As of 2006, according to the Centers for Disease Control and Prevention, 4.5 million children in the United States between the ages of 5 and 17 have attention deficit hyperactivity disorder. A behavioral disorder, ADHD affects children’s attention, activity level and impulse control, which can affect their school performance, interpersonal relationships and mental health. The CDC notes that three to seven percent of school-aged children have the disorder, though the prevalence does differ by gender: 9.5 percent of boys in that age group have ADHD, compared to 5.9 percent of girls.
The causes of ADHD are still being investigated, though the disorder can result from a combination of factors, such as genetics and environment. For example, the Mayo Clinic’s website notes that prenatal exposure to polychlorinated biphenyls (PCBs), a type of environmental poison, increases the child’s risk of ADHD. Another possible cause of ADHD is organophosphate exposure, as indicated by a new study published in the journal Pediatrics.
According to the National Pesticide Information Center, run by Oregon State University in cooperation with the U.S. Environmental Protection Agency (EPA), organophosphate insecticides are the most widely used type. Organophosphates are used in a variety of settings, including homes, veterinary offices and farms, but carry the risk of acute and subacute toxicity. When a person is exposed to an organophosphate, the organophosphate interferes with the acetylcholinesterase enzyme (AChE), causing excess acetylcholine (ACh). The accumulation of ACh causes behavioral changes, respiratory depression and coordination problems when it affects the central nervous system (CNS).
However, people can be exposed to organophosphates just by ingesting contaminated food and water. Bouchard et al. point out that children become exposed to organophosphates predominantly through their diet, and are “at greatest risk for organophosphate toxicity, because the developing brain is more susceptible to neurotoxicants and the dose of pesticides per body weight is likely to be larger for children.” The United States Department of Agriculture notes that certain commercially produced fruits and vegetables detectable amounts of organophosphates.
Link Between ADHD and Organophosphates
Organophosphate exposure in children has been linked to multiple problems, though the type varies depending on the time of exposure. Bouchard et al. notes that “prenatal organophosphate exposure was associated with increased risk of pervasive developmental disorders, as well as delays in mental development at 2 to 3 years of age,” while “postnatal organophosphate exposure has been associated with behavioral problems, poorer short-term memory and motor skills, and longer reaction times in children.”
But organophosphate exposure also may cause ADHD. In the study, the authors used data from 1,139 children, gathered from the National Health and Nutrition Examination Survey, which was conducted between 2000 and 2004. As part of the study, the researchers used diakyl phosphate (DAP) metabolites, which are the markers of organophosphate exposure. Urine samples were taken during the National Health and Nutrition Examination Survey. Certain children, including those with low birth weights and those who received care in an ICU or in a premature nursery after birth, were excluded from the study due to the high risks of developmental disorders. The Diagnostic Interview Schedule for Children IV (DISC-IV), which uses modified criteria from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), was used to test for ADHD). The DISC-IV identified 119 children with ADHD, though another 30 children in the study who did not meet the diagnostic criteria were taking medication for the disorder. As a result, ADHD was defined in this study as based on matching the criteria from the DISC-IV or having taken an ADHD medication for the past year.
The participants were more likely to fulfill the DISC-IV criteria for ADHD when they had higher urinary concentrations of total DAP metabolites. The type of DAP metabolites found did have some relation with the subtype of ADHD. For example, the authors said that “the odds of meeting the diagnostic criteria for hyperactive/impulsive ADHD subtype increased significantly with higher DEAP,” or diethyl alkylphosphate, a type of DAP metabolite. They also found that higher concentrations of another DAP metabolite, dimethyl alkylphosphate (DMAP), with children with the inattentive subtype of ADHD, though it was not statistically significant.
Longer-term testing would provide a better assessment of the role of organophosphates in ADHD onset. Nevertheless, further testing on organophosphates and other types of exposures may help pinpoint both what causes ADHD and potential means of preventing it.
Organophosphate Insecticides (PDF file)