Use of 99m Tc as tracer in surface waters pollution studies; in situ and Laboratory studies on sorption of pertechnetate

The sorption of 99m TcO4 from polluted waters to the organic-rich sediments was measured in laboratory and field conditions. Batch laboratory tests to study the influence of the Tc concentration, the system redox potential (Eh) and the liquid to solid ratio (V/m) were performed. While in aerated water no Tc sorption was observed, in heavily loaded waters under inert gas atmosphere, slight sorption was detected, indicating that TcO(OH)2 is the stable specie under strongly anaerobic conditions. The reduction rate shows no dependence on Tc-concentration in the range from 5 X 10 16 M to 5 X 10 9 M, but some influence of the V/m ratio can be observed. The results from laboratory experiments were confirmed in a field double tracing experiment, performed at two locations of the Almendares river basin. 99m TcO4 and Rhodamine WT-20% were injected simultaneously and the RTD-curves registered downstream. The recovery calculations and the shapes of the curves in each measuring site showed no retardation or sink of technetium. The results is consistent with the laboratory behavior previously observed and supports the hypothesis that Tc sorption is mainly a function of the redox potential of the system. The suitability of 99m TcO4 as tracer for short-term hydrological studies in polluted streams is concluded