Dynamics of Selenium in Mercury-Contaminated Experimental Freshwater Ecosystems

Abstract

The simultaneous movement of radiolabeled Se and Hg was followed in experimental aquatic ecosystems (.simeq. 105-l tube enclosures) set into a Hg-contaminated lake. The experimental treatments consisted of increasing stable Se or SO42- water concentrations, addition of an aquatic herbicide and isolation of a portion of the water column from contact with sediments. Se and Hg did not move together through the ecosystems either geochemically or biologically. Se bioaccumulation was rapid by fish, crayfish and haptobenthos and was enhanced by increased SO42- concentration and in the absence of exposure to bottom sediments. It was reduced in the presence of aquatic herbicides. A Se concentration of 0.1 mg/l did not affect the rate of movement of mercury out of the water column but did stabilize the movement of Hg among various compartments in the water column. Elevated Se appeared to retard the rate of Hg bioaccumulation by fish, crayfish and haptobenthos. Preliminary observations of Se toxicity to several aquatic organisms were carried out. The possibility of using Se as an ameliorating agent for heavy metal polluted freshwater systems is discussed.