Heavy metal concentrations in Chinese chicken eggs: insights from comparative study of urban and mining areas

The consumption of eggs in China accounts for over 40% of global egg consumption. Since eggs are a crucial source of daily dietary protein, and are relatively accessible and affordable protein foods, the issue of their food safety needs to be taken seriously. Research in some countries has reported excessively high heavy metal levels in eggs from areas surrounding mining sites. However, the extent of heavy metal contamination in eggs from mining regions in China remains poorly understood.

The concentrations of heavy metals (chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), and lead (Pb)) in eggs from five cities and three mining areas across China were determined by Inductively coupled plasma mass spectrometry (ICP-MS). Subsequently, the metal concentration was used to evaluate the degree of heavy metal pollution in local eggs, while the estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI), and carcinogenic risk (CR) were applied to assess the potential health risks of egg consumption.

The results showed that there were significant differences in the concentrations of heavy metals in eggs from different regions, but the overall concentrations (e.g., Cd < 0.05 mg/kg, Pb < 0.02 mg/kg) all complied with China's national food safety standards for eggs. Within the same region, free-range eggs contained higher heavy metal levels than commercial eggs. The heavy metal HIs of eggs in mining areas were higher than those in non-mining areas, and the HIs of eggs in heavy metal polluted areas were higher than those in non-polluted areas, which made free-range eggs relatively riskier than commercial eggs. This study indicates that free-range eggs may pose a higher risk of heavy metal exposure. In the vast rural areas of China, the potential risk of heavy metal pollution caused by free-range egg farming deserves greater attention.