KINETIC DETERMINATIONS OF TRACE-ELEMENT BIOACCUMULATION IN THE MUSSELMYTILUS-EDULIS

Laboratory experiments employing radiotracer methodology were conducte d to determine the assimilation efficiencies from ingested natural ses ton, the influx rates from the dissolved phase and the efflux rates of 6 trace elements (Ag, Am, Cd, Co, Se and Zn) in the mussel Mytilus ed ulis. A kinetic model was then employed to predict trace element conce ntration in mussel tissues in 2 locations for which mussel and environ mental data are well described: South San Francisco Bay (California, U SA) and Long Island Sound (New York, USA). Assimilation efficiencies f rom natural seston ranged from 5 to 18% for Ag, 0.6 to 1% for Am, 8 to 20% for Cd, 12 to 16% for Co, 28 to 34% for Se, and 32 to 41% for Zn. Differences in chlorophyll a concentration in ingested natural seston did not have significant impact on the assimilation of Am, Co, Se and Zn. The influx rate of elements from the dissolved phase increased wi th the dissolved concentration, conforming to Freundlich adsorption is otherms. The calculated dissolved uptake rate constant was greatest fo r Ag, followed by Zn > Am approximate to Cd > Co > Se. The estimated a bsorption efficiency from the dissolved phase was 1.53% for Ag, 0.34% for Am, 0.31% for Cd, 0.11% for Co, 0.03% for Se and 0.89% for Zn. Sal inity had an inverse effect on the influx rate from the dissolved phas e and dissolved organic carbon concentration had no significant effect on trace element uptake. The calculated efflux rate constants for all elements ranged from 1.0 to 3.0% d(-1). The route of trace element up take (food vs dissolved) and the duration of exposure to dissolved tra ce elements (12 h vs 6 d) did not significantly influence trace elemen t efflux rates. A model which used the experimentally determined influ x and efflux rates for each of the trace elements, following exposure from ingested food and from water, predicted concentrations of Ag, Cd, Se and Zn in mussels that were directly comparable to actual tissue c oncentrations independently measured in the 2 reference sites in natio nal monitoring programs. Sensitivity analysis indicated that the total suspended solids load, which can affect mussel feeding activity, assi milation, and trace element concentration in the dissolved and particu late phases, can significantly influence metal bioaccumulation for par ticle-reactive elements such as Ag and Am. For all metals, concentrati ons in mussels are proportionately related to total metal load in the water column and their assimilation efficiency from ingested particles . Further, the model predicted that over 96% of Se in mussels is obtai ned from ingested food, under conditions typical of coastal waters. Fo r Ag, Am, Cd, Co and Zn, the relative contribution from the dissolved phase decreases significantly with increasing trace element partition coefficients for suspended particles and the assimilation efficiency i n mussels of ingested trace elements; values range between 33 and 67% for Ag, 5 and 17% for Am, 47 and 82% for Cd, 4 and 30% for Co, and 17 and 51% for Zn.