Heavy metal contamination in duck eggs from a mercury mining area, southwestern China

This study measured Cr, Zn, Sr, Ba, and Pb concentrations in free-range duck eggs from the Wuchuan mercury mining area in Guizhou Province (southwestern China) compared to a background area (Anshun). The Wuchuan mine has operated for ~400 years; mining ceased ~20 years before sampling, but local environmental Hg (in soil, water, and rice) remains elevated and the mining area is known to carry elevated co-contaminants (Cd, Pb, Cr, As) in soil and crops. Duck eggs from the mining area had higher mean concentrations of all five measured metals than background-area eggs, with yolks consistently carrying higher metal loads than whites for all five metals at both sites. Single-factor pollution indices for the mining-area yolks exceeded 1 for every measured metal (with Pb and Ba highest); USEPA non-carcinogenic risk modelling using Chinese exposure parameters returned total hazard indices (HI) >1 for both adults and children consuming mining-area duck eggs, with HI for children 2.9× the adult value; carcinogenic risk (TCR) for Cr and Pb in mining-area duck eggs exceeded 1×10⁻⁶ in both populations and exceeded 1×10⁻⁵ for children consuming yolk. The paper does not measure total Hg, methylmercury, As, Cd, or Ni in duck eggs (its panel is Cr, Zn, Sr, Ba, Pb only).

Key numbers

All concentrations µg/g dry weight (= mg/kg DW) of separated freeze-dried yolk or white. n=10 per location. Quantification by ICP-MS (Thermo Scientific iCAP RQ) after HNO₃ + H₂O₂ digestion.

Table 2 — mean / median / range concentrations of Cr, Zn, Sr, Ba, Pb in duck egg yolk and egg white from the Wuchuan Hg mining area and the Anshun background area (µg/g DW):

Overall site means (combined yolk + white, abstract values, µg/g DW):

Table 3 — single-factor pollution index (Pᵢ) for Cr, Zn, Sr, Ba, Pb in duck egg yolk and white at the Hg mining area. Pᵢ = Cᵢ / Sᵢ; for Cr/Zn/Sr/Ba, Sᵢ is the corresponding Anshun mean (background standard); for Pb, Sᵢ is the GB 2762–2022 food-safety standard. Pᵢ > 1 indicates contamination above standard.

Reported descending order of single-factor pollution index in egg yolk: Pb (9.83) > Ba (7.87) > Sr (4.46) > Cr (2.07) > Zn (1.26). In egg white: Zn (58.12) > Pb (1.31) > Ba (1.01) > Cr (0.90) > Sr (0.83). Cr and Sr in egg whites have Pᵢ < 1; all other metal/matrix combinations exceed 1.

Table 4 — non-carcinogenic risk assessment (EDI, HQ, HI) for Cr, Zn, Sr, Ba, Pb in mining-area duck eggs, USEPA model. EDI in mg/kg-day; HQ and HI dimensionless. Adult: IR = 0.15 kg/d, BW = 70 kg, ED = 30 a, AT = 10950 d. Child: IR = 0.10 kg/d, BW = 16 kg, ED = 10 a, AT = 3650 d. EF = 365 d/a. Reference doses (RfD): Cr 0.003, Zn 0.300, Sr 0.600, Ba 0.200, Pb 0.0035 mg/kg-day. HI = ΣHQᵢ; HI > 1 indicates potential non-carcinogenic risk.

Total HI for egg yolk: adults 1.13, children 3.28 (both > 1, indicating non-negligible non-carcinogenic risk). Total HI for egg white: adults 0.49, children 1.43 (children > 1). The HI rank for adults and children consuming yolk is Cr > Zn > Ba > Pb > Sr; the child HI is 2.9× the adult HI across the panel.

Table 5 — carcinogenic risk (CR, TCR) for Cr and Pb in mining-area duck eggs. Slope factors: Cr 0.005, Pb 0.0085 mg/kg-day. USEPA acceptable threshold CR ≤ 1×10⁻⁶; potential risk at CR ≥ 1×10⁻⁴.

Total carcinogenic risk (TCR): egg yolk adults 5.78×10⁻⁶, children 16.86×10⁻⁶; egg white adults 3.96×10⁻⁶, children 11.56×10⁻⁶. Cr is the dominant contributor to TCR in both samples and both populations; children’s TCR exceeds adults’, and yolk TCR exceeds white TCR for both Cr and Pb. All TCRs are between the negligible threshold (≤1×10⁻⁶) and the potential-risk threshold (≥1×10⁻⁴), so the authors describe carcinogenic risk as “non-negligible” rather than unacceptable.

Chicken-vs-duck and free-range-vs-caged comparison (Figure 6 and Discussion §4.3). Within Wuchuan, duck-egg Cr, Zn, Sr, Ba, and Pb concentrations are higher than chicken-egg concentrations measured at the same site (the chicken-egg measurements come from the companion paper li2026-heavy-metals-chinese-chicken-eggs-urban-mining); mining-area free-range eggs are higher than caged or non-mining free-range eggs for Cr, Zn, Sr, Ba, and Pb. The authors attribute the duck > chicken pattern to ducks’ more varied free-range diet (crops, grasses, earthworms, fish, shrimps) and waterfowl exposure pathway.

Regulatory comparison cited by the authors. Pb single-factor pollution index uses GB 2762–2022 as the standard value; mining-area yolk Pᵢ mean of 7.70 corresponds to a measured mean of 0.08 µg/g DW Pb in mining-area yolk. The other four metals (Cr, Zn, Sr, Ba) lack Chinese food-safety standards for eggs, so the Anshun mean was used as the background-standard reference.

Methods (brief)

Sampling. Ten free-range duck eggs purchased from local households at each of two locations: Laohugou, Wuchuan County, Zunyi (28°60′ N, 108°01′ E), Guizhou Province — the Wuchuan Hg mining area — sampled 18 July 2022; and Chuanshi Village, Yangchang Town, Anshun (26°35′ N, 106°32′ E), Guizhou Province — the background area — sampled 25 July 2022. Households used similar feeding methods. Eggs transported to laboratory within 24 h and stored at 4°C until preparation.

Sample preparation. Eggs washed with 18.2 MΩ·cm water; yolk and white separated; each fraction freeze-dried and mixed. Each 0.500 g sample digested with 5 mL ultrapure HNO₃ (process ultrapure grade) and 1 mL 30% H₂O₂ (superior purity) at 160°C for 8 h. After cooling, inner chamber of the digestion tank was removed and rinsed with ultrapure water; placed on hot plate at 90°C; volume fixed to 10 mL with 2% HNO₃ and stored at 4°C before measurement.

Quantification. ICP-MS (Thermo Scientific iCAP RQ) for Cr, Zn, Sr, Ba, Pb. Quality control: standard reference materials VAR-CAL-2 (trace elements) and CLMS-1 (rare-earth elements). Reported RSD <10% and recovery 80–110%.

Pollution-index evaluation (Pᵢ = Cᵢ/Sᵢ). For Pb, Sᵢ = GB 2762–2022 food-safety standard. For Cr, Zn, Sr, and Ba (no GB 2762–2022 standard listed for eggs), Sᵢ = Anshun mean concentration. The Anshun-as-standard convention means Pᵢ values for Cr/Zn/Sr/Ba are relative pollution ratios versus background, not regulatory exceedance ratios.

Health risk assessment. USEPA model. EDI = (Cᵢ × IR × ED × EF) / (AT × BW), with IR = 0.15 kg/d (adult) or 0.10 kg/d (child), BW = 70 kg (adult) or 16 kg (child), ED = 30 a (adult) or 10 a (child), AT = 10950 d (adult) or 3650 d (child), EF = 365 d/a. HQ = EDI / RfD; HI = ΣHQᵢ; CR = EDI × SF; TCR = ΣCRᵢ. Cr and Pb are the carcinogenic-risk metals (no carcinogenic slope factors used for Zn, Sr, Ba). HI or TCR > 1 = potential risk; CR/TCR threshold ≤1×10⁻⁶ negligible, ≥1×10⁻⁴ unacceptable.

Statistics. ArcGIS used for site mapping; SPSS 26.0 for analysis. Wilcoxon rank-sum test applied uniformly to test concentration and pollution-index differences. Mean, median, minimum, and maximum reported.

Implications

Certification: Duck eggs from mercury-mining-adjacent areas in Guizhou Province carry elevated Pb, Cr, Zn, Sr, and Ba in this corpus, with mining-area yolk Pb mean of 0.08 µg/g DW (single-factor pollution index 7.70 against the GB 2762–2022 Pb standard). The paper documents that 20 years after cessation of mining at Wuchuan, the pathway from contaminated soil/water/feed to free-range duck eggs remains active, and that this paper’s panel — Cr, Zn, Sr, Ba, Pb — does not measure the metals (Hg, As, Cd, Ni) where mining-area soils are reported as most enriched. Audit programs sourcing whole-egg ingredients from southwestern China should request geographic origin data, especially for free-range eggs from this region.

Courses: Useful for teaching multi-metal contamination pathways in mining-adjacent food systems. The Wuchuan site has been active for ~400 years; this paper illustrates how legacy industrial contamination propagates to free-range poultry decades after operational cessation, and how the contamination signal depends on the production system (free-range > caged) and the species (duck > chicken in the same area, per the companion chicken-egg paper).

App: Contributes duck-egg yolk and white concentration data for Cr, Zn, Sr, Ba, and Pb in Chinese mining-area and background-area free-range eggs, with EDI, HQ, HI, and CR values for adults and children using Chinese exposure parameters. Population-specific HI values (adult vs child) and dose-by-matrix data (yolk vs white) supplied.

Wiki pages this source may touch

• eggs
• lead
• chromium
• zinc
• barium

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 …a mercury mining area.pdf and pointed to a non-existent file (the actual filename ends in , southwestern China.pdf). Corrected to the full filename; verified the file exists at the corrected path (SHA-256 61d928d0e9a2bc1a51c48eea4a53c5bbb39b23a387f9f20dc8798d9955d33635).

(b) metals: previously listed only [Pb, Cr]. The paper’s measurement panel is explicitly Cr, Zn, Sr, Ba, Pb (Methods §2.2.3), and the body referenced all five. Expanded to [Cr, Zn, Sr, Ba, Pb] to match the actual measurement panel and routing-layer needs.

(c) ## Key numbers previously reported only the abstract-level combined (yolk + white) means for the two sites with no Table 2, Table 3, Table 4, or Table 5 reproduction. Expanded to reproduce the full per-matrix Table 2 (mean/median/range for each metal × yolk/white × site), the single-factor pollution-index Table 3, the non-carcinogenic risk-assessment Table 4 (EDI, HQ, HI for adults and children, by yolk and white), and the carcinogenic-risk Table 5 (CR and TCR for Cr and Pb in adults and children). The “Note: This paper did not directly measure tHg or As in the duck eggs” was retained and moved into the lead-paragraph framing, since this is a defining scope limitation of the paper.

(d) ## Methods (brief) previously had compact method detail. Expanded to specify exact sampling locations and dates, sample-prep parameters (0.500 g, 5 mL HNO₃ + 1 mL H₂O₂, 160°C, 8 h, 2% HNO₃ final fix to 10 mL), instrument (Thermo Scientific iCAP RQ; “ThermoFisher” in prior revision was a slight mis-naming — Thermo Scientific is the current brand), CRMs (VAR-CAL-2, CLMS-1), pollution-index formulae, USEPA exposure parameters, and statistics (Wilcoxon rank-sum, SPSS 26.0, ArcGIS). Instrument and software vendor names retained per the 2026-05-17 scientific-method exception (verification-checklist.md §4).

(e) ## Implications previously contained the line “Proposes duck-eggs as a new page.” Per verification-checklist.md §4 (Wiki/HMTc firewall): suggestions that a source warrants a new ingredient/product page are moved to the verification notes for Karen’s review, not stated in the page body. New-page proposal moved here: the source treats duck eggs as a distinct food category (Discussion §4.3 contrasts duck eggs vs chicken eggs and free-range vs caged eggs, and the chicken-egg companion paper Li 2026 uses overlapping sites). Karen may want to evaluate creating [[ingredients/duck-eggs]] once a few more duck-egg-focused papers accumulate (current corpus: this paper, the cfia2025 toxic-metals-foods study that includes duck eggs as one matrix among many, and the companion li2026 chicken-egg paper that does not measure duck eggs).

(f) The body previously contained the cross-source claim “The companion paper by the same group (Li et al. 2026, PeerJ) covers chicken eggs at overlapping sites with a broader metal panel.” This is a true factual link and is preserved, but reframed as a direct wikilink ([[sources/li2026-heavy-metals-chinese-chicken-eggs-urban-mining]]) in the Discussion §4.3 paragraph rather than a free-standing editorial note, to avoid wiki/HMTc-style synthesis framing.

(g) The legacy heading ## Wiki pages updated on ingest was renamed to ## Wiki pages this source may touch per the current Part 6 template; ingredient/metal slugs updated to include [[metals/zinc]] and [[metals/barium]] (paper measures both, but [[metals/strontium]] not added because no strontium page exists in current taxonomy — Sr is captured in metals: frontmatter).

Sample size. sample_n = 20 = 10 (Wuchuan) + 10 (Anshun), consistent with §2.1 (“We collected ten duck eggs each…”) and Table 1 (n=10 per location). The prior revision had sample_n: 20 correct; preserved.

Speciation. The paper does not separate Cr-VI from total Cr; metal slug is Cr, page link is [[metals/chromium]] (not chromium-hexavalent). Hg/As/Cd/Ni not measured (paper scope is Cr, Zn, Sr, Ba, Pb only).

Paper-internal numerical inconsistency. The Results §3.1 narrative text states Wuchuan egg-white means of Cr/Zn/Sr/Ba/Pb = 0.35, 47.73, 7.62, 2.18, 0.02 µg/g and Anshun egg-white means of 0.36, 3.75, 1.35, 0.10, 0.01 µg/g. Table 2 reports the corresponding means as 0.35, 47.73, 2.87, 2.18, 0.01 (Wuchuan white) and 0.16, 0.35, 1.35, 0.10, 0.01 (Anshun white). The Sr and Pb values differ in the Wuchuan white row; the Cr and Zn values differ in the Anshun white row. Table 2 is the formal data table and is used throughout this page; the prose-vs-table discrepancy appears to be a typesetting/manuscript error in the published version. Flagged here for transparency.

Brand firewall. No consumer-brand names appear in the source. Methods section names instrument vendor and CRMs (Thermo Scientific iCAP RQ; Millipore Milli-Q water; VAR-CAL-2; CLMS-1); these are retained per the 2026-05-17 scientific-method-vendor exception.

Wiki/HMTc firewall. No HMTc threshold proposals, consumer risk advisories, or cross-source synthesis claims. The ## Implications section limits itself to what this single paper contributes; the proposed new ingredient page is held in verification notes for Karen’s review per protocol.

Products field. products: ["[[products/poultry-product]]"] is preserved from the prior revision and aligns with the routing-audit row. Duck eggs are not the locked HMTc Category 11 “Eggs” row (which the eggs-product page covers and which the companion li2026 chicken-egg page routes to); the broader poultry-product slug is the correct routing destination for duck-egg evidence until/unless a duck-specific Step 0 Lock is authored.

Duplicate-page note (escalation to Karen). A second wiki source page exists for the same paper: wiki/sources/guo2024-duck-eggs-hg-mining-china.md (raw_handle FM_10932963, raw_path raw/markdown/FM_10932963/FM_10932963.md). Both pages share DOI 10.3389/fpubh.2024.1352043. The FM_ page has fabricated authors (Guo Y, Li Y, Wang Q, Zhang H, Liu J, Feng X) — the correct author list is in the present (MFK) page and matches the PDF byline. The FM_ page also has incorrect sample design (claims 5 sites × n=10 = 50; the actual study is 2 sites × n=10 = 20), incorrect title (“near mercury mining areas” vs the published “from a mercury mining area, southwestern China”), and thin Key numbers with no Table 2/3/4/5 reproduction. The two pages are linked via near_duplicates: [guo2024-duck-eggs-hg-mining-china] in this page’s frontmatter so the relationship is discoverable. Recommend Karen retire the FM_ page (and its routing row) in favor of this MFK page, since this page is the verified-against-PDF version. This duplicate predates the current ingest cycle and is not introduced by this skill execution.

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.