Toxicity of chlorine dioxide to adult zebra mussels

Effective kills depend on the right combination of concentration and exposure time. Chlorine dioxide (ClO 2 ) 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 ClO 2 or higher concentration induced at least 50 percent mortality. NaOCl, KMnO 4 , and H 2 O 2 were ineffective under the same conditions. Intermittent chemical exposure for 30 min each day indicated that ClO 2 at concentrations of 10–20 mg/L can induce significant mortality over three to seven consecutive days (LC 50 = 13.0 mg/L), but 1–5 mg/L ClO 2 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 ClO 2 for four days was effective at concentrations >0.5 mg/L (LC 50 = 0.35 mg/L), and 100 percent mortality at ClO 2 concentrations >1 mg/L was achieved. NaOCl and KMnO 4 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 ClO 2 and NaOCl, respectively.