Historical respirable quartz exposures of industrial sand workers: 1946-1996

Background Besides a clear relationship to silicosis, crystalline silica-qu artz-has been associated with lung cancer nonmalignant renal disease, and a uto-immune disease, To study diseases associated with crystalline silica fu rther NIOSH conducted a cohort mortality study of workers from 18 silica sa nd plants, which had quarry, crushing, and bagging operations to produce in dustrial sand. Twelve of these plants also had grinding mills to produce fi ne silica powder: The historical crystalline silica exposures of workers at these plants were estimated to facilitate exposure-response analyses in th e epidemiologic study. Methods NIOSH obtained personal respirable dust measurement records from Mi ne Safety and Health Administration (MSHA) compliance inspections at all 18 plants and from the archives of seven plants which had collected samples. These samples had been analyzed for quartz content by x-ray diffraction. Al though no personal samples were available before 1974, impinger dust measur ements were reported for 19 silica sand plants in 1946; these data were con verted and used to estimate exposures prior to 1974. Statistical modeling o f the samples was used to estimate quartz exposure concentrations for worke rs in plant-job-year categories from the 1930s when mortality follow-up of the cohort began until 1988 when follow-up stopped. Results Between 1974 and 1996 there were 4,269 respirable dust samples coll ected at these 18 plants. The geometric mean quartz concentration was 25.9 mu g/m(3) (GSD = 10.9) with a range from less than I to 11, 700 mu g/m(3). Samples below 1 mu g/m(3) were given a value of 0.5 mu g/m(3). Over one-thi rd of the samples (37%) exceeded the MSHA permissible exposure limit value for quartz (PEL = 10 mg/m(3)/(%quartz + 2)) and half (51%) of the samples e xceeded the NIOSH recommended exposure limit (REL=50 mu g/m(3)). The sample s were collected from workers performing 143 jobs within the 18 plants, but too few samples were collected from many of the jobs to make accurate esti mates. Therefore, samples were combined into 10 categories of jobs performi ng similar tasks or located within the same plant area. Conclusions The quartz concentrations varied significantly by plant, job, a nd year: Quartz concentrations decreased over time, with measurements colle cted in the 1970s significantly greater than those collected later The mode led exposure estimates improve upon duration of employment as an estimate o f cumulative exposure and reduce exposure misclassification due to variatio n in quartz levels between plants, jobs, and over time. Published 2000 Wile y-Liss, Inc.