Exposure to common household pesticides has now been associated with attention deficit hyperactivity disorder in children and young teens, with the association between the two being stronger in boys than in girls.

In a new study led by researchers at Cincinnati Children's Hospital Medical Center, researchers found an association between exposure to pyrethroid pesticides and hyperactive impulsivity.

Pyrethroid pesticides are commonly found in over 3,500 registered products, according to the Environmental Protection Agency (EPA). The rise in the use of these pesticides was originally brought about by the ban on organophosphate pesticides in 2000-2001 because of the level of toxicity they presented to birds and mammals compared to pyrethroids.

However, other animal studies have shown that pyrethroid exposure increased the vulnerability of mice, in particular males, to hyperactivity, impulsiveness and abnormalities in the dopamine system. Dopamine is a neurochemical that is involved in many activities of the brain, including those that govern ADHD.

For the new study, researchers studied a national representative sample of 687 participants, from ages 8 to 15. The data was taken from the 2000-2001 National Health and Nutrition Examination Survey and included a diagnostic review of children's ADHD symptoms and pyrethroid pesticide biomarkers, using the levels of the pyrethroid metabolite 3-phenoxybenzoic acid (3-PBA) found in the children's urine samples.

ADHD identification was defined by either meeting the Diagnostic Interview Schedule for Children (DISC) criteria, which assesses 34 common psychiatric diagnoses of children and adolescents, or caregiver report of a prior diagnosis.

"Our study assessed pyrethroid exposure using 3-PBA concentrations in a single urine sample," says Dr. Tanya Froehlich, a developmental pediatrician at Cincinnati Children's and one of the study's coauthors.

The study found that boys with detectable urinary 3-PBA were three times more likely to have ADHD compared to those without the detectable 3-PBA. Also, for every 10-fold increase in these levels in boys, impulsivity increased by 50 percent. These increased odds of ADHD diagnosis, however, were not found in girls.

Researchers admit that data regarding behavioral effects from pyrethroid exposure is limited. Dr. Froehlich suggested that "measurements over time would provide a more accurate assessment of typical exposure and are recommended in future studies before we can say definitively whether our results have public health ramifications."

However, Dr. Froehlich emphasized that the proliferation of pyrethroid pesticides should now be viewed with caution.

"Given the growing use of pyrethroid pesticides and the perception that they may represent a safe alternative, our findings may be of considerable public health importance."