The Influence of Organic Acids on Mercury Bioavailability: Insight from an Earthworm Assessment Protocol
JENNIFER J. HINTON AND MARCELLO M. VEIGA
Normal B. Keevil Institute of Mining Engineering, University of British Columbia, Vancouver, BC, Canada
Between 10 and 15 million artisanal and small-scale miners in more than 50 countries directly rely on gold mining for their livelihoods. Mainly due to the rudimentary techniques that characterize artisanal mining, these activities are frequently accompanied by extensive environmental degradation and deplorable socio-economic conditions. Mercury, cheap, easy-to-use and effective, is commonly used to recover gold through amalgamation. Due to its misuse, between 800 and 1000 tonnes of mercury are released into the air, water, and soils by artisanal gold miners every year. This generates serious health hazards for miners involved in gold extraction, as well as for surrounding community inhabitants, who may be exposed via high levels of mercury in fish they consume. The metallic mercury discharged by miners into the environment has the potential to undergo many changes, including the transformation to a readily bioavailable and highly toxic form of mercury, methylmercury. A laboratory methodology using the earthworm Eisenia foetida was developed to assess mercury bioavailability in mine tailings and aqueous solutions and examine the influence of certain factors, in particular organic acids, on the transformation of metallic mercury into bioavailable forms. The earthworm protocol provides a quick, inexpensive and simple means to examine the role of specific factors on mercury transformations and is a valuable tool for prioritizing contaminated sites based on the potential for mercury incorporation into biota. Through a series of tests using metallic mercury dissolved in humic, tannic and fulvic acids and mine tailings and soils saturated with organic acids, this research indicates that earthworms (E. foetida) are capable of accumulating Hg from solutions and the reaction of mercury with organic acids is an important pathway for the incorporation of mercury into the food chain. This finding is significant in terms of understanding biogeochemical cycling of Hg in darkwaters and assessing ecological and human health risks from Hg in these aquatic systems. The influence of organic acids on Hg bioaccumulation and intestinal methylation is extremely significant in terms of understanding biogeochemical cycling of Hg in darkwaters and assessing ecological and human health risks from Hg in these aquatic systems.
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