Experimental Kinetic Rates of Food-Chain and Waterborne Radionuclide Transfer to Freshwater Fish: A Basis for the Construction of Fish Contamination Charts
J. Garnier-Laplace, C. Adam, J. P. Baudin
Arch. Environ. Contam. Toxicol. (2000), 39, 133-144
A standardized procedure is proposed to obtain from laboratory experiments the kinetic accumulation and release rates necessary to calibrate dynamic models to quantify radionuclide direct and trophic transfer in fish. ne model takes into account the food-chain effect, the feeding rate, and the growth of organisms. It takes as examples 54Mn, 6OCo, and 137Cs transfer dynamics through a simple pelagic food-chain (phytoplankton, zooplankton, prey fish, and predator fish). The estimated kinetic rates used in quantifying all the transfers of the three radioactive pollutants through the pelagic food chain are compared from the radioecological point of view. For fish, comparison was based on the calculation of concentration factors referring to direct transfer from water and trophic transfer factors. For the prey fish and the predator fish, direct transfer gave the following order for accumulation 54Mn, 6OCo, and 137Cs. Values reached at equilibrium in L/kg WW were respectively for the prey fish and the predator fish: 8.7 < 27.4 < 107 and 4.14 < 6.59 < 13.4. For the trophic route, 137Cs is the most accumulated (TTFeq = 0.485 in 291 days for the prey fish and TTFeq = 1.45 in 17 years for the predator fish). A sensitivity analysis adapted to the case of a chronic contamination scenario of a watercourse was run. It showed that the phytoplankton biomass, the contact time of these drifting particles from a release point to the station where they are ingested and the feeding rates of the fish are the most influential parameter with regard to the concentration in fish, whatever the trophic level. Contamination charts are constructed for the predator fish to illustrate the relationship between the most influential ecological parameters and the radionuclide concentration in fish for simple contamination scenarios. They are shown to be effective tools for helping in the choice of the most relevant value of aggregated concentration factors (ACFs: radionuclide concentration ratio between the organism and the water, referred to steady-state and to all possible transfer pathways) for a given key ecological situation in a given ecosystem. An example is given of a simple chronic release scenario of I BqfL and a phyEoplanktonic bloom period. For 137Cs, the ACF increases with increasing contact time and increasing feeding rate, to nearly 550 l/kg WW at equilibrium. For 54Mn, ACF reaches 65 L/kg WW. For 6OCo, the general pattern of the relationship is due to the rapid kinetic rates governing the distribution of the radionuclide between dissolved and solid (phytoplankton) phases with a maximum value for ACF of 7.2 L/kg WW for the case study. Analysis of these charts provides a basis for overall guidelines for chronic releases in a given watercourse.