Pesticide Exposure May Degrade Human Cognitive Function

by Kahea Kanua

Pesticides are widely used toxins, yet research is only beginning to understand their effects on human brain and body functioning. In the United States, it is estimated that close to 8 billion dollars is spent on pesticides each year, yet only a few studies have examined the cognitive and neuropsychological impact of pesticide exposure, to mixed results. Schultz and Ferraro (2013) compared neuropsychological test performance of individuals with an occupational history of pesticide exposure to individuals with no such exposure history. The results suggested that occupational exposure to pesticides results in significant, and age-related, decline in some aspects of neuropsychological performance and information processing.

This study was conducted in the Red River Valley in North Dakota and Minnesota, where mainly barley, durum, spring wheat, edible beans, and canola are farmed in over 4,000 farms across over 4.8 million acres. Participants in the study were prescreened and placed into one of two groups: farmers or nonfarmers. Farmers were defined as individuals with a history of chronic pesticide exposure (defined in this study as pesticide exposure on three consecutive work days) and having performed farm or farm-related work for 1 week of the previous month. Nonfarmers were defined as the individuals who had never performed farm work or been acutely exposed to pesticides.

Each participant went through a battery of neuropsychological tests and surveys, including a demographic survey, the Geriatric Depression Scale—Short form, the State—Trait Anxiety Inventory, selected subtests from the Wechsler Adult Intelligence Scale (third edition), the Mini-Mental Status Exam (MMSE), Boston Naming Test (Short Form), and selected subtests of the Wechsler Memory Scale (Third Edition).

The authors correlated number of years worked with pesticides with the various demographic and neuropsychological measures for the farmer group. Individuals occupationally exposed to pesticides over the course of a number of years developed some aspects of mild cognitive dysfunction. Results showed positive and significant correlations with scores on the MMSE, Logical Memory 1 Recall Total, Logical Memory 1 Thematic Unit Total, Logical Memory 2 Recall Total, and Logical Memory 2 Thematic Unit Total. There was a negative and significant correlation with the State Anxiety raw score, a measurement of present anxiety level. Other correlations were not significant.

There was a significant negative correlation between age and MMSE performance among the farmers, but no significant correlation between age and MMSE performance among the non-farmers, indicating that cognitive ability declines faster with age in the sample of farmers as compared to the sample of nonfarmers although the two groups were not significantly different in age or other current demographic and psychological variables. MMSE is one of the most used measures of cognitive ability and is consistent with other studies performed in this area.

The authors do not claim that pesticide exposure caused cognitive decline, but their results do suggest that pesticide use and exposure may reflect subtle changes in brain function among those exposed to pesticides.

Schultz, C.G. and Ferraro, F.R., 2013. The impact of chronic pesticide exposure on neuropsychological functioning. The Psychological Record 63,175–184. Abstract: http://eric.ed.gov/?id=EJ1008504

Singhvi, R., Koustas, R.N., Mohn, M, 1994. Contaminants and remedial options at pesticide sites. Risk Reduction Engineering Laboratory, U.S. Environmental Protection Agency.

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