**4. Mercury in food chain**

Mercury enters the food chain *via* various pathways. Chloralkali industry is one of the European users that pollute Europe's aquatic environments with tones of mercury [20]. In aquatic environments, inorganic mercury biotransforms into methyl mercury, which makes mercury biomagnify in food chains [13]. High acidity and high concentration of dissolved organic carbon in the water enhance the mobility of mercury that enters the food chain [26, 27]. People, who eat a lot of fresh or marine food, have the high risk of mercury intake [28].

On the other hand, this pollutant (Hg) is highly mobile in soils; and can be absorbed easily by plant roots [12]; yet, in the presence of organic additives, the mobility of inorganic and organic forms of Hg could be diminished considerably, forming low mobile complexes [29]. Also, Hg in the atmosphere is taken up in substantial amounts by areal plant parts *via* gas exchange [30], accumulates in edible plant parts [8], and hence enters the food chain [6, 18, 19]. Additionally, sewage irrigation practices account for further soil contamination with Hg [31]. Anyhow, this contaminant has no identified biological role in plants [8]; nevertheless, it exhibits high affinity to forms complexes with soft ligands such as sulfur in the form of insoluble and stable compounds [32]. This in turn inactivates numerous enzymatic reactions, amino acids, and sulfur-containing antioxidants [33].
