Bioaccumulation kinetics and internal distribution of the fission products radiocaesium and radiostrontium in an estuarine crab

Crab has been designated by the ICRP as one of twelve reference/model organisms for understanding the impacts of radionuclide releases on the biosphere. However, radionuclide-crab interaction data are sparse compared with other reference organisms (e.g. deer, earthworm). This study used an estuarine crab (Paragrapsus laevis) to investigate the contribution of water, diet and sediment sources to radionuclide (Cs-134 and Sr-85) bioaccumulation kinetics using live-animal radiotracing. The distribution of each radionuclide within the crab tissues was determined using dissection, whole-body autoradiography and synchrotron X-ray Fluorescence Microscopy (XFM). When moulting occurred during exposure, it caused significant increases in Sr-85 bioaccumulation and efflux of Cs-134 under constant aqueous exposure. Dietary assimilation efficiencies were determined as 55 +/- 1% for Cs-134 and 49 +/- 3% for Sr-85. Sr-85 concentrated in gonads more than other organs, resulting in proportionally greater radiation dose to the reproductive organs and requires further investigation. Cs-134 was found in most soft tissues and was closely associated with S and K. Biodynamic modelling suggested that diet accounted for 90-97% of whole-body Cs-137, while water accounted for 59-81% of Sr-90. Our new data on crab, as a representative invertebrate, improves understanding of the impacts of planned or accidental releases of fission radionuclides on marine ecology.