Pesticides and neurodevelopment of children in low and middle-income countries: A systematic review

Background: Pesticides are increasingly common in low- and middle-income countries (LMICs), where weaker regulations and multiple risk factors for poor neurodevelopment exist. Due to biological and behavioral factors, children are vulnerable to chronic pesticide exposure at a time when brain development is critical. The objective of this study is to systematically review studies assessing pesticides use with child neurodevelopment in LMICs. Methods: Using terms developed by a medical librarian, a search was performed in June 2023 across online databases, including OVID MEDLINE and EMBASE. For inclusion, studies required a measurement of pesticide exposure and neurodevelopmental outcomes using a standardized tool and study participants ≤18 years within an LMIC, as determined by World Bank criteria. Descriptive analyses were performed using extracted data, including published outcomes of significance. Results were assessed for internal validity and reported by the method of exposure measurement (biomarkers or questionnaires/region of residence). Results: A total of 31 studies spanning 11 LMICs met the inclusion criteria. An adverse association was found between pesticide exposure and at least one domain of neurodevelopment in 23 studies, including 12 studies with child-level measurements, 10 studies with maternal measurements in pregnancy, and one questionnaire-based study. Exposure to organochlorines, carbamates, chlorpyrifos, and fungicides were consistently associated with worse outcomes for neurodevelopment, specifically executive functioning, cognition, motor development, and behavior. Few studies found adverse associations with urine/serum organophosphate levels. Due to the heterogeneity of existing data, we were unable to quantify the relationship between pesticide exposure and neurodevelopment. Conclusions: While studies suggest that some domains of neurodevelopment may be negatively associated with pesticide exposure, extrapolation is limited due to the challenges in measuring pesticide exposure within these contexts and differing study designs. Several research gaps must be addressed to develop policy and regulations that protect children from potential neurodevelopmental deficits associated with pesticide exposure.