Health Effects of Exposure to Diesel Engine Emissions: A Summary of Animal Studies Conducted by the U.S. Environmental Protection Agency's Health Effects Research Laboratories at Cincinnati, Ohio

Impact of a gestational exposure to diesel exhaust on offspring gonadal development: experimental study in the rabbit

The aim of the present work was to address experimentally the possible impact of exposure to air pollution during gestation on the differentiation and function of the gonads of the offspring using a rabbit model. Rabbits were exposed daily to diluted diesel exhaust gas or filtered air from the 3rd until the 27th day of gestation, during which time germ cells migrate in genital ridges and divide, and fetal sex is determined. Offspring gonads were collected shortly before birth (28th day of gestation) or after puberty (7.5 months after birth). The structure of the gonads was analyzed by histological and immunohistological methods. Serum concentrations of testosterone and anti-Müllerian hormone were determined using ELISA. The morphology and the endocrine function of the gonads collected just at the arrest of the exposure were similar in polluted and control animals in both sexes. No differences were observed as well in gonads collected after puberty. Sperm was collected at the head of the epididymis in adults. Sperm motility and DNA fragmentation were measured. Among all parameters analyzed, only the sperm DNA fragmentation rate was increased three-fold in exposed males. Mechanisms responsible for these modifications and their physiological consequences are to be further clarified.

A perspective on the developmental toxicity of inhaled nanoparticles

This paper aimed to clarify whether maternal inhalation of engineered nanoparticles (NP) may constitute a hazard to pregnancy and fetal development, primarily based on experimental animal studies of NP and air pollution particles. Overall, it is plausible that NP may translocate from the respiratory tract to the placenta and fetus, but also that adverse effects may occur secondarily to maternal inflammatory responses. The limited database describes several organ systems in the offspring to be potentially sensitive to maternal inhalation of particles, but large uncertainties exist about the implications for embryo-fetal development and health later in life. Clearly, the potential for hazard remains to be characterized. Considering the increased production and application of nanomaterials and related consumer products a testing strategy for NP should be established. Due to large gaps in data, significant amounts of groundwork are warranted for a testing strategy to be established on a sound scientific basis.

Mechanisms Involved in A/J Mouse Lung Tumorigenesis Induced by Inhalation of an Environmental Tobacco Smoke Surrogate

Lung tumors have been reproducibly induced in A/J mice exposed to a surrogate for experimental environmental tobacco smoke (ETSS) in a 5-mo inhalation period followed by 4 mo without further exposure. In order to increase our mechanistic understanding of this model, male mice were whole-body exposed for 6 h/d, 5 d/wk to ETSS with a particulate matter concentration of 100 mg/m(3). Food restriction regimens were included to model or exceed the ETSS-related impairment of body weight development. Half of the mice were pretreated with a single ip injection of urethane to study the effect of the above treatments on lung tumor development induced by this substance. At 5 mo, the tumor response was statistically the same for all groups of non-pretreated mice; however, the expected urethane-induced lung tumorigenesis was significantly inhibited by approximately 25% by ETSS and food restriction. This inhibition was accompanied by a threefold increase in blood corticosterone as a common stress marker for both ETSS and food restriction. At 9 mo, in mice not pretreated, the lung tumor incidence and multiplicity were significantly increased by twofold in the ETSS group; in the urethane-treated groups, the same high tumor multiplicity was reached regardless of previous treatment. The predominant tumor type in all groups was bronchiolo-alveolar adenoma. There was no induction of a specific K-ras mutation pattern by ETSS exposure. These data suggest a stress-induced inhibition of lung tumorigenesis in this model, explaining the need for the posttreatment period.

Health Effects of Subchronic Exposure to Environmental Levels of Diesel Exhaust

Diesel exhaust is a public health concern and contributor to both ambient and occupational air pollution. As part of a general health assessment of multiple anthropogenic source emissions conducted by the National Environmental Respiratory Center (NERC), a series of health assays was conducted on rats and mice exposed to environmentally relevant levels of diesel exhaust. This article summarizes the study design and exposures, and reports findings on several general indicators of toxicity and carcinogenic potential. Diesel exhaust was generated from a commonly used 2000 model 5.9-L, 6-cylinder turbo diesel engine operated on a variable-load heavy-duty test cycle burning national average certification fuel. Animals were exposed to clean air (control) or four dilutions of whole emissions based on particulate matter concentration (30, 100, 300, and 1000 microg/m(3)). Male and female F344 rats and A/J mice were exposed by whole-body inhalation 6 h/day, 7 days/wk, for either 1 wk or 6 mo. Exposures were characterized in detail. Effects of exposure on clinical observations, body and organ weights, serum chemistry, hematology, histopathology, bronchoalveolar lavage, and serum clotting factors were mild. Significant exposure-related effects occurring in both male and female rats included decreases in serum cholesterol and clotting Factor VII and slight increases in serum gamma-glutamyl transferase. Several other responses met screening criteria for significant exposure effects but were not consistent between genders or exposure times and were not corroborated by related parameters. Carcinogenic potential as determined by micronucleated reticulocyte counts and proliferation of adenomas in A/J mice were unaffected by 6 mo of exposure. Parallel studies demonstrated effects on cardiac function and resistance to viral infection; however, the results reported here show few and only modest health hazards from subchronic or shorter exposures to realistic concentrations of contemporary diesel emissions.

Health effects of subchronic exposure to diesel-water-methanol emulsion emission

The U.S. Environmental Protection Agency's National Ambient Air Quality Standards for ozone and particulate matter (PM) require urban non-attainment areas to implement pollution-reduction strategies for anthropogenic source emissions. The type of fuel shown to decrease combustion emissions components versus traditional diesel fuel, is the diesel emulsion. The Lubrizol Corporation, in conjunction with Lovelace Respiratory Research Institute and several subcontracting laboratories, recently conducted a health assessment of the combustion emissions of PuriNOx diesel fuel emulsion (diesel-water-methanol) in rodents. Combustion emissions from either of two, 2002 model Cummins 5.9L ISB engines, were diluted with charcoal-filtered air to exposure concentrations of 125, 250 and 500 microg total PM/m3. The engines were operated on a continuous, repeating, heavy-duty certification cycle (U.S. Code of Federal Regulations, Title 40, Chapter I) using Rotella-T 15W-40 engine oil. Nitrogen oxide (NO) and PM were reduced when engines were operated on PuriNOx versus California Air Resources Board diesel fuel under these conditions. Male and female F344 rats were housed in Hazleton H2000 exposure chambers and exposed to exhaust atmospheres 6 h/day, five days/week for the first 11 weeks and seven days/week thereafter. Exposures ranged from 61 to 73 days depending on the treatment group. Indicators of general toxicity (body weight, organ weight, clinical pathology and histopathology), neurotoxicity (glial fibrillary acidic protein assay), genotoxicity (Ames assay, micronucleus, sister chromatid exchange), and reproduction and development were measured. Overall, effects observed were mild. Emulsion combustion emissions were not associated with neurotoxicity, reproductive/developmental toxicity, or in vivo genotoxicity. Small decreases in serum cholesterol in the 500-microg/m3 exposure group were observed. PM accumulation within alveolar macrophages was evident in all exposure groups. The latter findings are consistent with normal physiological responses to particle inhalation. Other statistically significant effects were present in some measured parameters of other exposed groups, but were not clearly attributed to emissions exposure. Positive mutagenic responses in several strains of Salmonella typhimurium were observed subsequent to treatment with emulsion emissions subfractions. Based on the cholesterol results, it can be concluded that the 250-microg/m3 exposure level was the no observed effect level. In general, biological findings in exposed rats and bacteria were consistent with exposure to petroleum diesel exhaust in the F344 rat and Ames assays.

Chronic nose-only inhalation study in rats, comparing room-aged sidestream cigarette smoke and diesel engine exhaust

Nose-only exposure of male and female Wistar rats to a surrogate for environmental tobacco smoke, termed room-aged sidestream smoke (RASS), to diesel engine exhaust (DEE), or to filtered, fresh air (sham) was performed 6 hours/day, 7 days/week for 2 years, followed by a 6-month post-exposure period. The particulate concentrations were 3 and 10 mg/m3. Markers of inflammation in bronchoalveolar lavage showed that DEE (but not RASS) produced a dose-related and persistent inflammatory response. Lung weights were increased markedly in the DEE (but not RASS) groups and did not decrease during the 6-month post-exposure period. Bulky lung DNA adducts increased in the RASS groups, but not in the DEE groups. Cell proliferation in the lungs was unaffected by either experimental treatment. Histopathological responses in the RASS groups were minimal and almost completely reversible; lung tumors were similar in number to those seen in the sham-exposed groups. Rats exposed to DEE showed a panoply of dose-related histopathological responses: largely irreversible and in some cases progressive. Malignant and multiple tumors were seen only in the DEE groups; after 30 months, the tumor incidence (predominantly bronchiolo-alveolar adenomas) was 2% in the sham-exposed groups, 5%in the high RASS groups, and 46% in the high DEE groups (sexes combined). Our results suggest that in rats exposed to DEE, but not to RASS, the following series of events occurs: particle deposition in lungs --> lung "overload" --> pulmonary inflammation --> tumorigenesis, without a significant modifying role of cell proliferation or DNA adduct formation.

Health effects of subchronic exposure to diesel-water emulsion emission

The U.S. Environmental Protection Agency (EPA) National Ambient Air Quality Standards for ozone and particulate matter are requiring urban nonattainment areas to implement pollution-reduction strategies for anthropogenic source emissions. A type of fuel shown to decrease combustion emissions components versus traditional diesel fuels is the diesel-water emulsion. The Lubrizol Corporation in conjunction with Lovelace Respiratory Research Institute and several subcontracting laboratories recently conducted a rodent health assessment of inhaled combustion emissions of PuriNO(x) diesel fuel emulsion. Combustion emissions from either of two 2001 model Cummins 5.9-L ISB engines were diluted with charcoal-filtered air to exposure concentrations of 100, 200, and 400 microg total particulate matter/m(3). The engines were operated on a continuously repeating, heavy-duty certification cycle (U.S. Code of Federal Regulations, Title 40, Chapter I) using Rotella-T 15W-40 engine oil. Nitrogen oxide and particulate matter were reduced when engines were operated on PuriNO(x) versus California Air Resources Board diesel fuel under these conditions. Male and female F344 rats were housed in Hazleton H2000 exposure chambers and exposed to exhaust atmospheres 6 h/day, 5 days/wk for the first 11 wk and 7 days/wk threafter. Exposures ranged from 58 to 70 days, depending on the treatment group. Indicators of general toxicity (body weight, organ weight, clinical pathology, and histopathology), neurotoxicity (glial fibrillary acidic protein assay), genotoxicity (Ames assay, micronucleus, sister chromatid exchange), and reproduction and development were measured. Overall, effects observed were mild. Emulsion combustion emissions were not associated with neurotoxicity, reproductive/developmental toxicity, or in vivo genotoxicity. Small decreases in serum cholesterol and small increases in platelet values in some groups of exposed animals were observed. Particulate matter accumulation within alveolar macrophages was evident in all exposure groups. These findings are consistent with normal physiological responses to particle inhalation. Other statistically significant effects were present in some measured parameters of other exposed groups but were not clearly attributed to emissions exposure. Positive mutagenic responses in several strains of Salmonella typhimurium were observed subsequent to treatment with emulsion emissions subfractions. Based on the cholesterol and platelet results, it can be concluded that the 100 microg/m(3) exposure level was the no-observed-effect level. In general, biological findings in diesel emulsion emission-exposed animals and bacteria were consistent with exposure to petroleum diesel exhaust in the F344 rat and Ames assays.

Carcinogenicity studies of diesel engine exhausts in laboratory animals: a review of past studies and a discussion of future research needs

Diesel engines play a vital role in world economy, especially in transportation. Exhaust from traditional diesel engines using high-sulfur fuel contains high concentrations of respirable carbonaceous particles with absorbed organic compounds. Recognition that some of these compounds are mutagenic has raised concern for the cancer-causing potential of diesel exhaust exposure. Extensive research addressing this issue has been conducted during the last three decades. This critical review is offered to facilitate an updated assessment of the carcinogenicity of diesel exhaust and to provide a rationale for future animal research of new diesel technology. Life-span bioassays in rats, mice, and Syrian hamsters demonstrated that chronic inhalation of high concentrations of diesel exhaust caused lung tumors in rats but not in mice or Syrian hamsters. In 1989, the International Agency for Research on Cancer (IARC) characterized the rat findings as "sufficient evidence of animal carcinogenicity," and, with "limited" evidence from epidemiological studies, classified diesel exhaust Category 2A, a "probable human carcinogen." Subsequent research has shown that similar chronic high concentration exposure to particulate matter generally considered innocuous (such as carbon black and titanium dioxide) also caused lung tumors in rats. Thus, in 2002, the U.S. Environmental Protection Agency (EPA) concluded that the findings in the rats should not be used to characterize the cancer hazard or quantify the cancer risk of diesel exhaust. Concurrent with the conduct of the health effects studies, progressively more stringent standards have been promulgated for diesel exhaust particles and NOx. Engine manufacturers have responded with new technology diesel (improved engines, fuel injection, fuels, lubricants, and exhaust treatments) to meet the standards. This review concludes with an outline of research to evaluate the health effects of the new technology, research that is consistent with recommendations included in the U.S. EPA 2002 health assessment document. When this research has been completed, it will be appropriate for IARC to evaluate the potential cancer hazard of the new technology diesel.

Case-control study on occupational exposure to diesel exhaust and lung cancer risk

The association between lung cancer and occupations with probable exposure to diesel exhaust (DE) was studied among 2,584 cases and 5,099 hospital controls. The crude odds ratio (OR) for probable exposure was 1.31 (95% confidence interval [CI] 1.09-1.57), but adjustment for smoking and other confounders reduced the estimate to 0.95 (95% CI = 0.78-1.16). Similar results were observed for truck drivers, the only occupational category large enough for separate analysis. Data on self-reported exposure for 477 cases and 946 controls revealed a crude OR of 1.45 (95% CI = 0.93-2.27), which was reduced to 1.21 (95% CI = 0.78-2.02) after controlling for smoking and other confounders. The present results and a review of the literature do not definitively support an etiologic association between DE exposure and elevated lung cancer risk.

Diesel exhaust exposure and mortality among males in the American Cancer Society prospective study

In 1982, the American Cancer Society enrolled over 1.2 million American men and women in a prospective mortality study of cancer and other causes in relation to different risk factors. The 2-year mortality of 461,981 males aged 40-79 years with known smoking habit has been analyzed in relation to exposure to diesel exhaust (DE) and to employment in selected occupations related to DE exposure. The relative risk (RR) for all causes of death for those exposed was 1.05 (95% confidence interval [CI]: 0.97-1.13). For lung cancer, the RR was 1.18 (95% CI: 0.97-1.44). A dose-response effect was present. Railroad workers, heavy equipment operators, miners, and truck drivers had a higher mortality both for all causes and for lung cancer when compared with subjects with other occupations and no exposure to DE. Truck drivers exposed to DE were not at excess risk of lung cancer if compared with truck drivers unexposed to DE, but a trend of increasing risk with duration of exposure was suggested. DE exposure was also associated with increase in mortality for accidents, cerebrovascular disease, arteriosclerosis, and cirrhosis of the liver. An association based on small numbers was also present for Hodgkin's disease and lymphoid leukemia. No association with chronic non-neoplastic pulmonary diseases or with bladder cancer was found.

Chronic effects on the respiratory tract of hamsters, mice and rats after long-term inhalation of high concentrations of filtered and unfiltered diesel engine emissions

A long-term exposure study with hamsters, mice and rats inhaling filtered and unfiltered diesel engine exhaust was carried out to investigate effects of chronic toxicity and, predominantly, carcinogenicity in the respiratory tract. The level of diesel exhaust in the exposure chambers corresponded to a concentration close to 4 mg m-3 in the unfiltered diesel exhaust. Satellite groups of animals were additionally treated with BaP, DBahA or nitrosamines in order to check for syncarcinogenic effects. In hamsters and rats, alveolar lung clearance and mechanical lung function tests as well as biochemical and cytological measurements in lung lavage fluids showed significant changes only after exposure to unfiltered diesel exhaust and, predominantly, in rats. No lung tumors were found in hamsters. Spontaneous tumor rates occurred in mice and both types of diesel exhaust increased the incidence of adenocarcinomas in the lungs. In rats, only the unfiltered diesel exhaust caused a lung tumor incidence. It amounted to 16% with no tumors in the controls. The heavy load of particulate matter in the lungs of rats was caused by an exposure-related impairment of the alveolar lung clearance and may have been instrumental in the induction of squamous cell tumors. However, an effect of particle-associated PAH cannot be excluded. Syncarcinogenic effects of diesel exhaust after initial carcinogen treatment were found only in the respiratory tract of rats.

Effect of diesel emissions and coal dust inhalation on heart and pulmonary arteries of rats

Fischer 344 (SPF) rats were exposed by inhalation to respirable particulate levels of 2 mg/m3 diesel emissions, diesel emissions plus coal dust, coal dust, or air for 7 h/d, 5 d/wk for 24 mo. The effects of treatment on body and heart weights, right and left ventricular wall thickness, severity of cardiomyopathy, and changes in the small pulmonary arteries were evaluated after 24 mo of exposure. In all dust-exposed animals, light microscopic examination of the lungs revealed dust-laden macrophages in alveolar spaces and focal accumulations of dust-laden macrophages near the respiratory bronchioles associated with hyperplasia of type II cells. This response was more prominent in animals exposed to diesel emissions alone. Age-related myocardial fibrosis and inflammatory infiltrates were common in all four groups. No statistically significant differences were detected between the groups for heart weights, ventricular wall thickness, and pulmonary arterial wall thickness. However, animals exposed to diesel emissions did show a consistent trend toward increased pulmonary arterial wall thickness, for all size categories of artery, compared to controls.

Chronic inhalation of diesel exhaust and coal dust: effect of age and exposure on selected enzyme activities associated with microsomal cytochrome P-450 in rat lung and liver

Male Fisher-344 rats were exposed by inhalation to low levels of diesel exhaust and coal dust, alone or in combination, or to filtered air, 7 h/d, 5 d/wk for 24 mo. Cytochrome P-450-associated benzo[a]pyrene hydroxylase and 7-ethoxycoumarin deethylase activities were assayed in lung and liver microsomes after 3, 6, and 24 mo. Age-related changes in enzyme activities were observed, but they were not altered by the exposures. When the data were adjusted for age, only one difference was observed. Lung benzo[a]pyrene hydroxylase activity in rats exposed to diesel exhaust and coal dust in combination was lower than that in animals exposed to coal dust alone (2.8 versus 4.4 pmol/min X mg protein). Neither value, however, differed significantly from the filtered-air controls, and no differences were observed in the other lung and liver activities. The data suggest exposure of the rats to diesel exhaust and/or coal dust had little or no effect on the selected lung and liver cytochrome P-450 activities under the conditions of the experiment.