Updated

Pregnant women exposed to the pesticide chlorpyrifos may be putting their kids at risk for potentially irreversible brain changes linked to lower intelligence, according to a study published Monday.

A team of US researchers used MRIs to look at the brains of 20 New York City children, ages five to 11, whose mothers tested highest for levels of chlorpyrifos during a previous study.

The researchers found "significant abnormalities" in the brain structure of those kids compared to 20 children whose mothers showed lower exposures.

Some of those abnormalities were associated with lower IQ scores and working memory shortfalls.

Additionally, the kids exposed to higher levels of the chemical did not exhibit the expected male/female differences in their brains, which could affect their development.

The study shows that "the prenatal period is a vulnerable time for the developing child," said lead author, Virginia Rauh, of Columbia University, adding that "toxic exposure during this critical period can have far-reaching effects on brain development and behavioral functioning."

The mothers in the study had been exposed to the pesticide before a 2001 ban on its household use in the US.

However, chlorpyrifos is still used throughout the country in farms, wood treatments, and public spaces such as some golf courses, parks and highway medians.

People can be exposed by inhaling the chemical from those sources and, to a lesser extent, by eating fruits and vegetables that have been sprayed.

The paper was published online Monday in the Proceedings of the National Academy of Sciences. Further study is likely needed to determine the long-term effects of the kids' brain changes.