Two-Compartment Kinetic Modeling of Radiocesium Accumulation in Marine Bivalves under Hypothetical Exposure Regimes

Interpreting the variable concentrations of ¹³⁷Cs in the field biological samples requires mechanistic understanding of both environmental and biological behavior of ¹³⁷Cs. In this study, we used a two-compartment model to estimate and compare the ¹³⁷Cs biokinetics in three species of subtropical marine bivalves. Significant interspecific difference of ¹³⁷Cs biokinetics was observed among oysters, mussels, and scallops. There was considerable ¹³⁷Cs assimilation from phytoplankton in the bivalves, but the calculated trophic transfer factors were generally between 0.04 and 0.4. We demonstrated a major efflux of radiocesium in the scallops (with a rate constant of 0.207 d^-1), whereas the efflux was comparable between oysters and mussels (0.035-0.038 d^-1). A two-compartment kinetic model was developed to simulate the ¹³⁷Cs accumulation in the three bivalves under four hypothetical exposure regimes. We showed that the bivalves respond differently to the exposure regimes in terms of time to reach equilibrium, equilibrium concentration, and maximum concentration. Bivalves suffering more frequent intermittent exposure may have higher maximum concentrations than those receiving less frequent exposure. The interspecific difference of ¹³⁷Cs accumulation in bivalves has important implications for biomonitoring and implementing management techniques. This study represents one of the first attempts to combine both dissolved and dietary pathways to give a realistic simulation of ¹³⁷Cs accumulation in marine bivalves under dynamic exposure regimes.