There is now a sizeable body of literature which is reasonably consistent in showing that renal disease is associated with silica exposure. There is some suggestion that the mechanism involves auto-immunity, although direct silica toxicity to the kidney is also possible. In the United States the background (nonexposed) lifetime male risk of end-stage renal disease (ESRD) incidence is 2%. For a worker exposed for 45 years at a current recommended limit of 0.10 mg/m3 the lifetime risk of ESRD is 19.1% (95% CI 2.5%, 82.0%), based on the only quantitative study to date (18 observed cases). For renal disease mortality (underlying cause), the lifetime risk of death at the same level of exposure is 2.1% (2.9%-10.0%), above a background risk of 0.3%, based on the only quantitative study (51 deaths). For death from any cause in the presence of renal disease (multiple cause), the lifetime risk is 7.2% (3.2%-15.6%), above a background risk of 1.5% (one study, 204 deaths). These risks should be compared with the risk of other outcomes associated with silica exposure. The risk of silicosis on chest X-ray (1/1 or above) is 55%-92% in four studies with follow up after employment (1583 cases) , but the risk of death from silicosis is 1.3% (170 deaths). There is no background risk for either silicosis incidence or death. The risk of from lung cancer due a 45 year exposure to 0.1 mg/m3 is increased from a background rate of 5.3% to 7.0% (5.5%-8.9%) (1072 cases, 10 pooled studies). Despite the relative scarcity of data for renal disease, these data indicate that the excess risk of death from renal disease (1. 8%) is similar to the excess risk from lung cancer (1.7%), and the absolute risk of death from silicosis (1.3%), and that renal disease mortality should be of equal concern to regulators as lung cancer and silicosis mortality. Furthermore, in many cases renal disease is a major contributory cause, and the excess risk of death from any cause in the presence of renal disease is 5.7%. All these risks exceed what the US OSHA considers acceptable, i.e., an excess risk of 0.1 %. Permissible exposure limits would need to be reduced ten-fold, to 0.01 mg/m3, to approximately attain acceptable excess mortality risks. Morbidity risks from renal disease and silicosis (diagnosed via chest X-ray) are much higher than mortality risks. End-stage renal disease, however, is a very severe disease, while silicosis diagnosed via X-ray opacities may be sub-clinical.
La Medicina del Lavoro. 3rd International Symposium on Silica, Silicosis, Cancer and Other Diseases, S. Margherita Ligure, 21-25 October 2002