Hernández-Montoya et al. 2026 — Heavy metal contamination in foods: scoping review of detection, regulation, and health risk

This PRISMA-ScR scoping review (121 studies from 255 initial records) synthesizes peer-reviewed literature on the occurrence of five priority toxic metals (As, Cd, Pb, Hg, Ni) in food matrices, emphasizing contamination pathways, analytical detection strategies, and documented human health effects. The review is qualitative — no quantitative meta-analysis was attempted because of methodological heterogeneity across included studies, and no formal risk-of-bias assessment was performed. Chromium and tin were excluded by design.

The review consolidates regulatory maximum levels from Codex Alimentarius CXS 193-1995 Rev. 2024, EU Regulation 1881/2006, EU Regulation 2023/915, and OIV 2021 (wine), and provides a comparative overview of conventional analytical methods (AAS, ICP-MS, ICP-OES, LC-ICP-MS, AFS, DMA) and emerging methods (portable XRF, Raman/SERS, electronic tongues, nanomaterial-based electrochemical biosensors, in situ environmental magnetism).

Key numbers

Regulatory limits (Table 1 of paper)

The review’s Table 1 consolidates maximum permissible levels for As, Cd, Pb, and Hg in food matrices according to Codex Alimentarius (CXS 193-1995, Rev. 2024), EU Regulation 1881/2006, EU Regulation 2023/915, and OIV 2021 (wine). Values are reproduced exactly as the review presents them; for HMTc purposes these should be re-verified against primary regulatory sources before citing in threshold-setting work.

Arsenic (As)

• Edible fats and oils: 0.10 mg/kg — Codex 193-1995 Rev. 2024
• Salt and food-grade salt: 0.50 mg/kg — Codex 193-1995 Rev. 2024
• Husked rice: 0.35 mg/kg — EU 1881/2006
• Polished rice: 0.20 mg/kg — EU 1881/2006
• Natural mineral water: 0.01 mg/L — Codex 193-1995 Rev. 2024 (most restrictive)
• Grains (wheat, maize, legumes): 0.20 mg/kg — Codex / EU 2023/915

Cadmium (Cd)

• Natural mineral water: 0.003 mg/L — Codex 193-1995
• Rice: 0.40 mg/kg — EU 1881/2006
• Leafy vegetables: 0.20 mg/kg — EU 1881/2006 (higher bioaccumulation)
• Legumes and tubers: 0.10 mg/kg — EU 1881/2006
• Chocolate >50% cocoa: 0.80 mg/kg — EU 1881/2006
• Chocolate >70% cocoa: 0.90 mg/kg — EU 1881/2006
• Seafood (mollusks, bivalves, cephalopods): 2.00 mg/kg — Codex 193-1995 Rev. 2024
• Food-grade salt: 0.50 mg/kg — Codex 193-1995 Rev. 2024
• Wine: 0.01 mg/L — OIV 2021

Lead (Pb)

• Infant foods (intended for infants and children up to 36 months): 0.01 mg/kg — Codex / EU 1881/2006
• Milk and dairy products: 0.02 mg/kg — Codex / EU 1881/2006
• Fruits and vegetables: 0.10 mg/kg — Codex 193-1995 Rev. 2024
• Cereals and grains: 0.20 mg/kg — Codex 193-1995 Rev. 2024
• Meat (beef, pork, poultry): 0.10 mg/kg — Codex 193-1995 Rev. 2024
• Fish: 0.30 mg/kg — Codex 193-1995 Rev. 2024
• Wine (year ≥ 2019): 0.10 mg/L — OIV 2021 (updated limit)
• Wine-based spirits: 0.15 mg/L — OIV 2021
• Food-grade salt: 1.00 mg/kg — Codex 193-1995 Rev. 2024

Mercury (Hg)

• Natural mineral water: 0.001 mg/L — Codex 193-1995 Rev. 2024
• Food-grade salt: 0.10 mg/kg — Codex 193-1995 Rev. 2024
• Fish (general, total Hg): 0.50 mg/kg — Codex 193-1995 Rev. 2024
• Methylmercury in large predatory fish (shark, marlin, tuna, etc.): 1.0–1.7 mg/kg — Codex 193-1995 Rev. 2024

Global contamination burden

Approximately 14–17% of agricultural soils globally contain toxic metal concentrations exceeding permissible limits, with Cd showing the highest exceedance rate, followed by Ni and Cr. A “metal-enriched corridor” extending across southern Europe, the Middle East, South Asia, and China — shaped by geological conditions, climatic and topographic factors, and long-term mining activity — is estimated to expose between 0.9 and 1.4 billion people to significant ecological and health risks (Hou et al. 2025, Science 388:316–321, cited as ref [4]).

Reported food-matrix concentrations cited by the review

Rice is repeatedly identified as a crop with high capacity to accumulate Pb and Cd, with concentrations in some contexts exceeding regulatory thresholds by several fold depending on crop variety, irrigation practices, soil properties, pH, and fertilizer use. Studies on widely consumed fruits and vegetables (spinach, lettuce, apples, bananas, grapes, berries) report concentrations exceeding Codex Alimentarius values in certain contexts. Elevated levels of As and Zn have been observed in leafy vegetables, Ni in fruits, and Cu in staple cereals such as rice and maize (cited as Rai et al. 2019, ref [31]).

One cited study (Cantoral et al. 2024, Toxics 12:318, ref [50]) analyzed Pb in 103 Mexican food and beverage samples by GF-AAS; 18% of samples showed Pb concentrations between 0.021 and 1.005 mg/kg, with the highest values reported in:

• Baby rice cereals: 1.005 mg/kg
• Whole-wheat bread: 0.447 mg/kg
• Precooked rice: 0.276 mg/kg
• Black pepper: 0.239 mg/kg
• Turmeric: 0.176 mg/kg

In the review’s Mercury subsection (page 19), studies conducted between 1971 and 2021 are summarized as having reported Hg concentrations of up to 25 µg/L, with approximately 25% of measurements exceeding the WHO drinking-water guideline of 1 µg/L. The review does not name the specific reference for this aggregate figure; the framing context throughout the paragraph is drinking-water exposure.

Human-exposure benchmarks cited

• WHO drinking-water inorganic arsenic guideline: 10 ppb; over 140 million people worldwide consume drinking water exceeding this value.
• WHO drinking-water mercury maximum: 1 µg/L.
• WHO blood-lead threshold for comprehensive exposure assessment: 5 µg/dL.
• EFSA cadmium tolerable weekly intake (2012): 2.5 µg/kg body weight (cited as refs [118,119]).
• Cd absorption: approximately 6% via oral route; 10–50% via inhalation; <1% dermal.
• Blood Pb in Nigerian populations associated with soft-drink consumption: 0.48–0.88 µg/dL in adults; 0.06–2.98 µg/dL in children.

Heavy metals and adverse health effects (Table 3 of paper)

Comparative analytical-methods overview (Table 2 of paper)

Methods (brief)

Scoping review following the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) framework. No protocol registration. Literature search via Scopus, Web of Science, ScienceDirect, SpringerLink, Wiley Online Library, and Google Scholar, with English-language peer-reviewed articles only, published through 2026. Core search terms: “heavy metals”, “food contamination”, “detection techniques”, “human health effects”, combined with Boolean operators. Selection: 255 initial records → 60 duplicates removed → 195 screened → 74 excluded by title/abstract → 121 included for qualitative synthesis. Inclusion focus: occurrence of As, Cd, Pb, Hg, Ni in food matrices; conventional or emerging analytical methods; human health effects of dietary exposure. Exclusions: studies on Cr or Sn, non-food matrices, theses or non-peer-reviewed materials, insufficient methodological detail. No quantitative meta-analysis attempted. No formal risk-of-bias assessment performed. Data extracted manually using predefined tables (publication year, food matrix, metal, analytical method, reported health effects). No imputation; only explicitly reported information was synthesized.

Implications

Certification: Useful as a high-level synthesis of the international regulatory-limit landscape for As, Cd, Pb, and Hg, updated through Codex Rev. 2024, EU 2023/915, and OIV 2021. The regulatory-limits table provides a convenient cross-reference, but every value should be verified against the primary regulatory source before being cited in HMTc threshold-setting work — the review is a B-tier secondary source, not a primary regulation document. The review does not propose certification thresholds, and its evidence-tier (B, review) precludes using it as primary evidence for any commodity concentration value; the underlying primary studies (121 papers cited in Supplementary Material S2) carry the primary-evidence weight.

Courses: Provides framing for the “why detection matters” and “regulatory complexity” course modules. The emerging-detection section (portable XRF, SERS, biosensors, electronic tongues, in situ environmental magnetism) is a useful update on field-deployable alternatives to laboratory-based reference methods, with a balanced discussion of their complementary role (screening) rather than replacement role (confirmation).

App: No new commodity-level concentration data is produced by the review itself; the concentration figures cited (e.g., the Pb in Mexican baby rice cereals at 1.005 mg/kg) come from primary studies that should be ingested separately. Use this page only as regulatory context, not as a contamination-data source.

Wiki pages this source may touch

• lead
• cadmium
• nickel
• arsenic
• mercury
• mercury-methyl
• eu-1881-2006-contaminants-superseded
• eu-2023-915-cadmium
• eu-2023-915-lead-infant-young-child-foods
• codex-cadmium-mls
• efsa-cadmium-twi

Verification notes

2026-05-28 merge-enhance pass. Original ingest (2026-05-14) carried multiple defects in the Key numbers regulatory-limits table; these were verified against PDF Table 1 (page 8 of 27) and corrected:

• “Husked rice 0.35 mg/kg (EU 1881/2006)” and “Polished rice 0.20 mg/kg (EU 1881/2006)” were listed under Cadmium in the prior page. Table 1 places both under Arsenic — corrected.
• “Grains (wheat, maize, legumes) 0.20 mg/kg (Codex/EU 2023/915)” was listed under Cadmium. Table 1 places this under Arsenic — corrected.
• “Seafood (mollusks, bivalves, cephalopods) 2.00 mg/kg” was listed under Lead. Table 1 places this under Cadmium — corrected.
• Cd Natural mineral water (0.003 mg/L), Cd Food-grade salt (0.50 mg/kg), Cd Wine (0.01 mg/L OIV 2021), Pb Wine ≥2019 (0.10 mg/L OIV 2021), Pb Wine-based spirits (0.15 mg/L OIV 2021), Pb Food-grade salt (1.00 mg/kg), Hg Natural mineral water (0.001 mg/L), and Hg Food-grade salt (0.10 mg/kg) were missing from the prior page — added.
• Table 3 health-effects synthesis was missing in the prior page — added as a structured table.
• Table 2 comparative analytical-methods overview was missing in the prior page — added.
• Cantoral et al. 2024 Pb-in-Mexican-foods data (cited at ref [50] in the review, page 18) was missing in the prior page — added under “Reported food-matrix concentrations”.
• WHO and EFSA exposure benchmarks (As 10 ppb, Hg 1 µg/L, Pb 5 µg/dL, Cd TWI 2.5 µg/kg bw, Cd absorption fractions) were missing — added.
• The “Wiki pages updated on ingest” section had three broken regulation wikilinks: regulations/codex-cxs-193-1995 (no general page exists; nearest existing slug is codex-cxs-193-1995-tin-canned-foods, which is tin-specific and not appropriate), regulations/eu-1881-2006 (correct slug: eu-1881-2006-contaminants-superseded), regulations/eu-2023-915 (split into eu-2023-915-cadmium and eu-2023-915-lead-infant-young-child-foods). The codex-cxs-193-1995 general-standard target was dropped (no canonical page); replaced with codex-cadmium-mls and efsa-cadmium-twi which exist and which the review references. The other two were corrected to valid slugs.
• jurisdictions: field used codex as a token; this is not the standard ISO/region vocabulary used across wiki/sources/. Replaced with international (used in 34 sibling source pages).
• Ingredients expanded from rice/cereals/vegetables/seafood to include the additional broad slugs the review centrally discusses (leafy-vegetables, fish, legumes, chocolate, spices, water) — all present in the taxonomy snapshot.
• Section heading “Wiki pages updated on ingest” renamed to “Wiki pages this source may touch” (current convention; the prior heading is the legacy form).

products: [] is retained as appropriate for a high-level scoping review with no product-category-specific measurements. The routing audit treats this as advisory.

Methylmercury speciation flag preserved. The review explicitly distinguishes total Hg vs MeHg in fish (Codex 193-1995 Rev. 2024 sets 0.50 mg/kg total Hg for fish generally vs 1.0–1.7 mg/kg MeHg for large predatory species). Both tHg and MeHg are retained in metals:.

matrices: vocabulary. The frontmatter retains the prior page’s [dietary-intake, food, food-general] tokens. dietary-intake is used across 30+ sibling source pages; food and food-general are non-standard but functional placeholders that flag this page as topic-agnostic (no single commodity matrix is the focus). The 2026-05-28 fresh-context audit flagged these as advisory-only (not in the typical matrix vocabulary, no ## Verification notes entry); this note documents the deliberate broad-scope choice for a scoping review with no commodity-specific measurements.

2026-05-28 audit application. Subagent verdict REVISE with two ⚠️ concerns, zero ❌ definite errors. Findings applied:

• Hg-25-µg/L sentence: prior wiki phrasing “environmental samples” was not supported by the source; PDF page 19 frames the figure within the WHO drinking-water 1 µg/L paragraph. Wording tightened to reflect the source framing.
• matrices: vocabulary: documented above as deliberate broad-scope choice (no source change required; verification-notes entry added per audit recommendation).

No findings rejected.

Page history

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