On the night of September 10, low-flying planes blanketed parts of Nassau County, New York, in a fine mist of Scourge, a mosquito-killing pesticide containing the pyrethroid resmethrin. It was the first time in a decade that concerns over West Nile virus prompted the county to conduct aerial spraying. The problem, though, as any good horror movie fan will tell you, is that the treatment may present more problems than the virus itself.

“I don’t want to downplay the importance of preventing the disease,” said Dr. Michael Gochfeld, professor of environmental and occupational health at Robert Wood Johnson Medical School in New Jersey, “but I don’t think that aerial spraying is ever efficient, effective, or warranted.” Gochfeld was not talking about creating mutants, but the possibility of broad ecological disruption, since spraying might kill honey bees, birds, and aquatic organisms.

And that’s not the only potential risk. The New York City Department of Health and Mental Hygiene acknowledged in April 2007 that pesticides sprayed from planes and trucks “may cause certain adverse health effects,” according to the settlement of a lawsuit brought by the No Spray Coalition against the city.

Even the Nassau County Department of Health says that the human health effects of exposure to broad pesticide spraying are uncertain. A department information sheet on West Nile states: “There are no studies examining whether the use of Scourge to control mosquitoes has caused any long-term health effects in humans.”

Given the risks, are the chances of dying from West Nile encephalitis too slim to justify the aggressive chemical response? Last year, the Centers for Disease Control recorded 124 West Nile-related deaths nationwide; the worst year was 2002, with 284 fatalities. For comparison’s sake, at least 400 people are struck by lightning each year, according to the National Weather Service.

But a 2006 analysis by Robert K.D. Peterson at Montana State University’s Department of Land Resources and Environmental Sciences compared the human health risks of West Nile with those of exposure to insecticides, and concluded that the virus is more dangerous than aerial spraying.

Joseph Conlon, technical adviser for the American Mosquito Control Association, said the concerns about pesticides are overblown, spurred by the shock some people experience when aerial spraying reaches their communities for the first time. “Here in Florida you would be surprised if you didn’t see the planes,” he said. “None of us are running around here with five legs and seven arms.”

For more on this subject, check out the Center’s recent project Perils of the New Pesticides, along with our other blog coverage.