Effectiveness of the sulfur(IV) compound, sodium bisulfite, in reducing chlorine, chlorine dioxide, and chlorite toxicity to Daphnia magna in well water and pond water

Flow-through toxicity tests were conducted with Daphnia magna to determine the residual toxicity of chlorine, chlorine dioxide, and chlorite after tre atment with the sulfur(IV) compound sodium bisulfite. Daphnids were exposed separately to 0.5-mg/ L concentrations of each of the three compounds with out the addition of sodium bisulfite, with a low stoichiometric dose of sod ium bisulfite, and with a high stoichiometric dose of sodium bisulfite. Tes ts were performed in well water with a low total organic carbon (TOC) conte nt and pond water with a high TOC content. Analysis of results indicated th at sodium bisulfite did not eliminate the toxicity of chlorine dioxide or c hlorite to D. magna. Total residual oxidant (TRO) concentrations were reduc ed and survival times were extended, but acute toxicity persisted even with a S-IV concentration 10.0 times the stoichiometric ratio of oxidant. Morta lity occurred in chlorine dioxide treatments in which no TRO was detected, indicating that standard analytical (amperometric) techniques may be inadeq uate to detect toxicity. Sodium bisulfite did succeed in eliminating chlori ne toxicity except in pond water receiving a low (3.0X) sodium bisulfite do se. Oxidant reactions with organic substrates may have produced chlorinated residuals that were resistant to S-IV dechlorination.