If he's spraying near the house, he might tell the kids to say inside until the job is done. "By doing all this, it's a safe product," he says. "It's doing it's job and it's doing it well."

Fruit and vegetable farmers use this chemical on citrus trees, strawberries, broccoli and cauliflower. This can leave residues on those foods in the supermarket. Several environmental advocacy groups have gone to court to force the EPA to ban the use of chlorpyrifos by farmers because of the risks that the chemical poses to consumers and to people who live near fields where it's used.

"Based on the harm that this pesticide causes, the EPA cannot, consistent with the law, allow it in our food," says Patti Goldman, an attorney with the environmental advocacy group Earthjustice.

More than a decade ago, the EPA banned the spraying of chlorpyrifos indoors to get rid of household bugs.

At that time, though, the EPA thought that use on the farm posed little risk. The agency was relying on scientific studies that directly measured the immediate effect of chlorpyrifos on the nervous system. Residues on food weren't nearly enough to keep nerves from working normally.

But then new evidence surfaced. Jim Jones, who was assistant administrator of the EPA and responsible for pesticide regulation before he left the agency in January, says the new evidence came from studies in which scientists followed hundreds of mothers and their newborn children, monitoring their exposure to lots of chemicals. One of these studies, by researchers at Columbia University, measured the levels of chlorpyrifos in blood taken from umbilical cords when babies were born.

While the study was going on, the ban on indoor uses of chlorpyrifos came into effect. So over the course of those years, scientists were able to gather data on children who had been exposed to very different levels of the pesticide.

They found that exposure to chlorpyrifos caused small but measurable differences in brain function. At age 7, the average IQ of children who had been exposed to high levels of chlorpyrifos was a few percentage points lower than children who hadn't been exposed to much of the chemical at all. Other studies showed that some people are much more vulnerable to chlorpyrifos because of their genetic makeup.