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PH08 Metals in the Environment: Aquatic Biological Perspectives
(PH084) Assessing the Role of Mercury-Natural Organic Matter (NOM) Complexation on Toxicity to Ceriodaphnia dubia.
Pac, C1, Hereford, R1, Johnson, A1, Carraway, E1, 1 Clemson Institute of Environmental Toxicology (CIET), Clemson, South Carolina, United States
ABSTRACT- Toxic effects are known to result from the exposure of organisms to metals in aquatic environments. It has been well documented that natural organic matter can sequester metals, reducing these toxic exposures. In South Carolina, mercury (Hg) contamination is of great importance, with 37 bodies of water consistently on the fish consumption advisory list from the Department of Health and Environmental Control (DHEC). Although Hg is a metal of concern, the effect of Hg-NOM complexation and its relation to toxicity has not been well researched. This research attempts to address this lack of knowledge by quantifying the amount of mercury which complexes to NOM, while investigating the reduction in bioavailability occurring through this complexation. In this study, we examined the effectiveness of whole water samples from the Ogeechee River as well as samples subjected to NOM size fractionation in reducing Hg toxicity to Ceriodaphnia dubia. The Ogeechee River is a sixth-order black water river in southeast Georgia containing high concentrations of organic matter. This organic matter was initially separated according to pre-determined size fractions and allowed to complex with Hg(II) to examine each individual fraction for its ability to bind Hg. These specific fractions were then used in experiments to assess toxicity. Results of toxicity tests were compared to experimental measurements of Hg binding to Ogeechee River NOM as well as reported literature values of Hg complexation to other types of NOM. Results were interpreted with aqueous speciation models to assess complexation coefficients. Limited independent measurements, including fluorescence quenching, were used to determine both complexed and free Hg concentrations. Preliminary results indicate that individual size fractions can bind varying amounts of metals, thus decreasing bioavailability and, ultimately, reducing toxicity to aquatic organisms.
Key words: mercury, Ceriodaphnia dubia, natural organic matter (NOM), toxicity
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