Study of two cohorts of workers exposed to methyl methacrylate in acrylic sheet production

Objectives-To study mortality among 4324 workers at two United Kingdom fact ories, Darwen, Lancashire and Wilton, Cleveland, producing polymethyl metha crylate (PMMA) sheet. The Darwen factory is still active, but the Wilton on e was closed in 1970. Also, to investigate patterns of mortality after expo sure to methyl methacrylate; in particular, mortality ii om colon and recta l cancer. Il Methods-All male employees at the Darwen factory with a record of employmen t in 1939-88 and all men ever employed at the Wilton factory (1949-70) mere investigated. The vital status of both cohorts was ascertained on 31 Decem ber 1995. The exposure of 1526 subjects at the Darwen plant who were engage d from 1949 onwards could be characterised. The mean duration of exposure w as 7.6 years at 13.2 ppm (8 hour time weighted average), although exposures in some work groups were as high as 100 ppm. It was not possible to calcul ate the cumulative exposure of workers first employed at the Darwen plant b efore 1949 or workers at the Wilton factory. Results-In the Darwen cohort, 622 deaths were identified and a further 700 deaths in the Wilton cohort. Mortalities for the cohort were compared with national and local rates and expressed as standardised mortality ratios (SM Rs). In the subcohort of Darwen workers with more than minimal exposure to MMA, reduced mortalities compared with national and local rates, were found for all causes (SMR 94), and colorectal cancer (SMR 92), but mortality fro m all cancers was slightly increased (SMR 104). No relations were found wit h cumulative exposure to MMA. In the subcohort of Wilton workers, mortality from all causes of death was significantly reduced (SMR 89), but mortality from all cancers (SMR 103) and colorectal cancer (SMR 124) were increased. The excess of colorectal cancer was confined to employees with less than I year of employment. Conclusion-The study provided no clear evidence that employment at the fact ories or exposure to MMA had adversely affected the mortalities of workers.