USE OF RADIOTRACERS FOR STUDIES OF METAL SORPTION BEHAVIOR

Radiotracers provide a convenient tool to study the behaviour of metal ions and other contaminants in natural waters. Furthermore, the use o f radiotracers in controlled laboratory experiments provides an ideal approach for investigating, in a systematic manner, the role of indivi dual parameters on processes, at mass concentrations found in the envi ronment. A simplistic procedure has been developed to produce a thoriu m radiotracer (Th-234), in a similar chemical form (non-acidic) to tha t of the aquatic medium under investigation, to determine the kinetics of sorption to marine particulate material. The benefit of this proce dure is that the system is likely to be perturbed to a lesser extent b y changes in pH and dissolved Th species following tracer addition. Re sults from filtering different tracer batches through membranes, to de termine the sorption characteristics prior to use, indicate that the p hysico-chemical behaviour of individual batches was extremely variable . Not surprisingly, the amount of uptake immediately following tracer additions to solutions containing marine particulate material was also variable. It is suggested that the role of tracer may be underestimat ed if added in acid form. Nevertheless, having accounted for the initi al sorption, the subsequent uptake between different batches was reaso nably reproducible. The usefulness of radiotracers is discussed in the context of these observations.