Bioaccumulation and retention kinetics of cadmium in the freshwater decapod Macrobrachium australiense

The potential sources and mechanisms of cadmium bioaccumulation by the native freshwater decapods Macrobrachium species in the waters of the highly turbid Strickland River in Papua New Guinea were examined using ¹⁰⁹Cd-labelled water and food sources and the Australian species Macrobrachium australiense as a surrogate. Synthetic river water was spiked with environmentally relevant concentrations of cadmium and animals were exposed for 7 days with daily renewal of test solutions. Dietary assimilation of cadmium was assessed through pulse-chase experiments where prawns were fed separately ¹⁰⁹Cd-labelled fine sediment, filamentous algae and carrion (represented by cephalothorax tissue of water-exposed prawns).M. australiense readily accumulated cadmium from the dissolved phase and the uptake rate increased linearly with increasing exposure concentration. A cadmium uptake rate constant of 0.10. ±. 0.05. L/g/d was determined in synthetic river water. During depuration following exposure to dissolved cadmium, efflux rates were low (0.9. ±. 5%/d) and were not dependent on exposure concentration. Assimilation efficiencies of dietary sources were comparable for sediment and algae (48-51%), but lower for carrion (28. ±. 5%) and efflux rates were low (0.2-2.6%/d) demonstrating that cadmium was well retained by M. australiense. A biokinetic model of cadmium accumulation by M. australiense predicted that for exposures to environmentally relevant cadmium concentrations in the Strickland River, uptake from ingestion of fine sediment and carrion would be the predominant sources of cadmium to the organism. The model predicted the total dietary route would represent 70-80% of bioaccumulated cadmium.