Alinezhad et al. 2024 — Heavy metals in pasteurized and sterilized milk: systematic review
This PRISMA-compliant systematic review pooled data from 48 peer-reviewed studies (n=981 milk samples) published between 2000 and 2023 across multiple countries to characterize heavy metal contamination in commercially pasteurized and sterilized cow’s milk. The review found that Cu, Cd, Zn, and Pb were the metals most commonly exceeding regulatory maximum permissible limits (MPLs) set by the EU, Codex Alimentarius, and national standards. Exceedances were geographically uneven, with samples from Iran, China, Turkey, Egypt, Brazil, Pakistan, and India collectively accounting for the bulk of reported values.
Key numbers
Lead (Pb): reported concentrations ranged widely across studies; mean values in individual studies ranged from below 0.001 to as high as 0.52 mg/kg. Pb was among the four most frequently reported metals exceeding MPLs. Cadmium (Cd): mean values in individual studies ranged from below detection to approximately 0.05 mg/kg; Cd was the second most frequently cited metal exceeding limits. Aluminum (Al): present in multiple studies but not consistently the most-exceeded metal; mean values in individual studies ranged from below 0.1 to over 1 mg/kg in some regions. Copper (Cu): the most frequently reported metal exceeding MPLs across the pooled studies, with mean values in individual studies up to approximately 1.5 mg/kg. Arsenic (As): present in a subset of studies; mean values generally below 0.05 mg/kg but with elevated values reported from regions with known groundwater arsenic problems. Mercury (Hg), Nickel (Ni), Chromium (Cr), Cobalt (Co), Zinc (Zn), and Iron (Fe): all reported across subsets of the 48 studies; Zn and Fe at nutritional-range concentrations in most samples.
Analytical methods across included studies: AAS (most common), ICP-MS, ICP-OES. Detection limits varied substantially across the included primary studies; the review notes this as a limitation affecting pooled estimates.
Methods (brief)
Systematic review following PRISMA guidelines. Literature searches in PubMed, Scopus, and Web of Science through 2023. Inclusion criteria: peer-reviewed studies measuring heavy metal concentrations in commercial pasteurized or sterilized cow’s milk. Studies reporting only raw or unpasteurized milk, or milk from non-bovine species, were excluded from the main analysis but noted. Quality assessment of primary studies performed using a modified scoring system; results stratified by study quality. Quantitative pooling limited by heterogeneity in analytical methods, LOD/LOQ reporting, and unit conventions across studies.
Implications
Certification: The systematic evidence that Cu, Cd, Zn, and Pb most commonly exceed MPLs in commercially processed cow’s milk across global markets supports HMT&C’s inclusion of Pb and Cd as priority analytes for dairy-containing products. The review’s finding that exceedance rates are highest in studies from lower-income markets with weaker enforcement does not relieve the need for monitoring in certified supply chains drawing on global ingredients.
Courses: Useful as an introductory evidence anchor for modules on dairy contamination pathways and the regulatory patchwork for Pb and Cd in milk across EU, Codex, and national standards.
App: The global range of mean concentrations reported across studies (spanning roughly an order of magnitude for Pb and Cd) is too wide for a single point estimate; the app should represent cow’s milk contamination as a range with geography-conditional weighting.
Microbiome: Not applicable.