A VERY high risk of suicide among agriculturalists with chronic organophosphate (OP) poisoning is one of the findings West Country psychiatrists investigating mood disorders in confirmed OP sufferers.

Many of the UK's 50,000 sheep farmers - and others - could have ill health due to exposure to OP sheep dip insecticides.

''There must be well over 1000 victims nationwide. There are greater numbers involved than with Gulf war syndrome,'' said Dr Bob Davis, a consultant psychiatrist with the Avalon, Somerset NHS Trust.

In a study awaiting publication, he identifies chronic organophosphate syndrome (COS) as an illness related, but not identical, to chronic fatigue syndrome, also known as ME.

Of 22 patients he saw, with histories of chronic exposure to OP pesticides, 19 spoke of suicidal impulses. ''Almost all patients, though it must be said often with some prompting, admit to periods of intense impulsive suicidal thinking during which times they may go as far as loading and pointing shotguns at themselves and deliberately allowing farm vehicles to run out of control. These periods are generally of very short duration such that the patient comes to his or her senses before pulling the trigger. It may be presumed, however, that some commit a fatal act before the suicidal impulse subsides,'' Dr Davis writes.

''Significant and impulsive suicidal thinking'' was reported by 50% of the 211 organophosphate sufferers who responded to a detailed questionnaire, part of the ongoing follow-up study. Dr Davis commented: ''This is very high for a random population. If you asked the same question of people in the High Street, you would get maybe 5%, but that's a guesstimate.''

Full-blown chronic organophosphate syndrome follows an exacerbated episode of ''dippers flu'' and is the same illness as the main Gulf war syndrome, Dr Davis believes.

Dippers flu is relatively mild, usually lasts a few days after dipping and is regularly experienced by many who use OP-type sheep dips. Farmers use these and other treatments to protect their flocks against scab, which can be fatal, and other skin parasites - ticks, keds, lice and blowfly.

'''Normal' dippers seem to develop symptoms (of COS) after six to eight years, but often longer depending on the degree of protection used. Others, for example, contract dippers, develop the syndrome quicker,'' said Dr Davis.

''Greater exposure in a relatively brief time explains the rapid development of the illness in Gulf war veterans.'' The soldiers were exposed to high levels of OPs in a hot climate; physostigmine, given orally or by injection against insect-borne disease, pumps OPs across the blood/brain barrier; and combat stress does the same.

''It is universally acknowledged that acute high dose exposure to organophosphates produces serious ill health and is frequently fatal. What is less generally accepted, particularly in official and Governmental quarters, is that chronic exposure at lower levels also produces serious and significant illness. Official literature and information sheets refer almost exclusively to 'non-specific' symptoms; thus the significance and impact of these symptoms upon exposees lives is minimised,'' according to Dr Davis.

The Government line on sheep dips, given at the end of February by Agriculture Minister Douglas Hogg, is that OPs could continue to be used safely ''if used according to the manufacturers' instructions''. (Full waterproof protective clothing, etc.) Last month, in reply to Western Isles MP Calum MacDonald, Junior Minister Angela Browning said they were awaiting the results of a study, due in 1999, into the human health effects of OPs.

An immediate moratorium on the use of OP-type sheep dips is the policy of both Labour and the Liberal-Democrats. The Lib-Dems' environment spokesman Paul Tyler is a long-standing critic of OPs while his Labour counterpart, Michael Meacher, also wants ''a full-scale research programme into the role that OPs may play, not only in BSE/CJD, but in the development of diseases such as ME, MS, Alzheimer's, Parkinson's, depression and heart disease''.

The Scottish National Party's land spokesman Rob Gibson said: ''The evidence tends to an outright ban being implemented now.''

Other surprise results Dr Davis and his team have found are heightened sense of smell - 75% of questionnaire respondents - and a dramatic deterioration of handwriting (all respondents). ''It's weird,'' the doctor commented. ''Exposees report much enhanced olfactory acuity, particularly to substances such as perfumes. In some cases the experience is intensely unpleasant and may prevent them from undertaking essential tasks such as mucking out. The partners of patients frequently are forced to abandon the use of perfumes and other cosmetics.''

After handwriting deterioration, the strongest correlations between COS sufferers and symptoms are exacerbation of dippers flu and personality change (90%), followed by heightened sensitivity to OPs and impaired exercise tolerance.

''I would make the point forcibly - this is not ME,'' Dr Davis said. ''ME is basically fatigue and an ongoing low-grade depression. This is brief episodes of depression alternating with irritability, easy fatigue following initial full muscle power, and unstable mood rather than persistent depression. But there are strong parallels between ME and OP-delayed syndrome.''

''Chronic orgonophosphate exposure - towards the definition of a neuro-psychiatric syndrome'' by G M Ahmed and D R Davis will be published in September in the Journal of Nutrition and Environmental Medicine.

There are alternatives for controlling and treating sheep scab - the newer synthetic pyrethroids dips and systemic injectables, both more expensive. Dipping was compulsory from 1976 to 1992. For several years following the banning of the effective organochlorine dips in 1985, farmers had no alternative but to dip their sheep in OPs and safety information was not what it is now.