Early-Life Insecticide Exposure and Motor Function in Infants

Abstract

Introduction The neurodevelopmental effects of early-life exposure to non-persistent insecticides are not well understood. Laboratory studies suggest that low dose organophosphate (OP) exposure may inhibit myelination, a process critical to motor development. The aim here was to investigate the effects of prenatal exposure to OP and pyrethroid (PYR) insecticides on infant motor function. Methods 24 OP, 6 OP metabolites (OPm), 12 PYR, and 1 PYRm were measured using GC-tandem MS in umbilical cord blood plasma from a cohort of infants in Fuyang County, China (n=230). Motor function was assessed at 6 wk. and 9 mo. using Peabody Developmental Motor Scales- 2nd Ed. (PDMS-2). Composite variables were created for total OP and PYR detects. Individual insecticides were analyzed as dichotomous (non-detect [ND]/detect), 3-level ordinal (ND/medium/high), or continuous, depending on detection rates. Multivariate linear regression was used to evaluate relationships between insecticides and PDMS subtests (reflexes, stationary, locomotion, grasping, visual-motor integration), gross motor quotient (GMQ), fine motor quotient (FMQ), and total motor quotient (TMQ). Results 14 OPs, 4 OPm, 12 PYR, and 1 PYRm were detected in at least one sample. For OP analyses, infants with detectable chlorpyrifos (vs. ND) had significantly lower scores at 9 mo: visual-motor integration (β=-1.7 [95%CI: -3.3--0.2], p=0.03), FMQ (β=-2.4 [95%CI: -4.8--0.1], p=0.04), and TMQ (β=-5.8 [95%CI: -10.8--0.8], p=0.02). For PYR analyses, infants with high cypermethrin (vs. ND) also had significantly lower scores at 9 mo: locomotion (β=-3.0 [95%CI: -5.7--0.4], p=0.02), GMQ (β=-4.4 [95%CI: -8.4--0.4], p=0.03), and FMQ (β=-5.9 [95%CI: -11.5--0.3], p=0.04). Conclusions We found evidence of deficits in motor function in 9-month-old infants with prenatal exposure to chlorpyrifos or cypermethrin. Neural pathways involved in motor skill acquisition may be vulnerable to the effects of certain commonly used insecticides.