284 - Mercury Bioavailability in Contaminated Freshwater Sediment Amended with Carbon-based Sorbents

Mercury (Hg) remediation in contaminated aquatic environments is challenging due to the coupled complexity of Hg biogeochemical transformations in water environments. This study assessed the effects of three carbon-based sorbents and aging time on Hg and methylmercury (MeHg) bioaccumulation in benthic invertebrates. We conducted mesocosms tests in which contaminated creek sediments were amended with either biochar (BC), activated carbon (AC), or SediMiteTM (SM), and covered with surface water. After short-aging (7 days) and long-aging (90 days), deposit-feeders, California blackworm (Lumbriculus variegatus), were added to mesocosms. After 14 days, we quantified Hg levels and speciation in water, sediment, and blackworms. In short-aging mesocosms, MeHg burden in worms was reduced 75% in AC and 82% in SM amendments, respectively, but there was no significant reduction in BC amendments (p>0.05) compared to the unamended control. The MeHg levels in worms were positively correlated with MeHg in sediment (R = 0.84, p<0.001) and dissolved MeHg in surface water (R = 0.75, p<0.001) and porewater (R = 0.51, p=0.017). In long-aging mesocosms, MeHg in worms was reduced in all amendments by 35% (BC), 40% (AC), and 65% (SM) compared to control (p<0.05). Sorbent-aging generally lowered MeHg in surface water and porewater but elevated MeHg in sediment. Porewater and sediment chemical analyses reflected anaerobic microbial metabolism (e.g., low sulfate, high Fe2+ and S2-). The biota-sediment accumulation factors (BSAF) for MeHg were negatively associated with sediment: porewater partitioning for MeHg (Ksw, MeHg) (p<0.001) across both aging times. Nevertheless, despite different inorganic Hg partitioning (Ksw, inorganic Hg) behaviors between amendments, lower Hg in worms in amendments suggested additional mechanisms besides sorption were controlling biotic uptake in these experimental mesocosms. These results will be coupled with microbial community characterization (16s rRNA and hgcA sequencing) for a more complete assessment of the effects of sorbent amendments on sediment biogeochemistry.

Authors: Peijia Ku, Spencer Washburn, Alyssa Carrell, Omy Ogbughalu, Melissa Cregger, Simon Pouil, Teresa Mathews, Scott Brooks