A chemical used in the fight against Zika virus and a controversial insecticide used across the United States are associated with reduced motor function in Chinese infants according to a new study by the University of Michigan.

Researchers investigated how prenatal exposure to two organophosphate insecticides, naled and chlorpyrifos, affects infant motor skill development. The study, conducted in China, found exposure to the chemical naled via their mothers during pregnancy was associated with 3-4 percent lower fine motor skills scores at age 9 months for those in the top 25 percent of naled exposure, compared to those in the lowest 25 percent of exposure. Infants exposed to chlorpyrifos scored 2-7 percent lower on a range of key gross and fine motor skills. Girls appeared to be more sensitive to the negative effects of the chemicals than boys, according to the research team.

“Motor delays in infancy may be predictive of developmental problems later in childhood,” said first author Monica Silver, graduate student research assistant and research fellow in the School of Public Health Department of Environmental Health Sciences. “The findings may help inform policy as the debate over use of these chemicals continues.”

Naled is one of several chemicals in use by southern states to combat mosquitoes carrying the Zika virus. There is insufficient research into how it affects humans up until this point.

Chlorpyrifos, however, is the subject of a growing body of scientific research going back decades. The chemical gained widespread notoriety after a team of Columbia University scientists discovered that it was capable of causing brain damage in rat test subjects. It is still one of the most commonly used organophosphate insecticides in the United States. Although that has been slowly changing.

Chlorpyrifos Banned by the EPA?

In 2000, the Environmental Protection Agency banned homeowner use of chlorpyrifos in light of research indicating the threat it posed to adults and children. The EPA action also discontinued use of the chemical on tomatoes. Use on apples was restricted to pre-bloom and dormant application. Other minor alterations were made to grape tolerances.

In 2002, the EPA restricted chlorpyrifos use on citrus and tree nuts as well as other food crops.

Finally in 2012, the EPA significantly limited the rate at which farms were allowed to apply the chemical and created “no-spray” buffer zones around public spaces and residential areas.

Under President Obama, the EPA moved to fully ban the chemical in the United States on the basis of decades of research into the serious danger it posed. Before the rule took place, the new administration revoked the ban therefore allowing continued use despite widespread outcry from the scientific community. A California farm recently experienced a public health incident when dozens of farm workers were exposed to unsafe levels of the insecticide resulting in serious injuries.

Risk and Reward of Combatting Pests

Insecticides are a necessary and important aspect of modern farming. The question remains where do we draw the line? How toxic is too toxic? Science allows for a framework of safety and usage, but can often lag behind the decision to apply or distribute these chemicals to address issues such as Zika or year-to-year integrated pest management programs.

“Zika is a very serious public health threat. This information helps to highlight that the way we go about combating Zika and other vector-borne diseases needs to be thought out more completely in order to minimize other unintended consequences,” said John Meeker, U-M professor of environmental health sciences and senior author.

“For example, a focus on a more holistic integrated pest management approach may allow for the same or even improved effectiveness in reducing disease while using smaller amounts of these potentially harmful chemicals.”

The study, “Prenatal naled and chlorpyrifos exposure is associated with deficits in infant motor function in a cohort of Chinese infants,” is published in the journal, Environment International.