Aspects of the aquatic chemistry of cadmium and zinc in a heavy metal contaminated lake

Concentrations of the heavy metals cadmium (Cd) and zinc (Zn) were determined at several sites in Palestine Lake, Indiana, and in the stream (Williamson Ditch) which transports metal-bearing wastes to the lake. Average dissolved Cd and Zn concentrations in the lake were as high as 17.3 μg 1^-1 and 293 μg 1^-1, respectively, while corresponding suspended levels were 30.3 μg Cd 1^-1 and 270 μg Zn 1^-1. Average levels of both Cd and Zn in the dissolved fraction exceeded those in the suspended fraction, except at one site in the lake where suspended Cd was higher. During anaerobic conditions occurring in lake's hypolimnion, a marked decrease in the dissolved fraction and concomitant increase in the suspended fraction of both Cd and Zn were noted. A cadmium-specific ion electrode was used to determine the chemical forms of dissolved Cd present in the lake. Free Cd²⁺ was the dominant form; however, Cd-organic complexes sometimes comprised a significant portion of the total dissolved Cd.