Reaction of Cyanide with Hg0-Contaminated Gold Mining Tailings Produces Soluble Mercuric Cyanide Complexes.

Elemental mercury (Hg0) contamination in artisanal and small-scale gold mining (ASGM) communities is widespread, and Hg0-contaminated tailings are often reprocessed with cyanide (-CN) to extract residual gold remaining after amalgamation. Hg0 reacts with -CN under aerobic conditions to produce Hg(CN)42- and other Hg(CN)nn-2 complexes. The production of solvated Hg(CN)nn-2 complexes increases upon agitation in the presence of synthetic and authentic Hg0-contaminated tailings that aid in dispersing the Hg0, increasing its reactive surface area. Adult rats were exposed to various concentrations of Hg(CN)2, and accumulation in organs and tissues was quantified using direct mercury analysis. The primary site of Hg(CN)2 accumulation was the kidney, although accumulation was also detected in the liver, spleen, and blood. Little accumulation was observed in the brain, suggesting that Hg(CN)2 complexes do not cross the blood-brain barrier. Renal tissue was particularly sensitive to the effects of Hg(CN)2, with pathological changes observed at low concentrations. Hg(CN)2 complexes are handled by mammalian systems in a manner similar to other inorganic species of Hg, yet appear to be more toxic to organ systems. The findings from this study are the first to show that Hg(CN)2 complexes are highly stable complexes that can lead to cellular injury and death in mammalian organ systems.