Historical Estimation of Exposure to 1,3-Butadiene, Styrene, and Dimethyldithiocarbamate Among Synthetic Rubber Workers

Abstract

Quantitative estimates of exposure to 1,3-butadiene (BD), styrene (STY), and dimethyldithiocarbamate (DMDTC) were developed for a follow-up study of workers at six North American synthetic rubber plants. Procedures entailed identifying tasks and jobs involving exposure, identifying factors influencing historical changes in exposure potential, and using mathematical models to calculate job- and time-period-specific exposures. Exposure metrics included 8-hour time-weighted average (TWA) intensity, the annual number of peak exposures (BD: > 100 ppm, STY: > 50 ppm) and TWA intensity below and above the peak threshold. The 5th and 95th percentiles of the approximate probability distribution of each exposure estimate served as its 90% uncertainty interval. Job- and year-specific estimates were linked with subjects' work histories to obtain cumulative exposure indices. Exposure estimates varied among tasks, jobs, plants, and time periods. BD TWAs were approximately 10 ppm during the 1940s–1960s and declined during the 1970s and 1980s. STY TWAs were always < 2 ppm. DMDTC exposure began in the 1950s, was high through the 1960s, and later declined. BD peak exposure accounted for a large proportion of cumulative BD exposure, whereas almost none of the STY exposure was experienced at levels > 50 ppm. Exposure indices were correlated. Exposures were higher than previously estimated. Multiple correlations among DMDTC, BD, and STY exposure estimates make it difficult to estimate agent-specific effects. Limitations of the methodology include the potential inaccuracy of the estimates, the lack of adequate industrial hygiene data to validate the estimates, the additional inaccuracy of linkage with poorly specified job groups, and the potential for differential exposure misclassification because the jobs and work areas where excess leukemia mortality occurred were well-known at the time of this study. Nevertheless, the new exposure estimates were highly correlated with the old, yielding equivalent exposure ranking of workers and were comparable to limited industrial hygiene data published by NIOSH.

Keywords:

• 1,3-butadiene
• dimethyldithiocarbamate
• epidemiologic studies
• exposure assessment
• leukemia
• styrene

ACKNOWLEDGMENTS

The authors gratefully acknowledge the cooperation of the management of the participating companies and the long-term employees whose knowledge made this effort possible, the industrial hygiene consulting provided by Arthur Dunlop, and the technical assistance provided by Misty Sanders, Jeffrey Stover, and Matthew Smitha.

This study was funded by the International Institute of Synthetic Rubber Producers and the Olefins Panel of the Chemical Manufacturers' Association.

Notes

^A BD = 1,3-butadiene, STY = styrene, DMDTC = dimethyldithiocarbamate.

^B Units = ppm for BD and STY; = mg/cm for DMDTC.

^C 90% uncertainty interval.

^A D = 1,3-butadiene, STY = styrene, DMDTC = dimethyldithiocarbamate.

^B 90% uncertainty interval.

^A BD = 1,3-butadiene, STY = styrene, DMDTC = dimethyldithiocarbamate.

^B 90% uncertainty interval.

^A BD = 1,3-butadiene, STY = styrene, DMDTC = dimethyldithiocarbamate.

^B 90% uncertainty interval.

^A BD = 1,3-butadiene, STY = styrene, DMDTC = dimethyldithiocarbamate.

^A Units: BD and STY TWA, ppm; BD peaks, number > 100 ppm; STY peaks, number > 50 ppm; DMDTC TWA, mg/cm.

^A Units: BD and STY TWA, ppm; BD peaks, number > 100 ppm; STY peaks, number > 50 ppm; DMDTC TWA, mg/cm.

^A BD = 1,3-utadiene, STY = styrene, DMDTC = dimethyldithiocaramate.

^B Unit-years = ppm-years for D and STY; mg-years/cm for DMDTC.

^C Non-Hodgkin's lymphoma.

^A Non-Hodgkin's lymphoma.

^A Non-Hodgkin's lymphoma.

^A Non-Hodgkin's lymphoma.

^A BD = 1,3-butadiene, STY = styrene.

^B Non-Hodgkin's lymphoma.

^A From 1984–1987 extent-of-exposure survey ⁽¹⁰⁾ .

^B From 1974–1977 survey of two facilities ⁽⁹⁾ .

^C Uncertainty interval.