This study quantified ten heavy metals (Cr, Mn, Co, Ni, Cu, Zn, As, Se, Cd, Pb) in 90 chicken eggs from nine areas across China by ICP-MS, comparing free-range eggs from non-mining cities and three mining areas against commercial eggs from supermarkets. All samples complied with China’s National Food Safety Standard for Contaminants in Foods (GB 2762-2022) and with FAO/WHO and EU permissible limits as cited by the authors. Within the same region, free-range eggs consistently carried higher heavy-metal levels than commercial eggs; mining-area free-range eggs were 1.5 to 3.5 times higher in Cd, Pb, and Cr than commercial or non-mining free-range eggs. Monte Carlo–simulated 95th-percentile hazard indices remained below 1 for males, females, and children in every area. The 95th-percentile total carcinogenic risk for children exceeded the USEPA 1×10⁻⁴ threshold in seven of nine areas, driven primarily by Cr, which accounted for 60–75% of TCR across the four areas exceeding the threshold (DG-F, SJZ-F, DZ, EM).
Key numbers
All values are in mg/kg wet weight of whole-egg homogenate (yolk + white) unless noted. n=90 (70 free-range across 7 areas at n=10 each; 20 commercial across 2 areas at n=10 each). ICP-MS quantification; no arsenic or mercury speciation (total As reported; Hg not measured).
Whole-corpus concentration ranges across the nine areas (Results §3.1):
| Metal | Range (mg/kg ww) |
|---|---|
| Cr | 0.053 – 0.14 |
| Mn | 0.25 – 0.63 |
| Co | 2.3 × 10⁻³ – 7.1 × 10⁻³ |
| Ni | 0.015 – 0.063 |
| Cu | 0.47 – 1.38 |
| Zn | 9.99 – 25.09 |
| As (total) | 6.0 × 10⁻³ – 0.019 |
| Se | 0.14 – 0.57 |
| Cd | 1.5 × 10⁻³ – 2.3 × 10⁻³ |
| Pb | 5.4 × 10⁻³ – 0.018 |
Order of concentration in eggs from GZ, XY, SJZ, GY, and WC: Zn > Cu > Mn > Se > Cr > Ni > Pb > As > Co > Cd.
Regional pattern (free-range eggs, paper’s own classification):
- EM (Emin coal mine, free-range): highest Cr, Ni, and Cd among all sites.
- DZ (Danzhai mercury mine, free-range): highest As, Se, and Pb among all sites.
- WC (Wuchuan mercury mine, free-range): elevated relative to non-mining areas; higher overall HI for children.
- GY (Guiyang, free-range, designated clean background): lowest aggregate HI; used as the unpolluted reference.
- SJZ (Shijiazhuang, both free-range and commercial): elevated Cr and Ni reflecting electric-power, steel-smelting, chromium-salt production, and electroplating in the urban catchment.
- DG (Dongguan, free-range): elevated Ni and Cr reflecting electroplating, papermaking, and electronics manufacturing.
Free-range vs commercial within the same region: in SJZ, Cu, Zn, As, Se, and Cd differed significantly between free-range and commercial eggs (P < 0.05). In the DG-vs-GZ comparison (free-range vs commercial in southern Guangdong cities), Cr, Cu, Zn, As, Se, and Cd differed significantly (P < 0.05). Across all seven free-range sampling regions, harmful-metal levels in free-range eggs were higher than in commercial eggs from GZ and SJZ.
Mining vs non-mining (free-range only, Conclusions): Cd, Pb, and Cr in mining-area free-range eggs were 1.5 to 3.5 times higher than in commercial or non-mining free-range eggs.
Regulatory comparison cited by the authors: Mean Pb in this corpus was 0.012 mg/kg, below means reported for Thai gold-mining-area eggs (Aendo et al. 2022, 0.06–0.12 mg/kg), Italian contaminated-site eggs (Esposito et al. 2016), and Bangladeshi eggs (Islam et al. 2015).
Non-carcinogenic risk (Monte Carlo, 95th-percentile HI across nine areas, dimensionless; HI < 1 indicates no NCR):
| Population | Maximum 95th-percentile HI | Area where maximum occurs |
|---|---|---|
| Males | 0.238 | (range across nine areas) |
| Females | 0.283 | (range across nine areas) |
| Children | 0.893 | (range across nine areas) |
Children carried the highest HI in every area. The highest single-metal THQ values reported are for Se in DZ eggs: 0.123 (males), 0.148 (females), 0.476 (children). The lowest THQs are for Cd in XY eggs: 1.6 × 10⁻⁴ (males), 2.6 × 10⁻⁴ (females), 8.6 × 10⁻³ (children).
Carcinogenic risk (Monte Carlo, 95th-percentile CR by area and metal, Table 2). USEPA threshold for unacceptable risk is 1×10⁻⁴; values ≥1×10⁻⁴ are bold in the source table.
| Area | CR_Cr (children) | CR_Cd (children) | CR_Pb (children) |
|---|---|---|---|
| GY | 5.6 × 10⁻⁵ | 2.1 × 10⁻⁵ | 1.7 × 10⁻⁷ |
| WC | 7.7 × 10⁻⁵ | 2.0 × 10⁻⁵ | 2.3 × 10⁻⁷ |
| DG-F | 1.9 × 10⁻⁴ | 5.0 × 10⁻⁶ | 2.0 × 10⁻⁷ |
| XY | 7.2 × 10⁻⁵ | 3.0 × 10⁻⁵ | 2.3 × 10⁻⁷ |
| GZ-C | 7.2 × 10⁻⁵ | 3.5 × 10⁻⁵ | 2.0 × 10⁻⁷ |
| SJZ-C | 9.8 × 10⁻⁵ | 3.0 × 10⁻⁵ | 2.1 × 10⁻⁷ |
| SJZ-F | 2.0 × 10⁻⁴ | 4.9 × 10⁻⁶ | 2.4 × 10⁻⁷ |
| DZ | 1.0 × 10⁻⁴ | 2.8 × 10⁻⁵ | 4.2 × 10⁻⁷ |
| EM | 1.3 × 10⁻⁴ | 3.0 × 10⁻⁵ | 3.1 × 10⁻⁷ |
Across the four areas where children’s TCR exceeded 1×10⁻⁴ (DG-F, SJZ-F, DZ, EM), Cr accounted for 60–75% of the TCR.
Regulatory limits cited by the authors: China GB 2762-2022 for eggs: Pb ≤ 0.2 mg/kg, Cd ≤ 0.05 mg/kg (no listed limit for As, Cr, or Ni in eggs). FAO/WHO and EU permissible limits referenced for Mn (~6 mg/kg), As (~0.1 mg/kg), and Cr (~1.0 mg/kg) per Figure 2 MPL lines. All sampled eggs were below every cited limit.
Methods (brief)
Sampling: 90 chicken eggs collected July–August 2024 from nine geographic areas (latitudes/longitudes in Table 1). Free-range eggs (n=70) drawn from local poultry farms where hens were fed locally sourced corn and vegetables. Commercial eggs (n=20) purchased from local supermarkets in SJZ and GZ. Eggs washed with Milli-Q water, air-dried, broken; yolk and white mixed and combined in PTFE tubes and freeze-dried for 48 h.
Digestion: 0.50 g sample digested with 5 mL ultrapure HNO₃ + 1 mL ultrapure H₂O₂ at 160 °C for 8 h; inner chamber removed and placed on a hot plate at 90 °C to evaporate water; final volume fixed to 10 mL with 2% HNO₃.
Quantification: ICP-MS (ThermoFisher Scientific iCAP RQ, Waltham, MA, USA) at Guizhou University. Standard reference materials VAR-CAL-2 (trace elements) and CLMS-1 (rare-earth elements) measured with blanks and duplicates. Calibration curves built from six concentration points per element with R ≥ 0.99 for all ten elements. Spike recovery verified using CLMS-1. RSD below 10%; recoveries 80–110%. No arsenic speciation (total As reported as “As”). No mercury analyzed.
Risk assessment: USEPA framework (USEPA 1989, 2011) for EDI, THQ, HI, CR, and TCR computed for male adults, female adults, and children using Chinese exposure parameters. Monte Carlo simulation in Crystal Ball v11.1.2.4 (Oracle), 10,000 iterations, 95th-percentile threshold defined as the endangered exposed-population value. Statistics: SPSS 26.0 (IBM); maps in ArcGIS Desktop 10.8 (Esri); graphics in Origin Pro 2024. Group differences tested by one-way ANOVA with Tukey HSD at α = 0.05.
Implications
Certification: Free-range eggs from mining-adjacent areas in China carry Cr, Ni, As, Se, Pb, and Cd loads measurably above commercial supermarket eggs from non-mining cities, but all sampled eggs comply with GB 2762-2022 and with the FAO/WHO and EU permissible limits the authors cite. Audit programs sourcing whole-egg ingredients from China that rely on free-range or pastured supply chains should request geographic origin information, because mining-adjacent free-range eggs from this corpus reach Cr concentrations 2–3× higher than commercial eggs even where no regulatory limit is exceeded.
Courses: The study documents that the order of harmful-metal concentration in eggs from this corpus is Zn > Cu > Mn > Se > Cr > Ni > Pb > As > Co > Cd, and that Cr is the dominant contributor (60–75%) to total carcinogenic risk in mining and industrial areas, exceeding Cd and Pb in this corpus. The paper also documents the production-system gradient (commercial < non-mining free-range < mining-area free-range) for Cd, Pb, and Cr within China.
App: Contributes whole-egg-homogenate occurrence data (range, by area) for Cr, total As, Cd, Pb, and Ni in Chinese chicken eggs, with mining-area vs non-mining-area and free-range vs commercial stratification. Supports the eggs contamination profile for the Chinese supply chain.
Wiki pages this source may touch
Verification notes
2026-05-19 (Claude Code, merge-enhance from prior 2026-05-14 page). The prior revision had several defects corrected here:
(a) raw_path: was truncated to …insights from.pdf and pointed to a non-existent file; corrected to the full filename Heavy metal concentrations in Chinese chicken eggs_ insights from comparative study of urban and mining areas.pdf (verified the real file exists at that path).
(b) ## Key numbers previously listed only the abstract-level compliance summary and a few qualitative regional patterns; expanded to reproduce the per-metal concentration ranges (Results §3.1), the 95th-percentile HI and CR values from the Monte Carlo simulation (Tables 2 and S4 per Discussion), and the regulatory limits and prior-literature comparisons the authors cite. The “Free-range vs. commercial within same region” line in the prior revision singled out SJZ Pb and As as higher in free-range eggs; the source’s Results §3.1 lists the significant SJZ contrasts as Cu, Zn, As, Se, and Cd (not Pb), and the DG-vs-GZ contrast as Cr, Cu, Zn, As, Se, and Cd (not Pb or As). Corrected.
(c) The prior ## Key numbers compliance line read “Pb: <0.02 mg/kg in all samples (China national standard).” This conflated the measured Pb upper bound (the corpus maximum is 0.018 mg/kg) with the regulatory standard (GB 2762-2022 Pb ≤ 0.2 mg/kg for eggs). The two values differ by a factor of ten; the prior line implied the standard is 0.02 mg/kg. Corrected — the standards are now stated separately from the measured ranges.
(d) The prior ## Implications Certification line began “This study confirms that even in a heavily industrialized/mining country, eggs can meet national food safety standards…” — a synthesis claim about literature consensus that violates CLAUDE.md Part 2 (the wiki reports what this single paper found, not how it relates to other literature). Rewritten to describe what the paper itself documents about this corpus.
(e) The prior ## Implications Courses line (“free-range production systems that allow foraging on contaminated soil produce eggs with higher heavy metal loads, reversing the common consumer assumption that free-range means safer”) had consumer-audience risk-advisory tone with editorial framing (“reversing the common consumer assumption…”). Rewritten to state the paper’s documented finding without editorializing.
(f) The legacy heading ## Wiki pages updated on ingest was renamed to ## Wiki pages this source may touch per current Part 6 template. The metal list under that section was extended to use the speciation-correct slugs (arsenic-total not arsenic, given the paper does not separate iAs from tAs).
(g) metals: retained as [Cr, tAs, Cd, Pb, Ni] — these are the five metals the paper measures that are HMTc-analyte-relevant or that map to existing metal pages with carcinogenic-risk computation in the source. The full ten-metal panel is preserved in the ## Key numbers table; the frontmatter metals: field carries the routing-relevant subset.
Sample size. sample_n = 90 = 70 free-range + 20 commercial, consistent with Sampling and pre-treatment (p.4).
Speciation. The paper measures total As (no inorganic-vs-total speciation); metals: uses tAs and the body refers to “As (total)“. The paper does not measure any mercury species; no Hg entries are made. The paper measures total Cr (no Cr-VI speciation); metals: uses Cr and the metal-pages list links [[metals/chromium]] (total Cr) rather than [[metals/chromium-hexavalent]].
Brand firewall. No consumer-brand names appear in the source paper. The methods section names instrument and software vendors (ThermoFisher iCAP RQ; Crystal Ball v11.1.2.4 / Oracle; SPSS 26.0 / IBM; ArcGIS Desktop 10.8 / Esri; Origin Pro 2024) and reference materials (VAR-CAL-2, CLMS-1); these are retained per the 2026-05-17 scientific-method exception (Check 4 of docs/gpt-collaboration/audit-prompt.md). No brand-by-brand contamination ranking exists in the source or this page.
Wiki/HMTc firewall. No HMTc threshold proposals, consumer risk advisories, or cross-source synthesis claims are made. The ## Implications section limits itself to what this single paper contributes to threshold work and explicitly does not propose certification values.
Products field. products: ["[[products/eggs-product]]"] is retained because the eggs-product page is the Step 0–locked routing destination for HMTc Category 11 Row 6 (“Eggs”); the source’s whole-egg-homogenate matrix routes there directly.
Page history
The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.
| Commit | Date | Description |
|---|---|---|
| b0f3d38 | 2026-06-12 | batch | corpus rescreen b04 old terminal skips |