Exposure to even low levels of organophosphates in pesticides can cause lasting harm to the brain, scientists have concluded.
A review of 14 separate studies has shown that chemicals can reduce memory and the ability to process information quickly.
The findings, by researchers at University College London and the Open University, are the most comprehensive evidence yet that organophosphates can harm human health at low levels.
Doctors have long recognised that in high doses the chemicals, which are used to kill or repel insects and are also ingredients in aviation fuel and in some flame retardants, can be toxic, but the effects of lower doses have remained controversial.
Dr Sarah McKenzie Ross, a clinical psychologist and honorary senior lecturer at University College London, said that there now needed to be tighter safety rules for people exposed to the chemicals during their jobs.
She said: “The studies we looked at were in people who were exposed occupationally on a regular basis but were not getting ill from that exposure.
“The weight of evidence is that low level exposure is harmful. It targets memory, information processing speed, the ability to plan and have abstract thoughts. “
The report, which is published in the journal of Critical Reviews in Toxicology, examined evidence from 14 studies that had looked at the health of 1,600 participants.
Using statistical analysis, Dr McKenzie Ross and her colleagues concluded that low level doses could impact on memory and information processing, it did not impact on language or overall intellect.
Farmers are among those who are regularly exposed to organophosphates through sheep dips while aircrews are exposed from the additives in aviation fuel.
Veterans from the Gulf War are also known to have experienced the ill effects from pesticides they were exposed to during the conflict.
Dr McKenzie Ross added: “We have conducted our own study into UK farmers and those we interviewed said it was making it difficult for them to work at auctions where things happen fast.
“Aviation workers have also talked about struggling to retain information from air traffic control.
“We now need to be clear about what the risks are and make sure the correct safety measures are taken.”