Although cadmium concentrations of unpolluted sea water are low, ranging from 0.01 to 0.41 µg/1 (Goldberg, 1965; Preston, 1973; Chester & Stoner, 1974; Kremling & Petersen, 1977) concentrations in estuaries are from 10 to 100 times higher, as reported by Butterworth, Lester & Nickless (1972) for the Severn and Eustace (1974) for the Derwent estuaries. Unusually high cadmium concentrations of 50 µg/1 have been found by Chan, Cheung & Li (1974) in Hong Kong harbour water. The cadmium in the drinking water (225 µ/l) and the food (rice) of Japanese farmers is believed to have caused the ‘itai-itai’ disease (Kobayashi, 1971), a pathological syndrome characterized by kidney damage with bone disease.