To evaluate the possible association between occupational exposure to benzene and subsequent death from leukemia, the National Institute for Occupational Safety and Health (NIOSH) conducted a retrospective cohort mortality study of workers who had been exposed to benzene in the manufacture of rubber hydrochloride at two locations in Ohio. Ascertainment of vital status was accomplished for 98% of the cohort. Among 748 workers who had at least one day of exposure to benzene between 1940 and 1950, seven deaths from leukemia occurred; from United States death rates standardized for sex, age, and calendar time period, only 1.25 leukemia deaths would have been expected (standardized mortality ratio = 560; p less than 0.001). Mean duration of exposure to benzene was brief, and 437 (58%) of the cohort were exposed for less than 1 year. Evaluation of leukemia mortality for those workers exposed five or more years showed an SMR of 2100. All leukemia deaths were myelocytic or monocytic in cell type. Four additional cases of leukemia have been reorganized in workers at the study locations, but occurred in persons not encompassed by the strict definition of the cohort. Reconstruction of past exposures to benzene at the two locations indicates that in some areas of the plant airborne benzene concentrations rose occasionally to several hundred parts per million (ppm), but that for the most part, employee eight-hour time-weighted averages (TWA) fell within the limits considered permissible at the time of exposure. These data corroborate an initial analysis of the same cohort by Infante et al, and indicate that benzene is a human carcinogen at a range of exposures not greatly above the current legal standard.

On the basis of evidence from animal studies, polychlorinated biphenyls (PCBs) are considered potentially carcinogenic to humans. However, the results of studies in human populations exposed to PCBs have been inconsistent. The authors conducted a retrospective cohort analysis (1957-1986) comparing the mortality of 3,588 electrical capacitor manufacturing workers with known exposure to PCBs with age-, sex-, and calendar time-specific mortality rates for all whites in the United States. Proportional hazards modeling was also performed to examine the association between cumulative PCB exposure and site-specific cancer mortality. All-cause mortality (192 deaths observed, 283.3 expected) and total cancer mortality (54 deaths observed, 63.7 expected) were lower than expected. More deaths were observed than expected for malignant melanoma (8 observed, less than 2.0 expected) and cancer of the brain and nervous system (5 observed, 2.8 expected). The average estimated cumulative dose for the cases of brain cancer (22.9 units) was greater than for other workers (12.9 units), but the 95% confidence intervals around this difference were broad. The risk of malignant melanoma was not related to cumulative PCB exposure. These results provide some evidence of an association between employment at this plant and malignant melanoma and cancer of the brain. The possibility that the results are due to chance, bias, or confounding cannot be excluded.

To assess quantitatively the association between benzene exposure and leukemia, we examined the mortality rate of a cohort with occupational exposure to benzene. Cumulative exposure for each cohort member was estimated from historical air-sampling data and, when no sampling data existed, from interpolation on the basis of existing data. The overall standardized mortality ratio (a measure of relative risk multiplied by 100) for leukemia was 337 (95 percent confidence interval, 154 to 641), and that for multiple myeloma was 409 (95 percent confidence interval, 110 to 1047). With stratification according to levels of cumulative exposure, the standardized mortality ratios for leukemia increased from 109 to 322, 1186, and 6637 with increases in cumulative benzene exposure from less than 40 parts per million-years (ppm-years), to 40 to 199, 200 to 399, and 400 or more, respectively. A cumulative benzene exposure of 400 ppm-years is equivalent to a mean annual exposure of 10 ppm over a 40-year working lifetime; 10 ppm is the currently enforceable standard in the United States for occupational exposure to benzene. To examine the shape of the exposure-response relation, we performed a conditional logistic-regression analysis, in which 10 controls were matched to each cohort member with leukemia. From this model, it can be calculated that protection from benzene-induced leukemia would increase exponentially with any reduction in the permissible exposure limit.

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In surveys of three groups of workers occupationally exposed to polychlorinated biphenyls (PCBs) serum PCB concentrations were quantitated as lower chlorinated biphenyls (L-PCBs) and higher chlorinated biphenyls (H-PCBs). Serum L-PCB and H-PCB concentrations were many times greater among workers employed in power capacitor manufacturing than among the general population, even comparing employees never assigned to work in PCBexposed areas. Statistically significant positive correlations of symptoms suggestive of mucous membrane and skin irritation, of systemic malaise, and altered peripheral sensation were noted with increasing concentrations of serum PCB. No clinical abnormalities attributable to exposure to PCB were observed. Serum PCB concentrations were positively and significantly correlated with glutamic-oxalacetic transaminase (SGOT), serum gamma-glutamyl transpeptidase (GGTP), and plasma triglyceride, and inversely correlated with plasma high density lipoproteincholesterol. These correlations were present across all study sites. These findings are indicative of PCBs' physiological effect on the liver, whose long-range health significance is unknown. Nevertheless, the consistent positive association of serum PCB w'th plasma triglyceride and negative association with plasma HDL-cholesterol may have long-wrm cardiovascular consequences.Polychlonnated biphenyls (PCBs), a class of chlorinated aromatic hydrocarbon compounds, have become widely dispersed in the environment.