Pyrethroid pesticide use may be encouraging expression of an ADHD phenotype, according to researchers from the Cincinnati Children’s Hospital in collaboration with researchers from Rutgers, University of Rochester, Brown University, and Simon Fraser University.1 [pdf] To follow-up on murine and rodent studies that showed a correlation between pyrethroid exposure and ADHD symptoms that were especially pronounced in males, the researchers assessed exposure and ADHD symptomatology in a random sample of 687 US children, age 8 to 15 years.
These children were participants in the 2001-2002 National Health and Nutrition Examination Survey (NHANES), which was the only NHANES cycle that included a structured diagnostic interview regarding ADHD, pyrethroid pesticide biomarkers, and covariates (eg, sex, household income, age, race/ethnicity, health insurance status, prenatal tobacco exposure, blood lead level, and urinary organophosphate pesticide metabolite level).
Exposure was assessed by measuring concurrent urinary levels of the pyrethroid metabolite 3phenoxybenzoic acid (3PBA). An ADHD diagnosis was defined as either meeting DSM-IV criteria via the Diagnostic Interview Schedule for Children or a caregiver report of a past diagnosis. Multivariable logistic regression examined the link between pyrethroid exposure and ADHD, and poisson regression investigated the link between exposure and ADHD symptom counts.
In all, 15% of the study population met criteria for an ADHD diagnosis. Urinary 3-PBA levels were detected in 79% of the study participants (mean, 1.14 μg/L), with the means for the 10th, 50th, and 90th percentiles being 0.07, 0.29, and 1.94 μg/L, respectively.
After adjusting for covariates, the researchers discovered that children with detectable urinary 3PBA were twice as likely to have ADHD as those in whom 3PBA was undetected. Higher 3-PBA levels also were associated with an increasing number of hyperactive/impulsive symptoms. In fact, hyperactive/impulsive symptom counts were 77 % higher in children with detectable 3-PBA levels than in children with nondetectable levels. Whereas effect on inattentiveness was insignificant, hyperactive/impulsive symptoms increased by 50 % for every 10-fold increase in 3PBA level measured. This effect was also sex-specific.
Boys most at risk
In correlation with animal studies, boys were far more affected than girls. Boys with detectable urinary 3-PBA were nearly 3 times more likely to have ADHD than boys in whom urinary 3-PBA was undetectable. Further, a 10-fold increase in urinary 3-PBA level was associated with a 43% increased prevalence of ADHD whereas this pattern was not seen in girls.
Pyrethroid pesticides, such the insecticide permethrin, have been thought to be safer than organophosphates, which were banned for residential use by the US Environmental Protection Agency in 2000-2001. Pyrethroid pesticides are now the most commonly used pesticides for residential use and are increasingly being used in agriculture as well. Although additional investigation is warranted, given the findings of this study, residential and personal use of pyrethroid pesticides should be reconsidered. Clinicians serving the pediatric as well as obstetric care populations may want to inform patients and their caretakers of the health risks of pyrethroid-based pesticide/insecticide use in relation to ADHD symptomatology.
1. Wagner-Schuman M , Richardson JR , Auinger P, et al. Association of pyrethroid pesticide exposure with attentiondeficit/hyperactivity disorder in a nationally representative sample of U.S. children. Environ Health. 2015;14(1):44. http://www.ehjournal.net/content/pdf/s12940-015-0030-y.pdf