ACUTE AND SHORT-TERM CHRONIC EFFECTS OF CONTINUOUS AND INTERMITTENT CHLORINATION ON MYSIDOPSIS-BAHIA AND MENIDIA-BERYLLINA

Intermittent chlorination to inhibit biofouling in condensers is a widespread practice in the power generation industry. Because the U.S. Environmental Protection Agency's water quality criteria for chlorine were based on continuous chlorine exposure of test organisms, it is possible that effluent discharge limits derived from these criteria are overprotective to aquatic organisms exposed only intermittently. The toxicity of 96-h acute and 7-d short-term chronic exposures under continuous and intermittent chlorination (2-, 4-, 6-, and 8-h daily exposures) to two saltwater species was determined. Mysids (Mysidopsis bahia) were found to be more sensitive to chlorine than inland silversides (Menidia beryllina) when exposed continuously under acute and short-term chronic conditions. No difference was found between the acute toxicity responses of mysids and silversides exposed to intermittent chlorination. In contrast, a difference in short-term chronic toxicity was found between the two species exposed to intermittent chlorination. All intermittent chlorine exposures were less toxic to both species than the continuous exposures. The acute-to-chronic ratios (ACR) for silversides exposed to both continuous and intermittent chlorination indicate that ACRs of approximately 1.5 can be used with acute data to estimate chronic toxicity of chlorine. The ACRs for mysids exposed to both continuous and intermittent chlorine range from 3.1 to 6. 1.