Chen et al. 2023 — Heavy metals in human breast milk from an e-waste recycling area, China
This cohort study measured six heavy metals (Pb, Cd, Cr, As, Cu, Mn) in 102 human milk samples collected from mothers in Taizhou, Zhejiang Province, one of China’s largest e-waste recycling areas, and analyzed associations between metal concentrations and infant birth outcomes (birth weight and length). The central finding was that 34.3% of participants had Cr concentrations exceeding WHO guidelines for human milk, and a significant inverse association was identified between maternal milk Cd concentration and birth weight in female infants.
Key numbers
ICP-MS (iCAPQ, Thermo Fisher Scientific), µg/L in human milk, n = 102, overall population:
- Cr: mean 1.517 ± 0.849, median 1.410, range 0.598–7.453 µg/L (WHO permissible 0.8–1.5 µg/L; 34.3% exceeded upper limit)
- Mn: mean 1.214 ± 0.830, median 1.043, range 0.438–7.040 µg/L (WHO permissible 3–4 µg/L; 2.0% exceeded)
- Cu: mean 46.64 ± 17.73, median 45.81, range 13.07–98.07 µg/L (within WHO permissible 180–310 µg/L)
- As: mean 0.113 ± 0.086, median 0.089, range 0.012–0.440 µg/L (within WHO permissible 0.2–0.6 µg/L)
- Cd: mean 0.016 ± 0.014, median 0.013, range 0.002–0.078 µg/L (within WHO permissible <1 µg/L)
- Pb: mean 0.260 ± 0.385, median 0.176, range 0.050–3.449 µg/L (within WHO permissible 2–5 µg/L)
LODs: Pb 0.02, Cd 0.01, Cr 0.06, As 0.01, Cu 1.14, Mn 0.02 µg/L. 12 Cd measurements (12%) below LOD replaced with half-LOD.
Birth outcome association: Cd in maternal milk inversely associated with birth weight in female infants (β = −162.72, 95% CI = −303.16, −22.25 g per IQR increase in ln-Cd, p-interaction = 0.017). No significant association observed for male infants. BKMR analysis suggested additive rather than synergistic effects of mixed metal exposure on birth outcomes.
Methods (brief)
ICP-MS with microwave acid digestion (HNO3:HCl 1:3, Milestone Ethos D). Certified reference material GBW10017 used for QC. Cross-sectional exposure assessment using post-delivery human milk as proxy for prenatal exposure. Multivariable linear regression and Bayesian kernel machine regression (BKMR) for metal mixture analysis.
Implications
Certification: Human milk metal concentrations in e-waste proximity populations reflect cumulative environmental and dietary exposure. The Cd–birth weight association for female infants, even at concentrations within WHO permissible milk limits, underscores the sensitivity of this endpoint.
Courses: Demonstrates that e-waste proximity creates heavy metal profiles in human milk distinct from general population baselines; Cr exceedance in 34% of samples is the most notable finding relative to WHO guidelines.
App: Human milk is a sentinel matrix for cumulative maternal metal burden; not a direct product-concentration input but relevant for infant exposure modeling via breastfeeding.
Microbiome: Metal exposure in e-waste populations documented here may interact with infant gut microbiome development via breast milk; relevant to metals-infant-gut.