Malathion risks negligible, weed and pest officials say

Jul 21, 2014 By Katie Roenigk, Staff Writer

The City of Riverton honors insecticide "no spray" zones.

The City of Riverton sprays the insecticide malathion along local streets and alleyways each year in an effort to curb mosquito populations and protect residents from contracting West Nile Virus.

Some people believe the chemical is harmful, but Fremont County Weed and Pest assistant supervisor Nancy Pieropan said the amounts applied in Riverton are negligible.

"I don't think it's a risk at all," she said, "Getting WNV is riskier than anything from malathion."

WNV is a mosquito-borne disease that can cause a serious illness in humans, according to the Wyoming Department of Health. The Centers for Disease Control and Prevention says most infected people will not get sick, but about 20 percent have a fever and experience flu-like symptoms.

Fewer than 1 percent of people with WNV develop serious, sometimes fatal, neurologic illness.

"You're miserably sick for a really long time," Pieropan said. "A lot of people never fully recover. It changes your quality of life. And then there are the people who die."

One person in the Wyoming died of West Nile virus in 2013, in Park County.

In contrast, Pieropan said malathion has been used safely for "a really long time."

According to the National Pesticide Information Center, malathion was first registered for use in the United States in 1956. It kills insects by causing the nervous system to malfunction so the insect can't move or breathe normally.

The NPIC says malathion can affect people and animals in the same way, if they are exposed to enough of the chemical.

But Pieropan said the amount of malathion sprayed in Riverton will not have a negative impact.

She has seen studies that show how "terrible" malathion is, but she said those reports were based on high levels of exposure.

"It's people like migrant workers who have their houses in the middle of fields being sprayed with malathion a couple of times a summer at 8 ounces per acre, as opposed to one-eighth of an ounce per acre," Pieropan said.

"There are studies of kids that grow up in the projects in the inner city where they're treating for cockroaches in a really aggressive manner."

As a Lander City Council member, however, she said she is sensitive to the concerns of local citizens. Her town switched from malathion to zenivex, an oil-based formula for use in "ultra low volume" applications in urban and rural settings.

The city of Riverton honors "no spray" zones where residents have requested malathion not be applied. If WNV is detected locally, though, Pieropan said residents have no choice but to let city workers spray the chemical.

"It becomes a public health issue," she said.

For more information on Riverton's mosquito abatement program call 856-3687.

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