Intestinal solubilization of particle-associated organic and inorganic mercury as a measure of bioavailability to benthic invertebrates

The bioavailability of particle-associated inorganic mercury (Hg-I) and mon omethylmercury (MMHg) was evaluated in vitro using digestive fluid of the d eposit feeding lugworm, Arenicola marina. Digestive fluid, removed from the midgut of the polychaete, was incubated with contaminated sediment, and th e proportion of Hg-I or MMHg solubilized by the digestive fluid was determi ned. Digestive fluid was found to be a more effective solvent than seawater in solubilizing particle-associated Hg-I and MMHg. A greater percentage of MMHg than Hg-I was solubilized from most sediments, suggesting that sedime nt-associated MMHg is generally more readily available from sediment for bi ological uptake. The proportion of MMHg released from the sediment was inve rsely correlated with sediment organic matter content, decreasing exponenti ally with increasing organic matter content of the sediment. The results fo r Hg-I were equivocal. MMHg bioaccumulation factors (BAFs) from previous st udies showed a similar trend with organic content of sediment, suggesting t hat solubilization may be the process limiting the bioaccumulation of parti cle-bound MMHg. It is concluded that in vitro extraction with a deposit fee der's digestive fluid provides a potential tool to study the process of Hg bioaccumulation via ingestion routes, although its application to various s ediments and organisms needs further investigation.