Pesticide exposure implicated in ADHD development

Children with higher urinary concentrations of dimethyl thiophospate, a marker indicative of pesticide exposure, were twice as likely to have attention-deficit/hyperactivity disorder, according to recent study results.

Researchers from several U.S. and Canadian institutions assessed data gathered from 2000 to 2004 as part of the National Health and Nutrition Examination Survey to evaluate a potential correlation between dimethyl-containing organophosphate pesticide exposure and ADHD development. The researchers used the Diagnostic Interview Schedule for Children IV to determine a diagnosis of ADHD, and spot urine samples were collected during physical examinations.

One hundred nineteen children aged 8 to 15 years met inclusion criteria, 7.6% of whom had inattentive subtype of ADHD; 1.5%, hyperactive/impulsive subtype; and 3%, combined subtype.

Results indicated that children with higher urinary dialkyl phosphate concentrations — especially those with high concentrations of dimethyl alkylphosphate — were more likely to have ADHD.

The researchers noted that a 10-fold increase in dialkyl phosphate concentration was associated with an adjusted OR of 1.21 (95% CI, 0.97-1.51), and a 10-fold increase in dimethyl alkylphosphate concentration correlated with an adjusted OR of 1.55 (95% CI, 1.14-2.10).

Data also showed that dimethyl thiophosphate was the most commonly detected dimethyl alkylphosphate metabolite, and the odds of having ADHD increased twofold in children with levels higher than the median detectable concentrations when compared with children who had undetectable levels (OR=1.93).

“Developmental exposure to organophosphates might have persistent effects on multiple neural systems that may underlie ADHD behaviors, such as inattention and cognitive deficits, similar to the effects of developmental nicotine exposure,” the researchers wrote.

The odds of having hyperactive/impulsive ADHD subtype increased with higher detectable urinary concentrations of diethyl alkylphosphate, dimethyl alkylphosphate and total dialkyl phosphate, according to the researchers. Although the odds of having inattentive subtype grew when higher concentrations of dimethyl alkylphosphate metabolites were detected, these results were not significant.

“The present study adds to the accumulating evidence linking higher levels of pesticide exposure to adverse developmental outcomes,” the researchers wrote. “Our findings support the hypothesis that current levels of organophosphate pesticide exposure might contribute to the childhood burden of ADHD.” – by Melissa Foster

Bouchard MF. Pediatrics. 2010;125:e1270-e1277.

This is an intriguing study showing an association between organophosphates and symptoms of inattention in children, suggesting a possible effect of pesticide exposure on cognition and learning. The effect on hyperactivity and impulsivity is weaker or absent. The findings merit further investigation and replication. Similarly, the biological effects of organophosphates on the dopaminergic systems in the brain must be considered.

This investigation is a reminder of the connections made between lead exposure and learning — the treatments and regulations that ensued and may give strength to those arguing for stricter control of pesticide use.

– Paul H. Lipkin, MD
Infectious Diseases in Children Editorial Board

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