Inhalation toxicology of automotive emissions as affected by an oxidation exhaust catalyst.

Preliminary data are given on the acute inhalation toxicology of automotive emissions as affected by an oxidation exhaust catalyst. The catalyst effectively reduced CO and HC in the exhause which apparently had an effect (at least in a closed exposure system) on oxidant and NO2 levels by altering the HC/NOx ratio. There was a resultant reduction in biological effects due to the exposure. The catalyst altered the type of particulate to one which probably contained sulfuric acid as a major component. No evidence was present in these acute exposures to suggest a toxic response due to the higher sulfate emissions or possible catalyst attrition products. The effects of long-term exposure have not yet been investigated.


Introduction
This report presents data from a series of acute animal exposure studies which were designed to assess certain health hazards of automobile exhaust from engines equipped with or without oxidative catalytic converters. It is expected that these catalytic converters will be widely used by the automobile manufacturers in order to control exhaust emission levels of carbon monoxide (CO) and hydrocarbons (HC). The concern, of course, is that use of these devices might release some other noxious or toxic substances into the environment. Three studies are discussed in this report: TAME I, J, and K. (TAME is an acronym used by us which means toxicologic assessment of mobile emis-* U.S. Environmental Protection Agency, National Environmental Research Center, Environmental Toxicology Research Laboratory, Cincinnati, Ohio 45268. sions.) TAME I was a study of the biological effects of whole exhaust from an automobile engine with no catalyst, which served as a reference or baseline study; TAME J was identical except for the addition of an oxidative catalyst to the exhaust train; TAME K had the catalyst plus additional organic sulfur compounds added to the fuel to maximize production of sulfate emissions.

Exposure System
The exhaust emission generation system used in these studies consisted of a 1973 Chevrolet 350 CID production engine equipped with exhaust gas recirculation (EGR), air pump, and turbohydramatic transmission coupled to an "eddy current" absorption dynamometer. In each study, the engine system was run continuously for 7 days on a modified California control cycle ( Table 1). The gasoline used in the Chevrolet engine as a reference fuel was American Oil Co. unleaded 91 octane test fuel, intermediate grade indolene clear ( Table 2). Note that in TAME K, thiophene was added to the reference fuel to produce a high sulfur fuel (1000 ppm). Some of the engine operating conditions are summarized in Table 3.
In TAME J and K, the exhaust passed through a noble metal pelletized type oxidation catalyst (manufactured by Engelhard Co. to General Motors specifications) and a muffler before mixing with CBR filtered and conditioned air in a dilution tube. The diluted exhaust was piped to a large volume mixing chamber and then entered dynamic flow irradiation chambers lighted to simulate sunlight so that photochemical reactions might occur. The irradiated exhaust then entered animal exposure chambers. Additionally, the system provided nonirradiated exhaust in the same concentration to other exposure chambers. In each study there were clean air atmospheres, and in TAME I there was a CO atmosphere for control animal exposures. The catalyst was removed from the system for the TAME I exposure.

Aerometry
The major components characterized in the exhaust emissions and methods used are summarized in Table 4. Particulate samples   were collected on pure quartz fiber filters. Bubbler and impinger samples of the atmospheres were used for collecting ammonia and sulfur based gases.
The concentration in the exposure chambers of the various emission components are shown in Table V. The incorporation of the oxidation catalyst into the exhaust system resulted in a large reduction in CO, total HC, and various individual organic compounds. In TAME I, the photochemical reactions in the irradiated atmospheres were very pronounced as evidenced by the presence of ozone, the low value for NO, and the high value for particulate. The color and weight stability suggested the particulate to be organic in nature. In TAME J and K, the particulate was strongly acidic, was liquid in nature, lost significant weight on standing, and contained sulfate as a primary constituent. All of this suggested sulfuric acid as the major particulate component.

Biologic Systems and Effects
Infant Mortality and Body Weight Determinations: Groups of 10 lactating female outbred albino rats and their 2-week old offspring (10 suckling rats/litter) were exposed to each of the treatment atmospheres for 7 days. Animals were weighed at the beginning and end of the study. Infant mortality was noted on a daily basis. As may be seen from Table 6, there was a prominent effect on infant mortality in those animals exposed to exhaust in TAME I. This was obviously not a CO effect alone, but rather due to the combination of biologically active pollutants. A parallel effect was noted as far as body weight changes (Table 7) in both the adult and suckling animals. In TAME J and K, there were not pronounced treatment effects on either of these parameters. Clinical Pathology Determinations: Groups of 25 adult male outbred albino rats were exposed to each treatment atmosphere. Five animals per treatment were removed on days 2-6 of the study, anesthetized, and exsanguinated by abdominal aorta catheterization. The clinical laboratory determinations and treatment means are shown in Tables 8-11. Again, a treatment effect, if present, occurred only in TAME I in the exhaust exposure groups with the more prominent changes in the animals exposed to irradiated exhaust. The high CO levels had some effect on the hematologic parameters but was not totally responsible. It should be further noted that the high CO levels produced a rather striking increase in hemolysis resistant red blood cells which necessitated manual determinations of white blood cell counts. No treatment effect was noted in TAME J or K. Because of the historical association of platinum with allergic responses, it was particularly interesting to note no increase in eosinophils in TAME J or K.
Tissue Chemistry Determinations: Samples of lung, liver and kidney were collected from animals exposed to the exhaust atmospheres for determination of platinum (Pt) and palladium (Pd). The tissue samples were lyophilized and wet digested by using aqua regia, all nitric acid fumes being eliminated by other additions of hydrochloric acid and subsequent heating. The digested samples were transferred with hydrochloric acid and deionized water to a volumetric flask with an acid concentration of 10%o. After the samples were treated with potassium iodide, the metals were concentrated by organic extraction with methyl isobutyl ketone. Aliquots (50 ul) were analyzed by using a Perkin-  detected in any of the tissue samples from TAME I, J, or K. Morphologic Pathology Determinations: Tissues from adult outbred albino rats and adult male golden Syrian hamsters exposed to each treatment were collected and fixed in 10%'o formalin. Specimens of lung, liver, and kidney were processed, paraffinembedded, sectioned, stained with hematoxylin and eosin, and examined microscopically for evidence of morphologic changes attributable to the exposure.
There were no treatment-related changes in TAME J or K. In TAME I, however, there were extensive pulmonary changes which were more severe in hamsters and most severe in those animals exposed to irradiated exhaust. In the nonirradiated exhaust group, the pulmonary changes were relatable to the levels of NO2, with an increase in alveolar macrophages at the level of terminal bronchioles initially, followed by a proliferative phase with some apparent increase in epithelialization of respiratory ductules, and in thickness of alveolar septae. In the hamsters exposed to irradiated exhaust there was a very severe acute purulent bronchitis and bronchiolitis which progressed to a subacute purulent bronchopneumonia by the end of the study. Additionally, there were some degenerative changes in renal and hepatic tissue by the end of the study in these animals. The only lesion which could be related solely to CO levels was extramedullary hematopoiesis in the liver of the rats after 4 days exposure.

Discussion
The initiating force behind use of the oxidative catalytic converter in the automobile exhaust train is the emission standards for CO and HC as set forth in the Clean Air Amendments of 1970 (1). The aerometry findings in this study would suggest that there is in fact a very marked reduction in CO and HC levels due to the use of the catalyst.
It was further expected that the oxidative catalysts would have minimal effect on NO, levels, which again was corroborated by these studies. The catalyst did have an indirect effect in the exposure system used in these studies on levels of NO2 and other oxidants (i.e., ozone) which constitute some of the more biologically active exhaust compounds relative to biological effects. The reasons for this relate to findings that at HC/NOX ratios less than 3:1, no free oxidant is formed (2).
These same HC/NOX ratios have a similar effect on NO2 levels due to the overall NO-NO2 reaction systems. In TAME I, the HC/NOZ ratio was about 9:1; in TAME J and K the ratios were about 1.5-2:1. This helps explain the pronounced reduction in acute toxicity associated with the exposures, rather than the lower levels of CO alone. As noted, the oxidation catalyst did have an effect on the type of particulate with an increase in the acidic fraction (probably sulfuric acid). There were no demonstrable acute biological effects in any of the animals studied which were attributable to these altered particulates. The study did not rule out possible chronic effects due to long-term exposure, either as a result of the increased sulfate emissions or attrition products of the noble metal oxidation catalyst. It is therefore imperative that long-term studies be initiated to provide this additional information.