Biokinetics of selected heavy metals and radionuclides in the common Mediterranean echinoid Paracentrotus lividus: sea water and food exposures

Abstract

Uptake and loss kinetics of Zn, Ag, Cd, '=CS, and 241Am by the echinoid Paracentrotus lividus contaminated through either water or food were determined in controlled laboratory radiotracer experiments using low contaminant concentrations. The echinoid efficiently accumulated most of the elements from water. The only exception was '"CS (concentration factor at steady state = 2.71. With respect to relative metal bioavailability, concentrations in the different body compartments of P lividus were generally ranked in the order: digestive wall > gonads 2 body wall >Aristotle's lantern > coelomlc fluid. However, for2''~rn, body wall uptake was as efficient as that of the digestive wall. The loss kinetics for Zn, Ag, and 1 3 4 ~s were described by a 2-component model whereas loss of Cd and '"'Am was linear during the time course of the experiment. Loss of the different elements was relatively slow, except for 134Cs, whose long-lived loss component was characterized by a biological half-life of 6 d. Loss of the different elements ingested wlth food was described by a single-component model for Cd, '34Cs, and &;'.Am and by a 2-component model for Zn and Ag. Parameters of the kinetics ~n d ~c a t e that all (for Cd, I3Ts, and 'j1.4m) or most (for Zn and Ag) of the ingested amount of element is readily lost from the organism with the faeces. However, estimation of the assimilated fraction of elements ingested by the echlnoids suggests that food could contr~bute significantly to the total body burden of Ag in f? lividus.