Human health and occupational exposure to organophosphates

Symptoms
Treatment

Symptoms

The Health and Safety Executive in the UK has published advice on the effects of occupational exposure to organophosphates in a series of guidance notes 'Biological monitoring of workers exposed to organophosphate pesticides' (MS17). The effects of poisoning are summarised as follows:
1. Acute and subacute exposure to OP pesticides can produce harmful effects in man, and repeated exposure at lower levels can cause insidious cumulative toxicity.
2. The most common routes of absorption of OPs are via skin, respiratory tract and eyes.
3. OP formulations based on organic solvents are liable to penetrate protective clothing.
4. Repeated absorption of small doses has cumulative effects resulting in progressive inhibition of nervous tissue cholinesterase.
5. Symptoms of poisoning include
  1. headache, giddiness, loss of appetite, nausea and diarrhoea
  2. tremors, impaired co-ordination
  3. miosis, blurred vision, excessive salivation and sweating, bronchial gland secretion, bradycardia with decreased cardiac output and hypotension.
  4. urinary incontinence, abdominal pain, vomiting and broncho-constriction
  5. depression of the respiratory centre
  6. apprehension, anxiety, restlessness, irritability, depression, sleep problems, expressive language defects, changes of mood, lack of concentration, memory impairment and slowed reaction time.
The most commonly reported symptoms of chronic poisoning appear to be described by sections 5(d,e,f), with emphasis on weakness, short-term memory loss and depression. This sometimes leads the doctor to diagnose ME as the cause of the complaints; however if a case history of possible exposure to OPs is found then chronic OP poisoning should be suspected.
In his report Toxic Chemicals in Agriculture (1951) to the then Ministry of Agriculture, Fisheries and Foods Lord Zuckerman said of organophosphorus insecticides ' ...chronic toxicity is the main problem'.
In 1998 the Royal College of Physicians and Royal College of Psychiatrists collected evidence from patients and doctors on the effects of exposure to organophosphate sheep dips. They found the following health effects: headaches, limb pains, excessive tiredness, sleep disturbance, poor concentration, mood change and suicidal thoughts, memory loss. (See the summary of the Royal Colleges' report)
In 1995 the Institute of Occupational Health conducted a study to investigate the possible occurrence of chronic health effects in sheep dippers using OPs. The study found subtle chronic effects on the nervous system in sheep dippers compared to a control group. (More...)
The SCOPE project (Susceptibility to Chronic Organophosphate Exposure) run by the University of Manchester showed that people who have dipped sheep and become ill are more likely to have a variant in their genes that makes them less able to break down organophosphates once they get into the body. The results of the study support the idea that some people may be particularly at risk from working with organophosphates. (More...)
In 1999 the Lancet published a Research Letter Reduced bone formation after exposure to organophosphates (JE Compston et al, Vol 354 November 20 1999). Bone histomorphometric analysis in 24 agricultural workers with chronic organophosphate exposure showed significantly lower bone formation at tissue and cellular level than in healthy controls.

Treatment

Treatment of chronic OP poisoning which appears to be beneficial to the patient includes sympathy and understanding, listening to the history and symptoms of the patient, reassurance that the doctor understands the cause, and very careful treatment with very low doses of anti-depressants - not those which affect the cholinesterase levels. Some patients seem to respond to low doses of magnesium. It is our experience that a regime of physiotherapy including exercise is definitely not helpful, and can result in greater weakness and depression.