The pesticide Winnipeg wants to test as an alternative to malathion poses more potential health concerns to humans, says a University of Winnipeg entomologist.
If mosquito-trap counts rise this summer, the city's insect control branch intends to test out a product called Pyrocide 7067 in as many as one quarter of Winnipeg's insect-management areas.
Pyrocide is billed as a biological alternative to malathion, an insecticide Winnipeg has used to kill adult mosquitoes for decades. It has two components: the common neurotoxin pyrethrin, which kills insects; and a piperonyl butoxide, or PBO, which increases the effectiveness of the neurotoxin by deactiving insects' pesticide-fighting enzymes.
University of Winnipeg associate professor Rob Anderson said PBO may actually pose more of a threat to human health than malathion.
"The general concern is it's a potential carcinogen. The jury is still out," said Anderson, a mosquito biologist, noting PBO's chemical similarity to safrole, a sassafras derivative and known carcinogen.
Safrole was used to flavour root beer until 1960s, when it was banned in the United States. PBO, another sassafras derivative, has never been subject to rigorous safety tests, Anderson said.
"The disturbing thing about PBO is that because it is a synergist and not an active ingredient in pesticide formulations, it largely escaped toxicological evaluation as a poison against non-target organisms in most of the world, including North America until recently," Anderson said.
Although PBO is used as a synergist in many pesticides, the U.S. Environmental Protection Agency has started looking at the chemical because of pressure from toxicology watchdogs, he added.
So far, there's only "weak evidence" PBO is a human health threat, Anderson said. But there remain question marks about the chemical that need to be answered through further study, he said.
Malathion, meanwhile, has been tested and retested and continually found safe, he said.
"Despite all the scaremongering on the Internet, the actual science on malathion is under label directions and careful professional use, it's well within safety guidelines," he said.
He also questioned the characterization pyrethrin is a natural product, noting there are many compounds that exist in nature that pose a threat to human health.
"It's a false, phoney justification," he said of any characterization of Pyrocide as a biological alternative to malathion. Pyrocide kills a broad spectrum of insects, including pollinating species such as butterflies, bees, moths and ants.
The city has planned to field-test Pyrocide since 2011, but mosquito-trap counts have not been not high enough to warrant an adulticiding program over the past two summers. It could cost as much as four times more to use, as trucks spreading Pyrocide mist would have to travel at a lower speed than malathion trucks, increasing labour and fuel costs.
In a statement, the city noted Health Canada's Pest Management Regulatory Agency has approved the use of Pyrocide and considers it safe.
Anderson said he has sat on Pest Management Regulatory Agency panels and considers it a quirk they do not look at synergists, only active ingredients.