The acute toxicity of residual chlorine was determined for the copepod Cyclops bicuspidatus and the rotifer Keratella cochlearis. The 96-hour TL sub 50 value for Cyclops was 0.084 mg/l total residual chlorine added as monochloramine. When Cyclops was exposed to sodium hypochlorite the 96-hour TL sub 50 was 0.069 mg/l total residual chlorine. The 4-hour TL sub 50 value for Keratella was 0.019 mg/l total residual chlorine added as monochloramine. Chemical studies determined that sodium sulfite was an efficient, inexpensive chemical agent for reducing chlorine residuals which did not produce undesirable by-products. Bioassay studies indicated that sodium sulfite added to chlorinated water completely eliminated the acute toxicity of residual chlorine to both Cyclops bicuspidatus and Keratella cochlearis. Significant reductions in the populations of benthic organisms were observed in the effluent plume area after the start of chlorination.

Prepared by Center for Great Lakes Studies, University of Wisconsin-Wilwaukee, Milwaukee, Wisconsin, under grant no. R-801035-01. Includes bibliographical references (pages 64-72).