Cadmium in freshwaters: concentrations and chemistry

SUMMARY. 1. Concentrations of cadmium are reported for twenty largely unpolluted freshwaters in north-western England. They range from 15 to 117 ng l⁻¹ total Cd in the rivers and streams and from 18to51 ng l⁻¹ in the lakes, lying on the low side of values reported in the literature. The care required to obtain reliable data is stressed.
2. A comparison is made between the fraction of Cd found to be particulate (>0.2 μm) and that which is calculated to be adsorbed on particulate matter. This provides further insight into the speciation of Cd, as well as a test of the application of a simple adsorption model to the prediction of the observed speciation.
3.The adsorption model is found to be a poor predictor of the measured fraction of particulate Cd. Possible reasons for this are explored and the potentially important role of slow desorption kinetics is emphasized.