Diffusive Gradients in Thin-Films as a Predictor for Mercury Bioaccumulation in Lumbriculus variegatus

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2017-11-16

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Abstract

Freely available inorganic mercury can be predicted by using Diffusive Gradients in Thin-Film (DGTs) devices, which reject Hg associated with particles greater than a few tens of microns. Recent work is suggesting that this freely available inorganic mercury is a better indicator of availability for methylation than bulk solids or other conventional mercury measures. In this research, the ability of DGTs to predict uptake to benthic organisms is assessed by evaluating bioaccumulation of mercury by deposit feeding Lumibriculus variegatus compared to other bulk solid and DGT measures of inorganic mercury. L. variegatus were exposed to different mercury contaminated freshwater sediment matrices from the South River, VA.
L. variegatus were exposed in small microcosms (4 cm deep) with aerated overlying water for 28 days. The microcosms consisted of five different sediment matrices as well as different bulk mercury concentrations. Ion specific electrodes were used to measure changes in dissolved oxygen, sulfides and bulk redox conditions. DGTs were routinely deployed for 4 days prior to the start of the bioaccumulation test period and 4 days before the final day of testing. Bioaccumulation in the L. variegatus was measured by sacrificing the microcosms and measuring body burdens of mercury and methyl mercury as a function of time of exposure. Bioaccumulation of total mercury and methylmercury in L. variegatus demonstrated that the bulk of mercury in the organism is inorganic mercury. Total mercury measured by DGTs, methylmercury in bulk solids, AVS, total organic carbon (TOC), and other parameters were used to characterize the different sediment matrices as potential influences on bioaccumulation in benthic organisms. Correlations of inorganic mercury in L. variegatus vs total mercury in DGT measured porewater yielded a coefficient of determination (R2) of 0.97968294, whereas when the organism bioaccumulation is correlated to inorganic mercury in the bulk solids yielded a R2 of 0.97773217.

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Keywords

DGTs, Lumbriculus, Variegatus, Mercury

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