To the editor:
The State of Massachusetts has been unable to produce the records backing up its claim that the biggest aerial spraying of pesticides in Commonwealth history this July significantly reduced mosquito-borne disease risks, according to . Further, the state has no proof aerial spraying is an effective safeguard against Eastern Equine Encephalitis (EEE).
In a July 31 press release the Massachusetts Department of Public Health (DPH) announced that “aerial spraying the weekend of July 20-22 reduced the mosquito population by approximately 60 percent within the 21-community spray zone in Southeastern Massachusetts.” DPH Commissioner John Auerbach was quoted as crediting aerial spraying for causing “a significant reduction in the volume of mosquitoes.”
Immediately following that release, New England Public Employees for Environmental Responsibility (PEER) submitted a public records request for the materials supporting these claims. More than a month later, DPH has still been unable to produce any records on which it based its press release. The matter is on appeal before the Secretary of State, the last administrative hurdle PEER needs to jump over in order to sue DPH to force production.
PEER points out that agencies conducting aerial spraying concede that it does not eliminate risk from mosquito-borne diseases. So, even a 60% reduction of mosquitoes would not necessarily produce a concomitant reduction in disease risk. Moreover, a 60% kill rate claim is extremely dubious because:
• Droplet size of the sprayed pesticide is the primary factor affecting the efficacy of aerial spraying. In order for a mosquito to be killed by agent used in Massachusetts, the mosquito must be hit by 17 properly-sized pesticide droplets. If droplets are too big, they have less probability of making contact. If too small, they have lessened lethality and become more susceptible to atmospheric conditions, like wind;
• Vegetation prevents droplets from reaching their intended targets. One study on canopy penetration showed that only 7% of the target insects had been hit by pesticides; another showed the kill rate of mosquitoes under dense canopy was 0%. Other studies show no better than 34% mortality in vegetated areas. Significantly, mosquitoes prefer areas that are vegetated; and
• Spraying only targets flying adults and not the eggs, larva or pupae. That means sequential applications of pesticide are necessary to control emerging adult mosquitoes – otherwise, mosquito control lasts for five to seven days, at most. Massachusetts has conducted aerial spraying during five summers since 1990. Of those five, three consisted of a single aerial spray, and two consisted of two aerial sprays a few weeks apart. None of these sporadic applications could be expected to interrupt the life history of mosquito populations or significantly cut disease risk.
• The Department of Public Health is peddling snake oil when it suggests aerial spraying is demonstrably effective in protecting against EEE while downplaying the dangers posed by mass pesticide application to both the public and the environment. “To effectively kill mosquitos from an aircraft requires perfect conditions, ideal terrain and a pilot who is an aerial Annie Oakley. It is not surprising that the Department is reluctant to reveal the real numbers behind its press releases.”
Public Employees for Environmental Responsibility (PEER)
Ms. Bennett is a biologist and attorney formerly with the U.S. Environmental Protection Agency.