Cohort study among workers exposed to benzene in China: II. Exposure assessment.

This report describes a retrospective exposure assessment method used in a follow-up mortality study of workers exposed to benzene. The approach quantified historical exposure to benzene in a multi-industry, multicenter cohort, involving 672 factories in 12 cities in China. Historical exposure data were collected to obtain exposure information related to 1,427 work units (departments) and 3,179 unique job titles from benzene-producing or -using factories in which written records and other data sources were evaluated. The basic unit for exposure assessment was a factory/work unit/job title combination which was considered separately during each of seven calendar-year time periods between 1949 and 1987 for a total of 18,435 exposure assignments. Historical information collected to estimate exposure included benzene monitoring data; lists of raw materials and factory products, and the percentage of benzene in each; the total amount and dates of use of benzene or benzene-containing materials; use of engineering controls and personal protective equipment; and other available exposure information. Overall, 38% (ranging from 3% for the earliest periods to 67% for the last period) of the estimates were based primarily on benzene monitoring data. In the absence of job-specific benzene monitoring data for a given calendar period, measurement results or exposure estimates for similar jobs and/or other calendar periods were used in conjunction with other exposure information to derive estimates. Estimated exposure levels are presented by industries and occupations. The highest average exposures during 1949-1987 were observed for the rubber and plastic industry (30.7 ppm), and for rubber glue applicators (52.6 ppm).