Characterizing Mercury and Metal Concentrations in Soil and Sediment within Gold Mined Areas of Guyana

Artisanal gold mining can lead to contamination of soil and stream sediments, but the degree and extent of contamination varies widely. This study characterized Hg, As, Cd, Co, Cu, Mn, Ni, Pb, and Zn contamination in soils and sediments from two gold mines in Guyana. Soil sampled from the pit and overburden areas exhibited slightly higher concentrations of Co, Cu, Mn, Ni, and Zn, but below environmental guidelines. Similarly, stream sediments sampled within the mining area were not enriched relative to downstream areas. In contrast, soil and stream sediment was heavily contaminated with Hg, but the level of contamination was not higher within the mining area and was instead strongly related to organic matter content, which was much higher in soil at sites farther from the mines. These high organic matter soils father from the mining pits showed higher Hg concentrations (501–614 ng g−1). Leaching experiments showed that Hg leached from soil collected at distant (2–4 km) sites was as high as at sites close to mines, but the Hg/DOC ratio in leachate was much lower and Kd values (0.75–1.67 L mg−1) at all sites indicate that Hg is very loosely bound to soil.