Faced with the need to quickly kill hard-to-reach mosquitoes spreading the Zika virus through Wynwood, Miami-Dade County has turned to a controversial pesticide that’s toxic not just to the noxious flying parasites, but also to beneficial insects like honey bees, as well as birds, some fish — and people.
County mosquito-control officials and the U.S. Environmental Protection Agency play down the risks posed by aerial spraying of naled, which has been approved for use against adult mosquitoes in the United States since 1959, but is banned by the European Union. They say the minute concentrations of naled in the fine mist produced by spraying, though sufficient to kill mosquitoes on contact in the air, dissipate rapidly, and little of the pesticide reaches the ground.
When properly applied, the EPA’s website says, naled can be used in mosquito control “without posing risks to people” beyond some short-term effects such as skin, eye or nose irritation for those sensitive to chemicals. The agency acknowledges “risks to aquatic and terrestrial wildlife,” but says those “exist for only a short time.” It adds: “Long term exposure from its use for mosquito control is unlikely.”
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But that’s not what some scientists and anti-pesticide activists say.
Several studies suggest that long-term exposure to even low levels of naled can have serious health effects for children and infants as well as wildlife, including butterflies and bees, for whom exposure can be lethal. Some studies suggest it might have neurological and developmental effects on human fetuses, including on brain size, echoing the severe consequences that eradication of the Aedes aegypti mosquito that carries the Zika virus is meant to prevent.
“Widespread application of naled is very troubling,” said Nichelle Harriott, science and regulatory director at Beyond Pesticides, a Washington, D.C., organization. “We know it’s highly neurotoxic. Studies show that low-dose exposures are problematic over the life of a person.
“In cases such as this, they always say that people are just going to be exposed to small amounts for very short periods of time. But how long is it going to go on? How long are they going to be spraying? Those exposures do accumulate, and we need to look at those aggregate exposures.”
Harriott and other advocates note they’re not the only ones concerned about naled, one of a class of pesticides known as organophosphates. The EPA has banned some organophosphates while trying to restrict the use of naled, barring some applications and asking manufacturers to voluntarily eliminate household uses.
A spokesman for the county’s mosquito control program, Frank Calderon, referred questions about its use of naled to the Centers for Disease Control and Prevention. The CDC said its official in charge of Zika control was unavailable Thursday. The CDC recommended the use of naled to the county.
At larger doses, naled’s effects on people range from headaches, nausea and diarrhea to death. The insecticide, which can penetrate skin but is most harmful when breathed in, attacks the human nervous system with the potency of a chemical weapon, scientists say. Accidental exposure has led to deaths in India and other countries.
Miami-Dade officials began applying naled in Wynwood after its usual methods — using trucks and backpacks to spray a different type of pesticide known as pyrethroids — did not work fast enough. Federal officials at the CDC said the Zika-carrying mosquitoes are hard to find and eliminate because they can breed in tiny amounts of water in urban nooks and crannies. Those mosquitoes might also have become resistant to the pyrethroids, they said.
But naled spraying can penetrate those hidden spots and rapidly “knock down” the mosquito population, said Dr. Thomas Frieden, the CDC’s director.
“It can get to where no truck can get. It can get where no backpack sprayer can get,” Frieden said in Miami last week.
The county has sprayed naled in Wynwood three times, according to its mosquito-control webpage — dousing 10 square miles just after 6 a.m. August 4, again at 5:30 a.m. August 7 and at 6 a.m. Friday. Mosquito-control workers are also spraying a different insecticide, BTI, to attack the mosquitoes’ larvae.
Officials have not said how long the spraying will go on.
The EPA says naled is routinely sprayed over 16 million acres in the mainland United States, but has also been used after hurricanes and floods to control mosquitoes. In 2004, as part of response to a string of hurricanes, the insecticide was applied to eight million acres across Florida, the agency says. It was also deployed after Hurricane Katrina in 2005 over five million acres in Louisiana, Mississippi and Texas.
Naled’s toxicity is limited because the chemical breaks down quickly after it’s sprayed, though some studies suggest its residual components pose health risks of their own. The EPA maintains it’s “unlikely” people could touch or breathe in anything with enough of the material on it to cause harm.
Frieden, the CDC director, said last week that testing in places where the insecticide has been used showed no “measurable increase of naled in people’s bodies after spraying.”
“In fact, aerial spraying uses such a tiny amount, it provides a uniform amount with a lower risk,” Frieden said.
Just in case, though, the agency urges those concerned about potential effects to stay indoors with windows shut and air conditioning off during spraying. They should also cover cooking grills and furniture, bring pets, pet-food dishes and toys inside, and rinse anything left outside and uncovered.
Some studies have found that naled and another commonly sprayed pesticide have contributed to the precipitous decline of butterfly populations in South Florida, leading Miami-Dade mosquito control officials to stop spraying in some protected habitats. Aquatic invertebrates such as shrimp and water fleas are also vulnerable, the EPA says, while scientific studies have shown harm to some species of fish, including trout.
In Florida, naled is normally used mostly in agricultural areas, but has been deployed on occasion in urban areas as well.
But its use has been highly controversial in Puerto Rico, a hotbed not just for Zika but also dengue and chikungunya, both also spread by the same mosquito. The CDC sprayed naled over 177,000 acres of metropolitan San Juan in an unsuccessful effort to control a dengue outbreak in 1987.
Then street protests broke out earlier this year when the CDC announced it intended to spray naled again in response to the growing Zika epidemic on the island. Medical groups denounced its use, with some doctors accusing the CDC of using Puerto Rico as a lab to test naled’s efficacy in curbing Zika. Gov. Alejandro Garcia Padilla intervened to block the spraying.
The CDC’s dengue section in Puerto Rico did lab testing of naled’s efficacy against local Aedes aegypti mosquitoes, but the insecticide was not sprayed in the island, agency spokesman Banjamin Hayes said.
“Tests carried out in February and March 2016 by the CDC on 14 separate populations of Aedes aegypti from across Puerto Rico showed that the chemical was highly effective. In each test, 100 percent mortality of female Aedes aegypti was achieved,” the EPA webpage says.
The EPA cites the results as evidence that naled is effective against the mosquito and that it has not developed a resistance to the insecticide.
But some critics of the use of naled say that development of resistance is a clear risk as authorities turn to the insecticide as an alternative to pyrethroids, to which mosquitoes have already begun showing resistance. And while pyrethroids, which are also neurotoxins, pose health risks as well, those are not as severe as those associated with naled, Harriott said.
That means authorities should be extremely wary of deploying naled and, when they do so, should warn people about the risks — something some critics complain Miami-Dade officials have not done.
“It is very difficult to judge in a public-health situation like this,” Harriott said. “We urge a measured approach and an understanding of the risks involved. We have to think about the long-term implications.”
Miami Herald Staff Writer Jenny Staletovich contributed to this report.