**3.2 Poultry**

Among animal products, eggs are also a possible source of heavy metal contamination. The transferability of heavy metals between hens raised in improved cages and those raised outdoors and found that the extensive soil contamination with these pollutants resulted in free-range eggs having greater heavy metal concentrations than conventionally produced eggs [1, 75, 76]. A study revealed that Cd levels were 0.018 vs. 0.023 ppm in the free-range group, essential Cu levels were 2.591 vs. 2.734 ppm, and essential Zn levels were 5.386 vs. 5.522 ppm in improved cages [1, 76]. By attaching to protein sites and displacing the original metals from their native binding sites, heavy metals can lead to cell dysfunction and toxicity [77, 78]. Additionally, the binding of heavy metals to macromolecules like DNA and nuclear proteins causes oxidative distress [7, 79]. Albumin, the most prevalent protein in plasma, binds to their ions [77]. According to a study, [79] they attach to the free sulfhydryl group of terminal cysteine residues and to histidine residues, which disrupt mitosis, cell respiration, and cell enzymes, especially when arsenic is present [80]. In chicken meat, higher quantities of cadmium have been found [78, 81]. Exposure to cadmium can cause oxidative stress and change the antioxidant enzyme activity in the erythrocytes of adult poultry birds [82]. Cadmium primarily builds up in the proximal tubular cells, where it damages bones or interferes with kidney function to promote bone mineralization [83]. As metallothionein, cadmium binds to proteins that are high in cysteine [84]. As they have similar oxidation states, it can take the place of the zinc in metallothionein and prevent it from acting as a cell scavenger of free radicals, producing hepatotoxicity in the liver and circulating to the kidney, accumulating in the renal tissue, and causing nephrotoxicity [85–87]. Poisoning by lead can occur in poultry [88]. A report from a study revealed that, lead in the feed can significantly stunt chicken growth and decrease blood Delta-aminolevulinic acid dehydratase levels [89]. In hens, the bone has the highest concentrations of deposited lead, followed by the kidney, liver, and skeletal muscle [90]. Majority of investigations revealed that the most often found heavy metals in chicken liver were arsenic, cadmium, mercury, and lead residues. Due to its ability to bind to and deactivate vital enzymes, lead is the most hazardous element [1, 7, 25, 37]. The liver and kidneys bio-transform arsenic, and the methylated metabolites are distributed throughout the body [91]. The amount of accumulated element in the organs varies on the duration of exposure, the amount of ingested element, the animal's age, and breed [92, 93]. Since these effects are dose-dependent, prolonged exposure to heavy metals through contaminated feed is likely to result in more harmful changes to tissues [93].

### **3.3 Fish**

Fish may be a source of heavy metal exposure for people because it contains important proteins and n-3 polyunsaturated fatty acids [94]. Fish living in


### **Table 3.**

*Levels of some heavy metals in fishes as reported in WHO.*

contaminated waters have a tendency to accumulate heavy metals from the petroleum industry, air sources, and cosmetics in their tissues [11]. In general, accumulation activities depend on the amount of metal present, the length of exposure, the method used to prepare the metal for absorption, the environment (water, nuclear fuels, chromium and cadmium electroplating, temperature, pH, hardness, salinity), and intrinsic factors such as fish age and feeding habits [92, 93]. Rubber tire dust on the road surface contains cadmium, lead, and zinc [95]. Different fish tissues have a predilection for these tiny sizes [96]. Majority of these particles allow the harmful metals to rise on the wind, where they will primarily concentrate in the liver, kidney, and gills [97]. They may also be ingested or transferred to the soil or edible plants. Heavy metal build-up in fish tissues (**Table 3**) is mostly influenced by their concentrations in the water, in food, or in commercial feed [98]. The visceral tissues of fish, such as the liver, kidney, and intestines, which are typically discarded throughout the production procedures, tend to accumulate more metals than the muscles when compared to the other tissues in fish [1, 97, 99]. Significant correlations between lipid levels and concentrations of critical Cu and Zn [100] in two species of farmed fish (pompano and snapper). According to the research, lipid content may play a significant role in controlling the bioaccumulation of certain metals. Although copper is a necessary metal for both types of fish, its toxicity causes damage to the fish's gills, liver, and kidneys, which can result in death [101]. Lead has physiological and biochemical effects by acting as a mimicking agent to replace necessary metabolic components like calcium, iron, and zinc [102]. For example, it directly inhibits the action of sulfhydryl group-rich protein enzymes as well as zinc and iron in the production of heme [103]. Lead binds to a variety of transport proteins, including calcium-ATPase, calmodulin, transferrin, metallothionein, and metallothionein [104].
