Aendo et al. 2024 — Mercury, lead, cadmium, and manganese in eggs from poultry farms near a gold mine in Thailand
This study compared Hg, Pb, Cd, and Mn concentrations in eggs (yolk and albumen separately) from laying hen, laying duck, and free-grazing duck farms in contaminated (<25 km) and uncontaminated (>25 km) areas surrounding the largest gold mine in Thailand (Pichit Province, operating 2001–2016), which was legally paused at the time of sampling. Free-grazing duck eggs showed significantly higher Hg concentrations than confined laying hen or duck eggs in both areas, attributed to greater environmental exposure through grazing behavior. Pb and Mn were elevated in duck eggs (both confined and free-grazing) relative to laying hen eggs in the contaminated area. Hg and Cd preferentially partitioned into egg albumen, while Pb and Mn were concentrated in the yolk. Ecological risk assessment found Cd in soil around all farm types at considerable to high risk, driven by mining legacy contamination.
Key numbers
Analytical methods: Hg by mercury analyzer (MA-3000, Nippon); Pb, Cd, Mn by graphite furnace AAS (ZA-3000, Hitachi). Concentrations expressed as µg/kg dry weight in egg matrices. LOD: Hg 0.004 µg/L, Pb 1.01 µg/L, Cd 0.07 µg/L, Mn 10 µg/L. Recovery: Hg 99.0%, Pb 101.4%, Cd 102.9%, Mn 102.1%.
- Free-grazing duck eggs in contaminated area showed significantly higher Hg than laying hen eggs (P < 0.05). Exact means visible in Fig. 2 of source; Hg sequestered predominantly in albumen (consistent with prior studies reporting 92% in albumen of penguin eggs).
- Pb in eggs: laying duck and free-grazing duck eggs significantly exceeded laying hen eggs in contaminated area (P < 0.05). Pb concentrated primarily in yolk.
- Cd: partitioned to albumen of free-grazing duck eggs significantly more than yolk (P < 0.05); levels not significantly different between contaminated and uncontaminated areas for farm type comparisons (P > 0.05).
- Mn: elevated in duck eggs relative to hen eggs in contaminated area; concentrated in yolk; confounded by mineral supplementation of drinking water on 66–100% of duck farms.
- Soil ecological risk factor (ER) for Cd: ER > 80 but < 160 (considerable risk) at laying hen and duck farms in contaminated area; ER > 160 but < 320 (high risk) at laying duck farms in uncontaminated area. Hg and Pb soil ER values indicated low ecological risk.
- Hg–albumen Spearman correlations within farm type: r² = 0.71 (laying hen), r² = 0.77 (laying duck), both P < 0.0001.
Methods (brief)
Cross-sectional design with purposive sampling. Eggs dried at 60 °C, digested with 65% HNO₃ and 30% H₂O₂ on block heater. Soil dried at 105 °C. Total metals measured; no mercury speciation (total Hg reported, not MeHg). Dry weight basis for eggs; wet weight basis not reported. Ecological risk index follows Hakanson (1980) framework.
Implications
Certification: Eggs sourced from free-ranging ducks in regions with legacy gold mining contamination can carry elevated Hg (in albumen) and Pb/Mn (in yolk). Poultry egg procurement audits should screen for proximity to historical mining sites.
Courses: Illustrates differential contamination by production system (free-ranging vs. confined) and tissue-partitioning by metal (Hg to albumen; Pb/Mn to yolk).
App: Eggs from free-grazing duck operations in mining-adjacent regions warrant elevated tHg and Pb flags.