**4. Effects of heavy metals on human and animal health**

Heavy metals enter the human and animal body through the respiratory tract, sometimes even through the skin in the case of chemicals capable of crossing the skin barrier, and the digestive tract. Food is the main source of toxic elements. The deficiency of macro- and micro-nutrients in the body causes heavy metals to be absorbed in their place. When there is poor nutrition and a lack of essential nutrients in the body, the liver that performs detoxification cannot perform this important task [8, 38].

Copper is one of the elements with important functions in the human and animal body. It takes part in oxidation-reduction processes, regulates the metabolism, transport of iron. In the form of complexes with amino acids and albumin, it is transported to the liver, kidneys, intestines, and other tissues. Excess copper mainly causes decreased hemoglobin concentration, liver, and kidney damage [8, 14, 39].

Zinc accumulates in vertebrates in the liver, forming complexes with various proteins, and also in the kidneys and sex glands. Symptoms of zinc intoxication are—impaired immune response, reduction of HDL cholesterol fraction, decreased level of copper in the blood. On the other hand, acute zinc poisoning is manifested by vomiting, epigastric pain, fatigue, and sluggishness. Zinc chloride (ZnCl2) is

irritating to the skin, mucous membranes, and conjunctiva, causing burns in higher concentrations [8, 14, 39].

Cadmium is easily absorbed in living organisms. It enters the human body primarily through food, water, and inhalation as a result of tobacco smoking. Cadmium accumulates primarily in the kidneys and liver. Cadmium poisoning causes nausea, vomiting, salivation, abdominal pain, kidney damage, and circulatory failure. In addition, exposure to cadmium oxide fumes, exceeding the concentration of 0.5 mg Cd kg−3 causes, among others—emphysema, kidney function damage, changes in the skeletal system, pain in the limbs and spine [8, 14, 39].

Mercury poses a very high risk to living organisms. Mercury enters the body primarily from food via the digestive system and inhalation. Mercury compounds can interfere with most enzymatic reactions because they react with proteins containing sulfhydryl groups. The highest concentrations of mercury are found in the kidneys, but the brain is the most susceptible. Mercury vapor toxicly affects the lungs, eventually causing respiratory failure and death. In addition, chronic exposure to low concentrations of mercury vapor causes damage to the central nervous system with symptoms of weakness, memory impairment, mood swings, headache and limb pain, mucositis and gingivitis, and others [8, 14, 39].

Lead is also a highly toxic element. It enters the human body through the digestive system with water and food, and inhalation. It accumulates in the liver, heart, kidneys, as well as in the skin and muscles. Symptoms of lead poisoning of the human organism include disorders of the blood-forming system and the central nervous system. Lead is a mutagenic, carcinogenic, and embryotoxic element [8, 14, 39].

Kołacz et al. [40] conducted a study on the blood of cows from the copper industry region (LGOM) showed a significantly higher Cu content (1.67 mg l−1) compared to the agricultural region (0.72 mg l−1). In both regions, the content of Cd did not exceed 1.65 μg l−1, Pb in the industrial region was 0.021 mg l−1, and in the agricultural region 0.031 mg l−1. On the other hand, the level of Hg in the blood of cows, in both regions was similar and was about 0.03 μg l−1. It was found that the copper industry does not adversely affect the blood parameters of dairy cows. In the whole blood of dairy cows, a lead level of 0.1 mg l−1 is considered normal, 0.1–0.3 mg l−1 is considered elevated, and above 0.35 mg l−1 is considered toxic.
