Zika spraying in Miami: What you need to know

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Story highlights

  • Miami residents have voiced concerns about aerial spraying for Zika-carrying mosquitoes
  • The spraying was delayed after angry residents protested
  • There have been 56 locally transmitted cases of Zika in Florida, which has 20.6 million residents

(CNN)Aerial spraying for Zika-carrying mosquitoes, which happened in the predawn hours on Friday, is bugging out residents of Miami Beach, Florida.

But concerns about the consequences for human health and the environment may be overblown, according to experts.
    Originally scheduled for Thursday, the spraying was delayed for a day after angry residents protested.
    Maria de los Angeles' tweet is typical of the concerns being voiced by residents: "Nobody's here bc they're afraid #zika we care abt organic solutions not poison. We're skeptical Gov Scott $ interest" #naled #miamibeach."
    So far there have been 56 locally transmitted cases of the Zika virus in Florida, which has 20.6 million residents.
    As of Thursday, there were also 596 travel-related cases of Zika in Florida. According to the CDC, there are 2,977 cases of the virus in the continental United States.
    Here's what you need to know:

    Why are they spraying?

    Spraying is needed because the mosquitoes aren't gone yet even though authorities have sprayed on the ground.
    On July 29, Florida Gov. Rick Scott announced that the first local transmission of the virus in the continental United States had occurred in the Wynwood neighborhood, north of downtown Miami.
    A few days later, in an unprecedented move, the CDC announced a travel warning, advising pregnant women not to visit that area. Aggressive mosquito-control measures were taken, including mosquito spraying in the area.
    Mosquito samples test positive for Zika in Miami Beach
    Mosquito samples test positive for Zika in Miami Beach

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    Last month, the Centers for Disease Control and Prevention advised pregnant women not to travel to an area of Miami Beach limited to 1½ square miles. Scott said the area runs from the beach to the Intracoastal Waterway and from Eighth Street to 28th Street.
    Pregnant women are at greatest risk because the virus can have devastating consequences for an unborn baby, including the birth defect microcephaly and other neurological deficits, as well as miscarriage and stillbirth among women who were infected while pregnant.

    What are they spraying and how does it work?

    The main ingredient of the insecticide, Dibrom, is the chemical naled.
    The chemical kills mosquitoes on contact. Sprayers produce very fine droplets that are small enough to stay airborne and intercept mosquitoes in flight.
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    Naled spray droplets stay airborne for an extended period, and the chemical begins to break down once exposed to sunlight or water.
    Very little of the low-concentration spray settles on the ground. Those who worry that they may have come into contact with the chemicals should wash, according to officials.
    Any food that may have been exposed should be rinsed before eating. Since concentrations are far below what is harmful to humans, symptoms, such as skin irritation or headache, are unlikely.

    Are there health risks associated with naled?

    One South Florida resident quoted a coworker in a tweet as saying, "We're either gonna die of Zika or cancer."
    Naled does not pose a health risk to either people or pets when sprayed in low concentrations, according to both the Environmental Protection Agency (PDF) and the Centers for Disease Control and Prevention.
    CDC: Pregnant women should avoid travel to Miami-Dade County
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    In its own review of naled, however, the European Union came to a different conclusion.
    Naled degrades to dichlorvos, a toxic chemical, in the presence of sunlight, and according to the EU scientific commission, this can cause genetic mutations. As a result, the EU has banned agricultural use of products containing naled.

    Is this the first use of naled in Florida?

    In Miami-Dade County, the Department of Solid Waste Management's Mosquito Control Section commonly sprays in response to state Department of Health investigations -- and when residents request the use of insecticide.
    The Mosquito Control Section has applied naled via an ultra-low-volume spray for many years, officials said in a news release.
    In fact, Dibrom has been used in the United States over the past 50 years, said Timothy J. Donnelly, vice president, chief administrative officer and general counsel of AMVAC Chemical Corp., which makes the insecticide.
    "It is regularly sprayed in 12 states on over 15 million acres each year," Donnelly said last month.
    Miami-Dade County's aerial spraying alternates between naled and an insecticide called BTI (bacillus thuringiensis israelensis, a naturally occurring bacterium), which targets mosquito larvae instead of adult mosquitoes. BTI has been registered with the EPA since 1961 as a pesticide.

    What are the environmental risks of aerial spraying?

    On Thursday, a Twitter user described as a backyard bee keeper wrote, "@CDCgov Please stop the use of toxic NALED, it kills pollinators and wildlife and its toxic to environment."
    South Carolina beekeeper Juanita Stanley recently lost more than 3 million bees -- all 46 of her hives and her entire livelihood -- when Summerville officials decided to aerially spray a small area of the town for Zika-carrying mosquitoes.
    Stanley believes mosquito-control officials are overreacting to Zika.
    "This is crazy," she said. "It's like using a sledgehammer to crack a peanut. The devastation that it has already caused is beyond comprehension. We can't live without these honeybees."
    The spraying occurred, Dorchester County Administrator Jason Ward said, because four people in the county had developed Zika while traveling to areas of the world where the virus is actively circulating. Summerville residents then expressed concern about the virus. Zika is not actively circulating in South Carolina.
    Still, Aedes aegypti, the main mosquito that carries and transmits the virus, has been found in small numbers in the nearby Charleston area, according to Ward.
    The National Institute of Food and Agriculture and the National Bee Laboratory declined to comment on the issue.
    "We do recommend mosquito control to be done around travel-associated cases as well as locally transmitted cases if the mosquitoes that spread Zika are in the environment," said entomologist Janet McAllister of the CDC's Division of Vector-Borne Diseases. "We don't want the virus to take hold in the local mosquito population."
    The truth is the nation's bee population has long been stressed by the public's need for pest control.
    "I've seen it with West Nile virus and after hurricanes and major flooding," entomologist Jeffrey Harris said. "I always tell the beekeepers that human health is always going to trump bee health, and if there is a natural disaster that increases a dangerous mosquito population, they are going to spray."
    Harris runs the Honey Bee Extension and Research Program for Mississippi State University and is active in research on bees and how to best protect them from pesticides.
    "Aerial spraying is a tough one," he said. "The recommendations are difficult to follow. While maximum foraging for bees is between 10 a.m. and 2 p.m., in the summertime, the bees are already out at dawn, when aerial spraying is recommended. So spraying in the morning is the worst thing they can do for bees."
    Since the variety of mosquito that carries Zika is most active predawn and at sunset, all spraying must take place at those times. Special precautions are not necessary, Miami-Dade County officials said, though people with allergies may want to remain indoors. During any insecticide operation, it is recommended that beekeepers cover their bees.

    Are aquatic species at risk?

    Bryn Phillips, a specialist in the University of California, Davis environmental toxicology department, said his research indicates that the insecticide breaks down into different chemical versions of naled. One of these versions, dichlorvos, is quite toxic to aquatic species at the "low end of the food chain," like aquatic insects and frog larvae -- "basically fish food," Phillips said.
    "When naled gets sprayed, it knocks out the mosquitoes, but if sprayed over water, it breaks down quickly," he said.
    If the chemicals are rotated and managed properly, an environmental area can recover, Phillips noted.