US research suggests children who were exposed to organophosphate pesticides while still in their mother’s womb were more likely to develop attention disorders years later.
Organophosphates have been linked to neurobehavioral deficits in children but this new research is the first to examine the influence of prenatal organophosphate exposure on the later development of attention problems.
The study, conducted among Mexican-American children living in the agricultural Salinas Valley in the US, found that prenatal levels of organophosphate metabolites were significantly linked to attention problems at age 5, with the effects apparently stronger among boys. The research is published today in the journal Environmental Health Perspectives.
We approached toxicology experts for their views on the study and its significance.
Dr Ian Shaw, Professor of Toxicology, University of Canterbury comments:
“Organophosphorus pesticides (OPs) are designed to disrupt the nervous system – that’s how they kill insects, and therefore I am not at all surprised that they interfere with the development of the nervous system in the early stages of a child’s growth. As with many such findings the potential for a particular chemical to have some effect or another is suspected, but it takes a superb study like that just published by Amy Marks and her colleagues from Berkeley to provide strong evidence to link a chemical with an effect. The question is, what dose does a pregnant woman need to receive to result in neurological damage to her child? If it is low she could receive such a dose from residues of OPs in her food, if not this problem might only affect to woman in agricultural communities where their exposure to OPs would be greater, especially if they worked on farms during their pregnancy.”
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Our colleagues at the Australian SMC gathered the following comments:
Prof Chris Winder is Professor of toxicology and occupational health at the University of New South Wales:
“It has been known for many years that hyperactivity conditions can arise in children from chemical exposures, such as lead, tobacco smoke, phthalates, sodium benzoate, food dyes and some pesticides. Organophosphate pesticides are widely used in Australian agriculture, and all are known to be neurologically active. Most studies of developmental or reproductive effects of adverse exposures are complicated by establishing if exposure occurring during the critical periods of development in the first trimester or afterwards or even after birth. While this paper does not specify the period of exposure, it does make the point that it was prenatal. While development of the brain occurs early in pregnancy, its growth and differentiation continue throughout pregnancy and even after birth, as the complex interaction between brain and behaviour emerges. So it is not surprising that symptoms of pre-school ADHD arise in children known to be associated with pesticide exposure during the prenatal period. The paper also hints at gender and genetic background being factors.”
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Emeritus Professor Michael Moore is a toxicologist and former director of the National Research Centre for Environmental Toxicology at the University of Queensland:
“Outcomes are as might be expected excepting the gender variation at 5 (boys) which is unexplained. All of the co-variates seem to be covered, especially maternal education and exposures like smoking. Paternal influence does not seem to have been factored in. Mostly social science on a non-robust end point (ADHD). I was particularly struck by the high incidence of maternal depression (~50%) which could have an impact on infant behaviour. Since the study only looked at metabolites and there is evidence that those less able to metabolise (low PON1) have more neurodevelopmental delays, the study may under-represent the overall effects of exposure. None the less it does point to a likely outcome of exposure to neurotoxic agents during development.”
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Associate Professor Irina Pollard is Associate Professor of Biological Sciences at Macquarie University in Sydney:
“This paper is excellent but the findings are not a surprise. However, it’s good to see clear scientific data to reinforce and educate the general community about the use and abuse of synthetic chemicals – this publication acts as yet another instructive example. Many of the toxic effects of members of the organo-phosphate family rely on the fact that they are human-made synthetic hormone disruptors. Synthetic hormone disruptors, or xenohormones, are known to impair immune response, disrupt endocrine and reproductive function, including functional effects on the developing nervous system, and other adverse developmental effects. The organochlorine insecticides and a number of closely related hydrocarbons exhibit considerable estrogenic activity, so their adverse effects on fertility, early pregnancy and loss of function in the offspring, are not surprising. But to quantify the effects of prenatal environmental exposure to postnatal function against a continuum of confounding genetic and epigenetic factors is difficult because adverse effects on intellectual ability may take decades to be identified. I feel strongly that precautionary measures must be taken to minimize exposing children to xenohormones and other pollutants carrying long-term harmful consequences.”