Widespread and Persistent Mercury Contamination Beyond Disposal Sites: Case study on Challenges for Remediation in Artisanal Gold Mines of Tanzania Archives of Environmental Contamination and Toxicology

Many national and international initiatives aim to control and limit the use of mercury (Hg) in gold extraction. However, the feasibility of Hg eradication from the environment depends on understanding the extent of its distribution. This case study focuses on the spatial and vertical distribution of total mercury (THg) residues at five artisanal mining sites in Tanzania namely, Mgongo, Sekenke, Nyarugusu, Rwamgasa, and Mugusu to assess the feasibility of remediating the problem. The trend showed presence of THg residues in surface layers (0–20 cm), decreasing with depth but still detectable in deeper layers (> 20–100 cm). A horizontal distribution in surface-layer concentrations was also observed along the Mabubi River, which drains across Mugusu mine into Lake Victoria. Among all sites, the highest surface-layer (20 cm) total mercury (THg) concentration was 1.48 ± 0.02 mg/kg, measured from a sample collected at the Nyarugusu mine site, with a moderate decrease to 0.12 ± 0.001 mg/kg at a depth of 100 cm. Other soil samples from the Rwamgasa mine site showed THg concentrations of 0.048 ± 0.012 mg/kg and 0.082 ± 0.01 mg/kg at depths of 70 and 80 cm, respectively. These findings suggest that significant THg residues are detected from surface to deeper layers and wide area of river sediment distribution, mediated by physical, environmental, biological and chemical processes that support simultaneous Hg transport and suspension. The THg residues in soils and sediments challenge the feasibility of remediation efforts in areas with similar wide contamination extents. They demonstrate a long-term legacy of contamination that will continue to impact environmental quality in many regions affected by artisanal mining.