Toxicity of Candidate Molluscicides to Zebra Mussels ( Dreissena polymorpha) and Selected Nontarget Organisms

Abstract

Many compounds have been marketed for control of zebra mussels ( Dreissena polymorpha), but most compounds lack comparable toxicity data and have not been tested on nontarget organisms. We tested the toxicity of 18 chemicals to two sizes of zebra mussels, two nontarget fish (rainbow trout, Oncorhynchus mykiss and channel catfish, Ictalurus punctatus), and a unionid mussel (threehorn wartyback, Obliquaria reflexa) under standard conditions. Organisms were exposed to the chemicals for 48 h in “soft” reference water (pH 7.7, alkalinity 6 × 10 −4 m/L (30 mg/L) as CaCO 3, and total hardness 40 mg/L as CaCOj) at 17° C. Zebra mussels and unionid mussels were held in untreated reference water for another 48 h after exposure to measure delayed mortality. The LC 50 values and 95% confidence intervals were compared among test organisms. Potassium chloride, Bayluscide (a registered molluscicide), and Clamtrol CT-1 (a poly quaternary ammonium compound) were the most selective chemicals tested against zebra mussels. They were two to three times more toxic to zebra mussels than to the nontarget species. Most of the remaining chemicals lacked the desired toxicity or were more toxic to fish than to zebra mussels.