A pilot study: The importance of inter-individual differences in inorganic arsenic metabolism for birth weight outcome

•Women in an inorganic arsenic (iAs) endemic area show distinct metabolic patterns.•Underlying iAs methylation efficiency did not distinguish birth weight outcome.•Underlying partitioning of iAs toward excretion characterized birth weight outcome.•Evidence suggests a potential urinary iAs biomarker for low birth weight outcome.

Inorganic arsenic (iAs) exposure is detrimental to birth outcome. We lack information regarding the potential for iAs metabolism to affect fetal growth. Our pilot study evaluated postpartum Romanian women with known birth weight outcome for differences in iAs metabolism. Subjects were chronically exposed to low-to-moderate drinking water iAs. We analyzed well water, arsenic metabolites in urine, and toenail arsenic. Urine iAs and metabolites, toenail iAs, and secondary methylation efficiency increased as an effect of exposure (p < 0.001). Urine iAs and metabolites showed a significant interaction effect between exposure and birth weight. Moderately exposed women with low compared to normal birth weight outcome had greater metabolite excretion (p < 0.03); 67% with low compared to 10% with normal birth weight outcome presented urine iAs >9 μg/L (p = 0.019). Metabolic partitioning of iAs toward excretion may impair fetal growth. Prospective studies on iAs excretion before and during pregnancy may provide a biomarker for poor fetal growth risk.