Risk management framework for methylmercury in artisanal small-scale gold mining

Artisanal Small Scale Gold Mining (ASGM) is largely a poverty-driven activity that has become the largest contributor (i.e., 38%) to mercury pollution globally. There is growing evidence that the sector is expanding rapidly with an increased emission of mercury into the environment. Mercury is a toxic chemical that has a detrimental effect on human health. With methylmercury being the most toxic form of mercury, and having a bioaccumulative property, fish consumption poses a major health risk. Data on mercury in ASGM communities is scarce and therefore makes evaluating methylmercury health risks difficult. This research developed a methylmercury risk management framework aimed at addressing the gaps in the sector. This was achieved by applying a multi-species fugacity mass balance fate and transport model to predict mercury. The model incorporated uncertainty by defining statistical distributions for input parameters. The concentrations and fugacities of the various species of mercury were determined for the air, water, and sediment compartments. Subsequently, the 95th percentile of the bulk water concentration of methylmercury was used with a bioconcentration factor to determine fish tissue methylmercury concentration, which formed the basis for the development of a probabilistic health risk model. Following the estimation of chronic daily intake and using a reference dose of methylmercury, the health risk was found to be unacceptable beyond the 2.5th percentile on the hazard quotient distribution. However, scenario analyses demonstrated that reducing mercury emissions by 20% could reduce risk by about 60%. To help reduce/eliminate methylmercury health risk, the framework further provides an uncertainty-based multicriteria decision analysis model that will help make robust decisions in choosing relatively safer ASGM methods. Finally, a review of ASGM sector formalization was conducted to assess the impact of regulatory policies on mercury pollution. The assessment indicated that Ghana, like many other countries, largely failed in its quest to formalize the ASGM sector. The research concludes that reducing excessive bureaucratic steps to formalization, reviewing certain laws pertaining to the duration and sizes of ASM concessions, and properly engaging stakeholders are essential to effective sector regulation and a reduction in mercury pollution.