Household pesticides may cause some of the intellectual development problems in children previously associated with lead, an Australian toxicologist says.
In a commentary available online in the journal Science of the Total Environment, Professor Brian Gulson says there is no question lead has a detrimental effect on children’s intellectual development.
But the Macquarie University researcher says several studies have shown similar effects in children exposed to low levels of organophosphate pesticides.
He says the similarity in effects and the overlap in timing of the major use of these pesticides in the community and lead exposure studies could have resulted in confusion.
But his comments have been dismissed as an “interesting idea” that is “not well supported” by the science.
They come as regulatory bodies in the US, Canada and Australia are reviewing guidelines for acceptable levels of lead in the blood.
Gulson, who is contributing to Australia’s National Health and Medical Research Council review, says the US is pushing for to half the current blood lead level of 10 micrograms per decilitre.
He is against the move to 5 micrograms per decilitre saying the technology is not yet available to determine lead’s impact on IQ, or intellectual quotient, at that level.
Also he suggests not all the neurodevelopmental effects can be blamed on lead.
“Many of the lead studies have been undertaken in communities where the subjects may be exposed to rodents and insects [and] the chemicals used to eradicate them,” he writes.
Pesticide use in pregnancy
He points to a 2002 study of female ethnic minorities living in New York City in which 85% said pest control measures were used in their home while they were pregnant.
He says the organophosphate insecticide chlorpyrifos was banned for residential use in the US in 2002.
Yet in a 2007 paper, researchers said they detected residue of the insecticide in all participating New York City homes more than 2 years after the ban.
Gulson says because researchers tracking lead exposure have never asked about pesticides, his concern about their role in damaging intellectual development cannot be dismissed.
He says future lead studies need to include questions about pesticide use in the home, but admits the “horse might have bolted”.
“The current very low blood lead levels compared with the earlier longitudinal studies will limit the possibility to determine respective contributors to neurodevelopmental deficits,” he writes.
Where’s the evidence?
Toxicologist Professor Chris Winder, at the University of New South Wales, says while Gulson’s view is an “interesting idea” he does not support it.
“While some pesticides may affect neurological development, most typically the organophosphates, many household pesticides do not contain them,” says Winder, from the School of Safety Science.
“However, lead is a known neurotoxicant, and its effects on reproduction and neurodevelopment are extensive and very well known.”
Dr Helen Ritchie, of the University of Sydney’s School of Medical Sciences, says the fact there may be co-exposure to lead is plausible.
“But without data on dose or exposure then nothing really can be said,” says Ritchie, who specialises in the chemical causes of birth defects.
“You could equally ask whether the detrimental neurobehavioural effects attributed to lead could be due to any other chemical you might think of.”