# Potential Metal Contamination in Foods of Animal Origin--Food Safety Aspects
## 2 Major Toxic Metals in Food
### Lead (Pb)
Feeding diets with severe protein deficiency or very high protein and fat content also increases lead absorption. It can also enter the body through the lungs, which is significant if the particle size of lead-containing dust is <0.5 \(\upmu\)m.  
Lead absorbed from the intestinal tract is transported to the liver via the portal circulation, where some is excreted in bile. The excreted compounds may be reabsorbed depending on their lipophilic properties (showing enterohepatic circulation). The majority (>90%) of the lead entering the bloodstream is bound to hemoglobin in red blood cells [82]. It is also bound to albumin, \(\gamma\)-globulins, and low molecular weight compounds containing sulfhydryl groups. It is found bound to proteins in peripheral tissues [83]. The free fraction is partly excreted by the kidneys and salivary and intestinal glands, but a larger amount is incorporated into the hydroxyapatite crystal structure of bones as tertiary lead phosphate [84; 85]. The release of accumulated lead from bones is facilitated by the body's increased calcium demand (e.g., pregnancy, lactation). Similar consequences occur with heavy exertion (e.g., driving to grazing land), starvation, and pathological conditions (e.g., acidosis, osteoporosis). Lead can also be incorporated into horny materials, fur, and slouughed skin cells [86]. Depending on the type of placenta, lead can significantly pass to the fetus and cause damage or abortion. In rats and humans, the placental barrier does not protect embryos from it, but in pigs, it inhibits transport [87; 88]. It crosses the blood-brain barrier, causing neurological symptoms in adults and affecting fetal nervous system development. Excretion is slow and varies by species, occurring in urine (e.g., dogs) and feces (e.g., rats, sheep) [89]. In birds, it can be found in eggshells and yolks and also in mammal milk [90; 91]. The elimination half-life of lead from blood and soft tissues is about 1 month; from bones, it is much longer, and complete elimination is not expected. The Pb content measured in the following marine fish, shellfish, and other edible aquatic animals was variable: 0.95 \(\pm\) 1.12 mg/kg in shellfish species (_Mytitlus galolprovincialis_, _M. edule_, _Venerupis philippinarum_, _Glycymeris glycym_), 0.66 \(\pm\) 0.56 mg/kg in oysters (_Crassostra gigas_, _C. angulata_), 0.59 \(\pm\) 0.33 mg/kg in squids (_Loligo vulgaris_), 0.50 \(\pm\) 0.34 mg/kg in sardines (_Sardina pilchardus_), and 0.39 \(\pm\) 0.37 mg/kg in tuna (_Tlununus albacares_), respectively [26; 27; 28]. In freshwater fish, such as rainbow trout (_Oncorhynchus mykiss_), the measured lead concentration was 0.16 \(\pm\) 0.16 mg/kg [29]. The presence of lead in game meat poses a particular health concern. Various lead bullets--especially their explosive fragments--are secondary sources of lead in meat and can significantly increase its level. High lead levels can also be a problem in commercially sold game meat products, increasing human health risks [92]. Today, lead from ammunition represents a significant dietary exposure pathway for consumers who frequently eat game meat. This issue may primarily affect hunters and their families but also others who prefer to consume game meat for ethical, health, or other reasons [93]. The harmful effects of lead from various types of lead-containing ammunition can also affect consumers through multiple exposure routes, including ingestion of contaminated water and contaminated plant and animal organisms in contact with spent ammunition in the environment [94]. Lead can leach from bullets and their fragments [95]. Both humans and animals are sensitive to lead exposure, especially young organisms. However, in addition to age, the solubility of the lead compound is also a key factor [96]. The lead concentrations in game meat ranged from 0.05 to 6.13 mg/kg in wild boar (_Sus scrofa_), 0.13 to 91.57 mg/kg in European roe deer (_Carpelus caprelus_), and 0.03 to 19.42 mg/kg in red deer (_Cervus elaphus_) in various European countries (Table 1).