Calcium hypochlorite

1. Description: White powder or flat plates
2. Melting-point: Decomposes at 100°C
3. Density. Specific gravity = 2.35
4. Solubility: Soluble in cold water, 21.4% soluble at 25°C (Wojtowicz, 1979); insoluble in ethanol
5. Stability: Solid form decomposes exothermically when heated to 175°C, releasing oxygen (Mannsville Chemical Products Corp., 1987). Can react vigorously, and sometimes explosively, with organic and inorganic materials; aqueous solutions subject to decomposition which is influenced by concentration, ionic strength, pH, temperature, light and impurities (Wojtowicz, 1979).
6. Reactivity. Strong oxidizer of organic and inorganic materials; also acts as a chlorinating agent toward some classes of organic compounds (Wojtowicz, 1979)

Sodium hypochlorite pentahydrate

1. Description: Colourless crystals
2. Melting-point: 18°C
3. Solubility. In water (g/l): 293 at 0°C, 942 at 23°C
4. Stability. Highly unstable (Budavari, 1989)
5. Reactivity. Strong oxidizer of organic and inorganic compounds (Wojtowicz, 1979)

Sodium hypochlorite solution (aqueous)

1. Description: Clear or slightly yellow solution
2. Stability. Anhydrous hypochlorite is highly explosive; the solution is subject to decomposition, which is influenced by its concentration, ionic strength, pH, temperature, light and impurities; also susceptible to catalysis by trace metal impurities (Wojtowicz, 1979)
3. Reactivity. Strong oxidizer of many organic and inorganic substances and chlorinates some classes of organic compounds. Contact with acid releases chlorine gas (Jones Chemical, 1989). Reacts violently with ammonium salts, aziridine, methanol and phenylacetonitrile, sometimes resulting in explosion. Reacts with primary aliphatic and aromatic amines to form explosively unstable N-chloramines. Reaction with formic acid becomes explosive at 55°C (Sigma-Aldrich Company, 1989).

Sodium hypochlorite dihydrate

1. Description: Colourless hygroscopic crystals
2. Melting-point: 57.5°C
3. Solubility. Very soluble in cold water

The chemistry of hypochlorite ion in aqueous solutions is discussed in the monograph on chlorinated drinking-water (p. 50). All hypochlorite salts, as well as chlorine itself, in aqueous solution produce equilibrium mixtures of hypochlorous acid, hypochlorite ion and chlorine. In concentrated solutions, hypochlorite ion tends to disproportionate to form chlorate and chloride ions. The reaction is slow at room temperature, but in hot solutions (e.g., 80°C) the reaction is rapid and produces high yields of chlorate ions (Aieta & Roberts, 1986).

Calcium hypochlorite

Trade names: B-K Powder; Camporit; Chemichlor G; Chloride of lime; Eusol BPC; HTH; HTH (bleaching agent); Lime chloride; Losantin; Pittchlor; Solvox KS; T-Eusol

Calcium hypochlorite (bleach liquor) is produced commercially as a solution of calcium hypochlorite and calcium chloride containing some dissolved lime. Commercial products usually contain 50% or more calcium hypochlorite. The available chlorine content varies but is usually about 30–35 g/l (Wojtowicz, 1979; Budavari, 1989).

Calcium hypochlorite is one of the few metal hypochlorites that is stable enough to be produced as a solid salt. It is produced on a large scale as a 65–70% pure product (dihydrate salt) containing sodium chloride and water as the main impurities. It is also manufactured, to a smaller extent, in the form of bleaching powder (Wojtowicz, 1979), which contains approximately 37% available chlorine in a complex mixture of calcium hydroxide, calcium chloride and various calcium hypochlorite species. Calcium oxide is often blended with bleach powder as a desiccant in order to avoid deliquescence of the powder in hot and humid conditions; this blended product, tropical bleach, contains about 15–30% available chlorine (Baum et al., 1978).

Sodium hypochlorite (liquid bleach)

Trade names: Antiformin; B-K Liquid; Carrel-Dakin solution; Chloros; Clorox; Dakin’s solution; Deosan; Hyclorite; Javex; Klorocin; Milton; Neo-cleaner; Neoseptal CL; Parozone; Purin B; Surchlor

Commercial strength sodium hypochlorite is available as a solution that contains 12–15% available chlorine; a weaker solution that is marketed contains approximately 5% available chlorine. The main impurities in these solutions include sodium chlorate, sodium carbonate, sodium chloride and sodium hydroxide. Sodium hypochlorite solution produced on-site for industrial processes generally contains 30–40 g/l of available chlorine (Wojtowicz, 1979).

Lithium hypochlorite

Commercial lithium hypochlorite is a solid product usually containing 35% lithium hypochlorite, 34% sodium chloride and various additional salts (Baum et al, 1978; Wojtowicz, 1979).

(a) Production

Berthollet first used chlorine in a commercial textile bleaching process in the 1790s; he later discovered that chlorine could be absorbed by caustic potash to form potassium hypochlorite solution (Javel water). Labarraque replaced the expensive potash with caustic soda, and by the early 1800s Labarraque’s solution had replaced potassium hypochlorite in the bleaching of textiles. Tennant experimented with a solution of chlorine and milk of lime in 1798 and later discovered that when slaked lime was treated with chlorine a solid bleaching powder (calcium hypochlorite and other salts) was formed, representing the first solid form of chlorine bleach that could be easily transported. Bleaching powder remained the principal textile bleach throughout the 1800s. Tropical bleach, stable in high tropical temperatures, was produced by the addition of quicklime to bleaching powder. After the First World War, technology for shipping liquid chlorine and caustic economically was developed, allowing bleach solutions to be made at the point of use. In 1928, the first dry calcium hypochlorite with 70% available chlorine was produced in the USA and was used widely in the bleaching of textiles and pulp (Baum et al., 1978; Wojtowicz, 1979).

At the inception of the commercial laundry industry in about 1900, sodium hypochlorite solution made with bleaching powder and soda ash was used. When chlorine became more readily available, sodium hypochlorite was produced directly at the point of use. Dry calcium hypochlorite bleaches were introduced in the 1930s. Home bleaching became more common when sodium hypochlorite solutions began to displace bleaching powders in the 1930s; they came into extensive use in the 1940s (Baum et al., 1978). Other hypochlorites, such as lithium hypochlorite, first introduced in 1964, have had limited commercial use (Wojtowicz, 1979).

Calcium hypochlorite solution (bleach liquor) is prepared by adding chlorine to a diluted high quality lime slurry. Solid calcium hypochlorite is generally made by drying a filter cake of neutral calcium hypochlorite dihydrate prepared from hydrated lime, caustic and chlorine. Several industrial processes were developed to eliminate or minimize calcium chloride in the hypochlorite product (Wojtowicz, 1979).

Sodium hypochlorite is usually prepared by chlorinating aqueous sodium hydroxide solution at reduced temperatures to prevent excessive chlorate formation, which can contribute to lower stability. Conversion of sodium hydroxide to hypochlorite is usually limited to 92–94% to prevent overchlorination and to improve stability. Sodium hypochlorite is also prepared electrolytically using small diaphragm-less or membrane cells with a capacity of 1–150 kg per day of equivalent chlorine; these produce dilute hypochlorite solutions of 1–3 and 5–6 g/l from seawater and brine, respectively (Wojtowicz, 1979).

Solid lithium hypochlorite is produced by combining concentrated solutions of sodium hypochlorite and lithium chloride (Baum et al., 1978).

Production capacity of calcium hypochlorite in 1989–90 in countries for which data were available are presented in Table 2. Japanese production of sodium hypochlorite (12% solution) was 947 thousand tonnes in 1984, 954 in 1985, 996 in 1986, 972 in 1987 and 989 in 1988 (Anon., 1985; Ministry of International Trade and Industry, 1989).

Table 2.

Production capacity of calcium hypochlorite in selected countries (in thousands of tonnes).

Sodium hypochlorite is produced by two companies in Africa, three in the Middle East, five in Oceania, 13 in North America, 18 in South America, 30 in Asia and 48 companies in Europe (Chemical Information Services Ltd., 1988). Calcium hypochlorite is produced by 21 companies and potassium chlorite by three companies throughout the world (Anon., 1989).

(b) Use

Calcium hypochlorite is widely used as a sanitizer, oxidizer and bleaching agent. Calcium hypochlorite solutions are used primarily in pulp and textile bleaching, while the solid form is used in less developed countries for textile bleaching and commercial laundering (Baum et al., 1978). The largest use of calcium hypochlorite within the USA is in swimming pools to kill bacteria, control algae and oxidize organic contaminants. It is also used to destroy cyanides in industrial wastes, in disinfection and deodourizing of wastes generated from canneries, dairy plants, beet sugar plants and tanneries, as a biocide in controlling contamination in public, private and industrial water supplies, in sanitizing beverage plants and food processing operations and equipment, in disinfecting sewage disposal plants, in sanitizing fruits and vegetables during growth and following harvest, as a toilet tank sanitizer and in multistage pulp bleaching processes. It can also be reacted with acetone to produce USP chloroform (Mannsville Chemical Products Corp., 1987).

Consumption of calcium hypochlorite in 1989–90 was estimated to be 7.0 thousand tonnes in Japan, 80.1 thousand tonnes in the USA and 40 thousand tonnes in the rest of the world. Use distribution figures for 1989–90 were estimated to be 85% for swimming pools and 15% for other uses in the USA, and 55% for swimming pools and 45% for other uses in the rest of the world (PPG Industries, 1990).

The largest use for sodium hypochlorite solutions (5% concentration) is as a household bleach. More concentrated solutions are used in swimming pool sanitation, in commercial laundry bleaching, in paper and pulp production, in disinfecting municipal water (particularly in small water supplies) and sewage, in the sanitation of dairy plants and food processing operations, to control fungal plugging of oil production equipment, as a desulfurizing agent in oil refineries, and as a disinfectant and sanitizer in health care industries. Large quantities of sodium hypochlorite are used in the chemical industry, primarily in the production of hydrazine (see IARC, 1987) as well as in the synthesis of organic chemicals and the manufacture of chlorinated trisodium phosphate. Sodium hypochlorite solutions produced directly by electrolysis of seawater or brine are used primarily in sewage and wastewater treatment, commercial laundries, large swimming pools and aboard ships (Baum et al., 1978; Wojtowicz, 1979; White, 1986; Mannsville Chemical Products Corp., 1987).

Small quantities of lithium hypochlorite are produced for use in swimming pool sanitation (Mannsville Chemical Products Corp., 1987) and in household laundry detergents (Baum et al., 1978).

(a) Natural occurrence

Hypochlorous acid is generated in mammalian neutrophils by myeloperoxidase (MP) by the following reaction:

(Winterbourn, 1985).

(b) Occupational exposure

Due to the wide range of uses of hypochlorite salts, many workers may be exposed to them by dermal (and ocular) contact or inhalation. During routine monitoring in a US calcium hypochlorite manufacturing facility, personal samples contained an 8-h time-weighted average of 0.31 mg/m³ (geometric mean) and a 15-min short-term exposure level of 0.38 mg/m³ (geometric mean); work area samples contained an 8-h time-weighted average of 0.13 mg/m³ and a mean 15-min short-term exposure level of 0.88 mg/m³ (PPG Industries, 1990). No published data were available on occupational exposures to or the environmental occurrence of hypochlorites. No regulatory standards or guidelines have been established for exposures to hypochlorite.

(c) Water

The chemistry of hypochlorous acid and hypochlorite ion in aqueous solutions is discussed in the monograph on chlorinated drinking-water (p. 50). Residual chlorine in drinking-water is present in part as hypochlorite, indicating widespread exposure of the general population to low levels of hypochlorite in solution.

(d) Other

Another significant potential route of exposure to hypochlorite derives from its widespread use as a household sanitizer and bleach and in swimming pools. No data were found which directly characterize these exposures.

(a) Oral administration

Mouse: Groups of 50 male and 50 female B6C3F₁ mice, four to six weeks old, were given 500 or 1000 mg/l sodium hypochlorite (14% effective chlorine [purity unspecified]) in the drinking-water for 103 weeks. Groups of 73 male and 72 female mice served as controls. Survival at 106 weeks was: males—control, 48/73, low-dose, 39/50; high-dose, 37/50; females-control, 56/72; low-dose, 40/50; high-dose, 39/50. There was no effect upon tumour incidence in either male or female mice (Kurokawa et al., 1986).

Rat: A group of 60 male and female BDII (cPah albino) rats, 100 days old [sex ratio unspecified], was given tap water [organic content not analysed] containing 100 mg/l chlorine prepared with chlorine gas. The animals were mated and the treatment was continued for life through six generations, with the exception of F₃ and F4 animals, which were treated during the weaning period only. Altogether, 236 animals in five generations were exposed. Two groups of 20 and 36 rats [sex and age unspecified] from two previous experiments served as controls. There was no difference in survival or in tumour incidence in any generation group as compared to untreated controls (Druckrey, 1968).

Groups of 50 male and 50 female Fischer 344 rats, seven weeks old, were given 0, 500 or 1000 (males) and 0, 1000 or 2000 (females) mg/l sodium hypochlorite (14% effective chlorine [purity unspecified]) in the drinking-water for 104 weeks. Survival at 112 weeks was: males—control, 30/50; low-dose, 26/50; high-dose, 31/50; females—control, 31/50; low-dose, 36/50; high-dose, 35/50. The occurrence of tumours at any site was not significantly greater in rats receiving sodium hypochlorite than in controls. The proportions of low- and high-dose female rats with fibroadenomas of the mammary gland were significantly lower than among controls (control, 8/50; low-dose, 0/50; p < 0.01, chi-square test; high-dose, 1/50; p < 0.01). Similarly, the proportion of high-dose male rats with nodular hyperplasia of the liver was decreased (control, 23/49; low-dose, 17/50; high-dose, 10/50; p < 0.01) (Hasegawa et al., 1986).

(b) Skin application

Mouse: A group of 40 strain ddN female mice, five weeks old, was given 60 topical applications of sodium hypochlorite (10% effective chlorine solution) [purity, vehicle and frequency of application unspecified]. Another group of 40 female mice was given 20 applications of 4-nitroquinoline 1-oxide [dose, purity and frequency unspecified]; and a third group of 40 mice was given 45 applications of sodium hypochlorite following applications of 4-nitroquinoline 1-oxide [number and frequency of applications and dose unspecified]. No skin tumour occurred in mice given applications of sodium hypochlorite alone, whereas skin tumours occurred in 9/32 mice given applications of sodium hypochlorite following initiating doses of 4-nitroquinoline 1-oxide. The skin tumours included one fibrosarcoma, three squamous-cell carcinomas and five papillomas. No skin tumour occurred in mice given applications of 4-nitroquinoline 1-oxide only (Hayatsu et al., 1971). [The Working Group noted the lack of details on dose, frequency of applications, age at termination of the study, and survival.]

A group of 20 female Sencar mice, six weeks old, was given topical applications of 0.2 ml of a solution of 10 g/l sodium hypochlorite [purity unspecified] in acetone twice a week for 51 weeks at which time the study was terminated. A group of 15 female mice given applications of acetone served as controls. All mice survived to the end of the study and no skin tumour was observed in the treated or control groups (Kurokawa et al., 1984). [The Working Group noted the small number of animals used.]

In an initiation/promotion study, a group 20 female Sencar mice, six weeks old, was given a single topical application of 20 nmol [5 μg] 7,12-dimethylbenz[a]-anthracene in acetone followed by applications of 0.2 ml of a 10 g/l sodium hypochlorite solution [purity unspecified] in acetone twice a week for 51 weeks. A group of 15 female mice given a single application of 7, 12-dimethylbenz[a]-anthracene followed by applications of acetone served as controls. The effective number of mice was 20; the number of survivors was not given. A squamous-cell carcinoma of the skin occurred in 1/20 mice treated with 7,12-dimethylbenz[a]-anthracene and sodium hypochlorite; none occurred in the initiated controls (Kurokawa et al., 1984).

(a) Experimental systems

(iv) Genetic and related effects (Table 3)

Table 3.

Genetic and related effects of sodium hypochlorite.

In one differential toxicity test involving DNA repair-deficient bacteria, a positive result was obtained with sodium hypochlorite. Mutations were induced in Salmonella typhimurium.

In a single study, sodium hypochlorite caused chromosomal aberrations in Chinese hamster CHL cells but not in human fibroblasts. [The Working Group noted that lower doses were used in the latter tests.] It was reported in an abstract that sodium hypochlorite did not induce transformation in C3H 10T½ cells (Abernethy et al., 1983). The number of micronuclei was increased in erythrocytes of newt larvae reared in hypochlorite-containing water for 12 days. Neither micronuclei, chromosomal aberrations nor aneuploidy were observed in mice after repeated oral dosing; but abnormal sperm morphology was seen.

In a report lacking details, negative findings were reported in a Bacillus subtilis rec^+/- assay, in a mutation assay in silkworms and in a test for chromosomal aberrations in rat bone marrow in vivo (Kawachi et al., 1980).

(b) Humans

Overall evaluation

Hypochlorite salts are not classifiable as to their carcinogenicity to humans (Group 3).