In an article entitled “Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides,” researchers conclude that “…organophosphate [pesticide] exposure, at levels common among US children, may contribute to ADHD prevalence.” (Maryse F. Bouchard, David C. Bellinger, Robert O. Wright and Marc G. Weisskopf in Pediatrics, Official Journal of the American Academy of Pediatrics, published online May 17, 2010.)
Organophosphate pesticides are in very wide use in the USA in agricultural and residential settings. Children could be exposed to these pesticides through food products and pesticide use in their homes, schools, or even in parks or other recreational areas.
Although studies have been performed to explore the potential adverse effects of organophosphate pesticides on neurodevelopment, manifesting in behavioral problems and lower cognitive functioning, these previous studies have focused on populations with comparatively high levels of exposure. What is new about this study is that it focuses on the adverse effects of normal levels of exposure.
The researchers had access to a very large sample of children (1139 in total), but the questionable approach calls the conclusion into question:
- Exposure was determined by sampling the metabolites of organophosphates in a single one-time urine sample obtained from each study participant.
- The ADHD diagnosis was based exclusively on a phone interview with a parent or caretaker who responded to a questionnaire assessing the presence of hyperactivity, impulsivity, or inattention.
- The children or teens were not examined by a clinician for the presence of a diagnosis nor was an advanced differential diagnosis performed. In other words, the children may have suffered from a variety of mental health problems that were not excluded.
ADHD can be very difficult to diagnose even when both parents and the child are examined in person, the child undergoes a lengthy psychiatric examination, and extensive diagnostic questionnaires from parents and teachers are available.
The DSM IV concept of ADHD diagnosis requires, in addition to meeting a list of criteria, that “The symptoms do not occur exclusively during the course of a pervasive developmental disorder, schizophrenia, or other psychotic disorder and are not better accounted for by another mental disorder (e.g., mood disorder, anxiety disorder, dissociative disorder, or personality disorder).” This “rule out” had not been done by the researchers, which renders their diagnostic impression speculative.
Given the questionable nature of the study, concluding that ADHD is an environmental issue is premature. As the authors of this study point out, more studies are needed to establish whether the association of organophosphate pesticides with ADHD is “causal.” Until then, parents would be premature to stop giving their child fruits and vegetables. Limiting exposure to all pesticides, however, is good practice. Rinsing fresh fruit and vegetables and limiting the use of pesticides in and around the home can help contribute to a healthier household.