Munir et al. 2022 — Heavy metal contamination of natural foods: a review (Sustainability)
This open-access review in MDPI Sustainability synthesizes published research on heavy metal contamination in plant-based foods (vegetables, fruits, and cereals) with an emphasis on chromium, cadmium, copper, lead, and mercury, discussing their sources, toxicity mechanisms, and the health risks arising from dietary exposure. The authors retrieved literature from Science Direct, PubMed, Google Scholar, and DOAJ, and conclude that crops grown in polluted soils accumulate significantly higher levels of heavy metals than those from unpolluted soils, and that heavy metals in water, air, and soil reduce the benefits of consuming fruits and vegetables. Toxicity mechanisms are tabulated for the five main metals: for mercury, aquaporin mRNA reduction, glutathione peroxidase inhibition, and ROS production; for lead, heme synthesis disruption and CNS effects; for cadmium, calcium metabolism disruption and renal tubular damage; for arsenic, oxidative stress and genotoxicity; for chromium(VI), lung carcinogenesis and DNA damage.
Key numbers
This is a narrative review; it does not present primary occurrence data or new concentration measurements. Key regulatory and toxicological reference values cited include FAO/WHO Codex maximum levels (ML) in plant foods: Pb in cereal grains 0.2 mg/kg, root/tubers 0.1 mg/kg, fruity vegetables 0.05 mg/kg, leafy vegetables 0.3 mg/kg; Cd in cereal grains 0.1 mg/kg, rice 0.4 mg/kg, leafy vegetables 0.2 mg/kg; As ML not specified (cited as “Codex CXS 193-1995”). No p95 or typical ppb data are primary-generated by this source; all numbers derive from cited secondary sources.
The review notes that the top twenty toxic chemicals by USEPA include Pb, Cd, As, Cr, and Hg. Co, Cu, Ni, Fe, Mn, Zn, Mo, Se are classified as essential but toxic at excess concentrations.
Methods (brief)
Narrative literature review. No systematic review protocol (no PRISMA, no defined inclusion/exclusion criteria stated). Data retrieved from Science Direct, PubMed, Google Scholar, DOAJ. Published December 2021 in Sustainability vol. 14. Evidence tier B because this is a non-systematic secondary review lacking primary occurrence data; it is useful for its toxicology table and regulatory limit summary, not as a source of novel concentration measurements.
Implications
Certification: Useful for background section of certification documentation citing the toxicology basis for analyte selection (Pb, Cd, As, Hg, Cr). The Codex ML table (Table referenced in text) is a convenient secondary summary of plant-food regulatory limits, but should be verified against primary Codex CXS 193-1995 before citing thresholds.
Courses: Good introductory reference for course modules covering heavy metal sources, exposure pathways, and toxicity mechanisms in plant foods. Suitable as a gateway reading before primary studies.
App: Not a source of concentration values for the contamination_profile. Any values derived from this review should be traced back to the primary studies cited within it.