Prenatal exposure to toxic environmental metals can interfere with fetal growth and development. Fetal exposure to lead (Pb) can increase the risks of a preterm delivery, a low birth weight, and mental developmental impairment (Falcón et al., 2003). A longitudinal study indicated that Pb concentrations in the meconium were negatively associated with the birth length (Gundacker et al., 2010). Prenatal Pb exposure was associated with maternal age and the consumption of nutritional supplements (Al-Saleh et al., 2008). A birth-cohort study suggested that mercury (Hg) concentrations in cord blood were directly related to a poor birth weight, and indicated a direct path from fish consumption to cord blood Hg (Kim et al., 2017). Low-level erythrocyte cadmium (Cd) and Hg concentrations were inversely correlated with worse birth anthropometrics in a prospective birth-cohort in Sweden (Gustin et al., 2020). Low-level maternal arsenic (As) exposure during pregnancy appeared to decrease the birth weight and head and chest circumferences as determined from an analysis of 1578 mother-infant pairs recruited in Bangladesh (Rahman et al., 2009). However, few studies have evaluated the joint effects of fetal exposure to metal mixtures on birth outcomes. A birth cohort study conducted in Bangladesh indicated that mixed metal levels in cord blood were associated with reduced newborn anthropometrics (Lee et al., 2021). A significant negative relationship of a mixture of chromium, copper, molybdenum, and zinc in the meconium with the birth weight was shown in a cross-sectional study (Pavilonis et al., 2022).

The meconium has been applied in several studies as a biomarker of fetal exposure to heavy metals (McDermott et al., 2020; Ostrea et al., 2006; Pavilonis et al., 2022). The meconium is an accumulated material mixture formed by the fetus during the second and third trimesters of pregnancy and excreted by the newborn within the first 24–48 h (Michelsen et al., 2021; Ortega et al., 2006). Measurement of prenatal exposure using the meconium compared to maternal blood and urine or cord blood was more useful for assessing long-term fetal exposure to environmental toxicants in utero due to the meconium representing the accumulation of materials over approximately 6 months (Barr et al., 2007; Michelsen-Correa et al., 2021). Previous studies used a meconium analysis to evaluate fetal exposure to metals. A survey conducted in a community with high Hg contamination revealed a higher prevalence of Hg in the meconium compared to maternal fluid compartments such as blood and breast milk. Their results also showed that Hg concentrations in the meconium were positively correlated with those in maternal blood and in cord blood (Ramirez et al., 2000). An analysis of the meconium was effectively applied to measure fetal exposure to metals in a mining-exposed environment (McDermott et al., 2020) and in an urban area (Pavilonis et al., 2022).

The purpose of this study was to establish distributions of Hg, Pb, Cd, and As concentrations in the meconium among a large population living in urban areas of northern Taiwan and evaluate potential related factors. The combined effects of fetal exposure to a metal mixture on birth outcomes (i.e., birth weight, birth length, and head circumference) were evaluated. The importance of metal exposure variables on birth outcomes was also assessed.