Tuesday, November 15, 2005

Silica and Renal Disease

Brooklyndodger recalls that going to IH school, we wondered why asbestos caused fibrosis and cancer, while silica only fibrosis. Since then, silica has become a known human carcinogen, based on mortality studies in people given biological plausibility by laboratory bioassays.

Now we wonder whether carbon black, carcinogenic in laboratory bioassays, is also carcinogenic in people.

Now comes an account of end stage renal disease and silicosis. The investigator notes a strong association - that is, a high relative risk. BrooklynDodger now needs to look for laboratory evidence to provide biological plausibility.

Am J Ind Med. 2005 Jul;48(1):16-23.

One agent, many diseases: exposure-response data and comparative risks of different outcomes following silica exposure.
Steenland K.
Rollins School of Public Health, Emory University, 1518 Clifton Road, Atlanta, GA 30322, USA. nsteenl@sph.emory.edu

...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).

...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.

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