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

A Chronic Inhalation Toxicity Study of Diesel Engine Emissions and Coal Dust, Alone and Combined

To evaluate the potential health hazards of diesel engine emissions in underground coal mines, inhalation studies were performed using three species of animals. A wide range of toxicological responses was measured. Exhaust was provided by a 425 in.3 displacement four-cycle, water-cooled, naturally aspirated diesel engine (Caterpillar Model 3304) equipped with a water scrubber. Exposures were 7 h/day, 5 days/week, for periods up to 24 months. Micronized coal dust was generated using a Wright dust feeder. Four exposures were evaluated: (1) filtered ambient air, (2) 2 mg/m3 diesel particulate, (3) 2 mg/m3 respirable coal dust, and (4) 1 mg/m3 each of 2 and 3. Gaseous and vapor concentrations were similar in both exposures employing diesel exhaust. Male cynomolgus monkeys, Fischer-344 male and female rats, and female CD-1 mice were the experimental subjects. Monkeys were sacrificed at 24 months, rats at 3, 6, 12, and 24 months, and mice at 1, 3, and 6 months.

Gross morphology and histopathology demonstrated that both diesel and coal dust particles are deposited in the lungs and retained in alveolar tissue. Alveolar type II cell hyperplasia and pulmonary lipidosis occurred in rats, being most evident in rats exposed to diesel exhaust alone. There was, however, no evidence of emphysema or chronic bronchitis, and only minimal fibrosis was seen in association with the retained particulate. Both particulates affected the defense mechanisms of the lung. Exposure to coal dust activated responses associated with phagocytosis, whereas exposure to diesel exhaust depressed them. Severity of influenza challenge increased concomitantly with decreased interferon production in diesel-exposed mice. Exposure to diesel emissions did not result in genotoxic effects as measured by increases in sister chromatid exchange, chromosomal aberrations, micronucleus testing, and urine genotoxic assays. Pulmonary function studies in monkeys showed mild obstructive airway disease in coal dust, diesel exhaust, and the combined exposed animals. This effect was most pronounced in monkeys exposed to diesel exhaust. Evidence of restrictive lung disease was not seen in any group. Clearance of F3O4 particles appeared to be stimulated by exposure to diesel exhaust in the first 3 months, but long-term clearance of diesel particulate appeared to be inhibited. No evidence was found for increases in tumorogenicity (rats) or induction of xenobiotic metabolizing enzymes in the lung or liver (rats). Humoral and cellular immunities were not significantly affected by exposure (rats). No adverse seminal effects were observed in monkeys exposed for 2 years. There was no frank evidence of chronic toxicity as demonstrated by changes in mortality, body weight gains, organ-body weight ratios, or clinical parameters in rats or monkeys. Synergistic effects between diesel exhaust and coal dust were not demonstrated.

Bioavailability in vivo of benzo[a]pyrene adsorbed to diesel particulate

To evaluate health risks associated with exposure to particulates in the environment, it is necessary to quantify the bioavailability of carcinogens associated with the particulates. Direct analysis of bioavailability in vivo is most readily accomplished by adsorbing a radiolabeled form of the carcinogen to the particulate. A sample of native diesel particulate collected from an Oldsmobile diesel engine that contained 1.03 micrograms benzo[a]pyrene (BaP)/g particulate was supplemented with exogenous [3H]-BaP to produce a particulate containing 2.62 micrograms BaP/g. To insure that elution of BaP from native and [3H]-BaP-supplemented particulate was similar, in vitro analyses were performed. When using phospholipid vesicles composed of dimyristoylphosphatidylcholine (DMPC), 1.52% of total BaP was eluted from native particulate into the vesicles in 18 hrs; from [3H]-BaP supplemented particulate, 1.68% was eluted. Using toluene as eluent, 2.55% was eluted from native particulate, and 8.25% from supplemented particulate, in 6 hrs. Supplemented particulate was then instilled intratracheally into male Sprague-Dawley rats and distribution of radioactivity was analyzed at selected times over 3 days. About 50% of radioactivity remained in lungs at 3 days following instillation, with 30% being excreted into feces and the remainder distributed throughout the organs of the rats. To estimate the amount of radioactivity that entered feces through swallowing of a portion of the instilled dose, [3H]-BaP-supplemented particulate was instilled intratracheally into rats that had a cannula surgically implanted in the bile duct. Rate of elimination of radioactivity into bile was monitored; 10.6% of radioactivity was recovered in 6 hr, an amount slightly lower than the 12.8% excreted in 6 hrs into feces of animals with intact bile ducts. Our studies provide a quantitative description of the distribution of BaP and its metabolites following intratracheal instillation of diesel particulate. Because rates of elution of BaP in vitro are similar for native diesel particulate and particulate with supplemental [3H]-BaP, our results provide a reasonable estimate of the bioavailability in vivo of BaP associated with diesel particulate.