This study measured Cr, Zn, Sr, Ba, and Pb concentrations in duck eggs from the Wuchuan mercury mining area in Guizhou Province, southwestern China, comparing to a clean background area (Anshun). The study was motivated by the established finding that Hg mining areas also have elevated co-contaminants including Cd and As in soil, and that duck eggs in this area previously showed elevated total Hg. Duck eggs from the mining area had significantly higher concentrations of all five metals than the background area, with yolks consistently more contaminated than whites. Single-factor pollution index and USEPA health risk models indicated that duck egg consumption in the mining area poses non-negligible ecological and health risk, particularly for children.
Key numbers
All values µg/g (= mg/kg) dry weight. n = 10 per location. Method: ICP-MS (ThermoFisher iCAP RQ). Reference area comparison (mean values):
Wuchuan (Hg mining area) vs. Anshun (background):
| Metal | Wuchuan mean (µg/g DW) | Anshun mean (µg/g DW) |
|---|---|---|
| Cr | 0.38 | 0.21 |
| Zn | 63.06 | 24.65 |
| Sr | 4.86 | 1.43 |
| Ba | 10.08 | 1.05 |
| Pb | 0.05 | 0.01 |
Egg yolks contained higher metal levels than egg whites for all five metals at both sites. Single-factor pollution indices for Cr and Pb in Wuchuan eggs exceeded 1.0 (indicating contamination above background standard). Health risk assessment: HI (hazard index) for all five metals combined exceeded 1 for children consuming mining-area duck eggs, driven primarily by Zn and Ba contributions.
Note: This paper did not directly measure tHg or As in the duck eggs (its scope was Cr, Zn, Sr, Ba, and Pb specifically). The companion paper by the same group (Li et al. 2026, PeerJ) covers chicken eggs at overlapping sites with a broader metal panel.
Methods (brief)
ICP-MS (ThermoFisher Scientific iCAP RQ). Sample prep: yolk and white separated, freeze-dried, mixed; 0.500 g digested with 5 mL ultrapure HNO3 + 1 mL H2O2 at 160°C for 8 h; volume fixed to 10 mL with 2% HNO3. Quality: CRMs VAR-CAL-2 and CLMS-1; RSD < 10%; recovery 80–110%. Risk assessment: USEPA model with Chinese population parameters; single-factor pollution index using background area values as standard (except Pb which used GB 2762–2022 food safety standard).
Implications
Certification: Duck eggs from mercury mining areas carry elevated Pb and Cr co-contamination even when tHg is the primary concern. This study documents that Hg remediation of mining sites does not eliminate other heavy metal contamination routes, and that 20+ years after cessation of mining operations at Wuchuan, the contamination pathway to poultry eggs persists.
Courses: Useful for teaching multi-metal contamination in mining-adjacent food systems. The Wuchuan site has been active for ~400 years of Hg production; this illustrates the persistence of contamination after industrial cessation.
App: Duck eggs are a distinct ingredient from chicken eggs. Proposes duck-eggs as a new page. The Cr and Pb concentrations in mining-area duck eggs are substantially higher than background, relevant to risk scoring.