QUANTIFICATION OF HEAVY METALS IN LAYER & DOMESTIC HEN EGGS: METHODS, GLOBAL OCCURRENCE, EXPOSURE, AND RISK ASSESSMENT (2010–2025): A NARRATIVE REVIEW

Abstract

Background: Eggs are an essential component of human diets worldwide, valued for their high-quality proteins, essential fatty acids, vitamins, and minerals. However, concerns are growing about heavy metal (HM) contamination—particularly lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As), chromium (Cr), nickel (Ni), and copper (Cu)/zinc (Zn). These elements, while some are nutritionally essential, can pose toxicological risks when present in elevated concentrations and may enter eggs through contaminated feed, water, soil, or environmental exposure.

Objective: This narrative review aims to consolidate recent literature (2010–2025) on the occurrence of heavy metals in both commercial and domestic hen eggs, to discuss the factors influencing their transfer and partitioning, to evaluate dietary exposure and associated health risks, and to outline implications for food safety and public health.

Main Discussion Points: Available studies highlight considerable variability in HM contamination across regions and production systems, with domestic and backyard eggs often showing higher Pb and Cd levels than those from regulated commercial farms. Factors such as breed, age, season, housing systems, and feeding practices influence accumulation, with yolk generally exhibiting higher concentrations than albumen, especially for lipophilic compounds like methylmercury. Analytical techniques range from atomic absorption spectrometry (AAS) to advanced ICP-MS and speciation methods, though inconsistency in sample preparation, reporting units, and quality assurance limits cross-study comparability. Global occurrence data reveal higher contamination risks in low- and middle-income regions, particularly near industrial zones, while European surveys report comparatively lower levels due to stronger regulatory enforcement.

Conclusion: Despite their nutritional value, eggs can serve as a pathway for human exposure to hazardous metals. The current evidence underscores the need for harmonized analytical protocols, improved surveillance of backyard systems, and greater attention to toxicological speciation. Clinicians should consider egg-related HM exposure in dietary risk assessments, and policymakers must strengthen regulatory standards to safeguard consumer health.