Factors controlling the bioaccumulation of mercury and methylmercury by the estuarine amphipod Leptocheirus plumulosus

The bioaccumulation of inorganic mercury (Hg-I) and monomethylmercury (MMHg ) by benthic organisms and subsequent trophic transfer couples the benthic and pelagic realms of aquatic systems and provides a mechanism for transfer of sedimentary contaminants to aquatic food chains. Experiments were perfo rmed to investigate the bioavailability and bioaccumulation of particle-ass ociated Hg-I and MMHg by the estuarine amphipod Leptocheirus plumulosus to further understand the controls on bioaccumulation by benthic organisms. Hg -I and MMHg are particle reactive and have a strong affinity for organic ma tter, a potential food source for amphipods. Microcosm laboratory experimen ts were performed to determine the effects of organic matter on Hg bioaccum ulation and to determine the major route of Hg uptake (i.e. sediment ingest ion, uptake from water/porewater, or uptake from 'food'). Amphipods living in organic-rich sediment spiked with Hg accumulated less Hg than those livi ng in sediments with a lower organic matter content. Feeding had a signific ant impact on the amount of Hg and MMHg accumulated. Similarly, amphipods l iving in water with little organic matter accumulated more Hg than those li ving in water with a greater percentage of organic matter. MMHg was more re adily available for uptake than Hg-I. Experimental results, coupled with re sults from a bioaccumulation model, suggest that accumulation of Hg-I and M MHg from sediment cannot be accurately predicted based solely on the total Hg, or even the MMHg, concentration of the sediment, and sediment-based bio accumulation factors. All routes of exposure need to be considered in deter mining the accumulation of Hg-I and MMHg from sediment to benthic invertebr ates. (C) 2000 Elsevier Science Ltd. All rights reserved.