Researcher warns against permethrin use
By Jenn Watt
Use of a chemical called permethrin to rid properties of mosquitoes could have unintended consequences, a guest speaker at the Kennisis Lake Cottage Owners’ Association spring meeting told the audience.
Chris Brew, an academic who taught mathematics and science education, said she spent nearly a year researching the synthetic pyrethroid insecticide after she was alerted to its use near her home in the Muskoka region.
“You may have been told that it’s practically non-toxic for humans. You might be worried about the diseases that are carried by mosquitoes - that might be one of the reasons you’re doing it,” Brew said to the group assembled at the Logging Museum at Haliburton Forest on May 18.
“I see my role today is to help you or assist you to have an informed conversation about the practice. As a community, we do need to have that conversation because the chemical that’s being used is not benign.”
Brew pointed out that the effects of permethrin haven’t been adequately studied and she questioned the notion that the chemical would not drift in the wind to neighbouring properties. Research done by Karen Oberhauser of the University of Wisconsin showed that even with the slightest breeze (one to two miles per hour), she found 100 per cent mortality of mosquitoes 23 metres from the application site.
Permethrin interferes with nerve impulses, causing paralysis in insects, leading to death.
Brew said although application of permethrin may be only targeting mosquitoes, it is likely to affect many insects, including ones people treasure on their properties, such as monarch butterflies.
Health Canada and the Pesticide Management Regulatory Agency set limits on exposure and recently completed the re-registration process for permethrin. Brew said she expected the results of that consultation process to be released in the next month.
“Don’t hold your breath, because I don’t think there’ll be a different determination [than the status quo],” she said.
Health Canada’s website outlines its stance on the chemical, repeatedly noting that if it is used as directed, risks are low.
“Permethrin is not expected to pose a risk of concern when used according to proposed label directions,” the website reads. “Permethrin may pose a risk to aquatic organisms, bees, beneficial insects and birds; therefore, preventative measures to reduce risk to these organisms are proposed. When proposed label directions are followed, the risks are considered acceptable.”
Brew said the potential damage done by permethrin is hard to fully understand. For example, research has been done on honey bees, but little has been done on other native bees that may nest in leaf litter and be susceptible to spraying.
Ultimately, she said not enough was known about the insecticide and said it was her opinion that Canada should follow the lead of the European Union in banning it.
“I think we’re underestimating the risks associated with this chemical, particularly with chronic low-dose effects. I think we need to apply the precautionary principle,” she said.
With that outcome unlikely, Brew told association members that the best defence was education. Once people are aware of what the product does, they might choose something less toxic, for example using garlic spray to repel mosquitoes instead.