ACUTE TOXICITY OF POTASSIUM TO THE ADULT ZEBRA MUSSEL DREISSENA-POLYMORPHA

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 len gth, collected from Lake Ontario, were exposed to static concentration s of K+ for 3, 6, 12, and 24 h, and to a sublethal concentration of K prior to and during exposure to Clam-Trol(R) CT-2 for 6, 12, and 24 h . Tests were conducted at ambient lake temperatures of 12 degrees C an d 22 degrees C and mussels were subjected to a 96 h recovery period. V alve closure was inhibited in mussels exposed to sublethal as well as lethal concentrations of K+, resulting in mussels that were nonrespons ive to tactile stimulation. The median effective concentration (ED50) of K+ to induce nonresponsive mussels increased as the length of the r ecovery period was extended from 24 to 96 h, indicating that some nonr esponsive mussels were capable of recovering 96 h after exposure to th e K+ treatments. A recovery period duration of 96 h was critical in as sessing 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 degrees C (400 mg/L) was found to be sixfold higher than the LC50 reported by other investigators utilizing shorter recovery period s, 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 use ful in methods to control mussel infestations.