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Researchers find tentative link between pesticide use and ADHD

6.4 million children in the U.S. are diagnosed with Attention Deficit Hyperactivity Disorder, according to the Centers for Disease Control and Prevention.

Pesticides may be the cause of this disorder in children, according to research done by Jason Richardson, an associate professor in the Robert Wood Johnson Medical School.

Richardson conducted a study analyzing the effects of exposure to common pesticides on pregnant mothers and their children in both animal and human models. A specific group of pesticides, known as pyrethroid pesticides, were analyzed in the study.

“If you go into your grocery store, (or) Home Depot or something like that and get some bug spray, there’s (a 90 percent chance) it contains pyrethroid pesticides,” he said.

ADHD is a biological disorder that impacts a person's ability to focus and pay attention, said Kathy Loder-Murphy, a coordinator in the Office of Disability Services.

There are different types of ADHD, she said. Victims have issues with both hyperactivity and paying attention. The hyperactivity component differentiates people with ADHD from those with attention deficit disorder, she said. 

A person with ADHD would have difficulty sitting still, and other factors would further complicate their ability to focus, she said.

“If you have trouble just paying attention, it’s hard to handle any noise around you,” she said. “Even typing on a computer (can distract a patient).”

Certain tasks that unaffected students might find normal, such as writing notes while listening to a lecturer, are difficult for students with ADHD, Loder-Murphy said. Verbal lectures with few graphics or slides would be especially difficult for a student to learn from.

In the study, mice were used as animal models to determine if a link could exist between pesticides and ADHD, Richardson said.

“What we found was that if we gave pregnant mice fairly low levels of this pyrethroid pesticide, and we looked at her offspring, we found that their behavior was similar (to children diagnosed with ADHD),” he said.

Male mice offspring were more affected than female mice were, he said.

Because these mice were exposed while still in the womb, the effects of the pesticides persisted through their lives, he said.

This study was a preliminary one and the results presented are initial findings, said Brian Buckley, the executive director of Laboratories in the Environmental and Occupational Health Sciences Institute. 

The effects of pesticides in mice were analyzed, he said. The location of the pesticides within the animals were determined, as well as why the pesticides migrated to those tissues or areas of the brain.

One of the things to establish is mechanistic plausibility, he said. Looking at the effects in an animal or cell culture model can help determine what sort of effect can be expected in human children.

This can be estimated by determining the biochemical and physiological changes, he said. This helps the research team figure out what symptoms might show in humans.

“Obviously we can’t give little kids pesticides and say, ‘here, let’s see if you have ADHD later on’,” he said.

Previous studies have shown that pesticides may reside in a home environment long after they were expected to dissipate, he said. In a person’s room, this would mean residue would appear in soft, cloth-based items.

Bed sheets, pillowcases, plush toys or items with foam attract particles from pesticides, he said. Particles stay in the environment beyond their planned decomposition time, he said.

Typically, pesticides are expected to decompose three hours after they are used, he said.

Because the particles were relatively large, only specific groups were in danger from this, Richardson said.

“For most of us, it’s not really a problem, (because) we metabolize these pyrethroids really well,” he said. “The concerns are pregnant women, children and those who don’t metabolize (them) very well.”

Only objects out in the open where a pesticide might be used were analyzed, Buckley said. Dishes stored in cabinets or anything covered were not looked at in the study.

Inhaling pesticides was likewise not looked at in the study, but other means of transmission were, he said.

Pesticides migrated up walls and corners after being applied on cracks, he said. Children might not lick a wall, but it is likely they would touch it and then put their hands in their mouths.

There are ways to live with ADHD, Loder-Murphy said. These range from performing certain tasks to help concentrate to taking specific medications.

Simply sitting in a more quiet location in a classroom would help someone focus, she said. Some students may also use a timer on their phone to force them to refocus if they get distracted.

Exercise seemed to help some of the affected mice, Richardson said. Increased physical activity caused some changes in the brain. This may also help people affected by the disorder.

Presently, up to 40 percent of patients may not respond to medication, he said.

“As individual as a person is, it impacts them differently,” she said. “People who suffer from ADHD are compromised. It really impacts (those who suffer from it) every day.”

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