SREL Reprint #3498

Mercury speciation, bioavailability, and biomagnification in contaminated streams on the Savannah River Site (SC, USA)

Xiaoyu Xu, Albert L. Bryan, Gary L. Mills, and Alexis M. Korotasz

Savannah River Ecology Laboratory, University of Georgia, PO Drawer E, Aiken, SC 29802, USA

Abstract: Water, sediment, and biota from two streams on the Savannah River Site were sampled to study mercury (Hg) biogeochemistry. Total and methyl- Hg (MHg) concentrations were measured for all samples, speciation models were used to explore Hg speciation in the water, and Diffusive gradients in thin films (DGT) were applied to indicate the vertical profiles of labile Hg (DGT-Hg). Trophic position (δ15N) was estimated for biota and used to establish MHg biomagnification model. The speciation model indicated Hg methylation in the water occurred on settling particles and the most bioavailable Hg species to bacteria were complexes of inorganic Hg and labile organic ligands. Correspondingly, dissolved organic carbon concentrations were positively related to MHg concentrations in the water. In the sediment, the sharp increase of DGT-Hg around the sediment water interface underscores the importance of this interface, which determines the differences in the accumulation and generation of labile Hg among different waterbodies. The positive correlation between sediment MHg and sulfate concentrations suggested possible methylation reaction by dissimilatory sulfate reducing bacteria in the sediment. The food web magnification factors of MHg were 9.6 (95% CI: 4.0–23.4) and 4.4 (95% CI: 2.5–7.7) for the two streams established with trophic data of biofilm, invertebrates, and fish. Meanwhile, DGT-Hg concentrations in the water were positively correlated to biofilm Hg concentrations, which can be combined with the MHg biomagnification model to generate a modified biomagnification model that estimate MHg bioaccumulation with only labile Hg concentrations in the water. With this approach, Hg accumulation in abiotic and biotic environmental compartments was connected and the different bioaccumulation patterns of Hg in different waterbodies were explained with both geochemical and biological factors.

Keywords: Mercury; Speciation; Methylation; Bioavailability; Biomagnification; Diffusive gradients in thin films

SREL Reprint #3498

Xu, X., A. L. Bryan Jr., G. L. Mills, and A. M. Korotasz. 2019. Mercury speciation, bioavailability, and biomagnification in contaminated streams on the Savannah River Site (SC, USA). Science of the Total Environment 668(2019): 261-270.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).