Assessment of the environmental impact of mercury and cyanide in illegal gold mining in djekanou (Côte d'Ivoire)

Gold panning is an illicit gold mining activity that involves the uncontrolled use of toxic chemicals such as cyanide and mercury. The pollution generated by these two chemicals has negative repercussions on the environment and the health of populations living near illegal mining sites. The objective of this study is to assess the environmental impact of the use of mercury and cyanide in illegal gold panning in Djekanou. To this end, four (04) quarterly water, sediment, and soil sampling campaigns were conducted. The pH, temperature, electrical conductivity, and dissolved oxygen levels of the water were measured in situ. Mercury concentrations were determined in the water, sediment, and soil using atomic absorption spectrophotometry (AAS). Cyanide contents in different matrices were determined using a UV-visible photospectrometer (WFJ-752, China). Mercury and cyanide concentrations in surface water of the gold mining area range from 0.015 to 0.063 mg/L and from 0.04 to 0.08 mg/L, respectively. Mercury contents in sediments and soils range from 0.94 to 4.25 and from 0.96 to 4.71, respectively. As for cyanide, concentrations in sediments and soils range from 0.11 to 3.96 and from 0.96 to 4.71, respectively. The results obtained show that water, sediments and soils are contaminated by mercury and cyanide due to waste sludge released into the environment during ore washing. Mercury concentrations in water, sediments, and soils sometimes exceed WHO guideline values, thus constituting real sources of exposure for local populations and animal and plant species.