Detection And Measurement Of Crystalline Silica In Minerals

In 1987, the International Agency for Research on Cancer designated crystalline silica as a 2A probable carcinogen. As a result, crystalline silica is regulated under the Hazard Communication Standard as a probable carcinogen at a concentration of 0.1% or greater in the workplace. Crystalline silica will be listed as "reasonably anticipated to be a carcinogen" by the National Toxicological Program. This designation of crystalline silica as a probable carcinogen has created major issues for the mineral and chemical producer, including labeling, hazard communications, marketing a material with potential hazard exposure, and potential liability. The State of California also regulates crystalline silica under Proposition 65 in products as a carcinogen, based upon the IARC determination that it is a probable carcinogen. More federal and state regulations are anticipated as a result of the IARC classification of crystalline silica and its subsequent federal regulation. Respirable crystalline silica has been regulated as a hazardous dust for many years by OSHA. This regulation was initiated to prevent silicosis, another occupational disease. OSHA has established monitoring devices for determining the concentration of airborne respirable silica in order to measure exposure to this substance. The accurate determination of the crystalline silica content is critical to dealing with these health risks and regulations. In the past, crystalline silica was considered to be safe and, because of its ubiquitous nature, little effort was made to determine or quantify its presence in most materials. The Hazard Communication Standard requires that a1l products containing 0.1% or greater crystalline silica must be properly labeled for this material and its hazard. Unfortunately, the 0.1% threshold was not chosen on the basis of established analytical capabilities for crystalline silica, but results from general limits for potentially carcinogenic chemicals and substances. Numerous methods have been developed for the determination of crystalline silica in a variety of products. However, these methods are not generally applicable since they must be specific for silica in any of its crystalline states and not just for total silica content. Chemical tests for silica are not difficult and quite accurate at the 0.1% level; however, in addition to its crystalline phases, it occurs in amorphous phases and in a wide variety of crystalline and amorphous silicates. In general, there is little correlation between total silica content and crystalline silica.