Lead and mercury levels in repeatedly collected urine samples of young children: A longitudinal biomonitoring study

Early life exposures to lead (Pb) and mercury (Hg) were reported to be associated with various adverse health outcomes. However, limited data was available for urinary Pb and Hg levels in young children and the proportion of children at risk by age, as well as inter- and intra-subject variations of urinary Pb and Hg levels. Therefore, we collected total 491 urine samples from 241 children by urine collection at birth and at intervals of 3 months until 27 months of age for each child (at 10 monitoring time points), measured urinary Pb and Hg levels, and then evaluated the proportion of children at risk by age and the intra-class correlation (ICC) of the urinary Pb and Hg levels. Both the urinary Pb and Hg levels were significantly different according to the monitoring time points (p 0.0001 for both Pb and Hg). The number of children with Hg level over the Human BioMonitoring (HBM) I (7 μg/L) and II (25 μg/L) in the first urine at birth were 3 (2.2%) and 1 (0.7%), respectively, while the urinary samples at the other time points did not show Hg level over HBM I or HBM II. However, the exceedance rate for urinary Pb based on HBM values was not calculated due to unavailable HBM values. On the other hands, the proportion of the children with Pb and Hg levels over the reference value derived on the 95th percentile of representative samples (RV