BIOKINETICS OF SELECTED HEAVY-METALS AND RADIONUCLIDES IN 2 MARINE MACROPHYTES - THE SEAGRASS POSIDONIA-OCEANICA AND THE ALGA CAULERPA-TAXIFOLIA

Uptake and loss kinetics of Zn, Ag, Cd, Cs-134, and Am-241 by shoots o f the seagrass Posidonia oceanica and fronds of the green alga Caulerp a taxifolia were determined in controlled laboratory radiotracer exper iments using low contaminant concentrations. The two species accumulat ed most of the elements efficiently. The only exceptions were Cs-134 i n both P. oceanica and C. taxifolia and Cd in C. taxifolia (concentrat ion factors less than or equal to 6.4). Steady state in uptake was rea ched in C. taxifolia for each element except Ag. In P. oceanica, stead y state was noted for the uptake of Ag and Cs-134 whereas Zn, Cd, and Am-241 were linearly accumulated during the course of the experiment ( 15 d). With respect to relative metal bioavailability, the different c ompartments of P. oceanica shoots were generally ranked in the order: leaf epiphytes > adult leaves = intermediate leaves > leaf sheaths. Th e long-lived component of the loss kinetics for each element in P. oce anica was characterized by a relatively short biological half-life (T- b1/2 less than or equal to 28 d). However, observations for the indivi dual compartments indicated that adult leaves had a high retention cap acity for Ag and Cs-134, With virtually 100% retained after 21 d in un contaminated sea water. In C. taxifolia, the long-lived component of t he loss kinetics for each element was characterized by a T-b1/2 value that was not significantly different from infinity, an observation whi ch suggests that a substantial fraction of the metal or radio-nuclide incorporated during a contamination event would be irreversibly bound by this algal species. Copyright (C) 1996 Elsevier Science Ltd.