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Pyrethroid pesticide exposure is now attributed to hyperactivity and impulsivity in boys.

Common pesticide linked to ADHD — in boys

A new study links a commonly used household pesticide to attention deficit hyperactivity disorder (ADHD) in children and young teens — but strongest in boys.

The study found an association between pyrethroid pesticide exposure and ADHD, particularly in terms of hyperactivity and impulsivity, rather than inattentiveness. The association was stronger in boys than in girls.

The study, led by researchers at Cincinnati Children's Hospital Medical Center, is published online in the journal Environmental Health.

"Given the growing use of pyrethroid pesticides and the perception that they represent a safe alternative to managing insect pests, our findings may be of considerable public health importance," says Tanya Froehlich, MD, a developmental pediatrician at Cincinnati Children's and the study's corresponding author.

Due to concerns about adverse health consequences, the United States Environmental Protection Agency banned the two most commonly used organophosphate (organic compounds containing phosphorus) pesticides from residential use in 2000-2001. The ban led to the increased use of pyrethroid pesticides, which are now the most commonly used pesticides for residential pest control and public health purposes. They also are used increasingly in agriculture.

Pyrethroids have been considered a safer choice because they are not as acutely toxic as the banned organophosphates.

Animal studies, on the other hand, suggest a heightened vulnerability to the effects of pyrethroid exposure on hyperactivity, impulsivity and abnormalities in the dopamine system in male mice. Dopamine is a neurochemical in the brain thought to be involved in many activities, including those that govern ADHD.

Researchers studied data on 687 children between the ages of 8 and 15. The data came from the 2000-2001 National Health and Nutrition Examination Survey (NHANES), a nationally representative sample of the United States population designed to collect information about health.

The 2000-2001 cycle of NHANES was the only one in the study that included a diagnostic interview of children's ADHD symptoms and pyrethroid pesticide biomarkers. Pesticide exposures were collected in a random sample of the urine of half the 8-11 year olds and a third of the 12-15 year olds.

ADHD was determined by criteria on the Diagnosic Interview Schedule for Children [DISC], a diagnostic instrument assessesing 34 common psychiatric diagnoses of children and adolescents, by caregiver report or by a prior diagnosis.

Boys with detectable urinary 3-PBA, a biomarker of exposure to pyrethroids, were three times as likely to have ADHD compared with boys without detectable 3-PBA. Hyperactivity and impulsivity increased by 50 percent with every 10-fold increase in 3-PBA levels in boys. Biomarkers were not associated with increased odds of ADHD diagnosis or symptoms in girls.

However, Dr. Froehlich adds: "Our study assessed pyrethroid exposure using 3-PBA concentrations in one urine sample. Given that pyrethroids are non-persistent and rapidly metabolized, 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."

Abstract
Background Pyrethroid pesticides cause abnormalities in the dopamine system and produce an ADHD phenotype in animal models, with effects accentuated in males versus females. However, data regarding behavioral effects of pyrethroid exposure in children is limited. We examined the association between pyrethroid pesticide exposure and ADHD in a nationally representative sample of US children, and tested whether this association differs by sex. Methods Data are from 8–15 year old participants (N = 687) in the 2001–2002 National Health and Nutrition Examination Survey. Exposure was assessed using concurrent urinary levels of the pyrethroid metabolite 3-phenoxybenzoic acid (3-PBA). ADHD was defined by either meeting Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition criteria on the Diagnostic Interview Schedule for Children (DISC) or caregiver report of a prior diagnosis. ADHD symptom counts were determined via the DISC. Multivariable logistic regression examined the link between pyrethroid exposure and ADHD, and poisson regression investigated the link between exposure and ADHD symptom counts. Results Children with urinary 3-PBA above the limit of detection (LOD) were twice as likely to have ADHD compared with those below the LOD (adjusted odds ratio [aOR] 2.42; 95 % confidence interval [CI] 1.06, 5.57). Hyperactive-impulsive symptoms increased by 50 % for every 10-fold increase in 3-PBA levels (adjusted count ratio 1.50; 95 % CI 1.03, 2.19); effects on inattention were not significant. We observed possible sex-specific effects: pyrethroid biomarkers were associated with increased odds of an ADHD diagnosis and number of ADHD symptoms for boys but not girls. Conclusions We found an association between increasing pyrethroid pesticide exposure and ADHD which may be stronger for hyperactive-impulsive symptoms compared to inattention and in boys compared to girls. Given the growing use of pyrethroid pesticides, these results may be of considerable public health import.

This study was supported by National Institute of Health grants R01ES015991, R01ES015991-04S1, P30ES005022, K23 MH083881, K24 MH064478, R00 ES020346, and R01ES015517-01A1.

About Cincinnati Children's
Cincinnati Children's Hospital Medical Center ranks third in the nation among all Honor Roll hospitals in U.S.News and World Report's 2014 Best Children's Hospitals. It is also ranked in the top 10 for all 10 pediatric specialties. Cincinnati Children's, a non-profit organization, is one of the top three recipients of pediatric research grants from the National Institutes of Health, and a research and teaching affiliate of the University of Cincinnati College of Medicine. The medical center is internationally recognized for improving child health and transforming delivery of care through fully integrated, globally recognized research, education and innovation. Additional information can be found at http://www.cincinnatichildrens.org. Connect on the Cincinnati Children's blog, via Facebook and on Twitter.

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