• Accumulation and Toxicity of Mercury-Cyanide Complexes

      Ford IV, Earl Gilmore; School of Medicine
      Mercury is a heavy metal toxicant found in numerous occupational and environmental settings. A major source of mercury pollution in environmental settings comes from the occupational use of mercury in artisanal and small-scale gold mining (ASGM). ASGM utilizes elemental mercury (Hg0) for extraction of gold from ore, which leads to Hg0-contaminated tailings. These tailings are often reprocessed with cyanide (‾CN) to extract residual gold. Hg0 reacts with ‾CN to form mercury-cyanide (Hg(CN)) complexes, which are released into the environment with discarded tailings. These complexes create numerous environmental and health problems. To assess the disposition of Hg(CN)2 complexes in mammalian systems, wistar rats were injected with 0.5 mol/kg mercury chloride (HgCl2) or Hg(CN)2. Each injection solution contained radioactive mercury ([203Hg2+]) and/or radioactive cyanide ([14C]-NaCN). After 24 h, animals were euthanized and organ samples were collected for determination of Hg(CN)2 content and for histological analyses. To assess the disposition of Hg(CN)2 complexes in an aquatic organism, zebrafish (Danio rerio) were exposed to various concentrations of Hg(CN)2 and accumulation in both whole fish and specific organs was measured. The current data show that the disposition of Hg(CN)2 in zebrafish is similar to that when rats were exposed to HgCl2. Interestingly, when rats were exposed to NaCN alone, the uptake was significantly less than that of rats exposed to Hg(CN)2. Experiments using adult zebrafish showed that Hg(CN)2 accumulates readily in fish. Zebrafish embryos exposed to Hg(CN)2 experienced alterations in developmental processes. The current data provide important information about the handling of Hg(CN)2 complexes in mammalian systems and aquatic organisms.
    • An Analysis of the Toxic Effects of Mercury Cyanide Complexes on Zebrafish

      Pittman, Elizabeth; School of Medicine
      Mercury (Hg) is a unique heavy metal toxicant that is found in numerous environmental and occupational settings. A major source of environmental Hg is from artisanal and small-scale gold mining (ASGM), whereby metallic mercury (Hg0) is used to amalgamate gold from mined ore. Hg extraction of gold is inefficient and thus, a significant amount of gold remains in the ore. The leftover Hg-contaminated tailings are often subjected to cyanidation to extract the remaining gold. During this process, mercury and cyanide form mercuric cyanide complexes that are held together with a strong, covalent Hg-carbon bond. These toxic complexes are proposed to be prevalent in terrestrial and aquatic environments around mining sites. The purpose of the current study was to determine how mercuric cyanide complexes, particularly Hg(CN)2, affect the health of aquatic organisms in contaminated environments. We used adult and larval zebrafish (Danio rerio) as model organisms for this study. Zebrafish, in various life stages, were exposed to several different concentrations of Hg(CN)2 to determine the physical and behavioral effects of this exposure. Embryos were exposed to varying concentrations of Hg(CN)2 at one-hour post fertilization (4th cell cycle) until 72 hours post fertilization when hatching begins. Concentrations ranged from 0 to 0.1 mg/L Hg(CN)2. Embryos exposed to concentrations of Hg(CN)2 above 0.08 mg/L had a lower hatching rate and survival rate. Exposure of adult fish to various concentrations of Hg(CN)2 led to significant alterations in behavior and mercury content of muscle. The current study is the first to report the way in which Hg(CN)2 affects aquatic organisms in various stages of life.