The pesticide widely used to fight Zika-carrying mosquitoes in Florida and across the nation has been linked to deficits in motor functions in Chinese babies, according to a new study.
The study, whose authors say it is the first to examine real-world exposure to naled outside workplace accidents or lab experiments, used cord blood from 237 mothers who gave birth to healthy babies at a hospital in southeast China between 2008 and 2011. At six weeks, the babies displayed no problems. But at nine months, the babies suffered from slight problems with coordination, movement and other motor functions.
The University of Michigan study was published in the peer-reviewed journal Environment International on Thursday.
While the study provided only a close snapshot of a particular group of mothers, the authors say it suggests the need to take a closer look at using naled to fight mosquitoes, particularly since problems surfaced at lower exposure levels than previous studies.
“Just because changes are small, that doesn’t mean they should be discounted,” said lead author Monica Silver. “We really need to know more about it.”
Naled has been used for decades in Florida to control pesky marsh mosquitoes, sprayed by plane mostly over suburban fringes bordering marshes and mangroves before dawn. But last year, it drew more attention, and quick opposition, when Miami-Dade County and other urban areas battling Zika began using it in Wynwood and Miami Beach where active transmission of Zika was occurring. Zika began rapidly spreading through Brazil over the summer of 2015, leading to the births of an estimated 2,300 babies born with microcephaly and severe brain damage.
In South Florida, protesters prompted the county to put off using the pesticide in Miami Beach to give the city more time to notify residents. Federal officials also backed off a plan to use naled in Puerto Rico after its governor protested. Europe banned naled in 2012.
However, the Centers for Disease Control and Prevention recommended the use of naled in combination with organic larvicides that kill mosquito eggs in standing water, along with public campaigns to get residents to dump standing water where mosquitoes can breed.
This mosquito season, Miami-Dade County officials have said they will only use naled to fight the urban Aedes aegypti if they again have active transmission of Zika. They planned on an aerial spraying May 16 to kill marsh mosquitoes, but said the flight was canceled because of high winds. County spokeswoman Gayle Love said Wednesday she was unable to comment because she had not yet seen the study.
A spokesman for Amvac, the U.S. manufacturer of the pesticide, said the company had no record of selling naled in China so was puzzled by the findings and said the U.S. government has approved its use for mosquito control for five decades.
“We do not sell naled into China and have no idea how it may have been used or how much is applied,” spokesman Brian Maddox said in an email. “We cannot verify the validity of the China study, knowing nothing about the source of the product or how the population was selected. We recommend a measured, science-based reaction to the study, and look forward to its broader evaluation and peer review.”
Silver said it was impossible to determine how the Chinese mothers ended up with naled in their blood, although she suspected it was used on crops or mosquito spraying. The team used cord blood collected between 2008 and 2011 by co-author Betsy Lozoff for another study that looked at iron deficiency and brain development. They found a number of pesticides but focused on five that occurred in traceable levels.
To measure problems, researchers used a standard motor-skill test that looks at reflexes, body control, movement and hand and eye coordination. As exposure to naled increased, they found deficits also rose.
While Zika can have far worse consequences for infected mothers and babies, Silver said the findings show the need to avoid unintended consequences from battling the virus.
“That’s obviously the question of the day, right. Zika is a huge concern,” she said, making it important “to always make sure there’s a focus on integrated pest management and not to just jump straight to spraying a chemical.”
Due to a production error, an earlier version of this story included an outdated quotation from an Amvac spokesman. It also incorrectly named the company.
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