Influence of Activated Carbon on the Bioaccumulation of Methylmercury from Sediment by the amphipod, Leptocheirus plumulosus.

Abstract

We evaluated the potential for activated carbon (AC) amendments to reduce the bioavailability of methylmercury (MeHg) in field collected sediments. To do so, we adapted a standard 28-day bioaccumulation bioassay with the benthic invertebrate, Leptocheirus plumulosus, to address challenges associated with assessing the dynamic nature of MeHg biogeochemistry and the difficulty of testing a heavily vegetated marsh sediment. After method development, we compared the bioavailability of MeHg in unamended sediment, sediment amended with powdered AC, and sediment amended with the commercial AC product, SediMite. A subsequent study compared the bioavailability of MeHg in unamended sediment, sediment freshly amended with AC, and sediment amended with AC almost two years prior to the start of this study. AC amendments consistently reduced the bioavailability of MeHg to L. plumulosus, as indicated by a 2- to 4-fold decrease in the biota-sediment-accumulation-factor (BSAF), which normalizes tissue concentrations to sediment concentrations. However, AC amendments increased sediment MeHg concentrations in 5 of 7 studies, apparently by altering the balance between MeHg production and degradation. As a result, the net effect of AC amendment on absolute concentrations of MeHg in amphipods was mixed, with moderate reductions at some time points in some experiments but increasing concentrations or no effect in other cases. AC amendments significantly decreased Hg and MeHg in porewater in all cases, however. A literature review of BSAFs for other studies was also conducted. The mechanism by which AC influences the physical and biogeochemical drivers of net methylation and concentrations of MeHg in sediment remain unclear. Any potential use of AC for mercury remediation should undergo site-specific testing before implementation.