Gold mining in a tropical rainforest: Mercury sorption to soils in the mining region of Arakaka-Mathew\u27s Ridge, Guyana

Gold mining by artisinal (small-medium scale) miners causes an immense amount of damage to the environment (i.e. soil erosion, mobilization of heavy metals, etc.).1, 2 One of the most popular gold mining techniques employed by artisinal miners in Guyana is mercury amalgamation. During the amalgamation process approximately 300 metric tons/yr 11, 12 of mercury is used. Mercury once in the environment can be transported through the air, soil, and water column. It is estimated that 90-99% of total mercury (THg) is associated with the sediment. An understanding of the geochemical conditions that affect the fate of mercury in soils, which can act as potential sinks or sources for mercury, can provide solutions for reduced environmental impacts of mercury contamination. Local Guyanese agencies have become concerned with the quality of the water, soil, biota, and human impact in remote locations in the interior of Guyana. Therefore, soil samples were collected from two local mines in Guyana\u27s Arakaka-Mathew\u27s Ridge area. Two soil samples (Pakera Creek and Philip\u27s Mine) and a commercially available iron-oxide sorbent, Kemiron, underwent CVAAS, BET surface area analysis, electron dispersion spectroscopy, and x-ray diffractometry. THg concentrations for recovered soil samples were approximately 300 ng/kg. In addition, samples were subjected to batch equilibrium sorption studies as a function of pH and mercury species/concentration added as Hg(NO3)2 and HgCl2. All samples showed significant amounts of sorption between pH 3-9 for 100-1,000 ppb Hg added as Hg(NO3)2. When HgCl2.was added to the batch reactor containing Kemiron, an iron-oxide surface, the adsorption behavior of Hg2+ decreased. Philip\u27s Mine solids, characterized as silicon dioxide by BET, had the lowest surface area (4 m2/g) and sorption when added as Hg(NO3)2 and HgCl2. On the other hand, Kemiron and Pakera Creek displayed similar sorption behaviors with high sorption across all pH ranges. This may be due to similar chemistry and larger surface areas. Surface loadings were 200 mg/kg and 2,000 mg/kg for experiments with 100 ppb Hg and 1,000 ppb Hg, respectively. Further analysis is required to identify the binding mechanisms between mercury and samples as well as the role of organic matter content on samples