A CLUTCH of new research indicating that exposure to organophosphate pesticides during pregnancy may affect the intelligence of children will tighten the screws on an already closely-scrutinised class of chemical.
Three new studies out of the US argue there is a relationship between a pregnant mother's exposure to organophosphates and the cognitive abilities of her child.
Earlier research has drawn links between organophosphate exposure and attention-deficit/hyperactivity disorder (ADHD); and with lower birth weights and skull circumference.
About half the 40 OP chemicals available on the global market, which include fenitrothion, chlopyrifos, diazinon and malathion, are in use in Australia.
The new US papers, recently released pre-press by the journal Environmental Health Perspectives, all measured indicators of OPs in mothers during pregnancy, and then followed the development of their children.
Although the researchers relied on statistical relationships, they drew some strong conclusions.
Researchers from the University of California, Emory University, and medical research facilities from California and Canada studied Latino farmworkers in California.
Mothers with the greatest exposure to OPs had children that, at seven years of age, had IQs on average seven points lower than children from mothers with the lowest levels of exposure.
Researchers from Colombia and Emory universities who evaluated the effects of chlopyrifos—used for insect and rodent control—on inner-city families reported that by age seven, children from mothers with the highest levels of OP exposure ranked 5.5 per cent lower on a test of working memory and had IQs 2.7 per cent lower than children born to mothers with the lowest OP exposure.
Researchers from the Mt Sinai School of Medicine, and Emory and Cornell universities, wrote that their findings from New York City "suggest that prenatal exposure to organophosphates negatively impacts cognitive development, particularly perceptual reasoning, with evidence of effects beginning at 12 months and continuing through early childhood".
In 2007, 15 million kg of OP pesticides were used in the US, about 36 per cent of all pesticides applied there.
A 2002 assessment of Australian OP use estimated that about 5000 tonnes of active OP ingredient is used here each year, via about 700 products.
But while the statistical studies are "interesting, valuable, and are generally pointing in a certain direction," said Simon Cubit of the Australian Pesticides and Veterinary Medicines Authority (APVMA), "they don't give us enough to consider regulatory action".
"The studies do make us to pause and look at how we manage these products."
OPs as a class of chemical are gradually being phased out, Dr Cubit said, because the AVPMA recognises "the inherent problems" with products that are neurotoxins.
Of the 20-odd OP chemicals in use here, the AVPMA has recently reviewed, is reviewing or will soon re-review about 75 per cent.
However, the AVPMA won't be responding directly to the new US studies.
Regulation relies on science that shows cause-and-effect, Dr Cubit said, and cause-and-effect is difficult to research because people can't be knowingly exposed to OPs.
On the other hands, statistical relationship studies have inherent weaknesses from a regulatory point of view.
For instance, he said, how relevant is the experience of Latino farmworkers, with little or no training in chemical handling, to that of the Australian farmers with a high level of training? Are there social factors affecting IQ?
"Even if a direct association between OPs and intelligence can be made, under what circumstances does the effect occur, and do those circumstances apply in Australia? And can we control those circumstances?"
Dr Cubit said the AVPMA continues to monitor the research literature widely for further clues about OP management, and maintains tight controls and regular reviews of the chemicals.
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