This structured narrative review with systematic search elements synthesized 112 studies (2010–2025) on heavy metal contamination in human milk, with particular emphasis on maternal-infant transfer pathways, environmental and dietary determinants, and geographical variability. The review focused on Pb, Cd, tHg, tAs, Cr, and Al. Under typical exposure conditions, the authors report concentration ranges of approximately 2–5 µg/L for Pb, 1.4–1.7 µg/L for tHg, and below 1 µg/L for Cd. Substantially higher values occur in industrialized and mining regions, with extreme isolated reports exceeding 1000 µg/L for Pb and 100 µg/L for tHg. The review identifies bone mobilization of Pb during lactation, fat tissue mobilization for lipophilic organometals, and current dietary intake as the primary transfer mechanisms. Infants are particularly vulnerable due to immature detoxification, high gastrointestinal absorption efficiency, and ongoing neurodevelopment.
Key numbers
All concentrations in µg/L breast milk (approximate ranges across included studies, 2010–2025):
Lead (Pb):
- Typical range globally: 2–5 µg/L
- Highly contaminated regions: extreme values exceeding 1000 µg/L (isolated cases)
- Bone mobilization during lactation contributes substantially; elevated at early lactation (colostrum) and in women with high lifetime Pb exposure
Mercury (tHg):
- Typical range: 1.4–1.7 µg/L
- Highly contaminated regions: extreme values >100 µg/L
- Dietary fish consumption is primary determinant; speciation toward MeHg in fish-consuming populations
Cadmium (Cd):
- Below 1 µg/L under typical conditions
- 10-year biological half-life in kidneys means maternal body burden reflects decades of dietary exposure
- Transfer to breast milk is relatively limited compared to other metals
Arsenic (tAs):
- Detected at low concentrations; varies with rice consumption and geographic groundwater contamination
- Organic As forms (from seafood) dominate in fish-consuming populations; inorganic As from rice and drinking water in some Asian populations
Aluminum (Al):
- Detected in breast milk; influenced by dietary sources and antacid use
- No established health guidance value for infants via breast milk exposure
Chromium (Cr):
- Present in breast milk; stainless steel cookware and dietary sources contribute
- Total Cr measured; Cr-VI vs. Cr-III distinction not routinely made in breast milk studies
Methods (brief)
Structured narrative review with systematic search elements. Databases: PubMed, Scopus, Web of Science. Date range: 2010–2025. Languages: English only. Initial yield ~520 records; 148 selected for full-text; 112 included in final synthesis. Not formally registered as a systematic review; PRISMA not fully applied. Qualitative synthesis organized by metal, with additional structuring by geography, sample size, lactation stage, and analytical method. Greater weight given to ICP-MS studies with larger sample sizes and validated protocols.
Implications
Certification: This is the most comprehensive recent narrative review of heavy metals in human milk, synthesizing global data through early 2026. The 2–5 µg/L typical Pb range and <1 µg/L typical Cd range provide authoritative baseline reference ranges for synthesizing breastmilk contamination profiles.
Courses: Provides the integrative framework for teaching maternal-infant heavy metal transfer via breastfeeding: environmental sources → maternal accumulation (bone for Pb, fat for lipophilic metals) → mobilization during lactation → infant exposure. The bone-mobilization mechanism for Pb is particularly important for teaching, as it means women with historic occupational or environmental Pb exposure can transfer Pb to infants even when current dietary exposure is low.
App: Breast milk is not in the app’s product ingredient-list model but this review anchors the health sections on infant exposure.
Microbiome: Exposure of the infant gut to Pb, Cd, and Al during the colonization window (0–6 months) via breast milk is directly relevant to metal-microbiome interactions; cross-link when relevant microbiome pages are created.