BIOAVAILABILITY OF CR(III) AND CR(VI) TO MARINE MUSSELS FROM SOLUTE AND PARTICULATE PATHWAYS

Mussels have been extensively used as biological monitors of coastal c ontamination. This study measured the assimilation efficiencies (AEs) of Cr(III) and Cr(VI) in the mussel Mytilus edulis from ingested food, uptake from the dissolved phase, and the physiological efflux rates f ollowing uptake. A bioenergetic-based kinetic model was then employed to determine the relative contributions of different Cr species and th eir accumulation pathways to the overall concentration of Cr in mussel s. The concentration factors of Cr(III) in four diverse marine phytopl ankters ranged between 10(4) and 10(5), whereas for Cr(VI) they were 2 to 5 x 10(2). Rapid reduction of Cr(VI) to Cr(III) was observed in co astal sediments. AEs of Cr(III) in mussels from ingested sediments wer e consistently <1%, whereas the AEs of Cr(VI) from ingested phytoplank ton were 1-10%. The uptake rate of Cr(VI) from the dissolved phase was 3 times higher than Cr(III). The efflux rate constant was 0.011 d(-1) for mussels following 7 d dissolved uptake of Cr(VI) and 0.010 d(-1) following 8 d ingestion of Cr(III)-labeled diatoms. The model predicte d concentrations of Cr in mussels in South San Francisco Bay that are directly comparable to measured Cr concentrations. The model predicts that 13-38% of Cr in mussels is from dissolved Cr(VI), whereas the rem aining Cr is from ingested Cr(III); dissolved Cr(III) and ingested Cr( VI) contribute little to Cr accumulation in mussels. The AE of Cr and its concentration in seston critically influence Cr concentrations in mussels.