Mercury partitioning and dietary exposure risk in free-range eggs from China's polluted regions

This study collected free-range eggs from contaminated regions in China, with emphasis on legacy Hg mining areas. Total mercury (THg) and methylmercury (MeHg) were quantified in four egg compartments (white, yolk, shell membrane, and shell). THg concentrations ranged from 1.39 to 90.76 μg/kg wet weight (ww), and MeHg from 0.74 to 40.56 μg/kg ww. While most samples met the Chinese food safety limit (50 μg/kg ww), eggs from mining areas consistently exceeded this threshold. THg distribution followed egg white > yolk > shell membrane > shell. Hg concentrations in egg white strongly correlated with those in whole eggs (ρ = 0.90), indicating that egg white serves as a reliable, non-invasive biomarker for Hg contamination. Health risk assessment suggests that Hg exposure from egg consumption generally remained within safe limits (HQ < 1). Nevertheless, exposure risks were significantly higher in Hg mining areas than in other areas. Further dietary exposure comparison revealed that Hg intake via eggs was lower than that via rice for adults but higher for children. These findings highlight that free-range eggs represent a significant Hg exposure pathway in Hg mining areas, emphasizing the necessity of targeted monitoring strategies to protect vulnerable populations, especially rural children.