Chlorpyrifos, the world’s most widely-used insecticide, was shown to produce persistent nervous system damage measured by a test of visual search and shifting focus in a study published in NeuroToxicology (March, 2020) by Dr. Kent Anger, PhD and colleagues, titled, “Magnitude of behavioral deficits varies with job-related chlorpyrifos exposure levels among Egyptian pesticide workers”. The study identified these effects in Egyptian pesticide applicator teams that are uniquely exposed to chlorpyrifos (most applicators are exposed to many different pesticides). The publication documents that chlorpyrifos now meets all the Bradford Hill criteria for cause (exposure) and effect (test performance deficits) in epidemiological studies in adults exposed to chlorpyrifos at work. The unique contribution is that the study established that test deficits increased from engineers and technicians (with some work exposure) to applicators (with highest work exposure) as compared to the best test performance in controls who had no work exposure; the other 20+ studies of adult pesticide workers studied workers with only a single “exposed” dose level.
This field assessment of pesticide application teams applying primarily chlorpyrifos during their working lifetime revealed that workers with jobs that had higher exposures performed more slowly on a test of cognitive performance than those workers with jobs that had lower exposures, while controls with the lowest exposure had the fastest or best test performance. Established blood and urine measures of immediate and sometimes lethal exposure to chlorpyrifos did not correlate directly with individual performance indicating that chronic or repeated exposures cause cognitive effects through a different neurological mechanism than the measures associated with short-term exposures. A report of animal studies from the same grant will identify the class of biomarkers associated with chronic exposures based on the human study reported here. Chlorpyrifos, designed and used as a pesticide, has been identified by the US as a potential bioterrorism agent.