Quantifying Mercury Use and Modeling Its Fate and Transport in Artisanal and Small-Scale Gold Mining in the Lom Basin

This research quantifies mercury use and models its transport in artisanal and small-scale gold mining (ASGM) in the Lom River during two key periods of intense mining activities and high water flow. Mercury concentrations from mining surfaces were estimated using a soil input function approach. Industrial mercury releases were assessed with a ratio-based approach using official gold production data and the mercury-to-gold ratio. The PEGASE model was applied to simulate mercury transport and pollution in the Lom River and to analyze the pressure–impact relationships of ASGM activities on surface water. Field measurements of the mercury concentrations in the Lom River during the dry and rainy seasons of 2021 were used to validate modeling results. The results indicate that volatilization has a more significant impact on the predicted mercury concentrations than photodissociation. Three scenarios were modeled for mercury use: whole ore amalgamation (WOA), combined whole and concentrate ore amalgamation (WOA + COA), and concentrate ore amalgamation (COA). Mercury use estimates ranged from 2250–7500 kg during intense activity to 1260–4200 kg during high water for the gold production of 750 and 525 kg, respectively. Industrial discharges dominated mercury pollution during the dry season while leaching from mining surfaces was the primary contributor during the rainy season.