Abstract
Background: Exposure to pesticides has been associated with neurobehavioral deficits and structural brain anomalies in animals and humans. We examined the association between pesticide exposure and brain activity in 48 farm workers from the Zarcero County, Costa Rica. Methods: In May-August 2016, we collected urine samples from each worker and quantified concentrations of urinary metabolites for mancozeb (ethylenethiourea, ETU), chlorpyrifos (trichloropyridinol, TCPy), and pyrethroids (3-phenoxybenzoic acid, 3-PBA). We assessed brain activity throughout bilateral prefrontal cortices using functional near-infrared spectroscopy (fNIRS) while participants completed tasks related to verbal working memory (Sternberg test), executive function (Wisconsin Card Sort Test), and attention (go/no-go test). We estimated exposure-outcome associations using linear regression models adjusted for age and education. Results: Median (P25-P75) urinary ETU, TCPy, and 3-PBA creatinine-adjusted concentrations were 1.0 (0.5-1.8), 7.2 (3.3-13.6), and 1.4 (0.7-1.7) μg/L, respectively. We observed that higher urinary TCPy and 3-PBA creatinine-adjusted concentrations were associated with decreased working memory-related brain activity in all eight regions of interest. For example, brain activity at the most posterior region in the prefrontal cortex of the left hemisphere decreased 2.3 (-4.1, -0.5) and 3.3 (-5.5, -1.1) per two-fold increase in urinary TCPy and 3-PBA creatinine-adjusted concentrations, respectively. We also found that executive function-related brain activity at the most posterior region in the prefrontal cortex of the left hemisphere decreased 2.3 (-4.5, -0.1) and 3.6 (-6.7, -0.4) per two-fold increase in urinary ETU and 3-PBA creatinine-adjusted concentrations, respectively. Conclusion: Our findings indicate that farm workers with higher pesticide exposure levels may be under-recruiting neural resources compared to those with lower exposure levels.
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