MECHANISM FOR ENHANCED UPTAKE OF RADIONUCLIDES BY ZOOPLANKTON IN FRENCH-POLYNESIAN OLIGOTROPHIC WATERS

A study of natural radionuclides in zooplankton collected during 1990- 1992 from the low productivity waters of French Polynesia has demonstr ated the presence of enhanced uptake of Po-210 by zooplankton when zoo plankton biomass is low. Po-210 in zooplankton increases exponentially to previously unreported levels up to 3200 Bq/kg dry weight, as their biomasses decline to levels as low as 0.14 mg dry weight/cubic meter. A validated mathematical model, incorporating the established role of zooplankton in the removal of Po-210 from the water column, captures the shape of this empirical relationship and also explains this biomas s-related mechanism that increases Po-210 concentrations in zooplankto n. Our results and analysis point to the enhanced vulnerability of suc h low productivity marine systems to environmental contamination follo wing potential leakage of radionuclides from former weapons test sites and radioactive waste repositories that have been recently proposed f or the Pacific.