Subtle Effects of Acute Organophosphate Poisoning on the Simple Reaction Times of Agricultural Workers

Agricultural workers acutely poisoned by organophosphate pesticides were examined for signs of residual neurobehavioral impairment 2-10 years after their apparent recovery. Eighty-three cases of definite organophosphate poisoning (accompanied by cholinesterase inhibition) and 46 cases of probable poisoning (lacking evidence of cholinesterase inhibition) were identified from pesticide illness reports maintained by the California Department of Agriculture. An additional 45 individuals were identified as having had one or more episodes of cholinesterase inhibition without exhibiting overt symptoms of the poisoning. These subjects, and a group of non-exposed individuals, were given an assessment battery which included computerized tests of postural balance, affective mood, finger tapping speed, sustained attention, hand-eye coordination, short-term memory, and simple reaction time. As reported previously by Steenland et al. (1994), the poisoned individuals exhibited disturbances in affective mood states and deficits in sustained attention, but no impairment of simple reaction times. However, our subsequent reexamination of the reaction time data, using statistical models recently developed by Krieg et al. (1994), indicate that there are subtle differences in the reaction times of the individuals for whom definite or probable organophosphate poisonings had been reported. Significant interactions between poisoning status and age, and poisoning status and educational level, were observed when factors depicting learning and fatigue during the testing session were considered. These findings suggest that there may be additional residual effects of the acute poisoning episodes experienced by these individuals which ar not reflected in standardized tests of simple reaction time, but which reveal themselves as subtle deficits in task learning ability and in accelerated neuromotor fatigue.