THE EFFECTS OF DECHLORINATION USING SODIUM BISULFITE ON THE TOXICITY OF SODIUM PENTACHLOROPHENATE AND COPPER SULFATE ON THE MICROTOX® TEST

Abstract

Biologically-based toxicity sensors, including the Microtox® test, are highly sensitive to chlorine and chloramines, and their use with water samples with these disinfectants is problematic. A reducing agent such as sodium bisulfite (NaHS0₃) is commonly used to remove chlorine-related toxicity, but the effect of reducing agents on toxicity has received little attention. This study determined the effects of dechlorination using NaHS0₃ on the toxicity of an organic pesticide (sodium pentachlorophenate [PCP]) and a metal (copper sulfate) in the Microtox® test. The toxicity of PCP and copper sulfate was determined in NaHS0₃-reduced chlorinated and chloraminated water. At a concentration of NaHS0₃ minimally required for dechlorination, there was decreased copper toxicity but little effect on the PCP 15-minute EC50. Increasing concentrations of NaHS0₃ caused greater decreases in copper toxicity, but had no additional effect on PCP toxicity. These data demonstrate the need to minimize reducing agent use when evaluating dechlorinated water samples to avoid altering the toxicity of the original sample.