BIOKINETICS OF SELECTED HEAVY-METALS AND RADIONUCLIDES IN THE COMMON MEDITERRANEAN ECHINOID PARACENTROTUS-LIVIDUS - SEA-WATER AND FOOD EXPOSURES

Uptake and loss kinetics of Zn, Ag, Cd, Cs-134, and Am-241 by the echi noid Paracentrotus lividus contaminated through either water or food w ere determined in controlled laboratory radiotracer experiments using low contaminant concentrations. The echinoid efficiently accumulated m ost of the elements from water. The only exception was Cs-134 (concent ration factor al steady state = 2.7). With respect to relative metal b ioavailability, concentrations in the different body compartments of P . lividus were generally ranked in the order: digestive wall > gonads greater than or equal to body wall > Aristotle's lantern > coelomic fl uid. However, for Am-241, body wall uptake was as efficient as that of the digestive wall. The loss kinetics for Zn, Ag, and Cs-134 were des cribed by a 2-component model whereas loss of Cd and Am-241 was linear during the time course of the experiment. Loss of the different eleme nts was relatively slow, except for Cs-134, whose long-lived loss comp onent was characterized by a biological half-life of 6 d. Loss of the different elements ingested with food was described by a single-compon ent model for Cd, Cs-134, and Am-241 and by a 2-component model for Zn and Ag. Parameters of the kinetics indicate that all (for Cd, Cs-134, and Am-241) or most (for Zn and Ag) of the ingested amount of element is readily lost from the organism with the faeces. However, estimatio n of the assimilated fraction of elements ingested by the echinoids su ggests that food could contribute significantly to the total body burd en of Ag in P. lividus.