The chink in this superfood's armor is due to traces of a type of widely-used commercial pesticide called organophosphate. A recent study in the journal Pediatrics found that children with higher residue levels of organophosphates were about twice as likely to have ADHD.
Organophosphates are found on a variety of conventionally-grown fruits and vegetables, but some produce contain more residue than others. Traces of organophosphates were detected on 28% of non-organic frozen blueberries, according to the U.S. Pesticide Data Program's 2008 Annual Summary report.
Shop for organic blueberries, fresh or frozen, instead. Or wash conventionally-grown berries before eating - this will reduce but not completely eliminate pesticide residue.