Pesticides tied to ADHD in children in U.S. study
(Reuters) - Children exposed to pesticides known as organophosphates could have a higher risk of attention-deficit/hyperactivity disorder (ADHD), according to a U.S. study that urges parents to always wash produce thoroughly.
Researchers tracked the pesticides' breakdown products in children' urine and found those with high levels were almost twice as likely to develop ADHD as those with undetectable levels.
The findings are based on data from the general U.S. population, meaning that exposure to the pesticides could be harmful even at levels commonly found in children's environment.
"There is growing concern that these pesticides may be related to ADHD," said researcher Marc Weisskopf of the Harvard School of Public Health, who worked on the study.
"What this paper specifically highlights is that this may be true even at low concentrations."
Organophosphates were originally developed for chemical warfare, and they are known to be toxic to the nervous system.
There are about 40 organophosphate pesticides such as malathion registered in the United States, the researchers wrote in the journal Pediatrics.
Weisskopf said the compounds have been linked to behavioral symptoms common to ADHD -- for instance, impulsivity and attention problems -- but exactly how is not fully understood.
Although the researchers had no way to determine the source of the breakdown products they found, Weisskopf said the most likely culprits were pesticides and insecticides used on produce and indoors.
Garry Hamlin of Dow AgroSciences, which manufactures an organophosphate known as chlorpyrifos, said he had not had time to read the report closely.
But, he added" "the results reported in the paper don't establish any association specific to our product chlorpyrifos."
Weisskopf and colleagues' sample included 1,139 children between 8 and 15 years. They interviewed the children's mothers, or another caretaker, and found that about one in 10 met the criteria for ADHD, which jibes with estimates for the general population.
After accounting for factors such as gender, age and race, they found the odds of having ADHD rose with the level of pesticide breakdown products.
For a 10-fold increase in one class of those compounds, the odds of ADHD increased by more than half. And for the most common breakdown product, called dimethyl triophosphate, the odds of ADHD almost doubled in kids with above-average levels compared to those without detectable levels.
"That's a very strong association that, if true, is of very serious concern," said Weisskopf. "These are widely used pesticides."
He emphasized that more studies are needed, especially following exposure levels over time, before contemplating a ban on the pesticides. Still, he urged parents to be aware of what insecticides they were using around the house and to wash produce.
"A good washing of fruits and vegetables before one eats them would definitely help a lot," he said.
(Reporting by Reuters Health, Editing by Belinda Goldsmith)
Published online May 17, 2010
Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides
Maryse F. Bouchard, PhDa,b, David C. Bellinger, PhDa,c, Robert O. Wright, MD, MPHa,d,e, Marc G. Weisskopf, PhDa,e,f
Departments of Environmental Health and Epidemiology, School of Public Health, Harvard University, Boston, Massachusetts;
bDepartment of Environmental and Occupational Health, Faculty of Medicine, University of Montreal, Montreal, Quebec, Canada;
Departments of cNeurology and
dPediatrics, School of Medicine, Harvard University, and Boston Children's Hospital, Boston, Massachusetts; and
eChanning Laboratory, Department of Medicine, School of Medicine, Harvard University, and Brigham and Women's Hospital, Boston, Massachusetts
Objective The goal was to examine the association between urinary concentrations of dialkyl phosphate metabolites of organophosphates and attention-deficit/hyperactivity disorder (ADHD) in children 8 to 15 years of age.
Methods Cross-sectional data from the National Health and Nutrition Examination Survey (2000--2004) were available for 1139 children, who were representative of the general US population. A structured interview with a parent was used to ascertain ADHD diagnostic status, on the basis of slightly modified criteria from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition.
Results One hundred nineteen children met the diagnostic criteria for ADHD. Children with higher urinary dialkyl phosphate concentrations, especially dimethyl alkylphosphate (DMAP) concentrations, were more likely to be diagnosed as having ADHD. A 10-fold increase in DMAP concentration was associated with an odds ratio of 1.55 (95% confidence interval: 1.14--2.10), with adjustment for gender, age, race/ethnicity, poverty/income ratio, fasting duration, and urinary creatinine concentration. For the most-commonly detected DMAP metabolite, dimethyl thiophosphate, children with levels higher than the median of detectable concentrations had twice the odds of ADHD (adjusted odds ratio: 1.93 [95% confidence interval: 1.23--3.02]), compared with children with undetectable levels.
Conclusions These findings support the hypothesis that organophosphate exposure, at levels common among US children, may contribute to ADHD prevalence. Prospective studies are needed to establish whether this association is causal.
Key Words: attention-deficit/hyperactivity disorder . pesticides . organophosphates . National Health and Nutrition Examination Survey
Abbreviations: DAP = dialkyl phosphate . DMAP = dimethyl alkylphosphate . DEAP = diethyl alkylphosphate . OR = odds ratio . CI = confidence interval . ADHD = attention-deficit/hyperactivity disorder . NHANES = National Health and Nutrition Examination Survey . DISC-IV = Diagnostic Interview Schedule for Children IV . PIR = poverty/income ratio . DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition
Accepted Feb 23, 2010.
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