A comparison of factors affecting the small-scale distribution of mercury contamination in a Zimbabwean stream system
Artisanal small-scale mining (ASM) operations use mercury liberally in the gold extraction process, as compared to large scale industrial mining operations, and accounts for approximately one third of anthropogenic mercury consumption worldwide. These ASM operations are concentrated in many impoverished and poorly regulated countries such as Zimbabwe, resulting in a number of negative environmental and health impacts. There are three pathways by which mercury generally enters the environment from gold mining: 1) directly via private miners, 2) through stamp mill operations (also used by ASM miners), and 3) industrial-scale mining operations. To examine the levels of mercury contamination resulting in one such geographic locality, sediment and tailing samples in a single, heavily mined watershed in southern Zimbabwe were collected from May – June 2015. Samples were collected from the stream system, as well as six stamp mills and a single industrial mine in the watershed. GPS point location data were taken for mining operations and sampling sites to examine the spatial patterns of mercury concentration relative to each mining operation. Data were first analyzed using linear regression then a MARS model, followed by application of an ANCOVA model to assess the relationship between mercury concentrations and three factors; percent organic carbon, distance downstream, and distance from potential contamination source. Mercury concentrations within the study area ranged between 6-1,541 µg/kg dw (mean 142 µg/kg dw). Analyses of mercury concentrations indicated a positive relationship with percent organic carbon and a negative relationship with distance downstream and distance from potential contamination source. Results from this study will help to elucidate the relationship between gold production and the spatial scale of mercury contamination in aquatic ecosystems in Africa. These data may lead to a better understanding of the relationship between mercury use and community health, which may aid both the local and global communities in regulating mercury contamination of the environment, thereby reducing the suffering and early death of many people in impoverished countries where ASM is commonplace.