Radioisotope techniques in delineation of the environmental behavior of cadmium.

Radioisotope techniques are being developed and utilized at Oak Ridge National Laboratory (ORNL) for evaluating the environmental behavior of toxic elements such as cadmium in aquatic and terrestrial ecosystems. Tracer techniques using 109Cd in microcosm, field plot, and stream systems are providing information on biogeochemical cycling and distribution of cadmium in the environment. Parameters being measured include adsorption capacity for cadmium in mineral soils and sediments; uptake rates of cadmium in various plant species from both soils and nutrient solutions as affected by pH, competing cations, and chemical form of cadmium; and distribution of cadmium in various components of both aquatic and terrestrial ecosystems following application of 109Cd to soil vegetation, or directly to streams. Food chain parameters being estimated with 109Cd include uptake, assimilation, and turnover by both aquatic and terrestrial organisms. Information obtained in these radiotracer studies is providing insight into the behavior of cadmium in aquatic and terrestrial ecosystems, especially transport rates of cadmium and potential biomagnification or dilution in food chains. The factors which influence the incorporation of cadmium into vegetative material as well as those affecting residence time in ecosystems have been identified. Use of 109Cd also has permitted evaluation of a cadmium specific electrode as a tool for rapid assay of free cadmium ions in soil solutions.