A chemical currently being used to ward off mosquitoes carrying the Zika virus and a commonly used insecticide that was threatened with a ban in the United States have been associated with reduced motor function in Chinese infants, a University of Michigan study found.

Researchers at the U-M School of Public Health and U-M Center for Human Growth and Development tested children in China and 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.

Naled is one of the chemicals being used in several U.S. states to combat the mosquito that transmits Zika. Chlorpyrifos, around since the 1960s, is used on vegetables, fruit and other crops to control pests.

Both are insecticides called organophosphates, a class of chemicals that includes nerve agents like sarin gas. They inhibit an enzyme involved in the nerve signaling process, paralyzing insects and triggering respiratory failure. However, they may adversely impact health through other mechanisms at lower exposure levels that are commonly encountered in the environment.

In the children studied, naled affected fine motor skills or the small movements of hands, fingers, face, mouth and feet. Chlorpyrifos was associated with lower scores for both gross (large movements of arms and legs) and fine motor skills.