New report finds mosquito fogging chemical could be carcinogenic


It turns out the fogging machines used in Winnipeg to control mosquito outbreaks could be more harmful than the pesky bloodsuckers, a new study finds.

According to the International Agency for Cancer Research with the World Health Organization (WHO), malathion—the pesticide sprayed to kill mosquitos—“probably” causes cancer. The report found that that there is “limited evidence of carcinogenicity in humans for non-Hodgkin’s lymphoma, and prostate cancer” when exposed to the chemical. Malathion was also linked to tumours in rodents.

In Canada, the City of Winnipeg employs the chemicals using “fogging trucks” to control outbreaks. During these seasonal fogging programs, areas such as streets and lanes, golf courses and cemeteries are sprayed daily from 9:30 p.m. to 6:30 a.m. Residents can have their homes exempt from the program, but the trucks only provide a 90-meter buffer zone around their property.

The chemical of malathion works by disrupting the mosquito’s nervous system, eventually causing the insect to die.

In response to WHO’s findings, the City of Winnipeg has not stated whether or not they will continue using malathion. In an emailed statement, city spokesperson Michelle Finley wrote, “The City of Winnipeg Public Service will be reviewing the WHO report in consultation with Health Canada who license and regulate the use of malathion by municipalities.”

But you might want to take the news from WHO with a grain of salt—at least for now. Canadian scientist John McLaughlin, who was one of two Canadians involved with the WHO’s research, says that Winnipeggers need not be too concerned with the new report.

“What most people are exposed to is very, very low levels of the agent for short periods of time,” McLaughlin, who works as chief science officer and senior scientists for Public Health Ontario, told the CBC. “We do not expect there would be health effects from that.”

The WHO’s research was primarily focused on the effects of five insecticides and herbicides in a workplace setting where workers would be in contact with the chemical on a regular basis for long periods of time. This differs from the exposure levels Winnipeg residents face during fogging programs, which uses an ultra low volume.

Dr. Joel Kettner, another doctor based in Winnipeg, agrees that exposure plays a big role in malathion’s harmful effects.

“It’s all about dose. It’s best described in a simple statement: dose makes the poison,” Kettner said in an interview with the CBC. “[In Winnipeg,] it’s distributed high into the air. The amount that actually filters down, which could then be ingested or absorbed by the human body…the dose is so low it’s almost hard to measure.”

The use of malathion has been a controversial subject for Winnipeggers for more than 10 years. Some say the chemical wards off diseases like West Nile Virus, while others suggest the city employ safer options.