One agent, many diseases: exposure-response data and comparative risks of different outcomes following silica exposure.
BACKGROUND
Evidence in recent years indicates that silica causes lung cancer, and probably renal disease, in addition to its well-known relationship to silicosis. There is also suggestive evidence that silica can cause arthritis and other auto-immune diseases. Silica has, therefore, joined a handful of other toxic exposures such as tobacco smoke, dioxin, and asbestos which cause multiple serious diseases.


METHODS
The available exposure-response data for silica and silicosis, lung cancer, and renal disease are reviewed. We compare the corresponding excess risks (or absolute risks in the case of silicosis) of death or disease incidence by age 75 for these three diseases, subsequent to a lifetime (45 years) of exposure to silica at current US standard (0.1 mg/m(3) respirable crystalline silica).


RESULTS
The absolute risk of silicosis, as defined by small opacities greater than or equal to ILO classification 1/1 on an X-ray, ranges from 47% to 77% in three cohort studies with adequate follow-up after employment. The absolute risk of death from silicosis is estimated at 1.9% (0.8%-2.9%), based on a pooled analysis of six cohort studies. The excess risk of lung cancer death, assuming US male background rates, is 1.7% (0.2%-3.6%), based on a pooled analysis of ten cohort studies. The excess risk of end-stage renal disease (assuming male background rates) is 5.1% (2.2%-7.3%), based on a single cohort. The excess risk of death from renal disease is estimated to be 1.8% (0.8%-9.7%), based on a pooled analysis of three cohorts.


CONCLUSIONS
Keeping in mind that the usual OSHA acceptable excess risk of serious disease or death for workers is 0.1%, it is clear that the current standard is far from sufficiently protective of workers' health. Perhaps surprisingly, kidney disease emerges as perhaps a higher risk than either mortality from silicosis or lung cancer, although the data are based on fewer studies.
Steenland
Kyle
K
Rollins School of Public Health, Emory University, 1518 Clifton Road, Atlanta, GA 30322, USA. nsteenl@sph.emory.edu
D000328:Adult; D000368:Aged; D006801:Humans; D007674:Kidney Diseases / Q000453:epidemiology* / Q000209:etiology; D008175:Lung Neoplasms / Q000453:epidemiology* / Q000209:etiology; D008875:Middle Aged; D016273:Occupational Exposure / Q000009:adverse effects*; D018570:Risk Assessment; D012307:Risk Factors; D012822:Silicon Dioxide / Q000633:toxicity*; D012829:Silicosis / Q000453:epidemiology* / Q000209:etiology; D013997:Time Factors; D014481:United States / Q000453:epidemiology
D012822:Silicon Dioxide