This study reports on the development and evaluation of a predictive model for the accumulation of polychlorinated biphenyls (PCBs) in phytoplankton which incorporates the kinetics of the process. The model includes a surface sorption term, uptake and loss rate coefficients, and a biomass dilution term. Laboratory data collected from the accumulation of 40 representative PCB congeners in four representative algal species were used to parameterize the model, and the performance of the model was evaluated on a set of independent laboratory data and a set of field data collected from Green Bay, Lake Michigan. Model predictions were compared to predictions from an equilibrium model. Under low growth conditions, the predictions of the kinetics model and the equilibrium model were similar. However, for data collected during periods of intense growth, equilibrium predictions deviated significantly from the observed values and from the kinetics model predictions by as much as 3 orders of magnitude. Concentrations calculated on a lipid basis by both models significantly underestimated the observed accumulation and questioned the hypothesis that PCBs accumulate in the lipid portion of phytoplankton. However, on a relative basis, the kinetics model reproduced the observed accumulation significantly better than the equilibrium approach.

The objectives of this study were to test the hypothesis that bioaccumulation of hydrophobic organic compounds (HOCs) by phytoplankton is correlated to the compound's octanol/water partition coefficient (Kow) in a predictive relationship in laboratory experiments, and to confirm these findings with field observations. In laboratory experiments we measured the uptake of 40 representative polychlorinated biphenyl (PCB) congeners over time under conditions that inhibited and allowed phytoplankton growth. Results indicated that the bioaccumulation process is consistent with partitioning from water into cell lipids but is slower than previously thought. The uptake of PCBs was slow relative to growth of phytoplankton, preventing the chemical from reaching thermodynamic equilibrium in algal cells under conditions promoting growth (nonwinter). Thus under non‐winter field conditions, many PCB congeners never reach equilibrium concentrations. Food‐chain models that assume equilibrium between HOCs and the primary trophic level could be inaccurate and may need to use a kinetic framework.

This report presents empirical evidence for the use of organic carbon as the sorbing matrix in the kinetic modeling of PCB accumulation in phytoplankton. A kinetic-based model was used to predict congener-specific bioaccumulation factors of PCBs in phytoplankton samples collected from Green Bay, Lake Michigan. These values were compared to the measured bioaccumulation factors, and the sum of the residuals was used to evaluate the model's predictive quality. The sorbing matrix fraction (F M ) that minimized the sum of residuals of the model was then solved by iteration. The appropriateness of using dry weight, organic carbon fraction, or lipid fractions as the sorbing matrix fraction was determined by measuring their correlation to the optimum F M . It was determined that the F M correlated best with the organic carbon fraction, and this correlation appeared to be independent of both the spatial and seasonal differences of the field samples.

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