Validation of human physiologically based pharmacokinetic model for vinyl acetate against human nasal dosimetry data.

Vinyl acetate has been shown to induce nasal lesions in rodents in inhalation bioassays. A physiologically based pharmacokinetic (PBPK) model for vinyl acetate has been used in human risk assessment, but previous in vivo validation was conducted only in rats. Controlled human exposures to vinyl acetate were conducted to provide validation data for the application of the model in humans. Five volunteers were exposed to 1, 5, and 10 ppm 13C1,13C2 vinyl acetate via inhalation. A probe inserted into the nasopharyngeal region sampled both 13C1,13C2 vinyl acetate and the major metabolite 13C1,13C2 acetaldehyde during rest and light exercise. Nasopharyngeal air concentrations were analyzed in real time by ion trap mass spectrometry (MS/MS). Experimental concentrations of both vinyl acetate and acetaldehyde were then compared to predicted concentrations calculated from the previously published human model. Model predictions of vinyl acetate nasal extraction compared favorably with measured values of vinyl acetate, as did predictions of nasopharyngeal acetaldehyde when compared to measured acetaldehyde. The results showed that the current PBPK model structure and parameterization are appropriate for vinyl acetate. These analyses were conducted from 1 to 10 ppm vinyl acetate, a range relevant to workplace exposure standards but which would not be expected to saturate vinyl acetate metabolism. Risk assessment based on this model further concluded that 24 h per day exposures up to 1 ppm do not present concern regarding cancer or non-cancer toxicity. Validation of the vinyl acetate human PBPK model provides support for these conclusions.

Lymphohaematopoietic cancer risk among chemical workers exposed to benzene.

AIMS: To determine cause specific mortality in a cohort of 2266 chemical workers exposed to benzene in various manufacturing processes after 1935. METHODS: The cohort has accumulated over 80 000 person-years of observation; about 70% of the workers were followed for more than 30 years since first exposure. RESULTS: Mortality from non-malignant diseases of the blood was increased (SMR 2.17, 95% CI 0.87 to 4.48), and correlated with duration of benzene exposure, although risk had decreased from the previous investigation of this cohort. The risk for leukaemia was slightly above background (SMR 1.14, obs 12, 95% CI 0.59 to 1.99) but has also decreased since the earlier study of this cohort. SMRs for acute non-lymphocytic leukaemia (ANLL), chronic lymphatic leukaemia, and non-Hodgkin's lymphoma were 1.11, 0.42, and 1.06 respectively. There was evidence of a weak trend of increasing SMRs for leukaemia and possibly ANLL with increasing low-level cumulative exposure but not with other measures. CONCLUSION: Leukaemia and ANLL results were consistent with the mildly increased risk estimates from lower exposure subgroups of the Pliofilm cohort.

Cancer risk for chemical workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

AIMS: To describe the long term mortality experience of a cohort of 2187 male chemical production workers previously exposed to substantial levels of dioxin. METHODS: Vital status for a previously identified cohort was determined for an additional 10 years, to 1995. Dioxin exposures took place before 1983 and were sufficient to result in chloracne in 245 individuals. Mortality rates were compared with national figures and with a large pool of co-workers in unrelated production jobs. RESULTS: All cancers combined (standardised mortality ratio (SMR) = 1.0, 95% CI 0.8 to 1.1) and lung cancer (SMR = 0.8, 95% CI 0.6 to 1.1) were at or below expected levels. Rates for soft tissue sarcoma (SMR = 2.4, 95% CI 0.3 to 8.6) and non-Hodgkin's lymphoma (SMR = 1.4, 95% CI 0.6 to 2.7) were greater than expected overall, but below expectation in the update period. No trend of increasing risk with increasing exposure was observed for these cancers. Workers who developed chloracne had very low all-cancer rates (SMR = 0.5, 95% CI 0.3 to 1.0), and lung cancer rates (SMR = 0.3, 95% CI 0.0 to 1.1). CONCLUSIONS: We found no coherent evidence of increased cancer risk from dioxin exposure in this cohort. Our study highlights the wide range of cancer rates and the lack of consistency across dioxin studies.

Study on the cytochrome P-450- and glutathione-dependent biotransformation of trichloroethylene in humans.

OBJECTIVES: To investigate in humans the contribution of the cytochrome P-450- and glutathione-dependent biotransformation of trichloroethylene (TRI) under controlled repeated exposure in volunteers, and under occupational conditions. METHODS: Volunteers were exposed to TRI, using repeated 15 min exposures at 50 and 100 ppm. This exposure schedule resulted in internal doses of 1.30 and 2.40 mmol of TRI respectively. Urine samples were collected for a minimum of 45 h. Urine samples were also collected from occupationally exposed workers. The samples were analysed for the known human metabolites of TRI, trichloroethanol (TCE), trichloroacetic acid (TCA) and both regio-isomeric forms of the mercapturic acid N-acetyl-S-(dichlorovinyl)-L-cysteine (DCV-NAC), and for (dichlorovinyl)-L-cysteine (DCVC). In order to further elucidate the metabolism of TRI in humans, we analysed samples for dichloroacetic acid and for the proposed break-down products of 1,2 and 2,2-dichlorovinyl-L-cysteine after deamination: the S-conjugates of 3-mercaptolactic acid, 3-mercaptopyruvic acid and 2-mercaptoacetic acid. RESULTS: None of the glutathione metabolites was found in urine of volunteers. In workers occupationally exposed to TRI at levels between 0.4 and 21 ppm [8-h time-weighted average (TWA)], levels of DCV-NAC in urine samples collected at the end of the 4th working day and also next morning were below detection limit (0.04 mumol/l). This confirms the findings of Bernauer et al. (1996) that these metabolites are excreted at very low levels in humans. Urinary levels of DCVC and six postulated metabolites of dichlorovinyl-S-cysteine conjugates via deamination were also below 0.04 mumol/l, indicating that at most 0.05% of the dose is excreted in the form of these metabolites. These data further strengthen the argument for a very low activity of glutathione-mediated metabolism for chronically exposed workers. CONCLUSIONS: This study gives additional data which indicate that glutathione-mediated metabolism is of minor importance in humans exposed to TRI. In spite of indications to the contrary, significant metabolism of the cysteine conjugate via beta-lyase, which could result in a toxic metabolite, cannot be ruled out completely.

Personal air sampling and biological monitoring of occupational exposure to the soil fumigant cis-1,3-dichloropropene.

OBJECTIVES: To assess exposure of commercial application workers to the nematocide cis-1,3-dichloropropene (cis-DCP). METHODS: The study was conducted during the annual application season, August to 15 November, in the starch potato growing region in The Netherlands. 14 Application workers collected end of shift urine samples on each fumigation day (n=119). The mercapturic acid metabolite N-acetyl-S-(cis-3-chloro-2-propenyl)-L-cysteine (cis-DCP-MA) in urine was used for biological monitoring of the cis-DCP uptake. Inhalatory exposure was assessed by personal air sampling during a representative sample (n=37) of the fumigation days. Extensive information was collected on factors of possible relevance to the exposure and the application workers were observed for compliance with the statutory directions for use. The inhalatory exposure during all fumigation days was estimated from the relation between the personal air sampling data and the biological monitoring data. Exposure levels were correlated with the general work practice. The fumigation equipment and procedures were in accordance with the statutory directions of use, with the exception of the antidrip systems. Two antidrip systems were used: antidrip nozzles or a compressed air system. RESULTS: The geometric mean exposure of the application workers was 2.7 mg/m(3) (8 hour time weighted average); range 0.1-9.5 mg/m(3). On 25 days (21%) the exposure exceeded the Dutch occupational exposure limit (OEL) of 5 mg/m(3). This could mainly be explained by prolonged working days of more than 8 hours. The general work practice of the application workers was rated by the observers as good or poor. No difference in exposure to cis-DCP was found in the use of none, one, or two antidrip systems. Malfunctioning of the antidrip systems and lack of experience with the compressed air system were identified as possible causes for the lack of effectiveness of these antidrip systems. The use of personal protection was not always in accordance with the statutory directions of use. Dermal exposure to liquid cis-DCP was found four times during repair and maintenance, but the biological monitoring data did not suggest a significant increase in cis-DCP uptake. CONCLUSIONS: The application of cis-DCP in the potato growing industry can be performed at exposure concentrations below the Dutch OEL of 5 mg/m(3) if the working days are limited to 8 hours. An injector equipped with either kind of antidrip system which is in good working order, as well as the consistent use of personal protection in accordance with the statutory directions of use, may ensure exposure concentrations below the Dutch OEL.

Occupational exposure to cis-1,3-dichloropropene: biological effect monitoring of kidney and liver function.

OBJECTIVES: To investigate the possible effects of occupational exposure to the nematocide cis-1,3-dichloropropene (cis-DCP) on function of the kidney and liver in the starch potato growing region in The Netherlands. METHODS: The study involved 13 commercial application workers exposed to cis-DCP for 117 days, and 22 matched control workers. The inhalatory exposure of the application workers was estimated from biological monitoring data. All workers collected urine and serum samples before, during, and after the fumigation season for monitoring of variables for kidney and liver function. Renal effect variables were alanine aminopeptidase (AAP), N-acetyl-beta-D-glucosaminidase (NAG), retinol binding protein (RBP), and albumin (ALB) in urine, and beta(2)-microglobulin (beta(2)M-S) and creatinine in serum (Creat-S). Liver variables were alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), gamma-glutamyltranspeptidase (GGT), alkaline phosphatase (ALP), and total bilirubin (TBIL) in serum and the urinary ratio of 6-beta-hydroxycortisol to free cortisol (betaOHC/COR). RESULTS: The geometric mean exposure of the application workers was 2.7 mg/m(3) (8 hour time weighted average (8 hour TWA)); range 0.1-9.5 mg/m(3). No differences were found between the values of the renal effect variables or the liver variables of the exposed group and the control group, except a lower urinary ratio of betaOHC/COR in the exposed group. This was not considered to be related to the exposure to cis-DCP. No dose-effect relations were found between the exposure indices and the effect variables. CONCLUSIONS: The present study does not provide evidence that occupational exposure to cis-DCP in the starch potato growing region causes adverse effects on the kidney or liver at 8 hour TWA exposure concentrations below 9.5 mg/m(3) (2 ppm).

Mortality update of workers exposed to acrylonitrile in The Netherlands.

A retrospective cohort study investigating the cause-specific mortality patterns of 2842 workers occupationally exposed to acrylonitrile for at least 6 months before 1 July 1979 was updated. The comparison group consisted of 3961 workers from a nitrogen fixation plant during the same time interval. Industrial hygiene assessments quantified past exposure to acrylonitrile, the use of personal protective equipment, and exposure to other potential carcinogenic agents. All 6803 workers were followed for mortality until 1 January 1996. The follow-up was almost complete (99.6%), and for 99.3% the cause of death was ascertained. Age distribution, follow-up period, and temporal changes in background mortality rates were adjusted for in calculations of standardized mortality ratios for separate causes of death. Cumulative dose-effect relations were determined for 3 exposure categories and 3 latency periods. The results showed that, although cancer mortality fluctuated slightly, no cancer excess seems related to exposure to acrylonitrile.

The predictive value of animal data in human cancer risk assessment.

Carcinogenic effects of chemicals can be investigated in animal experiments and epidemiological studies of exposed humans, mostly in the workplace. In this article epidemiologic evidence is compared with the animal data for 35 chemicals. Risk calculations are compared for 22 chemicals. The chemicals showing no or unclear carcinogenic effects in humans were more likely to show toxic side effects in the animal studies, indicating that the test concentrations were above the maximum tolerated dose. In addition, the animal experiments with these chemicals more often showed neoplastic effects on multiple sites than chemicals for which clear positive epidemiological studies are available. These findings may explain the existence of discrepancies between the outcomes of animal testing and human studies. They suggest that carcinogenic effects in multiple organs in animals could be seen as ultimate manifestations of the side effects of the testing method and that they have limited predictive value for the human situation.

An update of mortality among chemical workers potentially exposed to the herbicide 2,4-dichlorophenoxyacetic acid and its derivatives.

Four years of additional mortality follow-up through 1986 are reported for a previously studied cohort of 878 chemical workers who were potentially exposed to 2,4-dichlorophenoxyacetic acid (2,4-D) and its derivatives between 1945 and 1983. Observed mortality was compared with expected levels based on death rates of the US population and of 36,804 "unexposed" workers from the same manufacturing location. Non-Hodgkin's lymphoma (NHL) was a particular focus of the study because of a suggested association with 2,4-D exposure in some case-control studies. For the total observation period, the standardized mortality ratios for all causes and for malignant neoplasms were 92 and 91, respectively. Analyses using the internal comparison group yielded virtually identical results. The initial study had found two deaths from NHL, both of which occurred under circumstances (ie, short latency and modest exposure) which made it less plausible that they were related to 2,4-D exposure. No new deaths from NHL were observed in the extended follow-up period and mortality for this cause showed a nonstatistically significant excess (standardized mortality ratio, 196; 95% confidence interval 24 to 708) for the total observation period. Analyses by production area, and by two different measures of exposure, combined with two different approaches to account for latency, did not show patterns suggestive of a causal relationship between exposure to 2,4-D or its derivatives and any particular cause of death.

Mortality of workers exposed to acrylonitrile.

A retrospective cohort study was carried out in The Netherlands to investigate the potential carcinogenic effects in humans of occupational exposure to acrylonitrile (AN). The total study group consisted of 6803 workers "from eight chemical plants and one control plant" of whom 2842 had been exposed to AN between January 1, 1956 and July 1, 1979 for at least 6 months. All workers were employed by one of eight chemical companies. An extensive review of the available industrial hygiene data was conducted to assess the magnitude of past exposure to AN, occurrence of peak exposures, exposure to recognized potential human carcinogens, and respirator use. The total cohort was observed for mortality until January 1, 1988. In collaboration with the Central Bureau of Statistics, the causes of death were traced for the workers who died before 01-01-1988. In the exposed as well as in the nonexposed cohorts the total mortality was lower than expected, based on national mortality statistics. The observed cancer mortality in the exposed cohort was similar to the expected mortality. Specific analyses were carried out to investigate dose-response relationships and latency for total mortality and lung cancer mortality. Overall, no indications were found for a carcinogenic effect in this cohort of workers exposed to AN.