The International Agency For Research On Cancer in its publication, “IARC Monographs On the Evaluation Of The Carcinogenic Risk To Humans – Silica, Some Silicates, Coal Dust and Paraaramid Fibrils” - Volume 68, 1997, has concluded that there is sufficient evidence of the carcinogenicity ofcrystalline silica in humans, and has, therefore, classified crystalline silica in, Group 1, Carcinogenic to Humans. The National Toxicology Program’s (“NTP’s”) Ninth Annual Report on Carcinogens 2000, lists crystalline silica (respirable) as a substance which is known to be a human carcinogen. In humans, a number of studies have found an association between lung cancer and exposure to dust containing respirable crystalline silica. In many of these studies, though not all, lung cancer risks were elevated and could not be explained by confounding factors such as cigarette smoking or arsenic or random inhalation. While the IARC
working group concluded there was sufficient evidence in humans for the carcinogenicity of inhaled crystalline silica in the
form of quartz or crystobalite, it noted that carcinogenicity in humans was not detected in all circumstances studied.