenic residues in cottonseed if applied to cotton after it has reached a height of 3 in. (7.6 cm) and before early bloom. They cause significant arsenic residues in cottonseed if applied as a directed spray after early bloom. 336 Apparently, either DSMA or MSMA translocated from leaves and stems to the immature ovule if applied at flowering, reached a maximum if applied when the seed was growing most rapidly, and decreased to a low concentration if applied to open cotton. On the basis of these and other results, the registered label restricts use of the methanearsonates from the time cotton is 3 in. (7.6 cm) high until first bloom. It permits no more than two directed applications of DSMA or MSMA of up to 3 or 2 lb/acre (3.4 or 2.2 kg/ha), respectively, per application. Within the specified limits of growth stage, application rates, and application methods, arsenic residues in raw undelinted cottonseed vary from 0 to 0.2 ppm above controls. The analysis of a large number of cottonseed samples from control fields has shown background arsenic concentrations varying from the limit of detection of the method (about 0.05 ppm) to about 0.3 ppm. Therefore, the total arsenic content of samples from treated fields varies from 0.05 to about 0.5 ppm. The report of the NACA Industry Task Force on Tolerance for Methanearsonates 705 therefore requested an arsenic tolerance of 0.5 ppm in cottonseed. The same report illustrates the human exposure likely to occur from this amount of arsenic in cottonseed flour. The average human would have to consume about 1.5 lb (0.68 kg) of cottonseed flour per day to reach 0.3 mg of arsenic from this source, assuming the cottonseed flour all contained the maximum of 0.5 ppm (0.3 mg is a 2,000-fold safety factor based on no-effect feed concentrations for rats). The average concentration of arsenic in cottonseed flour, assuming both added and background arsenic, is about 0.15 ppm. At this concentration, about 5 lb (2.3 kg) of cottonseed flour could be safely consumed per day. In reality, however, very little cottonseed flour is used in baking.

Residues in plants and plant products grown in soils that had been treated with arsenic or in material that had been sprayed itself are listed in Appendix A. Residues are highest in samples taken soon after spraying or dusting. The highest residues in hops came from treating them with impure sulfur. Cotton leaves contained high concentrations of arsenic, probably from being sprayed with arsenic acid before harvest. The treatment is used to defoliate cotton plants before mechanical harvesting. Grass had high concentrations from a sodium arsenite spray. Most other residue values were not very different from those in plant material grown on untreated soil. Although residues may have been high on food crops (e.g., apples) in the past, current surveys indicate that arsenic contamination is not significant. As mentioned previously, arsenic acid is used as a desiccant in Texas and parts of Oklahoma. The FDA analyzed cottonseed products and various commodities from areas where arsenical defoliation was known to be practiced. 96 The arsenic content of various commodities analyzed is shown in Table 3-15. Of another 159 cottonseed product samples tested, 143 were positive; three samples were above the established arsenic trioxide tolerance of 4 ppm allowed by the FDA, and the overall average was less than 0.9 ppm. The report concluded that “these results indicate that levels of arsenic in cottonseed products for human consumption from areas in which arsenical defoliation is practiced are well below established tolerances.”

TABLE 3-15. Arsenic (as As2O3) in Various Commodities, Texas, 1963.

TABLE 3-15

Arsenic (as As2O3) in Various Commodities, Texas, 1963.

Animals

Arsenic, because of its ubiquity, is eaten or drunk by all animals. The amounts of arsenic found in some animal tissues as a result of normal exposure are presented in Appendix B. Arsenic in abnormal amounts may be ingested by eating plants or drinking water contaminated with arsenic, breathing arsenic-containing dusts, or ingesting arsenic as a medicine or poison. Little arsenic is currently used in human medicine, although it was used extensively in the eighteenth and nineteenth centuries. Phenylarsonic formulations are used as feed additives to enhance growth in poultry and swine.

Arsenic concentrations in animals that have been subjected to high exposure are presented in Appendix B. The highest residues in man are generally in the hair and nails; high concentrations in other portions of the body are transitory. The highest residues—particularly in the stomach, intestines, liver, and kidneys—were from known cases of arsenic poisoning.

Animals subjected to arsenic pollution in the Helena Valley contained higher than normal arsenic residues, mainly in hair. 466 Horse hair contained up to 5.9 ppm, with the higher values in horses living closest to the smelter exhaust stack and eating locally grown hay. Organ analysis of a horse that died of unknown causes revealed residues of 0.7 ppm in the lung, 0.1 ppm in the liver, 0.11 ppm in flank muscle, 2.0 ppm in hair, and a trace in the kidney. Concentrations of cadmium, lead, and mercury were also high. Other miscellaneous animal products from within 3 km of the stack were analyzed. The results were: chicken muscle, trace; rabbit muscle, 0.6 ppm; whole milk, trace; beef liver, 0.2 ppm; beef muscle, 0.05 ppm; beef kneebone, not detected; swine heart, trace; and sausage, trace.

Arsenic concentrations may be increased in chickens and chicken products if they have received arsenic feed additives up to slaughter. Residues, however, decrease rapidly after additive withdrawal. Eggs apparently do not contain detectable residues. 50

Starlings, sampled as part of a nationwide monitoring program, contained low arsenic concentrations. 524 Only one sample (0.21 ppm) exceeded 0.05 ppm; most contained arsenic at 0.01–0.02 ppm on a wet-weight basis.

Fish and fish products contain the highest concentrations of the animal kingdom, although they are exposed to arsenic only in the sea or rivers. Crustacea generally have the highest arsenic concentrations of the seafood species, and oil from fish contains more arsenic than the flesh.

Bees have often been subject to injury wherever arsenic compounds are used, because only 4–5 µg of arsenic is necessary to cause death. However, analysis of dead bees and contents within a hive have often revealed high arsenic concentrations. 226 , 228

Foods

The FDA has conducted surveillance and monitoring programs on pesticides in food. In one survey, arsenic in foods was monitored in samples collected from 30 markets in 29 cities for the period June 1966–April 1967. 523 The sensitivity of the method for arsenic, as As2O3, was 0.1 ppm. In this survey, 33 of 360 composite samples collected were positive for arsenic (range, 0.1–0.40 ppm). In the survey covering the period June 1968–April 1969, 166 57 of 360 composite samples were positive for arsenic (range, 0.1–1.0 ppm). A breakdown of commodities, indicating the numbers of positive samples and the concentrations (or ranges), is as follows: meat, fish, and poultry, 15, 0.1–1.0 ppm; grain and cereal, 7, 0.1–0.2 ppm; fruit, 5, 0.1 ppm; sugar and adjuncts, 5, 0.1 ppm; dairy products, 2, 0.1 ppm; potatoes, 3, 0.1 ppm; leafy vegetables, 4, 0.1 ppm; legume vegetables, 3, 0.1 ppm; root vegetables, 3, 0.1 ppm; garden vegetables, 4, 0.1 ppm; oils, fats, and shortenings, 2, 0.1 ppm; and beverages, 3, 0.1 ppm. Detailed analysis of these data is not possible; however, it is interesting that the highest concentrations occurred in meat, fish, and poultry. The seaport city of Baltimore reported the highest concentrations in this category (four samples and a range of 0.2–1.0 ppm), whereas the inland cities of Kansas City and Minneapolis reported only three samples at 0.1 ppm. Arsenic from seafoods may account for the high concentrations in samples collected from Baltimore.

Arsenic in a sample institutional diet amounted to about 400 µg/day. 709 The amounts of arsenic found in an institutional diet containing no seafood are shown in Table 3-16. Arsenic in various foods is shown in Appendix A and Appendix B. Very little arsenic is currently found in food products other than fish and fish products. The estimate of Schroeder and Balassa 709 appears to be high in relation to other estimates that are available on total arsenic consumption per day.

TABLE 3-16. Arsenic in Institutional Diet.

TABLE 3-16

Arsenic in Institutional Diet.

The World Health Organization reported that average arsenic intakes for Canada, the United Kingdom, the United States, and France varied from 25 to 33 µg/day; specific values ranged from 7 to 60 µg/day. 881

A survey of food made in Great Britain indicated that 100 µg of arsenic would be consumed daily from all sources. 320 Analysis for arsenic resulted in the following values for foodstuffs: cereals, 0.18 ppm; fats, 0.05 ppm; fruits and preserves, 0.07 ppm; root vegetables, 0.08 ppm; milk, 0.05 ppm; meat, 0.10 ppm; and fish, 2.0 ppm. The Japanese consume between 70 and 170 µg of arsenic per day. 576 Food products in Canada are low in arsenic, only roots and garden fruits averaging arsenic residues higher than 0.01 ppm in 1971. 740 In 1970, meats, potatoes, and roots averaged greater than 0.01 ppm—0.18, 0.15, and less than 0.18 ppm, respectively. It is clear that the general population receives little arsenic in its food. 741

Several instances of accidental arsenic poisoning through contaminated foodstuffs have been reported in Japan. Soy sauce, which contained arsenic at 5.6–71.6 µg/ml, was implicated in a toxicity outbreak. The arsenic was in the amino acids (260–275 µg/ml) used in making the sauce; hydrochloric acid may have been the source of arsenic in the preparation of the amino acids. 589 Contaminated powdered milk was implicated in a similar outbreak in Japan. It contained arsenic at 13.5–21 ppm. 426 Contamination of the milk was from sodium phosphate (7.11% arsenic) used in its manufacture. 431

Air

There are three major sources of arsenic in air: smelting of metals; burning of coal, vegetation, and agricultural wastes; and use of arsenical pesticides.

Almost all arsenic produced for commercial use is recovered as a by-product in the smelting of lead, copper, and gold ores. It is removed from the smelter exhaust gases. These are treated to remove dangerous or valuable substances, many of which are emitted as dusts, including arsenic trioxide, metal and metal oxide particles, and fly ash. Arsenic trioxide is volatile, and nearly all of it is expelled from the ore as a sublimate during smelting. Crude flue dust is usually recycled to the furnace, with a consequent buildup of arsenic, sometimes to as much as 30%. The arsenic-rich flue dust and other arsenic-containing residues from domestic smelters are shipped to a single copper smelter, where the arsenic is separated by controlled roasting and processed to a commercial form. The arsenic-free calcine is smelted to recover other metals.

Even in the smelters where arsenic is not recovered for commercial use, the quantities involved are very large. A reverberatory furnace, for example, may smelt as much as 1,900 tonnes of charge per day and in doing so burn 218 tonnes of coal. The furnace would produce about 2,550,000 m3 of gas per day, containing up to 163 tonnes of solids. This means that it would be necessary to dispose of 5.4–54 tonnes of arsenic each day, with the lower value being more common. 425 , 520

Arsenic is brought into the air by a combustion process and exists as an oxide. However, arsenic is removed from the air by settling or rainfall, and atmospheric concentrations do not build up. Air samples may contain arsenic—for example, rural England, 0.4—6.4 ng/kg, 133 an industrial area of Osaka, Japan, 25–90 ng/m3; 515 urban United States, 20 ng/m3; 804 and rural Canada, 0.27—4.7 ng/m3. 657 Nonurban areas had a maximal average concentration of 20 ng/m3, with most values less than 10 ng/m3. 770 Concentrations of arsenic in fly ash increase by a factor of 10 as particle size decreases from 74 to 1.1–2.1 µg. Particles that escape most existing particle-collecting systems (less than 5 µg) contain high arsenic concentrations. 580 Large cities generally have a higher arsenic concentration in the air than do small cities, because of fuel combustion for electricity and heating. An air arsenic content of 30 ng/m3 was calculated on the basis of the amount of coal burned in New York City. This agrees well with the observed air concentrations for New York City. 770

Air quality data taken in 1950, 1953, 1961, and 1964 for 133 stations showed that the average arsenic content ranged from below detection to 750 ng/m3; the average for all stations was about 30 ng/m3. The Montana State Board of Health reported ambient air concentrations for some cities in Montana in 1961–1962. 766 The highest concentration in the state was 2,500 ng/m3 in Anaconda, the site of the smelter that treats most of the arsenical ore mined in the United States.

Two serious incidents of air pollution by arsenic from smelters in the United States have been recorded in the literature. The first incident took place in Anaconda, Mont., 328 , 338 where the rate of emission of arsenic trioxide was 26,884 kg/day (in 64,563 m3 of air per day) while the smelter was processing 9,070 tonnes of copper ore per day. Although no atmospheric concentrations were recorded, edible plants contained arsenic trioxide at up to 482 µg/g. The second incident occurred in a small western town near a gold-smelter. 79 (The exact location was not mentioned.) The mine had been operated intermittently since 1934. In 1962, the operation was resumed with a process that required converting sulfur and arsenic to sulfur dioxide and arsenic trioxide. The smelter processed sufficient ore to produce about 91 tonnes of sulfur dioxide and 36 tonnes of arsenic trioxide per day. The dust-collecting system designed to collect approximately 90% of the toxic dusts failed to operate as expected, and toxic fumes escaped into the atmosphere. These two episodes indicate that there may be some degree of arsenical air pollution at every smelter that treats arsenical ores, especially when dust-collecting equipment is inadequate or not working properly. An example of the arsenical pollution potential estimated for Colorado is shown in Table 3-17. The quantities of arsenic recovered in the concentrates and deposited in the mill tailings were not reported.

TABLE 3-17. Arsenical Pollution Potential from Mills in Colorado.

TABLE 3-17

Arsenical Pollution Potential from Mills in Colorado.

Arsenicals are used for weed control and as desiccants for cotton plants before machine picking. Thus, dust and gases emitted from cotton gins contain arsenic. At a distance of 46–91 m downwind from a west Texas cotton gin, concentrations of 600–141,000 ng/m3 were detected. The amount found was inversely proportional to the distance from the source. 805

The burning of cotton trash from a cotton gin is also a source of arsenic. Approximately 37% of the gins incinerate their trash, 58% return it to the land, and 5% handle it in some other manner. Arsenic emission from incineration is not known.

Arsenical pesticides constitute one of the primary uses of arsenic. From 1937 to 1940, the U.S. Public Health Service studied the effects of lead arsenate on orchard workers. 583 The amounts of lead and arsenic to which they were exposed in the air varied with the operation being performed. The arsenic concentration was highest when they were burning the containers (16,670 µg/m3), followed by mixing (1,850 µg/m3), picking the fruit (880 µg/m3), spraying (140 µg/m3), and thinning the fruit (80 µg/m3). It is noteworthy that the highest arsenic concentration in air came from burning the containers.

Disposal

The problems and methods of waste disposal associated with each of the major arsenic uses and processes are discussed in this section. Much of the available information on waste from the manufacture and use of arsenic compounds is in a profile report on disposition of hazardous wastes prepared for the EPA in 1973, 610 which was used extensively in the preparation of this section.

Waste from Agricultural Uses of Pesticides and Herbicides

  • Cacodylic acid: Cacodylic acid is a contact herbicide used to defoliate or desiccate a wide variety of plant species and was used as a defoliant for crop destruction in South Vietnam. It is registered for use in lawn renovation or as a silvicide. Ottinger et al. indicated that the major source of waste from the agricultural use of cacodylic acid was pesticide residue left in empty containers after use. 610 Residues from plant leaves or material sprayed or applied directly on the soil become bound to soil particles and are not readily leached from the soil or taken up by plant root systems. The present registered uses of the cacodylates preclude their application to food crops, so plant residues are not expected to enter the food chain. However, burning or other types of disposal of material from sprayed areas, as well as erosion of soil from sprayed sites, could constitute a potential hazard. The cacodylates are normally formulated as liquid solutions containing 2–3 lb of cacodylate per gallon of solution (about 240–360 kg/m3). Stojanovic et al. have estimated that 2.2–2.8% of the original contents is left in “empty pesticide containers.” 763 An average of 2.5% of the estimated annual use of 1,200,000 gal (4,540 m3) of cacodylate solutions—30,000 gal (114 m3)—is left in containers. 610 The safe and economical disposal of pesticide-contaminated containers is a serious problem that has not been solved. 610
  • Arsenic acid: Arsenic acid is used extensively as a cotton desiccant. The amount produced has been estimated at roughly 9,000,000 lb (4,080,000 kg) in 1971. 579 As expected from the use of arsenic acid as a cotton defoliant, residues are associated with the disposal of cotton wastes from cotton gins. Sullivan reported that dust from the ginning operation can have an adverse effect on vegetation downwind of cotton gins. 770 Also, about 37% of the gins burn trash that releases arsenic into the environment. The amounts released are not known. Bag filters and electrostatic precipitators are reasonably adequate for control of dust and particles from the burning of cotton trash. No specific information is available on the removal of arsenic acid residues remaining in containers after use, but it can be assumed that a small percentage of solution will remain. It is also unlikely that any adequate control program is in operation for the collection and disposal of empty arsenic acid containers.
  • Disodium methanearsonate and monosodium methanearsonate: DSMA and MSMA are used extensively in cotton-producing areas for selective weed control. There is no specific information on the disposal of used pesticide containers and crop residues contaminated with arsenic, but the potential problems with these compounds are probably the same as those with the cacodylates and arsenic acid. The magnitudes of the problems appear to be similar, because the estimated amounts of material used appear to be similar. The potential for contamination of the cotton plant or gin trash may be somewhat less with DSMA and MSMA, because the use of these compounds is restricted to the period between the time the plant is 3 in. (7.6 cm) high and the first bloom.
  • Arsenates (calcium, copper, lead, sodium, zinc, and manganese): Only two of these compounds, calcium arsenate and lead arsenate, are used extensively as agricultural pesticides. The remaining arsenates are not prepared for agricultural or any other use in any significant quantity. Approximately 2,000,000 lb (907,185 kg) of calcium arsenate and 7,700,000 lb (3,493,000 kg) of lead arsenate were produced in 1969. 802 In 1972, the EPA stopped the registration of lead arsenate, so its use is expected to decrease to the point of insignificance in the very near future. 610 Strict government controls on the use of calcium arsenate are expected to reduce its use in the near future. The three major sources of arsenate wastes are residues in empty containers; surplus pesticides stored by government agencies (the Department of Defense and the EPA), state and municipal facilities, and manufacturing plants; and soil contaminated from extensive use of arsenate pesticides. The latter constitutes the most important waste problem with respect to the arsenates. There is no wholly satisfactory procedure for the recovery of contaminated soils, except removal and mixing with clean soil to dilute the arsenic. Because calcium arsenate and lead arsenate are almost always formulated as dusts, granules, or wettable powder and shipped in siftproof, multiwall paper bags, there is less residue in empty containers. Nevertheless, disposal of empty paper bags could pose a problem, particularly if large quantities are burned or buried in landfills. There are no recommended procedures for the disposal of these kinds of pesticide containers. There is no information on the possible problems related to the disposal of contaminated crop residues. However, Table 3-14 indicates that, even with high application rates of lead arsenate, the residues in vegetable crops would probably be minimal.
  • Copper acetoarsenite and sodium arsenite: The production and use of these two compounds is not great. The production of copper acetoarsenite (Paris green) is estimated to be at least 100,000 lb/year (45,000 kg/year). 610 One of the uses of sodium arsenite is in livestock dips for cattle tick control. There are strict government controls on the use of these compounds, and the extent of use is expected to remain about the same or possibly to decrease. One of the major problems with the disposal of arsenite wastes involves the disposition of empty containers. The arsenites are generally shipped and stored as liquid solutions, and the problem is handling and disposing of metal and plastic containers. No satisfactory collection and disposal procedures have been devised, but, in view of the low volume of use (in comparison with other arsenicals) and its expected decrease, the problem is not particularly great. Disposal of sodium arsenite cattle dips has created some localized problems, because of the large volumes of liquid and the high concentration of arsenic involved. No totally satisfactory method for disposal is available, but landfill in very tight clay soil has been suggested.

Waste from Use of Arsenical Feed Additives

Arsanilic acid, 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone), 4-nitrophenylarsonic acid, and 4-ureidophenylarsonic acid (carbarsone) are approved for use in animal feeds as therapeutic or growth-promoting agents. These compounds are packaged and sold by a variety of feed ingredient and pharmaceutical manufacturers under many different trade names. Most are sold either pure or mixed with diluents—such as corn germ meal, corn cobs, and calcium carbonate—and are sold directly to feed manufacturers or individual farmers for mixing in poultry or swine feeds or for addition to the drinking water. 587

Because these materials are fed to animals, the major concern with respect to disposal has to do with the amounts that may be found in animal wastes. FDA regulations require that these arsenic compounds be withdrawn from animals 5 days before slaughter. There is evidence that almost all residues are depleted during this period, and evidence accumulated by Peoples 628 and Calvert 126 indicated that only about 10–15% of ingested arsenic is absorbed by the animals. Thus, it is very likely that nearly all the arsenic fed will eventually appear in animal excreta. It is unknown whether the amounts fed to animals and eventually excreted constitute a disposal problem.

As shown by Morrison, arsenic in animal wastes did not accumulate in soil or ground water after 20 years of poultry manure application. 562 The manure contained arsenic at 15–30 ppm, and the application rate was 4–6 tons/acre (9.0–13.5 tonnes/ha) per year. Messer et al. 540 reported that some poultry litter samples analyzed contained arsenic at up to 75 ppm (dry-weight basis), and Calvert 126 reported up to 45 ppm in dried broiler manure.

In many instances, swine and poultry wastes are stored in anaerobic lagoons for long periods before disposal. If these animals are fed arsenic for therapeutic or growth-promoting purposes, all the arsenic-containing compounds fed may accumulate in waste lagoons. In a recent study, 108 arsenic concentrations were measured in lagoons under swine fed arsanilic acid at 0, 90, and 180 g/ton (0, 99.2, and 198.4 g/tonne) of feed. The wastes were collected during the growing period (31–198 lb, or 14–90 kg) and retained for 120 days in experimental anaerobic lagoons. The only two significant effects observed in these lagoons were total arsenic contents (on a wet-sample basis) of 0.26, 5.77, and 10.60 ppm for 0-, 90-, and 180-g/ton feeding concentrations, respectively, and dry-matter contents in the lagoons of 6.20, 3.57, and 2.89%, respectively. No studies have been conducted on arsenic contents of lagoons used for long periods; inasmuch as lagoons may well be used for some 10–15 years, there may be significant accumulations of arsenic. The effects of these accumulations on microbial activity in the lagoons and on later disposal are unknown.

On the basis of the amount of these arsenicals used each year, estimated at a total of 3,000 tons (2,722 tonnes), and the fact that the manure will probably contain arsenic at only 75–100 ppm, it is unlikely that manure application will create any problem with regard to arsenic contamination of soil. Morrison indicated that, even to approach amounts of arsenic that might affect plant growth, application rates of manure containing arsenic at 30 ppm would need to be about 2,000 tons/acre (4,480 tonnes/ha). 562

There might be a more serious problem when animal wastes are approved for use as animal feeds. Arsenic in poultry and swine wastes in some instances may be incorporated into diets of animals for which no FDA clearance has been established. Studies by Calvert, 126 by Fontenot, 258 and by Long et al. 485 indicated that arsenic in manure fed to cattle and sheep can be detected in tissues and that a short withdrawal period was sufficient to reduce tissue arsenic to acceptable concentrations.

Waste from Industrial Uses of Arsenic

  • Arsenic trioxide: The American Smelting and Refining Company (ASARCO) accepts and refines flue dust from a large part of the U.S. copper, gold, zinc, and lead smelting industry. The principal methods for collection of flue dusts are discussed elsewhere in this report. The flue dust is treated with other high-arsenic material to sublime off arsenic oxide, which is condensed in a series of condensing chambers. This dust and dust that remains in the stream and is collected on bag filters or electrostatic precipitators is mainly impure arsenic oxide, which is refined to commercial arsenic trioxide. ASARCO currently accepts crude arsenic-containing ores and intermediate smelter products on a broad scale. With the possible exception of some problems with its own flue control system, this appears to be a key to adequate management of arsenic wastes from smelters. 610 This is not to say that all smelters have adequate flue-gas control; as reported by Ottinger, some plants refuse to release data on flue-gas composition, and the one plant reporting indicated emission of 1.1 tons (1 tonne) of particulate matter per day with a 34% arsenic content. 610

The major problem currently associated with arsenic management in the smelter industry, aside from the escape of flue gases from the filters and precipitators, is the fluctuating demand for the arsenic trioxide produced by ASARCO. Large overstocks of arsenic trioxide can and do result, but, fortunately, these are at one site, and controls are fairly easily implemented. Current methods for storage are large siftproof and weatherproof silos at the site of ASARCO's plant in Tacoma, Washington. It has been suggested that, with government subsidy, this system could become a national disposal site for all arsenic trioxide and related arsenic compounds.

Under some conditions of encapsulation, arsenic trioxide might be buried in landfill sites. However, there are insufficient data to determine whether such a system would be adequate. In any event, this method of disposal should be used only if there are large oversupplies of arsenic trioxide and if long-term storage facilities are not available.

The principal concern in metal smelting and arsenic trioxide refining processes is the more complete removal of arsenic from smelter flue gases. The following is a brief description of methods now used to remove dust from exhaust-gas streams:

1.

The use of electrostatic precipitators is the most common method, but they are only 70–90% effective and require flushing of grids; smaller, light particles normally escape entrapment; Ottinger et al. indicated that the negative responses received from their contacts with smelter operators suggested that this procedure was inadequate. 610

2.

Filter–bag house operations are normally 99% efficient, but they require more power than precipitators and are more expensive to purchase and install; they are expected to be used more extensively when more complete abatement compliance is required.

3.

Charged-droplet scrubbers use a stream of electrostatically charged water droplets, which are accelerated through a field between a positive-voltage nozzle and the negative-voltage collector plates on the side of the flue; the water droplets collide with dust particles and carry them to the collector plates, where they drain away; efficiency is estimated at 99%, and power requirements and installation expense are lower than for bag houses and precipitators.

4.

Sullivan reported on the use, in the U.S.S.R., of wet-vacuum pumps, instead of fabric bag filters; efficiency was reported to be 100%, although no specific information was made available on the process. 770

For the treatment of arsenic trioxide wastes, the recommended process is long-term storage. Improved flue-dust abatement equipment is needed. The use of fabric bag filters is currently the preferred method in the industry, but it is not entirely satisfactory.

  • Cacodylic acid: The Ansul Company of Marinette, Wisconsin, and the Vineland Chemical Company of Vineland, New Jersey, account for about 80 and 20%, respectively, of the U.S. production of cacodylic acid. The commercial production process, according to Ottinger et al., has three steps: Arsenic trioxide reacts with sodium hydroxide to yield sodium arsenite, methanearsonic acid is produced by the addition of methylchloride, and the mixture is reduced with sulfur dioxide and methylated to produce cacodylic acid. 610 There is no liquid waste from this process, because all liquid streams are cycled back into the system. A solid waste is produced; it consists largely of sodium chloride and sodium sulfate with about 1–1.5% cacodylate contaminants. Currently, about 27,200 tonnes of this solid material is stored in concrete vaults in the Marinette, Wisconsin, area. There are no plans for this waste, other than to store it indefinitely. The waste management systems in use are recycle and reuse, long-term storage, and landfill in “class 1” sites. As defined in Ottinger et al., 610 a class 1 site is over either non-water-bearing sediments or unusable water and is protected from surface runoff and flooding. The Ansul Manufacturing Company has indicated that it will accept unused cacodylates that were manufactured by the company and are returned in their original containers. 20 This seems to be an adequate means of waste management, if the materials are in a concentrated form. The long-term storage of cacodylates and the salt wastes appears to be the only system for handling such waste today. Storage containers should be constructed so as to avoid leakage or release of arsenic materials, and they should be inspected routinely. Landfill disposal is generally unacceptable for handling wastes, because of the potential danger to surface or ground water. There are, however, class 1 sites that could be used, but such should be considered only for small quantities of cacodylate wastes and only if no other system is available.
  • DSMA and MSMA: No information was found on the procedures used for management of wastes of these two compounds, but, inasmuch as the chemistry of their synthesis is similar to that of the cacodylates, the methods for waste management during manufacture should be similar. Ottinger et al. indicated that recycling and reuse, storage, and landfill procedures for handling waste products would be similar for MSMA, DSMA, and cacodylates. 610
  • Calcium arsenate and lead arsenate: These compounds are manufactured in a completely contained batch process. The only liquid effluents result from cleanup of equipment. The contaminated liquid is held in evaporating ponds at the plant site. Water used in the process is removed by drum or spray dryers, whose exhausts are cleaned by scrubbers. The scrubber liquids are then used in the preparation of the next batch of pesticide. Bag filters are used to remove particles that result from grinding and bagging. Any aqueous filtrates from the purification processes are recycled for the makeup of the next batch.
    Handling of waste after manufacture requires special consideration, because it is generally a solid material; but, in general, the procedures are similar to those for other arsenic materials. Recycling and reusing excess or unused materials are acceptable practices, and the companies involved have indicated that they would accept their own products in unopened containers. Long-term storage in weatherproof storage bins is considered adequate and is the practical method in use. Land spreading of unwanted stock of the arsenates using light applications on large areas of land is acceptable only if all alternative procedures have been considered. Export of unwanted stock to countries with less restrictive regulations on the use of arsenate has been considered; this procedure would conceivably solve some of our domestic problems, but it would not contribute to the control of global pollution from arsenicals. Another available option is the recovery of other metals, particularly lead; it should be remembered, however, that this would result in the production of arsenic trioxide, which might constitute as much of a disposal problem as the original product. Landfill is generally not acceptable as a disposal technique, because of the potential danger of contamination of ground and surface water; however, the use of class 1 sites is considered adequate for small stocks of arsenates, if all alternative systems have been ruled out.
  • Copper acetoarsenite and sodium arsenite: As described by Ottinger et al., copper acetoarsenite is believed to be a mixture of cupric arsenite and the copper salt of acetic acid in a ratio of about 3 : 1. 610 Paris green is manufactured by the reaction of sodium arsenite (made from the reaction of arsenic trioxide with sodium hydroxide) with copper carbonate and acetic acid by a batch process. The reaction is considered complete when a green product precipitates from solution, with only a white supernatant fluid remaining. The supernatant solution is said to be arsenic-free. Ottinger et al. indicated that only two companies remain as major manufacturers of sodium arsenite: the Chevron Chemical Company and the Los Angeles Chemical Company. 610 The total production from these companies is believed to be about 757–1,514 m3, containing 479–719 kg of sodium arsenite per cubic meter. The solution is filtered before it is put in drums, and the filter cake is buried. The composition of the filter cake is not known, but it might be expected to contain some arsenic as a contaminant. No other part of the manufacturing process has been identified as a source of arsenic pollution. In general, the sources of arsenic waste and its handling are the same as for the arsenates, except that copper acetoarsenite and sodium arsenite are usually sold and distributed in liquid solutions. The adequate management systems are: recycling and reuse; long-term storage; recovery of such metals as copper and lead and long-term storage of arsenic trioxide; and landfill in class 1 sites. In addition to the arsenic content of these pesticides, as is the case with the arsenates, the metal content should also be considered in the selection of an appropriate disposal system.
  • Miscellaneous industrial sources of arsenic waste: The glass industry, according to Ottinger et al., consumed about 4,100 tons (3,720 tonnes) of arsenic trioxide in 1968 and 3,000 tons (2,720 tonnes) in 1971. 610 Arsenic trioxide is used as a refining agent and is added in purified form to molten-glass batches in 0.2–0.75% loadings. The arsenic trioxide is volatilized and disperses through the glass. No waste is produced in the process, except for some glass slag, which apparently does not constitute a disposal problem.

The 400 million tons (363 million tonnes) of coal consumed each year produce an estimated 300–6,500 tons (272–5,900 tonnes) of arsenic trioxide per year. Urban areas generally have a slightly higher air arsenic content than rural areas. No particular recommendations have been made for the control of this source of arsenic, and it is unlikely, unless coal consumption increases dramatically, that it constitutes a special pollution hazard. Furthermore, the proper use and design of pollution control devices being incorporated by industries that use coal as an energy source will probably limit arsenic emission.

The recently renewed interest in the land application of municipal sewage sludge for disposal or as a source of plant nutrients has generated concern for the heavy-metal content of these materials and their effects on soil and ground water. Arsenic has not been one of the elements of major concern, and it has been difficult to obtain much information on the arsenic content of effluent wastewater and sewage sludge. In one study, the effluent wastewater and sewage sludge from 58 municipalities in Michigan, including Detroit, were analyzed for a variety of elements, including arsenic. 81 The amounts of arsenic detected ranged from less than 0.005 to 0.023 µg of total arsenic per liter of effluent and from 1.6 to 17 mg/kg of air-dried sludge. However, the content of arsenic and heavy metals probably will keep the use of sewage sludge and wastewater effluents well below the amounts needed to cause toxicity.

Summary

Table 3-18 summarizes the method of disposal of some of the principal arsenic compounds used in the United States. No one disposal system is being used to handle arsenic wastes from the manufacture of the various arsenic compounds; it is unlikely that any system would be wholly satisfactory for the entire arsenic manufacturing industry. In some instances, long-term storage is the only method for disposal until alternative procedures for disposal or recovery of arsenic or metals can be developed. Recycling or reusing arsenic from arsenic manufacture probably solves the greatest number of problems, as far as disposal is concerned. Unfavorable economics is, and will be, the major limiting factor in recycling of waste products. Landfill in general would be a last resort for adequate disposal, primarily because of the scarcity of class 1 sites near manufacturing wastes.

TABLE 3-18. Method of Disposal of Principal Arsenic Compounds Manufactured in the United States.

TABLE 3-18

Method of Disposal of Principal Arsenic Compounds Manufactured in the United States.

With respect to the disposal of arsenic compounds used in agriculture, few if any well-controlled systems for disposal of crop residues, empty arsenical containers, or other contaminated products are currently used. Most manufacturers will accept unused packages of arsenicals, but the user is generally left to his own devices when disposing of empty bags, barrels, and bottles. On the basis of the studies that have been conducted, around 2–3% of some arsenical solutions is probably left in containers after use; this represents a considerable potential hazard, as far as the whole environment is concerned. In many areas of the United States, a comprehensive program is needed whereby empty containers can be decontaminated or disposed of in a manner that will not create a hazard to the environment.

THE ARSENIC CYCLE

Frost proposed a closed organic arsenic cycle for the total environment in which some form of arsenic is present in all phases of the ecosystem (Figure 3-2). 268 Very few of the organic arsenicals were identified, but a volatile arsine was suggested as present. Allaway presented overall pathways of environmental movement of trace elements, which included arsenic. 10 Wood also proposed a cycle of toxic-element movement through the “geocycle,” with arsenic from natural weathering processes available later to microorganisms, plants, and animals. 871

Sandberg and Allen proposed a model (Figure 3-3) for the arsenic cycle in an agronomic ecosystem. 701 Their model contained 12 possible transfers to and from a field for the organoarsenical herbicides. They concluded that transfers involving reduction to methylarsines, soil erosion, and crop uptake were the primary redistribution mechanisms in this model. Treatment with cacodylic acid resulted in a theoretical buildup of arsenic of 2.6–3.3 ppm/ha per year, whereas MSMA accumulated at only 1.5–1.9 ppm/ha per year. They concluded that “arsenic is mobile and nonaccumulative in the air, plant and water phases of the agronomic ecosystem. Arsenicals do accumulate in soil, but redistribution mechanisms preclude hazardous accumulations at a given site.” 701 This model does not include the application of arsenic trioxide to desiccate cotton before harvest.

FIGURE 3-3.. A proposed model for the arsenic cycle in an agronomic ecosystem.

FIGURE 3-3.

A proposed model for the arsenic cycle in an agronomic ecosystem. Reprinted with permission from Sandberg and Allen. (Broken lines indicate minor or negligible transfers.)

Inputs into the environment and a redistribution of arsenic in the terrestrial ecosystem are presented in Figure 3-4. Natural inputs are from volcanic action, decay of plant matter, and weathering of minerals within the soil, whereas man-made sources of arsenic are combustion of coal and oil, smelting of ores, and use of fertilizers and pesticides. The largest sink for man-made arsenic in the environment is the soil.

FIGURE 3-4. Environmental transfer of arsenic.

FIGURE 3-4

Environmental transfer of arsenic.

Onishi and Sandell calculated a balance between igneous rocks (arsenic content, 2 ppm) and sedimentary deposits (shale and sediments, 10 ppm; sandstone and limestone, 1.5 ppm). 603 They observed that, if the amounts of sediments equaled that of weathered rocks, then much of the arsenic in sediments must come from volcanism. At present, this input is small, and weathering of continental rocks is in approximate balance with oceanic sediment deposition. Using estimates of arsenic weathering (45,000 tons/year, or 41,000 tonnes/year) and deposition rates, Ferguson and Gavis concluded that “there is no substantial imbalance between natural weathering and deposition of arsenic at present.” 249 The amount of arsenic from weathering transported to the oceans as part of the dissolved load of the rivers is 33,000 tons/year (30,000 tonnes/year). Arsenic from man-made sources is redistributed either through industrial processes, such as the burning of coal, or by the refining of oil for gasoline and fuel oil. Man's activity does cause high environmental concentrations at some locations.

Estimates are available for an arsenic balance at a coal-fired steam plant in Memphis, Tennessee. 85 The balance for most trace elements is satisfactory. Elements that can be present in a gaseous form (e.g., arsenic and mercury) are not completely recovered. Most arsenic recovered was in the precipitation inlet fly ash, but 52–64% of the arsenic in coal could not be found. It may have been lost in the gas stream. Coutant et al. 172a found that “only a small percentage of arsenic is emitted from the stacks” and that it did not pose an important problem from an air-pollution standpoint. “Arsenic tended to be distributed continuously through the system as a function of temperature,” and “there is a definite tendency for concentration of arsenic in the lower temperature deposits in the combustion system.” As coal utilization increases, the amount of arsenic escaping to the environment will increase, unless proper control measures are used.

Smelter activities have traditionally introduced large amounts of arsenic into the environment. The copper smelter at Tacoma, Washington, has been examined for arsenic emission into the environment. Crecelius et al. reported that input amounts to 200,000 kg of arsenic trioxide per year into the air via stack dust, 20,000–70,000 kg of arsenic per year into Puget Sound through dissolved arsenicals in its liquid effluent discharge, and 1,500,000 kg of arsenic per year in crystalline slag dumped into the Sound. 186 The installation of more pollution-control equipment at this smelter is planned, so the amount of arsenic released into the air and water will decrease significantly. 186

Information has been collected, to the extent available, to develop a pattern of arsenic emission into the environment. It included information on the arsenic associated with mineral raw materials and fuels, on the arsenic content of salable mineral products, on solid waste discarded by mineral processors, and on effluent from mineral plants. Complete material-balance reports were obtainable for only a few plants. However, considerable incomplete evidence was accumulated. These data were used to trace the disposition of arsenic—through mineral processing steps and consumption—in commodities containing significant quantities of arsenic. They were also used to determine the distribution of arsenic throughout commercial production and the disposition of arsenic used in agriculture and industry. Arsenic emission to the atmosphere was calculated with the factors listed in Table 3-19.

TABLE 3-19. Arsenic Emission Factors.

TABLE 3-19

Arsenic Emission Factors.

The principal source of atmospheric arsenic from manufacturing is the processing of nonferrous metals. Gualtieri classified 15% of copper and copper–lead–zinc ores as being arsenical and stated that they have an average arsenic : copper ratio of 1 : 50. 314 Analyses of nonferrous ores considered nonarsenical are not available. However, reference to mineralogic descriptions of other principal nonferrous mining districts indicates that arsenic minerals usually occur in trace quantities, are seldom visible in ore specimens picked at random, and have not caused serious pollution. It is apparent that the arsenic content of nonarsenical ores is less than one-tenth that of arsenical ores. Arsenic concentrations would be equivalent to 160 ppm in arsenical ore containing 0.8% copper and 12 ppm in nonarsenical ore containing 0.6% copper. The arsenic concentrations of rocks in the earth's crust are shown in Table 3-1 and Table 3-2 as: granite, 1.5 ppm; other igneous, 2.0–3.0 ppm; limestone, 1.7 ppm; sandstone, 2.0 ppm; and shales and clays, 14.5 ppm. We may assume rock distribution in nonferrous-metal deposits as: granite, 25%; other igneous, 25%; limestone, 25%; sandstone, 15%; and shale, 10%. The average arsenic content of unmineralized rock in mining districts would then be over 3 ppm. The average arsenic content of waste moved in mining is estimated as the average of the values for ore and unmineralized material, or 81 ppm for arsenical districts and 7 ppm for nonarsenical districts.

An estimated 40% of the arsenic in copper or copper–lead–zinc ore is left in the concentrator tailings. Much of the arsenic can be allowed to enter the tailing or can be depressed into an iron sulfide tailing, provided that the arsenic mineral does not contain valuable metals. The tailing is deposited on the surface, and some will be blown away by the wind; however, this quantity should not exceed 1% of the annual output. Arsenic in gold and uranium mill tailings is subject to similar wind losses. Arsenic minerals in tailing dunes may eventually weather to water-soluble compounds that will probably be transported over short distances before reacting with iron, aluminum, calcium, and magnesium in the soil to form largely insoluble substances.

Most of the arsenic emitted to the atmosphere during nonferrousmetal production results from smelting. At the primary smelter, arsenic contained in the ores and concentrates becomes distributed among the metal product, slag, speiss (a heavy metallic mixture of iron and nonferrous arsenides), flue dust, and atmospheric emission. Arsenic in metal is removed by pyrometallurgic or electrolytic refining methods; the arsenic-containing residues are recirculated to the smelting furnaces. After recovery of by-products, primary furnace slag is discarded. Speiss is sent to smelters with facilities for processing high-arsenic ma terial. Flue dust contains much of the volatile arsenic that is expelled from the furnace melt and collected in the stack-gas cleaning system. Some finely divided arsenic escapes ordinary dust-precipitating units, but additional cooling and cleaning of the furnace gases, as is done before sulfuric acid recovery, should capture most of the finely divided material. Flue dust is ordinarily recirculated to the furnaces, some of it being removed, if necessary, to keep excessive arsenic from accumulating in the system. The high-arsenic flue dust usually contains considerable metal value and, like the speiss, is shipped to the smelter equipped for processing it. At this smelter, the flue dust and speiss are roasted with fluxes to remove as much arsenic as possible. The arsenic is refined to commercial-grade material, and the calcine is smelted for its metal content.

Atmospheric arsenic emission during smelting was estimated for 1968 conditions by Davis and Associates on the basis of material balances and sampling data obtained from industrial sources. 196 Average arsenic emission was estimated at 4.9 lb/ton (2.5 kg/tonne) of copper produced, 1.3 lb/ton (0.65 kg/tonne) of zinc, and 0.8 lb/ton (0.4 kg/tonne) of lead.

Information obtained in February 1974 showed that arsenic emission at smelters processing arsenical copper ores was much reduced from the 1968 emission and that the average arsenic emission from copper smelting was 2.1 lb/ton (1.05 kg/tonne) of metal. No new data on emission from zinc and lead smelters are available. However, some information was obtained on the arsenic content of ores and concentrates. On the basis of the indicated smelter inputs of arsenical and nonarsenical concentrates and estimated percentage stack losses for smelters treating various types of ore, the recovery factors were estimated. These estimates are similar to those determined by the Davis study for lead and zinc smelters. 196

Arsenic is in all coal and may be associated with metal sulfides, clay minerals, or organic material in the coalbed. Using data developed by Abernethy, 2 Davis 196 estimated that U.S. coal contains arsenic at an average of 10 ppm in eastern fields, 5 ppm in midwestern fields, and 1 ppm in western fields. A small fraction of the arsenic in coal escapes dust-collecting equipment and reaches the atmosphere. Cuffe and Gerstle estimated the average arsenic discharge to the atmosphere from power plants at 0.000064 grains (0.004 mg) per standard cubic foot, with 1 lb (0.4536 kg) of coal being burned for each 160 scf of flue gas. 190 This is equivalent to 1.4 ppm of the coal burned. This factor should be applicable to industry-wide coal use, inasmuch as nearly all coal consumed is burned in plants with fly-ash control equipment. Assuming 600 million tons (544 million tonnes) of coal burned per year in the United States, this would correspond to the emission of 840 tons (762 tonnes) of arsenic. 85

The arsenic content of petroleum was investigated by Davis and Associates, who obtained analyses of 110 oils. 196 The average content was 0.042 ppm, or about 5.2 kg/million barrels. A future problem may arise from producing oil from shale. Oil from Colorado shale contained arsenic at 82 ppm. This arsenic, however, could be removed by contact with a mixture of nickel sulfide and molybdenum sulfide on alumina under reducing conditions. 572 All arsenic present was removed until there was 7.2% arsenic on the alumina; thereafter, arsenic was found in the effluent gases.

Inconsequential arsenic emission results from mining and processing of phosphate rock. The average arsenic content of mine run rock is estimated at 5.7 ppm; of washed rock, 12.0 ppm; and of discarded material, 2.6 ppm, on the basis of an analysis by Tremearne and Jacob 797 and production data shown in Bureau of Mines Mineral Yearbooks. 812 Total arsenic placed in waste impoundments would be about 200 tons (181 tonnes) annually, of which perhaps 1 ton (0.9 tonne) would be expected to enter the atmosphere through weathering. About 17% of phosphate rock is used for electric-furnace manufacture of elemental phosphorus. The total arsenic in the furnace feed is about 60 tons (54 tonnes), of which only a small proportion would reach the atmosphere.

Iron ore contains arsenic, but only insignificant quantities of it are emitted during iron and steel production. Boyle and Jonasson showed arsenic contents of hematite up to 160 ppm and of magnetite up to 3 ppm. 94 Arsenic occurs in part in the form of scorodite, a very stable arsenate of iron. In the blast furnace, the arsenic compounds are reduced to elemental arsenic, which combines with iron to form iron arsenide and dissolves in the metal; very little of the contained arsenic reaches the atmosphere. Table 3-20 shows an industrial balance for arsenic emission into the environment based on the estimated emission factors, the rate of consumption of mineral fuels, and the rate of production of nonferrous metals, including arsenic.

TABLE 3-20. Estimated Industrial Materials Balance for Arsenic, 1968 .

TABLE 3-20

Estimated Industrial Materials Balance for Arsenic, 1968 .

Carton 120 surveyed arsenic input and movement in the United States. He estimated a total movement of about 119,000 tons (108,000 tonnes) of arsenic per year (Table 3-21). He distinguished between arsenic that is found in end products and arsenic that is dissipated onto land, emitted in air and water, or destined for landfills. Of the 108,000 tonnes, most is fixed in products in which the arsenic is immobile or is deposited in landfills as waste material. The remainder is in a form that can move readily within the environment.

TABLE 3-21. Summary of U.S. Arsenic Flow, Dissipation, and Emission, 1974.

TABLE 3-21

Summary of U.S. Arsenic Flow, Dissipation, and Emission, 1974.

About half the mobile arsenic comes from the use of pesticides. That which is applied to land becomes predominantly fixed in insoluble compounds and is only minimally available for transport. Arsenic that is emitted into air or water is most mobile and of greatest concern to the general population surrounding the points of emission. It is the airborne arsenic trioxide residues that have been implicated in the arsenic–cancer question. This topic is discussed in Chapter 6.

Arsenic from man-made sources eventually reaches the soil. Processed arsenic is applied by way of pesticides and through natural contamination of fertilizer materials. Arsenic that is gaseous or is adsorbed onto particulate matter is removed from the atmosphere through fallout or in rain. It is deposited on vegetation, on soil, or in water. Once in the water, arsenic can be accumulated to some extent by various forms of aquatic life. Arsenate in solution is adsorbed or incorporated into phytoplankton and algae, and an organic compound is synthesized. Fish, when they consume the algae, incorporate this organic arsenic compound. In some cases, the arsenical is further metabolized to yield high-molecular-weight lipid materials, proteins, or easily soluble low-molecular-weight compounds. The arsenical from aquatic life, when consumed, is generally eliminated with very little accumulation. 171

Pesticidal arsenic that is deposited on the land may have several fates. A portion of methanearsonic acid and cacodylic acid may be reduced to volatile arsines (under both aerobic and anaerobic conditions), but the predominant degradation product is arsenate. 879 Under anaerobic conditions, these two compounds are reduced to volatile arsines. Arsenate and arsenite are also reduced or methylated to volatile arsines under some conditions. 175 , 499 Braman detected dimethylarsine and trimethylarsine or their oxidation products above grass that had been treated with sodium arsenite, methanearsonic acid, cacodylic acid, and phenylarsonic acid. 97 Volatile arsenicals were detected from soils treated with sodium arsenate, MSMA, and cacodylic acid. Volatilization occurred under both aerobic and anaerobic conditions. Amounts volatilized were 0.64, 8.22, and 14.10% of the applied arsenate, MSMA, and cacodylic acid, respectively, in 150 days under aerobic conditions. Under anaerobic conditions, the amounts produced from arsenate, MSMA, and cacodylic acid were 1.60, 0.84, and 4.48%, respectively. Regardless of initial form or oxidative condition, only dimethylarsine was detected. 875

Arsenate, from pesticide or from fallout and runoff, is fixed in the soil as slightly soluble salts of iron, aluminum, calcium, and magnesium. These may be true compounds or surface-adsorbed reaction products. In addition, some arsenic is bound in organic forms in the soil. The arsenic that is not in an insoluble form is available for leaching into ground water, is available for uptake by plants and trees, and appears in spring water. As indicated earlier, all vegetation contains arsenic. Burning of agricultural wastes and forest and grass fires redistribute arsenic into the atmosphere, from which it is redeposited on the earth through particulate fallout or rain. Fungi and bacteria in the soil metabolize arsenic and the methylated derivatives to methylarsines. The methylarsines are unstable and are oxidized to As(V). Some of the reactions are shown in Table 3-22. These processes are mediated by microorganisms, as well as by chemical action. The faster reactions are the more environmentally important ones. The stable forms of man-made arsenic in the environment are o-arsenic acid and its salts. All other forms of methylated arsenic compounds yield o-arsenic acid in soil as a major sink. This form, however, can be methylated and put back into the cycle in nature. Braman detected arsenic in the III, V, methanearsonic, and cacodylic forms in Florida water. 99 His samples could not have been contaminated by pesticide application, so these forms appear to be part of the natural cycle.

TABLE 3-22. Chemical and Biologic Transformation of Arsenicals in Soil.

TABLE 3-22

Chemical and Biologic Transformation of Arsenicals in Soil.

The most important concept with respect to arsenic cycling in the environment is constant change. Arsenic appears everywhere in every living tissue and is constantly being oxidized, reduced, or otherwise metabolized. In the soil environment, insoluble or slightly soluble compounds are constantly being resolubilized and the arsenic presented for plant uptake or reduction by organisms and chemical processes. Man has modified the arsenic cycle only by causing localized high concentrations.

Copyright © National Academy of Sciences.
Bookshelf ID: NBK231016

Views

  • PubReader
  • Print View
  • Cite this Page
  • PDF version of this title (5.0M)

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...