Dynamics of Selenium in Mercury-Contaminated Experimental Freshwater Ecosystems

The simultaneous movement of radiolabeled selenium and mercury was followed in experimental aquatic ecosystems ([Formula: see text] tube enclosures) set into a mercury-contaminated lake. The experimental treatments consisted of increasing stable selenium or sulfate water concentrations, addition of an aquatic herbicide, and isolation of a portion of the water column from contact with sediments. Selenium and mercury did not move together through the ecosystems either geochemically or biologically. Selenium bioaccumulation was rapid by fish, crayfish, and haptobenthos and was enhanced by increased sulfate concentration and in the absence of exposure to bottom sediments. It was reduced in the presence of aquatic herbicides. A selenium concentration of 0.1 mg/L did not affect the rate of movement of mercury out of the water column but it did stabilize the movement of mercury among various compartments in the water column. Elevated selenium appeared to retard the rate of mercury bioaccumulation by fish, crayfish, and haptobenthos. Preliminary observations of selenium toxicity to several aquatic organisms were carried out. The possibility of using selenium as an ameliorating agent for heavy metal polluted freshwater systems is discussed.Key words: selenium, mercury, methylmercury, fish, crayfish