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Associations between ADHD and organophosphate insecticide exposure

27 August 2010

The APVMA notes a study recently published in Environmental Health Perspectives (external site) that reported an association between organophosphate pesticides and attention deficit hyperactivity disorder (ADHD) in children of Mexican-American farmworkers in California’s Salinas Valley.

Researchers tracked the development of more than 300 Mexican-American children after first testing their mothers for organophosphate metabolite traces in their urine during pregnancy. The results suggested an association between these traces and attention in young children as assessed by maternal reports, professional observation, and direct behavioural testing.

This is the second study in recent times to suggest such an association and, to this extent, is of concern to the APVMA. It adds to the body of work that suggests a relationship, albeit no study to date has demonstrated a direct link.

One of the key issues for the APVMA is the relevance of the findings to likely exposures to organophosphate insecticides in Australia. The subjects of the current study worked in an agricultural area where pesticide exposures are greater than the urban population would typically experience. Also, it is likely to be the case that the Mexican-American women were subjected to additional levels of exposure because of a range of social and cultural reasons.

The risks that organophosphates present are well known in Australia. As a class of chemicals they have been extensively reviewed by the APVMA, with many removed from the market. A number are still under review and face regulatory action if the APVMA assesses that there are use patterns that present risks that cannot be mitigated.

Exposure to organophosphate pesticides as residues in food is not significant in Australia. Levels routinely measured in Australian food are extremely low. Residues in food crops are closely and regularly scrutinised by Australian regulatory authorities.

Potential exposures through the skin and inhalation from exposure through use is thoroughly assessed, and where risks are identified and cannot be mitigated through restrictions on use or through personal protective equipment, chemicals are de-registered. The APVMA, for example, recently discontinued a use of one organophosphate (diazinon) as a sheep dip because dermal exposure exceeded safe limits.

The APVMA is confident that urban Australians have no cause for concern given their limited exposure to organophosphate products. Australian farm workers can also have confidence that occupational exposure has been assessed by the regulator and that they are not at risk provided they follow the label instructions. These assessments, importantly, also include developmental impacts on unborn children. If information emerges suggesting a new concern, the APVMA is able to review its original assessment and provide warnings to workers and impose additional controls.

Nonetheless the APVMA will continue to follow ongoing research between ADHD and pesticides to see if the associations observed in the current study are shown to reflect a direct causal relationship.

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Last updated on 27 August, 2010