Copper more effective than chlorine on dreissenid mussels

A study conducted at a Toronto drinking water treatment plant found that ionic copper is more effective than chlorine for controlling adult and larval dreissenid mussels. Drinking water treatment facilities within Canada are currently limited to pre-chlorination of raw water as their sole method of controlling zebra mussels (Dreissena polymorpha) and quagga mussels (D. rostriformis bugensis). Chlorine requires near continuous exposure to achieve full mortality and, in some cases, can produce toxic disinfection by-products (DBPs).

The pilot study compared chlorine to EarthTec^® QZ, a copper-based molluscicide. Even at the lowest dose, the copper solution was more effective than chlorine at commonly used concentrations. EarthTec QZ achieved full adult mussel mortality in 30 days at 30 µg/L versus chlorine at 1 mg/L over 42 days. Previous research has shown similar mortality rates in adult dreissenid mussels exposed to ionic copper.

The study also suggests that copper is more effective than chlorine on larval dreissenid mussels, called veligers. Unlike chlorine, EarthTec QZ does not provoke behavioral changes in veligers. They do not perceive EarthTec QZ as a noxious substance and continue to filter water at a normal rate. Eventually they accumulate a lethal dose of copper in their bodies.

EarthTec QZ is manufactured by Earth Science Laboratories, Inc. (ESL). EarthTec QZ is EPA approved for controlling zebra mussels and quagga mussels in open waters and pipelines. It is NSF Certified to Standard 60 as an additive to drinking water.

Research for this study was conducted independently of ESL with approval from Health Canada’s Pesticide Management Regulatory Agency (PRMA). The results were presented at the International Conference on Aquatic Invasive Species (ICAIS) in Montréal, Québec, October 27-31, 2019. The poster is republished here with permission from the authors. EarthTec QZ is presently undergoing registration with the PMRA for use in Canada.