Infant toenails as a biomarker of in utero arsenic exposure

Abstract

A growing body of evidence suggests that in utero and early-life exposure to arsenic may have detrimental effects on children, even at the low to moderate levels common in the United States and elsewhere. In a sample of 170 mother-infant pairs from New Hampshire, we determined infant exposure to in utero arsenic by evaluating infant toenails as a biomarker using inductively coupled plasma mass spectrometry. Infant toenail arsenic concentration correlated with maternal postpartum toenail concentrations (Spearman's correlation coefficient 0.34). In adjusted linear models, a doubling of maternal toenail arsenic concentration was associated with a 53.8% increase in infant toenail arsenic concentration as compared with 20.4% for a doubling of maternal urine arsenic concentration. In a structural equation model, a doubling of the latent variable integrating maternal toenail and urine arsenic concentrations was associated with a 67.5% increase in infant toenail arsenic concentration. A similar correlation between infant and maternal postpartum toenail concentrations was observed in a validation cohort of 130 mother-infant pairs from Rhode Island. In utero exposure to arsenic occurs through maternal water and dietary sources, and infant toenails appear to be a reliable biomarker for estimating arsenic exposure during the critical window of gestation.

Figure 1

The relationship between log₁₀-transformed infant toenail arsenic concentration and maternal biomarkers including log₁₀-transformed maternal toenail arsenic concentration (a) and log₁₀-transformed maternal urinary arsenic concentration (b). In both panels, the r_s represents Spearman’s correlation coefficient, the black line represents least-squares regression, and the dashed line represents LoWeSS (locally weighted scatterplot smoothing) moving average fitted curve.

Figure 2

The relationship between log₁₀-transformed infant toenail arsenic concentration and maternal arsenic intake variables including arsenic from water (a) and rice consumption (b). In both panels, the r_s represents Spearman’s correlation coefficient, the black line represents least-squares regression, and the dashed line represents LoWeSS (locally weighted scatterplot smoothing) moving average fitted curve.

Figure 3

Structural equation model based on observed maternal biomarkers and arsenic intake variables. The latent maternal arsenic biomarkers variable includes both log₁₀-transformed maternal toenail arsenic concentration and log₁₀-transformed maternal urinary arsenic concentration as loading factors. Effect estimates represent the change based on the respective unit increase in the corresponding independent variable. The P-value of the likelihood ratio comparing the above model with a fully saturated model is 0.48, the root mean squared error approximation is 0.00, the comparative fit index is 1.00, and Tucker–Lewis index is 1.01.