William C. Griffith

Diesel Exhaust Is a Pulmonary Carcinogen in Rats Exposed Chronically by Inhalation

Male and female F344 rats were exposed 7 hr/day, 5 day/week for up to 30 months to automotive diesel engine exhaust at soot concentrations of 0.35, 3.5, or 7.0 mg/m3 or were sham-exposed to clean air. Rats were terminated at 6-month intervals to measure lung burdens of diesel soot and for histopathology. Other rats either died or were terminated after 30 months of exposure. Lungs were fixed, sectioned into 3-mm slices, and examined by a dissecting microscope to detect tumors. Lesions were stained and examined by light microscopy. Survival and body weight were unaffected by exposure. Focal fibrotic and proliferative lung disease accompanied a progressive accumulation of soot in the lung. The prevalence of lung tumors was significantly increased at the high (13%) and medium (4%) dose levels above the control prevalence (1%). Four tumor types, all of epithelial origin, were observed: adenoma, adenocarcinoma, squamous cyst, and squamous cell carcinoma. Logistic regression modeling demonstrated a significant relationship between tumor prevalence and both exposure concentration and soot lung burden. These results demonstrate that diesel exhaust, inhaled chronically at a high concentration, is a pulmonary carcinogen in the rat.

Comparison of organophosphorus pesticide metabolite levels in single and multiple daily urine samples collected from preschool children in Washington State

A total organophosphorus pesticide exposure study was conducted in Washington State in 1998 in a sample population of 13 children aged 2.5–5.5 years. The children were roughly split between rural and suburban populations and had been previously identified as having potentially elevated organophosphorus pesticide exposures. One component of the study was urine collection and analysis. Urine samples were collected from each subject up to four times in 24 h in two different seasons. Samples were collected at specific time points: before bed, first morning void, after lunch, and before dinner. Urine samples were analyzed initially for the six nonspecific dialkylphosphate (DAP) metabolites and subsequently for eight specific metabolites including malathion dicarboxylic acid (MDA), 3,5,6-trichloro-2-pyridinol (TCPy), and paranitrophenol (PNP). Relatively large percentages of the urine samples contained quantifiable amounts of two of the nonspecific DAP metabolites (DMTP—97%; DETP—67%), and three of the specific metabolites (MDA (71%), TCPy (79%), and PNP (96%)). A percent deviation analysis was employed to determine which of the spot sample time points was the best predictor of the estimated volume-weighted daily average. Of the four spot samples collected, first morning void samples were consistently found to be the best predictors of weighted-average daily metabolite concentration. This finding also held when the data were creatinine-adjusted. The results of this analysis suggest that if spot sampling is to be conducted as part of a biological monitoring study, first morning void samples should be preferentially collected.

Lung Tissue Responses and Sites of Particle Retention Differ between Rats and Cynomolgus Monkeys Exposed Chronically to Diesel Exhaust and Coal Dust

Several chronic inhalation bioassays of poorly soluble, nonfibrous particles have resulted in an increased incidence of lung tumors in rats, no increase in lung tumors in Syrian hamsters, and inconsistent results in mice. These results have raised concerns that rats may be more prone than other species to develop persistent pulmonary epithelial hyperplasia, metaplasia, and tumors in response to the accumulation of inhaled particles. In addition, particle deposition and the rate of particle clearance from the lung differ between rats and primates, as does the anatomy of the centriacinar region. For these reasons, the usefulness of pulmonary carcinogenicity data from rats exposed to high concentrations of particles for quantitatively predicting lung cancer risk in humans exposed to much lower environmental or occupational concentrations has been questioned. The purpose of this investigation was to directly compare the anatomical patterns of particle retention and the lung tissue responses of rats and monkeys exposed chronically to high occupational concentrations of poorly soluble particles. Lung sections from male cynomolgus monkeys and F344 rats exposed 7 hr/day, 5 days/week for 24 months to filtered ambient air, diesel exhaust (2 mg soot/m3), coal dust (2 mg respirable particulate material/m3), or diesel exhaust and coal dust combined (1 mg soot and 1 mg respirable coal dust/m3) were examined histopathologically. The relative volume density of particulate material and the volume percentage of the total particulate material in defined pulmonary compartments were determined morphometrically to assess the relative amount and the anatomic distribution of retained particulate material. In all groups, relatively more particulate material was retained in monkey than in rat lungs. After adjustment for differences between rat and monkey controls, the coal dust- and the combined diesel exhaust and coal dust-exposed monkeys retained more particulate material than the coal dust- and the combined diesel exhaust and coal dust-exposed rats, respectively. There was no significant difference in the relative amount of retained particulate material between diesel exhaust-exposed monkeys and rats. Within each species, the sites of particle retention and lung tissue responses were the same for diesel soot, coal dust, and the combined material. Rats retained a greater portion of the particulate material in lumens of alveolar ducts and alveoli than monkeys. Conversely, monkeys retained a greater portion of the particulate material in the interstitium than rats. Rats, but not monkeys, had significant alveolar epithelial hyperplastic, inflammatory, and septal fibrotic responses to the retained particles. These results suggest that intrapulmonary particle retention patterns and tissue reactions in rats may not be predictive of retention patterns and tissue responses in primates exposed to poorly soluble particles at concentrations representing high occupational exposures.

Organophosphate Pesticide Exposure and Work in Pome Fruit: Evidence for the Take-Home Pesticide Pathway

Organophosphate (OP) pesticides are commonly used in the United States, and farmworkers are at risk for chronic exposure. Using a sample of 218 farmworkers in 24 communities and labor camps in eastern Washington State, we examined the association between agricultural crop and OP pesticide metabolite concentrations in urine samples of adult farmworkers and their children and OP pesticide residues in house and vehicle dust samples. Commonly reported crops were apples (71.6%), cherries (59.6%), pears (37.2%), grapes (27.1%), hops (22.9%), and peaches (12.4%). Crops were grouped into two main categories: pome fruits (apples and pears) and non-pome fruits. Farmworkers who worked in the pome fruits had significantly higher concentrations of dimethyl pesticide metabolites in their urine and elevated azinphos-methyl concentrations in their homes and vehicles than workers who did not work in these crops. Among pome-fruit workers, those who worked in both apples and pears had higher urinary metabolites concentrations and pesticide residue concentrations in dust than did those who worked in a single pome fruit. Children living in households with pome-fruit workers were found to have higher concentrations of urinary dimethyl metabolites than did children of non-pome-fruit workers. Adult urinary concentrations showed significant correlations with both the vehicle and house-dust azinphos-methyl concentrations, and child urinary concentrations were correlated significantly with adult urinary concentrations and with the house-dust azinphos-methyl concentration. The results provide support for the take-home pathway of pesticide exposure and show an association between measures of pesticide exposure and the number of pome-fruit crops worked by farmworkers.

Organophosphate pesticide exposure and residential proximity to nearby fields: evidence for the drift pathway.

Objectives:Residential proximity to pesticide-treated farmland is an important pesticide exposure pathway. Methods:In-person interviews and biological samples were collected from 100 farmworker and 100 non-farmworker adults and children living in Eastern Washington State. We examined the relationship of residential proximity to farmland to urinary metabolite concentrations of dimethylphosphate (DMTP) and levels of pesticide residues in house dust. Results:DMTP concentrations were higher in farmworkers than non-farmworkers (71 &mgr;g/L vs 6 &mgr;g/L) and in farmworker children than non-farmworker children (17 &mgr;g/L vs 8 &mgr;g/L). Compared to non-farmworker households, farmworker households had higher levels of azinphos-methyl (643 ng/g vs 121 ng/g) and phosmet (153 ng/g vs 50 ng/g). Overall, a 20% reduction in DMTP concentration was observed per mile increase in distance from farmland. Conclusions:Lower OP metabolite concentrations correlated with increasing distance from farmland.

Cadmium-Induced Differential Toxicogenomic Response in Resistant and Sensitive Mouse Strains Undergoing Neurulation

Common inbred mouse strains, such as the C57BL/6 (C57) and the SWV, display differences in sensitivity to environmental teratogens during gestation. For example, the C57 is more sensitive than the SWV to cadmium (Cd) exposure during neurulation, inducing a higher incidence of neural tube defects (NTDs). Here, we report, using Cd as a model teratogen, the first large scale toxicogenomic study to compare teratogen-induced gene expression alterations in C57 and SWV embryos undergoing neurulation, identifying toxicogenomic responses that associate with developmental toxicity and differential sensitivity. Using a systems-based toxicogenomic approach, comparing Cd-exposed and control C57 and SWV embryos (12- and 24-h postinjection [p.i.] [gestational day 8.0, ip]), we examined differentially expressed genes at multiple levels (biological process, pathway, gene) using Gene Ontology (GO) analysis, pathway mapping and cross-scatter plots. In both C57 and SWV embryos, we observed several gene expression alterations linked with cell cycle-related classifications, however, only in the C57 we observed upregulation of p53-dependent mediators Ccng1 and Pmaip1, previously associated with cell cycle arrest, apoptosis and NTD formation. In addition, we also identified a greater reduction in expression of nervous system development-related genes (e.g., Zic1, En2, Neurog1, Elavl4, Metrn, Nr2f1, Nr2f2) in the C57 compared to the SWV (12-h p.i.). In summary, our results indicate that differences in Cd-induced gene expression profiles between NTD resistant and sensitive strains within enriched biological processes (including developmental and cell cycle-related categories) associate with increased sensitivity to developmental toxicity as determined by observations of increased NTD formation, mortality (resorptions) and reduced fetal growth. Such observations may provide more detailed and useful mechanistic clues for identification of differences in life-stage specific teratogenic response.

Para Niños Saludables: A Community Intervention Trial to Reduce Organophosphate Pesticide Exposure in Children of Farmworkers

Background Exposure to organophosphate (OP) pesticides is an occupational hazard for farmworkers and affects their children through the take-home pathway. Objectives We examined the effectiveness of a randomized community intervention to reduce pesticide exposure among farmworkers and their children. Methods We conducted a baseline survey of a cross-sectional sample of farmworkers (year 1) in 24 participating communities. Communities were randomized to intervention or control. After 2 years of intervention, a new cross-sectional survey of farmworkers was conducted (year 4). Farmworkers with a child 2–6 years of age were asked to participate in a substudy in which urine was collected from the farmworker and child, and dust was collected from the home and the vehicle driven to work. Results The median concentration of urinary metabolites was higher in year 4 than in year 1 for dimethylthiophosphate (DMTP) and dimethyldithiophosphate in adults and for DMTP for children. There were significant increases within both the intervention and control communities between year 1 and year 4 (p < 0.005); however, the differences were not significant between study communities after adjusting for year (p = 0.21). The dust residue data showed azinphos-methyl having the highest percentage of detects in vehicles (86% and 84% in years 1 and 4, respectively) and in house dust (85% and 83% in years 1 and 4, respectively). There were no significant differences between intervention and control communities after adjusting for year (p = 0.49). Conclusions We found no significant decreases in urinary pesticide metabolite concentrations or in pesticide residue concentrations in house and vehicle dust from intervention community households compared with control community households after adjusting for baseline. These negative findings may have implications for future community-wide interventions.

Toxicity of inhaled plutonium dioxide in beagle dogs.

This study was conducted to determine the biological effects of inhaled 238PuO2 over the life spans of 144 beagle dogs. The dogs inhaled one of two sizes of monodisperse aerosols of 238PuO2 to achieve graded levels of initial lung burden (ILB). The aerosols also contained 169Yb to provide a gamma-ray-emitting label for the 238Pu inhaled by each dog. Excreta were collected periodically over each dogs life span to estimate plutonium excretion; at death, the tissues were analyzed radiochemically for plutonium activity. The tissue content and the amount of plutonium excreted were used to estimate the ILB. These data for each dog were used in a dosimetry model to estimate tissue doses. The lung, skeleton and liver received the highest alpha-particle doses, ranging from 0.16-68 Gy for the lung, 0.08-8.7 Gy for the skeleton and 0.18-19 for the liver. At death all dogs were necropsied, and all organs and lesions were sampled and examined by histopathology. Findings of non-neoplastic changes included neutropenia and lymphopenia that developed in a dose-related fashion soon after inhalation exposure. These effects persisted for up to 5 years in some animals, but no other health effects could be related to the blood changes observed. Radiation pneumonitis was observed among the dogs with the highest ILBs. Deaths from radiation pneumonitis occurred from 1.5 to 5.4 years after exposure. Tumors of the lung, skeleton and liver occurred beginning at about 3 years after exposure. Bone tumors found in 93 dogs were the most common cause of death. Lung tumors found in 46 dogs were the second most common cause of death. Liver tumors, which were found in 20 dogs but were the cause of death in only two dogs, occurred later than the tumors in bone and lung. Tumors in these three organs often occurred in the same animal and were competing causes of death. These findings in dogs suggest that similar dose-related biological effects could be expected in humans accidentally exposed to 238PuO2.

Animal models of beryllium-induced lung disease.

The inhalation Toxicology Research Institute (ITRI) is conducting research to improve the understanding of chronic beryllium disease (CBD) and beryllium-induced lung cancer. Initial animal studies examined beagle dogs that inhaled BeO calcined at either 500 or 1000 degrees C. At similar lung burdens, the 500 degrees C BeO induced more severe and extensive granulomatous pneumonia, lymphocytic infiltration into the lung, and positive Be-specific lymphocyte proliferative responses in vitro than the 1000 degrees C BeO. However, the progressive nature of human CBD was not duplicated. More recently, Strains A/J and C3H/Hej mice were exposed to Be metal by inhalation. This produced a marked granulomatous pneumonia, diffuse infiltrates, and multifocal aggregates of interstitial lymphocytes with a pronounced T helper component and pulmonary in situ lymphocyte proliferation. With respect to lung cancer, at a mean lung burden as low as 17 micrograms Be/g lung, inhaled Be metal induced benign and/or malignant lung tumors in over 50% of male and female F344 rats surviving > or = 1 year on study. Substantial tumor multiplicity was found, but K-ras and p53 gene mutations were virtually absent. In mice, however, a lung burden of approximately 60 micrograms (-300 micrograms Be/g lung) caused only a slight increase in crude lung tumor incidence and multiplicity over controls in strain A/J mice and no elevated incidence in strain C3H mice. Taken together, this research program constitutes a coordinated effort to understand beryllium-induced lung disease in experimental animal models.

The induction of liver tumors by 239Pu citrate or 239PuO2 particles in the Chinese hamster.

The influence of radiation dose distribution on the frequency of 239Pu-induced liver tumors was evaluated in the Chinese hamster. Different concentrations of 239Pu citrate 239PuO2 particles of known sizes were injected intravenously via the jugular vein. About 60% of the injected 239Pu citrate was deposited in the liver and 40% in the bone. The 239Pu citrate was rather uniformly distributed throughout the liver parenchyma. Injected plutonium oxide particles were taken up by the reticuloendothelial system with 90% of the body burden deposited in the liver. The 239PuO2 particles were localized in the Kupffer cells and produced nonuniform dose distributions that were dependent on particle size. There was an activity- and dose-dependent increase in the incidence of total liver parenchymal cell tumors following injection with either plutonium particles or citrate. For animals that received 14.0-, 2.7-, 0.3-, and 0.04-Gy dose to liver from 239Pu citrate the cumulative tumor incidence was 39, 32, 5, and 0%, respectively. Animals that were injected with the 0.24 micron 239PuO2 particles had doses of 42.0, 7.2, and 0.8 Gy to the liver and tumor incidences of 34, 26, and 5%, respectively. Plutonium citrate also produced hemangiosarcomas of the liver and tumors in bone and bone marrow. The latent period for liver tumor appearance in animals exposed to 239Pu citrate or 239PuO2 particles increased as the injected activity decreased. For animals injected with a similar total activity (7.4 Bq/g), the lifetime cumulative liver tumor incidence was similar for animals exposed to either 239Pu citrate (32%) or 239PuO2 (26%). There was little effect of particle size on liver tumor incidence. These data indicate that, in Chinese hamster liver, local radiation dose distribution is less important in altering tumor incidence than injected activity or average dose. However, the more uniform irradiation from 239Pu citrate administration was more effective in cancer production than the nonuniform irradiation from 239PuO2 particles.