Research into chronic neuropsychological and neurological effects of OP exposure

In 1995 the Institute of Occupational Health in Birmingham conducted an investigation into chronic neuropsychological and neurological effects of OP exposure in sheep farmers ('An investigation into the possible chronic neuropsychological and neurological effects of occupational exposure to organophosphates in sheep farmers', Stephens et al, Institute of Occupational Health, Birmingham, HSE Contract Research Report No 74/1995)

The aim of the study was to investigate whether chronic effects occur in sheep farmers who experience repeated exposure to organophosphates (OPs) through sheep-dipping. A cross-sectional design was employed in which sheep farmers exposed to OPs were compared with non-exposed quarry workers on a range of outcome measures which assessed mood and symptom reporting after acute exposure, and cognitive functioning, psychiatric state and neurological symptoms in the absence of recent exposure.

The exposed group consisted of a randomly selected group of sheep-dippers which was judged to be representative of the farming community as a whole. It was not composed of self-selected individuals who had previously judged themselves to be suffering from the effects of organophosphates. In addition those with medical or lifestyle factors which might result in effects on the nervous system were excluded from the investigation.

Among the conclusions in the report are the following:

The performance of the sheep-dippers was significantly poorer than that of the quarry worker controls on three of the neuropsychological tests, namely Simple Reaction Time, Symbol Digit Substitution and Syntactic Reasoning. These results indicate the presence of chronic effects in certain areas of cognitive functioning occurring in the sheep-dippers. These effects are subtle in nature and relate to the ability to sustain attention and the speed of higher level information processing, particularly in areas where a linguistic component is involved. There are several reasons to support the view that, although these effects are subtle, they are real effects, and are likely to be associated with exposure to organophosphate pesticides.

See here for the full summary of the report and its recommendations.