Arsenic methylation capacity and developmental delay in preschool children in Taiwan

Environmental exposure to lead or mercury can cause neurodevelopmental damage. Arsenic is another neurotoxicant that can affect intellectual function in children. This study was designed to explore the difference of arsenic methylation capacity indices between with and without developmental delay in preschool children. We also aimed to identify whether blood levels of lead or mercury modify the effect of arsenic methylation capacity indices. A cross sectional study was conducted from August 2010 to March 2012. All participants recruited from the Shin Kong Wu Ho-Su Memorial Teaching Hospital. In all, 63 children with developmental delay and 35 children without developmental delay were recruited. Urinary arsenic species, including arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MMA^V) and dimethylarsinic acid (DMA^V) were measured with a high-performance liquid chromatography-linked hydride generator and atomic absorption spectrometry. Lead and mercury levels of red blood cells were measured by inductively coupled mass spectrometry. All participants underwent developmental assessments to confirm developmental delays, including evaluations of gross motor, fine motor, speech-language, cognition, social, and emotional domains. Urinary total arsenic and MMA^V percentage were significantly positively associated and DMA^V percentage was negatively associated with the risk of developmental delay in a dose-dependent manner after adjustment for blood lead or mercury levels and other risk factors. A multivariate regression analysis indicated that blood lead level and arsenic methylation capacity each independently contributed to the risk of developmental delay. This is the first study to show that arsenic methylation capacity is associated with developmental delay, even without obvious environmental arsenic exposure.