Abstract
Introduction: Organophosphate insecticides (OPs) are neurotoxic at high doses, however effects of low dose exposure are not well understood. Laboratory studies have shown that OPs at low doses may inhibit neuronal myelination, a process critical to visual pathway development early in life. Grating visual acuity (VA) rapidly improves in infancy, reflecting visual pathway myelination. VA might thus be sensitive to OP exposure. The aim here was to investigate the effect of prenatal OP exposure on infant VA. Methods: 24 OPs and 6 OP metabolites were measured using GC-tandem MS in umbilical cord blood plasma from infants in Fuyang County, China. VA was measured using Teller Acuity Cards at 6 wk (N=300), 9 mo (N=291), and 18 mo (N=288). Composite variables were created for total OP detects and total OP metabolite detects. Individual OPs and metabolites 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 OP variables and VA. Results: 16 OPs and 6 metabolites were detected in at least one sample. Analyses of composite and dichotomous OP variables did not yield significant associations with VA. Chlorpyrifos, methamidophos, and trichlorfon were detected in 40, 66, and 56% of samples, respectively, and analyses as 3-level ordinal variables revealed suggestive, but not statistically significant, inverse associations between chlorpyrifos and trichlorfon and VA at 9 and 18 mo. Naled was detected in 94% of samples and continuous analyses found inverse associations with VA at 6 wk (β=-0.01; 95%CI:-0.02--0.001; p=0.03). Conclusions: VA in infancy may be adversely affected by certain OPs, though our results are largely inconclusive. Visual system development in infancy is critical to later learning processes and altered timing of visual pathway maturation may potentially contribute to poorer developmental outcomes later on.
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