Silica Exposures in Artisanal Small-Scale Gold Mining in Tanzania
(School of Public Health (UMD) Epidemiology & Biostatistics Master's Student)
A major occupational health hazard associated with mining is exposure to respirable crystalline silica dust. Gold miners exposed to crystalline silica are at risk of silicosis and lung cancer, and experience higher incidence rates of pulmonary tuberculosis. Although mercury exposure among artisanal small-scale gold miners has been documented, no published data was available on crystalline silica exposures among this population of artisanal gold miners. An exposure assessment was conducted in several Western Tanzania villages on July 14-16, 2014, to characterize miners’ exposure. The goal of the assessment was to evaluate exposure and quantify the risk to better inform policy makers of the need for worker protections, and to assess the potential for implementation of protective controls to reduce exposure. Air monitoring in the breathing zone of workers using battery operated pumps and aluminum cyclones was conducted during five artisanal mining and processing operations, including drilling, manual hammering, loading, crushing, and miscellaneous processing operations. Samples were collected on 5 µm polyvinyl choride filter cassettes, and analyzed at an accredited laboratory with X-ray diffraction. Bulk samples were collected to measure the type and concentration of crystalline silica in the ore. Air monitoring results indicated that airborne concentrations of respirable silica dust exceeded the occupational exposure limit set by the American Conference of Governmental Industrial Hygienists (ACGIH), called the thereshold limit value (TLV). The average exposure to respirable silica for above ground ore processing tasks (0.19 mg/m3) was 8 times greater than the ACGIH TLV of 0.025 mg/m3. Individuals involved in below ground drilling operations had average exposures of 16.85 mg/m3, or 674 times the ACGIH TLV. The highest exposures measured underground raise concern that workers may be at risk of developing an accelerated form of silicosis that may occur within a few years of working in this environment. In addition, all of the work area exposures measured are at levels known to increase the risk for chronic silicosis and are known to significantly contribute to the risk of Tuberculosis among miners. Health effects, including lung cancer and silicosis, are irreversible and may not become apparent until 10 to 20 years after exposure, and after having worked in the mining industry. The use of wet methods could greatly reduce exposures and the risk silica-related diseases. Ongoing efforts to address mercury and other hazards in ASGM should incorporate crystalline silica dust controls.