Retrospective assessment of exposure through modeling in a study on cancer risks among workers exposed to phenoxy herbicides, chlorophenols and dioxins.

OBJECTIVES: The study aimed at developing a model for the retrospective assessment of exposures in epidemiologic studies when little or no data on past exposures are available. METHODS: A deterministic model was developed for the level of exposure by industrial hygienists involved in an international study on cancer risks among phenoxy herbicide or chlorophenol manufacturing workers and pesticide sprayers. The general source-receptor model was used as the conceptual framework for the model. RESULTS: The model included variables related to job, the emission of chemicals, contact with chemicals, personal protection, and other relevant determinants of exposure. Cumulative dose indices were calculated from the duration of exposure (from the work histories) and the level of exposure (from the model). CONCLUSIONS: Deterministic modeling in complex exposure situations may provide more valid and reliable results than its conventional alternative, subjective assessment by an expert.

Quantitative determination of trucking industry workers' exposures to diesel exhaust particles.

As part of a case-control mortality study of trucking industry workers, exposures to diesel aerosol were measured among the four major presumably exposed job groups (road drivers, local drivers, dock workers, and mechanics) in the industry. Eight industrial hygiene surveys were conducted during both warm and cold weather at eight U.S. terminals and truck repair shops. A single-stage personal impactor was used to sample submicrometer-sized diesel particles on quartz fiber filters. Laboratory and field studies demonstrated that the elemental carbon content of the particles is a useful and practical marker of exposure to vehicular diesel exhaust. A thermal-optical analysis technique was used to determine the concentration of elemental carbon in the filter samples. Overall geometric mean exposures to submicrometer-sized elemental carbon ranged from 3.8 micrograms/m3 in road (long distance) drivers (N = 72) to 13.8 micrograms/m3 in dock workers (N = 75). Geometric mean background area concentrations, measured in the same cities where workers were sampled, were 2.5 micrograms/m3 on major highways (N = 21) and 1.1 micrograms/m3 in residential areas (N = 23). A factorial analysis of variance indicated that exposures in two job groups, dock workers (particularly those exposed primarily via diesel forklift trucks, introduced relatively recently) and mechanics (working in poorly ventilated shops during cold weather), were significantly higher than background concentrations and were significantly higher than the exposures in the local and road drivers. The exposures of the truck drivers could not be distinguished from background highway concentrations but were significantly higher than background concentrations in residential areas.

Cancer mortality in workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

BACKGROUND: In both animal and epidemiologic studies, exposure to dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, or TCDD) has been associated with an increased risk of cancer. METHODS: We conducted a retrospective cohort study of mortality among the 5172 workers at 12 plants in the United States that produced chemicals contaminated with TCDD. Occupational exposure was documented by reviewing job descriptions and by measuring TCDD in serum from a sample of 253 workers. Causes of death were taken from death certificates. RESULTS: Mortality from several cancers previously associated with TCDD (stomach, liver, and nasal cancers, Hodgkin's disease, and non-Hodgkin's lymphoma) was not significantly elevated in this cohort. Mortality from soft-tissue sarcoma was increased, but not significantly (4 deaths; standardized mortality ratio [SMR], 338; 95 percent confidence interval, 92 to 865). In the subcohort of 1520 workers with greater than or equal to 1 year of exposure and greater than or equal to 20 years of latency, however, mortality was significantly increased for soft-tissue sarcoma (3 deaths; SMR, 922; 95 percent confidence interval, 190 to 2695) and for cancers of the respiratory system (SMR, 142; 95 percent confidence interval, 103 to 192). Mortality from all cancers combined was slightly but significantly elevated in the overall cohort (SMR, 115; 95 percent confidence interval, 102 to 130) and was higher in the subcohort with greater than or equal to 1 year of exposure and greater than or equal to 20 years of latency (SMR, 146; 95 percent confidence interval, 121 to 176). CONCLUSIONS: This study of mortality among workers with occupational exposure to TCDD does not confirm the high relative risks reported for many cancers in previous studies. Conclusions about an increase in the risk of soft-tissue sarcoma are limited by small numbers and misclassification on death certificates. Excess mortality from all cancers combined, cancers of the respiratory tract, and soft-tissue sarcoma may result from exposure to TCDD, although we cannot exclude the possible contribution of factors such as smoking and occupational exposure to other chemicals.

Chloracne associated with employment in the production of pentachlorophenol.

To evaluate the association between exposure to pentachlorophenol (PCP) and the occurrence of chloracne, we studied the medical and personnel records for individuals employed in the manufacturing of PCP. Forty-seven cases of chloracne were identified among 648 workers (7.0%) assigned to PCP production at a single plant between 1953 and 1978. The annual incidence rate varied considerably, ranging from 0 (in 1953) to 1.46 (in 1978). No linear trend in the risk of chloracne was observed with the duration of employment in the pentachlorophenol department. Workers with a documented episode of direct skin contact with PCP had a significantly increased risk of chloracne compared with workers who did not have a documented episode of direct skin contact (cumulative incidence ratio = 4.6; 95% confidence interval 2.6-8.1). Our results confirm that chloracne is associated with exposure to PCP contaminated with hexachlorinated, heptachlorinated, and octachlorinated dibenzo-p-dioxins and dibenzofurans.

Levels of polychlorinated dibenzo-p-dioxins and dibenzofurans in workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Review of employment and chemical production records at a Missouri chemical plant and of questionnaires with self-reported occupational exposure to 2,3,7,8-tetrachloro-dibenzo-p-dioxin (2,3,7,8-TCDD) for 16 Missouri workers has explained the wide diversity of 2,3,7,8-TCDD levels previously reported in the workers' adipose tissue (3.5-750 ppt on whole-weight basis). We show that the highest exposures reported to date in the United States occurred in a group of nine production workers who made products contaminated with 2,3,7,8-TCDD. The nine workers had adipose tissue levels with a mean of 246 ppt and a range of 42 to 750 ppt. Seven persons who worked at the same chemical company, but not in the 2,3,7,8-TCDD-contaminated process, had a mean of 8.7 ppt and a range of 3.5 to 25.8 ppt. We also report serum levels of 2,3,7,8-TCDD in these individuals. The adipose tissue from a subset of four production workers with elevated levels of 2,3,7,8-TCDD and seven Missouri residents with normal 2,3,7,8-TCDD levels was also analyzed for other isomers of the PCDDs and PCDFs. The mean adipose tissue level of 2,3,7,8-TCDD in the subset of production workers was 45 times higher than the mean level in the unexposed Missouri residents, but similar levels of the other PCDDs and PCDFs were found in both groups.

Hexachlorobenzene exposure in the production of chlorophenols.

Workers involved in the production of pentachlorophenol (PCP) may be exposed to one of its contaminants, hexachlorobenzene (HCB). PCP is produced commercially in the USA by direct chlorination of phenol with chlorine gas in the presence of a catalyst at gradually rising temperatures up to 200 degrees C. Other contaminants formed in PCP production are isomers of hexa-, hepta- and octachlorodibenzo-para-dioxin and isomers of tetra-, penta-, hexa-, hepta- and octachlorodibenzofuran. This paper presents the analytical results of personal breathing-zone, area-air and surface-wipe samples collected at a typical PCP manufacturing plant. The personal breathing-zone samples showed that workers were exposed to HCB concentrations ranging from less than 0.0001 to 0.12 mg/m3. Area-air samples taken throughout the manufacturing plant showed that HCB concentrations ranged from less than 0.0001 to 0.63 mg/m3. Surface-wipe samples showed contamination ranging from less than 0.1 to 3.7 micrograms/wipe.