Effect of bioirrigation on sediment-water exchange of methylmercury in Boston Harbor, Massachusetts.

Coastal marine sediments are important sites of methylmercury (MMHg) production, and dissolved efflux provides an important source of MMHg to near-shore, and possibly offshore, water columns and food webs. We measured the flux of MMHg across the sediment-water interface at four stations in Boston Harbor that span a range of infaunal population densities and bioirrigation intensities. At each station we carried out total MMHg flux measurements using core incubations and collected near-surface pore waters to establish MMHg gradients for diffusive flux calculations.

Mercury methylation independent of the acetyl-coenzyme A pathway in sulfate-reducing bacteria.

Sulfate-reducing bacteria (SRB) in anoxic waters and sediments are the major producers of methylmercury in aquatic systems. Although a considerable amount of work has addressed the environmental factors that control methylmercury formation and the conditions that control bioavailability of inorganic mercury to SRB, little work has been undertaken analyzing the biochemical mechanism of methylmercury production. The acetyl-coenzyme A (CoA) pathway has been implicated as being key to mercury methylation in one SRB strain, Desulfovibrio desulfuricans LS, but this result has not been extended to other SRB species.

Estimation of mercury-sulfide speciation in sediment pore waters using octanol-water partitioning and implications for availability to methylating bacteria.

The octanol-water partioning of inorganic mercury decreased with increasing sulfide, supporting a model that predicts decreased fractions of neutral Hg-S species with increasing sulfide. These results help explain the decreased availability of Hg to methylating bacteria under sulfidic conditions, and the inverse relationship between sulfide and methylmercury observed in sediments.