The U.S. government wants to use an insecticide, naled, to control the zika outbreak in Puerto Rico, one of the regions worst hit by the virus, with more than 4,400 cases detected and 400 pregnant women infected.
The aerial spray is the best solution to fight the Aedes aegypti mosquito that transmits the virus, the government says, but scientists, academics and other professionals from the island are strongly opposed to the chemical which they consider toxic.
Zika can cause a rash, fever, joint pain and conjunctivitis, often with more serious consequences. The presence of the virus in pregnant women has been linked to the birth of children with microcephaly and other neurodegenerative disorders.
Naled has been used to control mosquitoes in the United States since 1959 and presents no risk to humans as the amount of active ingredient released per acre of land is very small, according to the Environmental Protection Agency (EPA)
"If Puerto Rico decides to do aerial spraying, EPA-registered insecticides would be used," the Centers for Disease Control and Protection (CDC), said in a statement. "EPA-registered insecticides have been studied for their effectiveness and safety when used according to label instructions," it added.
Aerial spraying, using Naled and other insecticides, has been used in many populated areas of the continental United States, including Miami, Tampa, and New Orleans, to help control mosquitoes. In 2014, almost 6 million acres of land in Florida was aerial sprayed with Naled by mosquito control programs, the CDC added.
It has been far less widely used in Puerto Rico, except during a dengue outbreak in 1987 in metropolitan San Juan.
Many who oppose the fumigation are part of the scientific and medical community in Puerto Rico, organized by the United Front Against aerial spraying to prevent the use of the pesticide. This group, made up of institutions such as the College of Physicians and the College of Chemistry, says that Naled is toxic because it contains phosphorus, a dangerous chemical that affects the nervous and respiratory systems, and can cause cancer.
The CDC's own website warns that it is " very toxic to aquatic organisms," and "may be hazardous in the environment," especially honey bees, if not used properly.
The Agronomists Association of Puerto Rico oppose the spraying of Naled, arguing it will cause some farmers to lose their organic status, as well as the impact on bees.
As a broad-spectrum insecticide, naled can cause death of many insects, including bees, says Raul Perez Rivera, professor in the Department of Biology at the University of Puerto Rico. "The crops of citrus and coffee, to mention two important crops in the island, are dependent on pollination by these insects," he wrote in a university newsletter.
But CDC director, Thomas Frieden, insists it can be used safely in weak solutions of only ounce (two tablespoons) per acre (4,046 square meters) or about the size of a soccer field.
Fears over its use in Puerto Rico were not surprising as it has not been used on this scale before, he added. "There is a potential risk to bees, so (fumigation) is done when they are not active and in different places," he said, adding that no problems have been reported with bees after previous use.