Airborne lead exposures during artisanal lead mining and gold ore processing in Zamfara, Nigeria

Abstract

Artisanal mining in Nigeria is growing along with the increase in the price of metals. However, self-employed miners, particularly in the northwest of the country, have brought extensive environmental contamination and severe lead poisoning from the lead content in the ore. This study assessed airborne lead exposures to miners during lead mining and gold ore processing in three villages in Zamfara State, Nigeria. Personal air samples were collected and analyzed for lead content. Gold processing operations were classified by task, including: manual mortar and pestle grinding, hammer crushing, and mechanical stone crushing and grinding operations with diesel-powered equipment. Separately, exposures were evaluated among underground lead miners. This study collected a total of 47 air samples, including 32 from gold ore processing sites and 15 from lead mining sites. The results indicated that underground miners were exposed to airborne lead at a mean concentration of 0.48 mg/m3, or approximately 10-fold the United States Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL). Furthermore, miners at gold processing sites were exposed to airborne lead at a mean concentration of 1.59 mg/m3 for both mechanical and manual tasks, which is approximately 32-fold the PEL. Manual gold ore processing resulted in mean airborne lead exposures of 1.74 mg/m3, and those using mechanical methods had a mean concentration of 1.52 mg/m3. The results also indicated that the order of airborne lead level exposure was as follows: mortar and pestle operators > crusher operators > hammer operators > grinder operators > underground lead miners. Lead mining operations and gold ore processing consistently had elevated airborne lead at levels, posing risks of acute lead poisoning, and are likely contributing to take-home lead exposures observed in these communities. These results are consistent with the lead contamination of soil observed in housing compounds and at processing sites in this region. To address these risk factors, safer mine training and the adoption of wet methods were encouraged along with changes to personal hygiene practices and other measures to mitigate exposure and to protect miners and their communities.