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

Abstract

Background Besides a clear relationship to silicosis, crystalline silicaÐquartzÐhas been associated with lung cancer, nonmalignant renal disease, and auto-immune disease.To study diseases associated with crystalline silica further, NIOSH conducted a cohort mortality study of workers from 18 silica sand plants, which had quarry, crushing, and bagging operations to produce industrial sand. Twelve of these plants also had grinding mills to produce ®ne silica powder. The historical crystalline silica exposures of workers at these plants were estimated to facilitate exposure±response analyses in the epidemiologic study. Methods NIOSH obtained personal respirable dust measurement records from Mine 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. Although no personal samples were available before 1974, impinger dust measurements were reported for 19 silica sand plants in 1946; these data were converted and used to estimate exposures prior to 1974. Statistical modeling of the samples was used to estimate quartz exposure concentrations for workers 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 collected at these 18 plants. The geometric mean quartz concentration was 25.9 mg/m 3 (GSD 10.9) with a range from less than 1 to 11,700 mg/m 3 . Samples below 1 mg/m 3 were given a value of 0.5 mg/m 3 . Over one-third 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 exceeded the NIOSH recommended exposure limit (REL 50 mg/m 3 ). The samples 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 estimates. Therefore, samples were combined into 10 categories of jobs performing similar tasks or located within the same plant area. Conclusions The quartz concentrations varied signi®cantly by plant, job, and year. Quartz concentrations decreased over time, with measurements collected in the 1970s signi®cantly greater than those collected later. The modeled exposure estimates improve upon duration of employment as an estimate of cumulative exposure and reduce exposure misclassi®cation due to variation in quartz levels between plants, jobs, and over time.

Temporal trends in respirable dust and respirable quartz concentrations within the European industrial minerals sector over a 15-year period (2002–2016)

“…Like in our study, the corresponding quartz concentrations decreased at a slower rate of −1.2% per annum 15. Our findings concur also with other studies that previously reported downward trends for respirable dust (−5%)13 and quartz (−11%),12 (−7%),13 (−6%)23 and (−10%)24 within several industries worldwide.…”

“…The body of literature regarding (recent) long-term temporal trends in occupational exposures to RCS is small. Within the US silica sand industry, a clear annual downward trend in quartz exposure of 11% per year for the period 1946–1996 has been reported 12. In China, for the years 1950 to 1987, exposures to total dust and respirable silica were assessed in 20 mines and 9 pottery factories.…”

Quantitative Crystalline Silica Exposure Assessment for a Historical Cohort Epidemiologic Study in the German Porcelain Industry

“…Conversion of particle count results to gravimetric mass results for historical exposure assessment has been conducted in several epidemiologic studies of crystalline silica exposure, such as the Canadian Hardrock Miners Study, (26) the U.S. Diatomaceous Earth Industry Study, (27) the U.S. Industrial Sand Workers Studies, (28,29) the East German uranium mine study, (30) and the British Pottery Workers Study. (18) The derived conversion factors in this study are somewhat higher than reported in most U.S. studies but similar to those derived empirically for the Industrial Sand Workers study.…”

National trends in silicosis mortality in the United States, 1981–2004

“…These limits, together with recommendations such as that by NIOSH (that occupational exposures to respirable crystalline silica shall not exceed 0.05 mg/m 3 (time weighted average concentration), for up to 10 hr/day, during a 40-hr work week) [NIOSH, 1974[NIOSH, , 1988, should have led to reduced silica dust exposures from about 1970 to the present. For example, a study on historical respirable quartz exposures of industrial sand workers for reported that quartz concentration decreased over time, indicating significantly greater measurements (average100 mg/m 3 ) in the 1970s than those measured (below 10 mg/m 3 ) since 1990 [Sanderson et al, 2000]. It follows that those dying towards the end of the study period, that is, around 2004, would have worked at least part of their life in lower silica dust levels than did their older colleagues.…”