Organophosphate (OPs) pesticides were derived from World War II nerve gas agents
and are being increasingly used around the world for a variety of agricultural, industrial
and domestic purposes. Concerns have been expressed about the effects of these
chemicals on human health. Chronic ill health may follow recovery from acute
organophosphate poisoning, but the possibility that repeated low level exposure may
cause ill health is controversial as previous research has yielded inconsistent results. As
an occupational group, farmers are considered to be at risk of low level exposure only.
METHOD: The present study compared neuropsychological performance of 25 agricultural
workers, exposed to organophosphate pesticides in the course of their work with 22 nonexposed healthy volunteers (controls) who were matched to the exposed group for age,
gender, years spent in education and level of intelligence. All ofthe agricultural workers
were involved in litigation.
OBJECTIVE: To establish whether agricultural workers with a history of prolonged
exposure to OPs show evidence of cognitive impairment and to determine whether the
pattern of cognitive deficit relates to exposure history.
FINDINGS: A range of cognitive and emotional problems were identified in agricultural
workers. Although general intellectual ability was relatively well preserved in the
exposed cohort, they obtained lower scores on tests of auditory verbal memory span,
verbal learning, verbal fluency, mental flexibility, reading, visuo-spatial skill and
information processing speed, than non-exposed controls. In addition, over 70% of the
exposed cohort complained of clinically significant levels of anxiety and depression.
They also reported a range of physical symptoms, the most prominent being fatigue,
aching muscles and joints, headaches, sleep disturbance and irritability. Exposure history
varied enormously amongst individuals who seemed to have similar jobs and many
appeared to have a history of undiagnosed acute poisoning. This highlights the
importance of taking an adequate exposure history.
CONCLUSIONS: The question of whether low level exposure to OPs causes ill health will
never be resolved without agreed definitions of acute versus low level exposure,
adequate assessment of exposure history and consideration of individual vulnerability
factors or synergistic effects of chemical combinations that may mediate the dose-response relationship.