Comparison of chlorine and chlorine dioxide toxicity to fathead minnows and bluegill

Abstract

The comparative toxicity of total residual chlorine (TRC) and chlorine dioxide (ClO 2) was evaluated by conducting 96 h flow-through bioassays with three types of fish. The fish were subjected to an intermittent exposure regime in which biocide residuals were present for approx. 2-h periods beginning at 0, 24, 48 and 72 h into the tests. These conditions simulated the antifouling procedure (1 h day −1 biocide addition) used to control biofouling of nuclear reactor heat exchangers at the Savannah River Plant near Aiken, South Carolina. LC 50 values showed that ClO 2 was approx. 2–4 times more toxic than TRC to: (1) juvenile and 1-year-old fathead minnows ( Pimphales promelas); and (2) young-of-the-year bluegill ( Lepomis macrochirus). The TRC mean 96-h LC 50 values were: 0.08 mg l −1 for juvenile fathead minnows, 0.35 mg l −1 for adult fathead minnows and 0.44 mg l −1 for young-of-the-year bluegills. The ClO 2 mean LC 50 values were: 0.02 mg l −1 for juvenile fathead minnows, 0.17 mg l −1 for adult fathead minnows and 0.15 mg l −1 for young-of-the-year bluegills.