This study evaluated mortality rates from
leukemia and other diseases during the time period 1944 through 1998 among 17,924 men employed in the
synthetic rubber industry. In this group, there were 6237 deaths, which is 14% fewer than the 7242 deaths expected based on general population rates. Numbers of observed versus expected deaths (shown hereafter as observed/expected) were 1608/1741 for all
cancers combined, including 71/61 for
leukemia, 53/53 for
non-Hodgkin lymphoma (NHL*), and 26/27 for
multiple myeloma. The higher than expected number of deaths from
leukemia (16% increase) was concentrated in workers paid hourly who had started work 20 to 29 years earlier, had worked 10 or more years in the industry, and had worked in subgroups employed in polymerization, coagulation, maintenance labor, and laboratory operations. The overall higher
leukemia mortality rate, as well as the higher rate in the subgroup of hourly workers who had 20 or more years since hire and 10 or more years worked, was not limited to a particular form of
leukemia. Cumulative exposure to
1,3-butadiene (BD) was associated positively with all
leukemias, with
chronic myelogenous leukemia and, to a lesser extent, with
chronic lymphocytic leukemia (CLL). Exposure to
styrene or to
dimethyldithiocarbamate (DMDTC) also was associated positively with
leukemia. Exposures to these two agents were correlated with exposure to BD; data were limited on the independent effects of each of the three chemicals on
leukemia. After controlling for the effects of BD, we found no consistent exposure-response relation between either
styrene or DMDTC and all
leukemias, chronic myelogenous leukemia, or CLL. However, a positive association between any exposure to DMDTC and
leukemia persisted. The data from this study indicate that employment in the
synthetic rubber industry is related causally to
leukemia. Uncertainty remains about the specific agent or agents responsible for the association. The carcinogenic mechanisms through which BD,
styrene, or DMDTC could cause
leukemia in humans have not been established, and epidemiologic support for a leukemogenic role is limited for these agents.
Styrene and DMDTC were associated positively with NHL. External support for this relation has not been reported from other epidemiologic studies. The study did not find any clear relation between exposure to BD,
styrene, or DMDTC and
multiple myeloma. Some subgroups of subjects had more than the expected number deaths from
colorectal cancer,
prostate cancer, and other diseases. These increases did not appear to be related to occupational exposure in the industry.