Heavy Metal Residue (As, Cd, Hg, and Pb) in Hen Eggs after Applying Different Cooking Methods

Abstract

As a nutritious food, eggs are capable of accumulating heavy metals and are a good indicator of environmental contamination. This study is aimed at determining the levels of heavy metal residues (As, Cd, Hg, and Pb) in hen eggs after applying different cooking methods. In an experimentally designed study, forty-four hen egg samples were selected from 22 best-selling brands of supermarkets in Tehran and categorized into one of four groups (raw, dry-frying, and boiling with and without eggshells). The levels of heavy metal residues were analyzed by using inductively coupled plasma mass spectrometry (ICP-MS). The average levels of heavy metals (As, Cd, Hg, and Pb) in raw samples were 0.307, 1.654, 0.121, and 6.5 (μg.kg-1), respectively. After applying cooking methods, the residue of two heavy metals in boiling without eggshells (As: $0.228\pm 0.197$ ; Cd: $1.985\pm 0.037$ ) was lower than boiling with eggshells (As: $0.457\pm 0.918$ ; Cd: $2.11\pm 0.223$  μg.kg-1), while the dry-frying method had the lowest level of heavy metal residue (As: $0.222\pm 0.109$ ; Cd: $1.54\pm 0.223$ ) ( $p<0.05$ ) and could be identified as efficient in reducing the amount of these heavy metals. In addition, different cooking methods did not make a significant difference in other heavy metal residues (Hg and Pb). To explain this reduction, two hypotheses can be proposed to explain the reduction of heavy metals after applying different cooking methods. First, the eggshell is permeable; the second is the association of heavy metals bonding with sulfur groups and weight loss due to evaporation. All heavy metal residues were found to be within acceptable permissible thresholds. Therefore, policymakers should protect the health of the population by continuously monitoring heavy metals in foods and prioritizing education and research on how to reduce them in the food chain.