Enhanced mortality of the biofouling zebra mussel, Dreissena polymorpha, through the application of combined control agents

Abstract

Intuitively, cumulative and synergistic effects of combined biocides seem a promising avenue to explore in managing the biofouling zebra mussel. However, such an approach has not been comprehensively examined. In this study, the potential of a binary mixture of poly(diallyldimethyl ammonium chloride) and potassium chloride for zebra mussel control was investigated. The toxicity of the mixed biocides to both adults and veligers was evaluated in laboratory static bioassays. The combined toxicity of the chemicals was observed to depend on the life stage of the mussels. For adults, it was shown to vary with the magnitude of the response under consideration. When producing low lethal effects (below around 25% mortality), the chemicals acted synergistically on the mature organisms and tended to be additive, whilst at high mortality levels, they operated more than additively. In contrast, regardless of the response level under consideration, the toxins appeared to exert additive or less than additive effects on the veligers depending on the potassium chloride dosage. These results have direct practical implications for zebra mussel control. They suggest that the mixture under analysis is very promising for use in mitigation programmes targeted at adults, but its potential for use in proactive treatments to control veligers is not as definitive. The paper also includes a discussion on the contribution the ecotoxicological background on mixture toxicity may have to the development of combined chemical treatments for pest mitigation. Therefore, it may have further application in the setting of experimental protocols for designing control methods.