Silica and Silica Compounds

Abstract

Crystalline silica is one of the most abundant minerals on Earth. More than 230 million individuals around the world, and more than 2 million workers in the United States, predominantly in construction and mining occupations, are exposed to silica every year. Inhalation of crystalline silica leads to the development of silicosis, a progressive pneumoconiosis characterized by chronic lung inflammation and fibrosis, for which no specific therapy is available. Silicosis is also associated with increased risk of tuberculosis, lung cancer, chronic obstructive pulmonary disease (COPD), kidney disease, and autoimmune disease. These health risks remain elevated even after silica exposure has ceased. Although preventive measures have decreased the mortality attributable to silica exposure in the past decade, this occupational lung disease still kills about 100 people every year in the United States, according to the National Institute for Occupational Safety and Health (NIOSH). Between 1999 and 2013, silicosis was the underlying or contributing cause of death for about 2000 people, and 300 deaths occurred each year between 1991 and 1995, while it decreased to about 100 per year in 2012 and 2013. Data from NIOSH show that a large number of workers are at increased risk for silicosis because of exposure to silica levels that exceed current regulatory standards. Therefore, regulatory agencies have been forced to further reduce the permissible exposure levels (PEL) to 25 μg/m 3 (micrograms of silica per cubic meter of air) over an 8‐h shift, to improve prophylaxis. Despite these efforts, silicosis remains a global health threat.