Crystalline silica: quartz and cristobalite – espirable fraction Documentation of proposed values of an occupational exposure limit (OEL)
Journal Title: Podstawy i Metody Oceny Środowiska Pracy - Year 2014, Vol 30, Issue 4
Abstract
Crystalline silica is the name of a group of min-erals composed of silicon dioxide. Quartz and cristobalite are the most common forms of crys-talline silica. Siliceous raw materials are widely applied in the production of building materials, glass, ceramics, silicon and ferro-silicon, orga-nosilicon compounds, and many others. Work-ers in the following industries are exposed to crystalline silica: mining, fuel and energy, chemical, foundry, metallurgical, building ma-terials, glass and construction.In Poland, according to data of the Central Sta-tistical Office, about 50,000 people are occupa-tionally exposed to dust causing pulmonary fibrosis (mainly containing crystalline silica). The median concentrations of respirable dust containing 2 to 50% crystalline silica, calculated on the basis of the results of almost 50,000 measurements made in 2001-2005, was 0.56 mg /m3. Every year in Poland about 100new cases of silicosis are recorded. The harmful effects of quartz and cristobalite in humans results most-ly from long (over 10 years) inhalation of dust, which can enter the area of gas exchange in the lungs, where it can be toxic to macrophages, pneumocytes and other cells, causing a chronic inflammation and nodular (focal) or diffused pulmonary fibrosis. The development of silico-sis and, in many cases, of lung cancer follows those processes. Autoimmune diseases, chronic kidney disease, bacterial and fungal complica-tions of silicosis and systemic silicosis are other health effects of exposure to crystalline silica. Epidemiological studies of people exposed to crystalline silica have shown that the risk of silicosis is proportional to the dose of dust. After 40 to 45 years of exposure it is to 2–3% up to the concentration level of 0.025mg/m3; from a few to several percent when concentration is 0.05mg/m3, and from a few to about 70 per-cent at 0.1mg/m3. On the basis of the results of epidemiological and experimental studies, the Working Group of the International Agency for Research on Cancer (IARC) has classified quartz and cristobalite as group 1 (carcinogens to hu-mans). The relative risk of lung cancer in work-ers exposed to crystalline silica is usually esti-mated at 1.3–1.4. However, among workers with silicosis it is 1.7–2.4, and in those exposed with-out radiological changes in the lungs it is 1.0–1.2. Experimental studies in rats have confirmed carcinogenic effects of quartz and cristobalite. Studies with other animal species did not pro-duce similar results. The test results of genotox-ic effects of crystalline silica are also not clear. Taking into account the results of epidemiolog-ical studies on the fibrotic effect of quartz and cristobalite, and no NOAEL or LOAEL values, adopting occupational exposure limit value (OEL) for respirable crystalline silica of 0.1 mg/m3 has been proposed. Compliance with this OEL will greatly help to improve the work-ing conditions of people exposed to crystalline silica.
Authors and Affiliations
Aleksandra Maciejewska
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