Suarez-Lopez_2026_J.Expo.Sci.Environ.Epidemiol__

BACKGROUND: Acetylcholinesterase (AChE) activity is a key biomarker for neurophysiological health and exposure to cholinesterase inhibitors, including organophosphate pesticides. While widely used to screen for toxic pesticide exposure in agriculture, there are no reference standards for AChE in children and adolescents, limiting its use for younger populations involved in farming worldwide. OBJECTIVE: To establish age- and sex-specific reference values for AChE activity from childhood to young adulthood and evaluate the impact of pesticide exposure proxies on AChE activity METHODS: We measured AChE activity in fresh fingerstick blood from 746 participants ages 4 to 26 years who resided in an agricultural county in Ecuador, totaling 3119 observations. We used generalized estimating equations to predict AChE activity levels per year of age, incorporating nonlinear aging patterns, exam wave-specific effects, and adjustments for hemoglobin, anthropometric measures, and pesticide exposure parameters. We also directly evaluated the impact of pesticide exposure proxies on AChE activity. RESULTS: At age 5 years, both males and females had AChE activity levels of 2.90 U/mL. In males, AChE activity increased linearly by 0.11 U/mL per year through age 17, slowed to 0.04 U/mL per year until age 21, and then plateaued at 4.40 U/mL. In females, AChE activity rose linearly at 0.11 U/mL per year until age 11, slowed to 0.02 U/mL per year through age 15, and then plateaued at 3.80 U/mL. Males had higher AChE activity than females beginning at age 12. Greater floricultural area within 300 meters of participants' homes was associated with lower AChE activity, suggesting potential pesticide drift effects. SIGNIFICANCE: Our findings provide reference levels for AChE activity across childhood, adolescence, and into early adulthood that can be used by clinicians and researchers in the context of assessing potential exposure to cholinesterase inhibitors from a spot measurement. IMPACT: Acetylcholinesterase activity serves as a key marker of neurophysiological health and, when depressed, indicates exposure to organophosphate and carbamate insecticides. Despite the widespread involvement of children, adolescents, and young adulthoods in agriculture globally, normative levels of acetylcholinesterase activity in younger populations have not been established. We address this knowledge gap, presenting acetylcholinesterase activity levels from ages 5 to 25 years from 3119 samples from 746 participants collected eight times over 16 years. These findings provide a basis for establishing standard values and assessing exposure to cholinesterase-inhibiting pesticides in vulnerable populations.