Scientists have noted a potential heightened risk for attention disorders in kids who were exposed to organophosphate pesticides while inside the womb.

The effect was not obvious at the age of 3, but showed up by the age of 5, so said the report from California researchers that appears in the Aug 19 issue of Environmental Health Perspectives.

A professor of environmental medicin at the University of Rochester Medical Center, Bernard Weiss, said the delayed effects did not surprise him.

Studies of monkeys have shown the same thing, with the behavioral problems not coming to fruition until the "brain had become mature enough to support that kind of complex behavior," he explained.

In kids, "you wouldn't really see [hyperactivity] bloom until the child gets into school," he added.

The findings are far from showing a direct causal link. Weiss said that he thought "these are very significant studies and are another form of warning to us about how many kinds of unrecognized threats there are to child development in the environment."

Senior study author Brenda Eskenazi said that the past five or seven years have seen more studies looking into low-dose organophosphate exposure in children's neurodevelopment. Before this, researchers only had focused on high-dose exposure.

Including this study, three studies have found effects of low-dose exposure on neurodevelopment, including one earlier this year that found exposure to high levels of organophosphate pesticides raise the chances of developing attention-deficit/hyperactivity disorder (ADHD).

The current data was based on attention tests given to more than 300 child subjects of Mexican-American farm workers in the Salinas Valley of California. The researchers also took measures of organophosphate metabolites in the mother's urine and collected behavioral reports from the mothers and from professional observers.

Though there is only a small link between attention problems and exposure at the younger age, the association became significantly larger at age 5, especially among males.

"We saw that the children were making more errors on the test and that it was significantly related to the mother's prenatal metabolite levels for these pesticides," said Eskenazi, who is director of the Center for Children's Environmental Health Research at the University of California Berkeley School of Public Health.

It is worth noting that these children had more exposure than the “average” child.

And "attention problems are so multifactorial that it would be hard to say that this is a major agent if it is causal at all," she added.

A second paper by the same group of researchers that appears in the same journal reported that "children don't have the level of an enzyme needed to metabolize these organophosphates the same as adults until they're much older than we expected," said Eskenazi. "Their metabolism is different, and now we have hard evidence of that."

There is also “suggestive evidence” that kids may harbor genetic alterations that make them more vulnerable to the neurocognitive effects of pesticide exposure.

"If research consistently shows that symptoms of ADHD are related to the quantity of the organophosphate pesticide exposure, then it seems prudent for families to at least try to limit exposure," said Dr. Nakia Scott, a clinical assistant professor of psychiatry and behavioral science at Texas A&M Health Science Center College of Medicine and a child psychiatrist with Lone Star Circle of Care.

There are things people can do to protect themselves.

"You can wash produce thoroughly before you eat and try to invest in organic produce when you can," she added. "This may [also] be a reason to grow your own garden. Or families can consider using less toxic alternatives when taking care of lawns."