An assessment of the impact of artisanal and commercial gold mining on mercury and methylmercury levels in the environment and fish in Cote d'Ivoire.

Artisanal and small-scale gold mining (ASGM) activities are an important source of mercury (Hg) to the atmosphere globally, and in most countries in West Africa, where gold production has increased dramatically in the last decade from both commercial and ASGM activities. This study focused on examining the concentrations of Hg and methylmercury (MeHg) in water, sediments and fish in four regions associated with gold mining activities in Cote d'Ivoire to assess the potential exposure of the local communities to MeHg from fish consumption. Concentrations of dissolved total Hg and MeHg in water and sediment were elevated at some locations sample and were indicative of local contamination. Several locations had sediment total Hg above 100 ng g-1 and sediment %MeHg ranged from 0.03 to 4.4%. Fish concentrations exceeded 0.3 μg/ g wet wt., especially for carnivores and fish caught in the western region of the country. Bioaccumulation factors, relative to dissolved MeHg, were higher for carnivores than omnivores and varied with region, suggesting other factors besides MeHg concentration alone were impacting uptake and trophic transfer. Given that people in Cote d'Ivoire consume fish at a higher level than other countries, the levels in fish were sufficient to exceed the US EPA's guidance criteria even at average consumption levels, and particularly for people consuming fish at a higher rate. Overall, this study provides compelling evidence that ASGM activities in Cote d'Ivoire are leading to elevated exposure and likely impacting the health of the local populations in regions where such activity is occurring.