Bioavailability of dissolved and sediment-bound metals to a marine deposit-feeding polychaete

Assimilation efficiencies (AEs) of trace elements (Ag, Cd, Co, Se and Zn) in a marine deposit-feeding polychaete, Nereis succinea, from ingested sediments were measured using a pulse-chase radiotracer feeding technique. Radiolabeled sediments were encapsulated and fed to the worms for 1 h, after which the worms were allowed to depurate their ingested materials for 3 d. The ranges of AEs were 12 to 36 % for Ag, 5 to 44 % for Cd, 35 to 96 % for Co, 29 to 60% for Se and 21 to 59 % for Zn. Trace metal assimilation was little affected by sediment source and sediment grain size. Metals (Ag, Cd, Co and Zn) associated with anoxic sediments were assimilated with a significantly lower efficiency than metals from oxic sediments. The AE of Cd decreased with the duration of sediment radiolabeling; AEs of Ag, Co, Se and Zn were weakly affected by sediment aging. Metal uptake in worms from the dissolved phase was proportional to metal concentration in the dissolved phase, although there was some evidence of Cd and Zn regulation in response to an increase in ambient concentrations. Uptake rate constants were highest for Ag, followed by Zn > Co > Cd > Se. By incorporating metal influx from both the dissolved and particulate (sediment) phases, a bioenergetic-based kinetic model indicates that most (> 98 %) of the Cd, Co, Se and Zn in polychaetes arises from sediment ingestion due to the high ingestion rates of these animals and the low uptake rate of metals from the dissolved phase (porewater or overlying water). For Ag, approximately 5 to 35 % is due to uptake from the dissolved phase. Our study suggests that the establishment of sediment quality criteria must consider sediment as a potentially important source for metal uptake in benthic invertebrates.