Farm experts called for a ban on sheep-dips based on organophosphates this week until more is known about their link to neurological damage, mental instability and suicide among farmers.
According to Andrew Watterson of De Montfort University, decades of data strongly suggest that regular exposure to organophosphates (OPs) results in progressive damage to the nervous system and neuropsychiatric problems.
The sheep-dips have been widely used in the United Kingdom since the 1980s but the risk to human health has never been properly assessed.
"The shortcomings of these risk assessments are in stark contrast with the weight of toxicological and occupational hygiene evidence about organophosphates and the obvious need for a tougher precautionary policy on dip usage," said Dr Watterson, director of the university's centre for occupational and environmental health.
Fears about the long-term effects on farmers of sheep-dips comes amid mounting concern for the long-term health of Gulf war veterans, who may have been exposed to OP-laden pesticides in Kuwait and Saudi Arabia.
According to Ministry of Defence research made public last week, servicemen and women suffering from so-called Gulf war syndrome may have been poisoned when pesticides were sprayed on British military tents to protect them against disease-carrying insects in the Gulf.
More than 1,100 Gulf war veterans are now suffering from a range of illnesses, including chronic fatigue, headaches, depression and swollen joints. But MoD medical experts insist poisoning would be limited to those involved in carrying out the spraying.
Health and safety agencies have given contradictory advice on safe handling of OPs. The protective properties of gloves approved by the Health and Safety Executive, for example, are found to be destroyed by certain sheep-dip solvents.
"The official attitude has been: 'We don't know what they do; we'll count the bodies at the end of the line'," said Dr Watterson.
A recent study of suicide rates in four large rural areas of Spain concludes that farmers who come into regular contact with OPs are four times more likely to commit suicide than the average.
In Britain, this finding is supported by a map recently published by the Office of Population Censuses and Surveys. This shows peak suicide figures in hill farming areas of south-west England and Wales in men aged 45 and over.
In an unpublished study of 40 farmers suffering from apparent OP-induced sickness, consultant psychiatrist Robert Davies found that in 38 cases, the presence of one symptom of poisoning is accompanied by a list of others. They include episodic mood instability, bouts of anger that can lead to homicidal urges, suicidal tendencies, loss of attention and memory, a heightened sense of smell, deterioration of handwriting, and a dramatic decline in alcohol tolerance.
"Until the evidence on ill-health is conclusive, they should be banned," said Dr Davies of the OP dips.