# Potential Metal Contamination in Foods of Animal Origin--Food Safety Aspects
## 2 Major Toxic Metals in Food
### Lead (Pb)  
Lead is present in the Earth's crust at a concentration of about 13 mg/kg, but this varies by region and soil type. It can be detected in different concentrations in different types of soil (volcanic and sedimentary rocks: 10-20 mg/kg; sandstone and coal-bearing shale: 10-70 mg/kg; phosphate-bearing rocks: 100 mg/kg) [64; 65]. Lead pollution due to anthropogenic activities (e.g., smelting, foundry, chemical production, battery production) is of greater importance than natural occurrence. The use of tetraethyl and methyl leads as fuel additives was banned after 1995. Despite this, due to its very persistent nature, this \"historical source\" remains the most significant pollutant. Dissolved lead concentrations in surface, ground, and marine waters are low because it is usually present in the form of carbonates, sulphates, and phosphates, which have low water solubility. It is not subject to biomagnification. The highest concentrations are generally found in aquatic and terrestrial organisms living near lead-contaminated areas. [PERSON] and [PERSON] measured elevated lead levels in the blood of cattle grazing near a lead processing plant [66]. In aquatic environments, lead is found in higher amounts in algae and benthic organisms than in carnivorous predatory fish at higher trophic levels. Lead concentrations in raw edible plants are usually <0.05 mg/kg. However, silage, for example, can be an important intermediate source if the plant used for ensiling is contaminated from the soil. [PERSON] et al. measured 25.89 mg/kg of lead in alfalfa at harvest, which \"migrated\" during three weeks of ensiling and accumulated at the bottom of the silo (118.6 mg/kg) [67]. In the body, lead most likely binds to proteins and alters their function, inhibits or mimics the effects of calcium (e.g., activation of calmodulin and protein kinase C), and can be incorporated into various enzymes instead of zinc causing oxidative stress [68; 69; 70; 71]. It can influence the capacity and activity of different enzymes because it can bind to their functional groups (e.g., sulfhydryl, amine, phosphate, carboxyl). In bones, it is incorporated in the form of tertiary lead phosphate instead of calcium. Lead inhibits the function of several enzymes (\(\delta\)-aminolevulinic acid dehydratase, ferrochelatase), thus causing disturbances in heme synthesis. As a result, the amount of \(\delta\)-aminolevulinic acid increases in plasma and urine, and iron incorporation into the protoporphyrin molecule is blocked. Due to reduced hemoglobin production and damage to red blood cells, hypochromic normocytic anemia and reticulocytosis develop [72; 73]. Cardiovascular effects can be attributed to the fact that Pb can cause nerve conduction velocity disturbances (contractility disorders, arrhythmogenic effects), degenerative structural and biochemical changes in the heart muscle, and increased tone of the smooth muscles of blood vessels, causing vasoconstriction [74; 75]. By blocking voltage-gated calcium channels, lead inhibits the influx of calcium, which, under physiological conditions, regulates neurotransmitter efflux. However, when it enters cells--using calcium channels--it acts as a calcium agonist, increasing the spontaneous efflux of neurotransmitters [76]. It can cross the placenta (depending on the animal species) and be present in significant amounts in fetal brain tissue, disrupting the synaptic organization and functional development of neurons in the early stages of postnatal development, leading to later learning problems [77; 78; 79]. The absorption of lead is influenced by the chemical form of the compound, the composition of the feed (diet), and the age and health status of the animals. Soluble salts are more readily absorbed than insoluble derivatives. In adults, absorption varies between 10 and 80% and is more efficient in young animals. The calcium and phosphate content of the feed reduces [80; 81] and iron deficiency and magnesium increase lead resorption from the duodenum.