A KINETICS MODEL FOR PREDICTING THE ACCUMULATION OF PCBS IN PHYTOPLANKTON

This study reports on the development and evaluation of a predictive m odel for the accumulation of polychlorinated biphenyls (PCBs) in phyto plankton which incorporates the kinetics of the process. The model inc ludes a surface sorption term, uptake and loss rate coefficients, and a biomass dilution term. Laboratory data collected from the accumulati on of 40 representative PCB congeners in four representative algal spe cies were used to parameterize the model, and the performance of the m odel was evaluated on a set of independent laboratory data and a set o f field data collected from Green Bay, Lake Michigan. Model prediction s were compared to predictions from an equilibrium model. Under low gr owth conditions, the predictions of the kinetics model and the equilib rium model were similar. However, for data collected during periods of intense growth, equilibrium predictions deviated significantly from t he observed values and from the kinetics model predictions by as much as 3 orders of magnitude. Concentrations calculated on a lipid basis b y both models significantly underestimated the observed accumulation a nd questioned the hypothesis that PCBs accumulate in the lipid portion of phytoplankton. However, on a relative basis, the kinetics model re produced the observed accumulation significantly better than the equil ibrium approach.