THE TOXIC EFFECT OF SELENIUM ON THE ZOOPLANKTON, DAPHNIA MAGNA AND DAPHNIA PULICARIA, IN WATER AND THE FOOD SOURCE (CHLAMYDOMONAS REINHARDTII)

Zooplankton are important components of the aquatic food web. They provide a route for the passage of energy as well as toxic substances to higher trophic levels. Acute and chronic toxicity experiments were performed on the zooplankton, Daphnia magna and Daphnia pulicaria, to investigate the toxicity of selenium on these aquatic invertebrates. The acute 48 h LC(,50) of sodium selenate for Daphnia magna and Daphnia pulicaria were 1.01 and 0.25 mg Se/1, respectively. The 48 h LC(,50) of sodium selenite for D. magna and D. pulicaria were 0.45 and 0.006 mg Se/1, respectively.;Chronic 28-day toxicity tests were performed on D. magna at 0.05, 0.10, 0.50, and 1.00 mg Se/1 as sodium selenate in the water and with two food types. One food type was algae raised in clean Lake Michigan water and the second treatment was algae raised in media with selenium concentrations corresponding to those in the water cited above. When compared to Daphnia fed selenium-free algae, D. magna fed selenium-laden algae had greater survival, a greater number of offspring produced, and a greater intrinsic growth rate, "r", at the toxicant concentration in the water of 0.05, 0.10, and 0.50 mg Se/1. These parameters were, however, lower than those observed in the controls. Uptake of ('75)Se as sodium selenate in D. magna was reduced in the presence of selenium-laden algae and DL-selenomethionine, while L-methionine increased the uptake of ('75)Se. Selenium bound to an amino acid such as DL-selenomethionine or organically bound within an algal food source appears to be preferentially incorporated thereby reducing the uptake of inorganic forms from the water.;Chronic tests were run at 0.05, 0.10, 0.50, and 1.00 mg Se/1 as sodium selenate for both species of Daphnia. A dose related decrease in survivorship, total number of offspring, and the intrinsic growth rate, "r", were observed at the 0.05, 0.10, and 0.50 mg Se/1 concentrations in both species. At the 1.00 mg Se/1 concentration, all animals died without reproducing.