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.

A comprehensive review of occupational and general population cancer risk: 1,3-Butadiene exposure–response modeling for all leukemia, acute myelogenous leukemia, chronic lymphocytic leukemia, chronic myelogenous leukemia, myeloid neoplasm and lymphoid neoplasm

“…These 1995 data were updated in 2000 [5,6] to include substantially revised estimates of exposure. The most recent update of the data was in 2004, when the UAB added seven more years of follow-up (through 1998) and included the most recent estimates of exposures developed in 2000 [14,18]. Exposure estimates are available for 6 of the 8 plants in the UAB study, and our exposure-response modeling is based on these 6 plants.…”

“…The 2004 UAB study includes data on five non-exposure variables (age, years since hire, calendar year, race, and plant) and nine exposure variables (cumulative BD ppm-years, cumulative STY ppm-years, cumulative DMDTC mg/cm-years, cumulative number of BD high intensity tasks (HITs), cumulative number of STY HITs, cumulative ppm-years with BD 6100 ppm, cumulative ppm-years with BD >100 ppm, cumulative ppm-years with STY 650 ppm, and cumulative ppm-years with STY >50 ppm) that may have an effect on the endpoints analyzed. (Macaluso et al [14] describes the 100 ppm cutoff for BD and the 50 ppm cutoff for STY as ''. .…”

“…EPA's risk assessments have never been updated beyond their use of the initial study data even though UAB added seven more years of follow-up and substantially improved their exposure estimates [5,6,14,18]. While cumulative BD ppm-years may be a convenient variable to use as a basis for regulations, cumulative BD ppm-years is only one of the exposure variables considered by UAB and is not necessarily the best one.…”

NTP‐CERHR Expert Panel Report on the reproductive and developmental toxicity of styrene

“…Reported mean 8-hr TWA levels of styrene in air of glass-reinforced plastic facilities ranged from 3-82 ppm with individual 8-hr TWA levels up to B140 ppm. Some studies or reviews reported data indicating that generally styrene exposures have tended to decrease over time (Pfäffli and Säämänen, 1993;Welp et al, 1996;Macaluso et al, 2004). However, styrene exposures in the reinforced plastic facilities as reported by Lemasters et al (1985a) were essentially similar to the exposure levels reported by Lees et al (2003) and Luderer et al (2004).…”

“…In a study reviewed by Harvard, maintenance workers in nonproduction departments of international paper mills were exposed to a mean TWA of 9.9 ppm styrene; the maximum value reported was 100 ppm and 4 of 93 TWA values exceeded 50 ppm. Macaluso et al (2004) estimated historical exposure to styrene in six North American styrene-butadiene rubber plants using a model that considered job tasks and factors affecting exposure potential (e.g., work practices, equipment used, exposure reduction mechanisms). Across all job categories, mean estimated TWA styrene exposures were within 2 ppm since the 1940s and declined to 0.5 ppm in the 1980s.…”