BIOAVAILABILITY OF INORGANIC AND METHYLMERCURY TO A MARINE DEPOSIT-FEEDING POLYCHAETE

We measured the assimilation efficiencies (AEs) from various types of sediments and the uptake rate constants from the dissolved phase of in organic mercury (Hg(ll)) and methylmercury (CH3Hg(II)) in the marine d eposit-feeding polychaete Nereis succinea. AEs of Hg(li) ranged betwee n 7 and 30% and were unaffected by sediment composition, whereas AEs o f CH3Hg(II) ranged between 43 and 83% and were strongly affected by se diment composition. Sediment grain size had no apparent effect on Hg(i l) and CH3Hg(II) assimilation. AEs for Hg(ll) associated with anoxic s ediment 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(ll). A b ioenergetic-based kinetic model was used to separate the pathways (sol ute vs sediment) and sources [Hg(ll) vs CH3Hg(II)I of Hg accumulation in N. succinea. The model predicted that, under conditions typical of coastal sediment environments, CH3Hg(II) accumulation contributes abou t 5-17% of total Hg accumulation in polychaetes. Most of the Hg(ll) (> 70%) accumulation is predicted to derive from sediment ingestion, wher eas for CH3Hg(ll) the relative importance of dissolved vs sediment ing estion depends greatly on its partition coefficient for sediments. Upt ake from the dissolved phase and sediment ingestion can be equally imp ortant for CH3Hg(II) accumulation in N. succinea.