Biodynamic modelling and the prediction of Ag, Cd and Zn accumulation from solution and sediment by the polychaete Nereis diversicolor

Biodynamic modelling has been used to predict bioaccumulated concentrations of Ag, Cd and Zn in the deposit-feeding polychaete Nereis diversicolor from 5 metal-contaminated estuaries in SW England and a relatively non-contaminated estuary in SE England. The modelling employed previously measured physiological parameters of bioaccumulation - uptake rate constant, assimilation efficiency (AE) and efflux rate constants after uptake from water and sediment ingestion - and measured sediment metal concentrations specific for each population. AEs were considered to relate to metals in the organic component of the ingested sediment and ingestion rates were therefore expressed in these terms, with the further assumption that the total sediment metal concentration is a proxy for the metal concentration in the sediment organic component. A range of growth rate constants was extracted from the literature, as were concentration ranges of dissolved Ag, Cd and Zn in contaminated coastal waters. The model showed that >99 % Cd and >98 % Zn accumulated by N. diversicolor is derived from sediment ingestion; more bioaccumulated Ag is derived from solution, the percentage contribution of the dissolved source increasing from 46 to 80 % with an increase in Ag dissolved concentration from low to high values for coastal waters. Bioaccumulated metal concentrations predicted from the model generally showed excellent agreement with independently measured concentrations in field-collected worms, supporting the assumptions made in the model.