Background: The organophosphate insecticide chlorpyrifos (CPF), widely used for agricultural purposes, has been linked to neurodevelopmental deficits. Possible motor effects at low to moderate levels of exposure have not been evaluated. Methods: Prenatal exposure to CPF was measured in umbilical cord blood in a sample of 263 inner-city minority children, who were followed prospectively. At approximately 11 years of age (mean age 10.9. ±. 0.85 years, range = 9.0-13.9), during a neuropsychological assessment, children were asked to draw Archimedes spirals. These were rated by a senior neurologist specializing in movement disorders who was blind to CPF exposure level. Results: Compared to all other children, those with prenatal CPF exposure in the upper quartile range (n= 43) were more likely to exhibit mild or mild to moderate tremor (≥1) in either arm (p= 0.03), both arms (p= 0.02), the dominant arm (p= 0.01), and the non-dominant arm (p= 0.055). Logistic regression analyses showed significant CPF effects on tremor in both arms, either arm, the dominant arm (p-values <0.05), and the non-dominant arm (p= 0.06), after adjustment for sex, age at testing, ethnicity, and medication. Conclusion: Prenatal CPF exposure is associated with tremor in middle childhood, which may be a sign of the insecticide's effects on nervous system function.
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