Acute Toxicity of Potassium to the Adult Zebra Mussel Dreissena polymorpha

Abstract.

The acute toxicity of potassium (K⁺) to adult zebra mussels, Dreissena polymorpha, and the efficacy of using K⁺ to enhance the toxicity of a commercial biocide was examined. Mussels, 15–20 mm in total shell length, collected from Lake Ontario, were exposed to static concentrations of K⁺ for 3, 6, 12, and 24 h, and to a sublethal concentration of K⁺ prior to and during exposure to Clam-Trol^®

CT-2 for 6, 12, and 24 h. Tests were conducted at ambient lake temperatures of 12°C and 22°C and mussels were subjected to a 96 h recovery period. Valve closure was inhibited in mussels exposed to sublethal as well as lethal concentrations of K⁺, resulting in mussels that were nonresponsive to tactile stimulation. The median effective concentration (ED₅₀) of K⁺ to induce nonresponsive mussels increased as the length of the recovery period was extended from 24 to 96 h, indicating that some nonresponsive mussels were capable of recovering 96 h after exposure to the K⁺ treatments. A recovery period duration of 96 h was critical in assessing mortality in mussels exposed to high K⁺ levels and the use of tactile stimulation to test for valve responsiveness was insufficient to identify mortality. The 24 h median lethal concentration (LC₅₀) of K⁺ at 22°C (400 mg/L) was found to be sixfold higher than the LC₅₀ reported by other investigators utilizing shorter recovery periods. The LC₅₀ of the biocide to mussels treated with K⁺ was not reduced, suggesting that the use of K⁺ to inhibit valve closure may not be useful in methods to control mussel infestations.