1021 Organophosphates and Attention Deficit Hyperactivity Disorder (ADHD)

In May 2010 the South African Department of Agriculture, Forestry and Fisheries published an order banning the use of “household, garden, home and domestic setting” products containing the organophosphate chlorpyrifos as an active ingredient as it presented a risk for ADHD and autism. Classed as a moderately toxic insecticide by the WHO and already removed from most household pesticides by manufacturers, chlorpyrifos has nevertheless remained as a constituent of garden products and pet sprays. Depending on the route and dosage absorbed, symptoms of poisoning may occur acutely or be delayed, and be overt with the full range of signs and symptoms or be more subtle. In terms of the latter an association has been shown between the chlorpyrifos and both mental and developmental indices in a US cohort of children, but research has also focused specifically on the relationship between exposure and subsequent development of ADHD. In a recent study published in Pediatrics, researchers looked at ADHD and urinary levels of organophosphate metabolites (dialkyl phosphates). Cross-sectional data from the 2000-2004 US-based NHANES survey were used, yielding 1139 children, of which 119 had ADHD according to DSM-IV criteria. Higher levels of dialkyl phosphates, particularly DMAP (dimethyl alkyl phosphate) were associated with a greater likelihood of ADHD. For example, a 10-fold increase in DMAP concentration was associated with an odds ratio of 1.55 (95%CI 1.14-2.10). For dimethyl thiophosphate, children with levels higher than the median of detectable concentrations had a two-fold increase in ADHD (adjusted OR 1.93; 95%CI 1.23-3.02). But it is also worth noting that another study, also based on the NHANES population found other relationships with ADHD. That study also found ADHD prevalence rates of roughly the same magnitude (~8.7%) and concluded that while both prenatal tobacco and childhood lead exposure can increase the risk of ADHD, the combination appears to have an odds ratio of 8.1 (95% CI 3.5-18.7). While not suggesting that organophosphate, tobacco or lead controls are inappropriate, clearly more research is needed to establish how three such diverse toxins could have a similar clinical outcome.

Read more:
Pediatrics 2010; 125: e1270-e1277
Pediatrics 2009; 124: e1054-63
Am J Public Health 2010; Mar 18 [Epub ahead of print].