Control of the Biofouling Mollusc,Dreissena polymorpha (Bivalvia: Dreissenidae), with sodium hypochlorite and with polyquaternary ammonia and benzothiazole compounds

Small adult zebra mussels (Dreissena polymorpha), 2–8 mm valve length, collected from Lake St. Clair were exposed to a range of concentrations of three biocides in static, acute toxicity tests in the laboratory. Laboratory conditions (22°C; pH 7.8; water hardness ≈ 100 mg/L) were representative of midsummer conditions in the nearshore of Lakes Erie and St. Clair. Mussels actively colonized styrene test substrates which were transferred to three replicate, 1-L test vessels. Sodium hypochlorite was an effective biocide at concentrations exceeding 1.00 mg/L and resulted in complete mortality of mussels by 157 and 264 h at concentrations of 5.00 and 2.50 mg/L, respectively. Poly [oxyethylene (dimethylimino) ethylene (dimethylimino) ethylene dichloride] at 1,2,4 and 8 mg/l and (2-(thiocyanomethylthio) benzothiazole) at 0.5,1,2 and 4 mg/L resulted in 100% mortality at all concentrations in times ranging from 144 to 250 h and 110 to 192 h, respectively. Biocide concentration significantly affected the mean time of death for all three of the compounds tested. Mussel valve length had a significant positive effect on time of death in (2-(thiocyanomethylthio) benzothiazole) but only explained a maximum 18% of the variance. Resistance of these actively colonizing mussels to biocides was greater than that found by other laboratory studies, perhaps because of lowered handling stress in our experimental manipulations.