The United States research found that children exposed to organophosphate pesticides while in their mother’s womb are more likely to show attention disorders before they reach school age.

Researchers from the National Institute of Environmental Health Sciences monitored American-Mexican families in California’s Salinas Valley, a major horticultural area.

They found that the presence of metabolites indicating exposure to organophosphates in a mother’s urine during pregnancy was correlated with attention disorders in their children at the age of five.

The association was stronger for boys than girls.

The findings “are not a surprise”, Irina Pollard, Associate Professor of Biological Sciences at Macquarie University, told the Australian Science Media Centre.

“Many of the toxic effects of members of the organo-phosphate family rely on the fact that they are human-made synthetic hormone disruptors,” Prof. Pollard said.

“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.”

Because organophosphate insecticides affect oestrogen, “their adverse effects on fertility, early pregnancy and loss of function in the offspring, are not surprising”.

Australians are becoming increasingly wary of chemicals. The latest Organic Market Report said that 91 per cent of those surveyed considered “chemical-free” a desirable attribute in food, although only 60pc had bought organic-labelled food in the past year.