Bioavailability of Inorganic and Methylmercury to a Marine Deposit-Feeding Polychaete

Abstract

We measured the assimilation efficiencies (AEs) from various types of sediments and the uptake rate constants from the dissolved phase of inorganic mercury (Hg(II)) and methylmercury (CH3Hg(II)) in the marine deposit-feeding polychaete Nereis succinea. AEs of Hg(II) ranged between 7 and 30% and were unaffected by sediment composition, whereas AEs of CH3Hg(II) ranged between 43 and 83% and were strongly affected by sediment composition. Sediment grain size had no apparent effect on Hg(II) and CH3Hg(II) assimilation. AEs for Hg(II) associated with anoxic sediment were slightly lower than with oxic sediment, whereas CH3Hg(II) displayed comparable AEs for both oxic and anoxic sediment. Dissolved uptake rate constants of CH3Hg(II) were 2.2 times those of Hg(II). A bioenergetic-based kinetic model was used to separate the pathways (solute vs sediment) and sources [Hg(II) vs CH3Hg(II)] of Hg accumulation in N. succinea. The model predicted that, under conditions typical of coastal sediment environments, CH3Hg(II) accumulation contributes about 5−17% of total Hg accumulation in polychaetes. Most of the Hg(II) (>70%) accumulation is predicted to derive from sediment ingestion, whereas for CH3Hg(II) the relative importance of dissolved vs sediment ingestion depends greatly on its partition coefficient for sediments. Uptake from the dissolved phase and sediment ingestion can be equally important for CH3Hg(II) accumulation in N. succinea.