Academic journal article Iranian Journal of Public Health

Risk Assessment of Occupational Exposure to Crystalline Silica in Small Foundries in Pakdasht, Iran

Academic journal article Iranian Journal of Public Health

Risk Assessment of Occupational Exposure to Crystalline Silica in Small Foundries in Pakdasht, Iran

Article excerpt

Introduction

"Silica is a chemical term for silicon dioxide (SiO2). Silica can crystallize as one of at least eight polymorphs (a-quartz, P-quartz, cristobalite, tridymite, stishovite, coesite, moganite, and keatite), each of which occurs in nature. In addition, silica can occur in noncrystalline forms, and several amorphous materials" (1). -Numerous studies have demonstrated that samples of quartz can be biologically active, and under some conditions exposure to quartz appears to result in fibrosis or tumors or both" (1). Silica is a mineral, composed of one atom of silicon and two atoms of oxygen (Sio2), with melting point of 1600 °C; it is an odorless, colorless, non-combustible solid (2).

Crystalline silica is used in many industries including cement production, glass, concrete products, ceramic, clay soil (clay and bricks), casting, sandblast, abrasives, pottery, porcelain, and many construction activities (3, 4). Silica dust is considered an inhalation risk. Considering improved working conditions and dust control in developed countries, incidence rate of silicosis is decreasing in these countries (5). However, in developing countries, contact with dust is still an important health hazard National Institute for Occupational Safety and Health (NIOSH) estimates that at least 1.7 million American workers are potentially exposed to inhalable crystalline silica (6). Silicosis is the most important work-related lung disease, resulting from constant inhalation of crystalline silicacontaining dust, in which lung tissue is damaged, thereby reducing the capacity for oxygen intake (2, 7). Silicosis is usually a pulmonary nodular fibrosis, and is primarily associated with exposure to inhalable crystalline silica. Despite reduced silicosisrelated mortality rate in the past few decades, annually 300 silicosis-related deaths still occur in America (8). Depending on the amount of exposure to crystalline silica, every worker may have one of the three types of silicosis: acute, chronic, and accelerated (9). Reports on exposure to free silica in casting industry indicate the incidence of exposure to quartz. Recently, International Agency for Research on Cancer (IARC) conducted an epidemiological review study on lung cancer and occupational exposure to crystalline silica, and introduced silica in the form of quartz and cristobalite as group 1 carcinogenic humans (2, 16).

Risk assessment is one of the latest toxicology methods that express risk of harm to the population exposed through scientific data obtained on hazardous properties of toxic agents and the amount of exposure. This scientific process attempts to identify and estimate real risks. It is in fact the result of assessment of potential risk of toxic substances, dose-response relationship (effects) and risk characteristics, which is the same as management of rational risk statement (10). Mannetje et al., as the pioneers in risk assessment of exposure to crystalline silica reported that risk of silicosis-related deaths per 1000 people exposed, in relation to cumulative exposure, is continuously increasing. They classified cumulative exposure in various ranges from 0 to 28.1 mg/m3- year, and reported the risk of silicosis-related death in different cumulative exposures between 1 and 63 per 1000 exposures (11). Lately, using Mannetje et al. model, risk of silicosis-related deaths, up to the age of 65 years and 45 years of crystalline silica exposure in the range of 0.1 mg/m3 (common standard in some countries) was reported at 13 per 1000 persons exposed (12). Rice et al. presented risk assessment of lung cancer in workers exposed to crystalline silica, and anticipated lifelong risk of mortality due to lung cancer, assuming 45 years continuous work history and 10-year interval (13). According to this model, constant lifelong risk of inhalable crystalline silica within the proposed standard range of American Conference of Governmental Industrial Hygienists ACGIH (0.05 mg/m3) was 19 per 1000. …

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