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PETROLEUM WORKER STUDIES AND BENZENE RISK ASSESSMENT

Epidemiologic studies involving benzene-exposed workers can be broadly classified as those that involve workers who used benzene-based solvents, and those that involve workers exposed to benzene from petroleum products. Risk assessments have focused upon the former (e.g., Rinsky et al., 1987) and have not directly used the results of the latter group of studies. However, this latter group of studies reflects exposure scenarios that are more like those of the general population, the ultimate target population for many risk assessments. The focus of this article is on the latter group of studies, and their potential use in comprehensive benzene risk assessments. Epidemiologic studies of the petroleum industry include subjects who may have worked as early as 1900 as well as others who worked through the 1980s. The benzene content of gasoline has always varied (Garner & Evans, 1932), but probably rose somewhat following the introduction of catalytic cracking technology in the late 1930s. From that time forward, the benzene content of gasoline has typically been in the range of 1–5%, although rare instances where benzene-enriched fuels were used have been noted. Worker benzene exposure from refinery operations probably increased from the 1920s to 1960s and then decreased over time due to fugitive emission control and other exposure control initiatives. Benzene exposures in distribution and retail operations also probably increased from the 1920s to 1950s, but then remained relatively stable. Typical 8-h exposure concentrations in distribution and retail operations average less than 1 ppm, although exposures can reach 2–3 ppm for briefer (e.g., 30–120 min) periods. These exposures are one to two orders of magnitude lower than those present in workers exposed to benzene through past solvent use (e.g., Rinsky et al., 1987). Several similarly designed petroleum worker cohort studies have been reported (Wong & Raabe, 1995). Unfortunately, benzene exposure has not been directly measured for each study subject, although reasonable bounds can certainly be placed on benzene exposure in the aggregate study populations.