Sushila et al. (2024) conducted a PRISMA-compliant systematic review of 22 studies reporting heavy metal concentrations in human breast milk across multiple countries, supplementing the literature survey with estimated daily intake (EDI) and hazard quotient (HQ) calculations to assess non-carcinogenic risk, and cancer risk (CR) calculations for cadmium and arsenic. The review reveals extreme geographic variation: cadmium EDI in Iran reaches 4.7 mg/kg/day with HQ=4.7, indicating unacceptable non-carcinogenic risk, while lead concentrations were highest in Cyprus (Ci=1.19 mg/kg), substantially above most European and Asian reporting. Overall, the review concludes that heavy metal contamination of human milk remains a significant concern globally, with several country-level estimates exceeding WHO/JECFA tolerable intakes for infants.
Key numbers
| Metal | Country/Region | Reported Ci | EDI (mg/kg/day) | HQ | CR | Notes |
|---|---|---|---|---|---|---|
| Cd | Iran | NR | 4.7 | 4.7 | NR | Severe outlier; HQ>1 indicates unacceptable non-carcinogenic risk |
| As | Cyprus | 0.73 mg/L | NR | 0.20 | 9.86E-05 | CR below 1E-04 threshold |
| Pb | Cyprus | 1.19 mg/kg | NR | NR | NR | Highest reported Pb concentration in review |
| Hg | Multiple | Varies | NR | NR | NR | Elevated in fish-consuming populations |
| Ni | Multiple | Varies | NR | NR | NR | Less frequently reported |
| Cr | Multiple | Varies | NR | NR | NR | Less frequently reported |
Number of studies included: 22 (PRISMA protocol). Countries represented: Iran, Cyprus, Pakistan, China, India, Turkey, Nigeria, Poland, Italy, Sweden, Spain. Arsenic was not speciated in the primary studies reviewed; concentrations cited represent total arsenic unless individual studies specified otherwise. The Iranian cadmium outlier is discussed as potentially reflecting industrial or dietary contamination specific to the sampling regions and should not be generalized as representative of Iran broadly.
Methods (brief)
Systematic review with PRISMA methodology. Studies included if they measured heavy metal concentrations (Pb, Cd, Hg, As, Ni, Cr) in human breast milk and were published in peer-reviewed journals. EDI calculated using: EDI = (Ci × BFI) / BW, where BFI = breast-feed intake, BW = body weight. HQ calculated against reference doses; CR calculated using cancer slope factors from EPA or equivalent. No meta-analytic pooling of concentrations was performed; the review reports individual study values. Analytical methods of primary studies varied (ICP-MS, AAS, GFAAS); these are noted study-by-study but not harmonized across the review.
Implications
Certification: Confirms that breast milk is a major exposure route for infants, but the extreme geographic variability (especially the Iran Cd outlier and Cyprus Pb outlier) underscores that population-level risk is highly context-dependent. HMT&C threshold work cannot rely on pooled breast-milk data from heterogeneous geographic samples without weighting by population and exposure context.
Courses: Valuable for illustrating the global distribution of heavy metal exposures via breast milk and for discussing why geographic context matters in risk assessment. The Iran Cd case is a strong teaching example of how EDI and HQ can reveal unacceptable local exposures even when individual concentration values might not immediately appear alarming.
App: Limited direct applicability (breast milk is not an ingredient in food products tracked by the app). Provides supporting context for maternal exposure-to-infant-dose modeling.