Effects of daily exposure to pyrethroid pesticides during infancy on children neurodevelopment at age four: a prospective study in rural Yunnan, China.

Introduction: Exposure to pyrethroid pesticides (PYRs) of children in infancy at ages 1 and 2 may affect their neurodevelopmental outcomes at age 4.

Objectives: The study aimed to explore the longitudinal association of infancy PYRs exposure with neurodevelopment at age 4.

Methods: This study based on Xuanwei birth cohort study that started from January 2016 in rural Yunnan, China. Urine samples (n=263) at ages 1 and 2 were tested for PYRs metabolites 3-phenoxybenzoic acid (3-PBA), 4-fluoro-3-phenoxybenzoic acid (4-F-3-PBA), and cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (DBCA). PYRs metabolites were classified as low and high exposure using the 75th percentile values. Neurodevelopment of children aged 4 was assessed by Griffiths Development Scales-Chinese Edition (GDS-C). The development quotient below 85 was defined as low development level. Multiple linear regression and logistic regression were used to analyze the association of children's PYRs exposure with their neurodevelopmental outcomes.

Results: Children's PYRs metabolites detection rates were 98.48% in infants at both age 1 and 2. The average levels of 3-PBA, 4-F-3-PBA and DBCA were 0.51µg/L, 0.30µg/L and <0.09µg/L, respectively at age 1; and 0.88µg/L, 0.82µg/L, and 0.52µg/L at age 2. The levels of three metabolites in 2-year-olds were higher than those in 1-year-olds. The children aged 4 had a general developmental quotient of 90.87 ± 11.37, with 28.14% classified in low development level. Multiple linear regression analysis showed that higher 3-PBA level at 2-year-old was negatively associated with the quotient in locomotor (β=-14.61, 95% CI: -24.93, -4.23) and language (β=-10.89, 95% CI: -19.38, -2.41). Logistic regression displayed that higher 3-PBA level aged 2 was positively correlated with low development level in the language domain (OR=3.23, 95% CI: 1.33, 7.83), but negatively correlated with personal social domain (OR=0.23, 95% CI: 0.07, 0.79).

Conclusion: Children were widely exposed to PYRs in infancy, which may impact on their neurodevelopment at age 4. Age 2 may be a sensitive window when PYRs exposure may negatively impact locomotor and language development. This study suggests that PYRs exposure should be minimized or avoided in child care, especially in children aged 2 years.