AWWA JAW41462

Chlorine dioxide (ClO2) was evaluated as a control agent for adult zebra mussels using single, intermittent, and continuous exposures. A single 30-min exposure to 20 mg/L ClO2 or higher concentration induced at least 50 percent mortality. NaOCl, KMnO4, and H2O2 were ineffective under the same conditions. Intermittent chemical exposure for 30 min each day indicated that ClO2 at concentrations of 10-20 mg/L can induce significant mortality over three to seven consecutive days (LC50 = 13.0 mg/L), but 1-5 mg/L ClO2 applied over 28 consecutive daily exposures are ineffective (<30 percent mortality). Identical intermittent exposure to NaOCl was ineffective at all tested concentrations up to 30 mg/L. Continuous exposure to ClO2 for four days was effective at concentrations >0.5 mg/L (LC50 = 0.35 mg/L), and 100 percent mortality at ClO2 concentrations >1 mg/L was achieved. NaOCl and KNmO4 were less effective. Pooled data yield median lethal dosages at which 50 percent mortality occurred of 14.5 and 82.5 mg h/L for ClO2 and NaOCl, respectively. Includes 40 references, tables, figures.