**3.7 Toxicity of copper (Cu)**

Copper is a trace element, component of many enzymes, including ceruloplasmin and cytochrome C oxidase, tyrosinase and dopamine beta-hydrolase, zinc-copper superoxide dismutase (antioxidant defense) and others, having function in transport functions, detoxification, antioxidant defense, immune function, pigmentation and melanin production [10, 74]. When it is present in high levels in the body, it may become toxic [3].

Human exposure take place through its release from water carrying pipes, fungicides, cooking utensils, birth control tablets, food. Copper has the highest redox activity, which lead to production of reactive oxygen species. Also, it binds to thiol groups of proteins and cause changes in liver enzymes involved in biotransformation processes [3].

At cell level, it can change the activity of natrium (Na<sup>+</sup> )/potassium (K<sup>+</sup> ) ATP-ase and change of plasma membrane permeability, due the affection of the natrium/ potassium pumps and increases of level of natrium in cytoplasm [3]. Large amounts of copper are stored in the liver [74], while the target organs are nervous system organs, including ganglia, neurons, cerebellum and hippocampus [3].

Excess of copper in the body or hypercupremia, occurs naturally during pregnancy, but also by chronic exposure to it, being associated with a number of diseases including Wilson's disease, hepatic disorders (cirrhosis, hepatitis, gastroenteritis), neurodisorders, hyperceruplasmin [3, 10, 74]. Neurodisorders produced by chronic exposure to copper include neurodegenerative disorders, like Alzheimer and Parkinson, but also Huntington disease, amyotrophic lateral sclerosis [3], cognitive impairment, personality and behavioral changes [74].

Cells studies demonstrated that copper is accumulated in some cancer cell, such as colon cancer cell, ovarian cancer cells, breast cancer cell, more than in normal cells. Also, at cellular level, it can cause oxidative damage of DNA, their reduction can be made by use of Cu specific chelating agents [3].

Hypocupremia or copper deficiency are represented by serum level less than normal value of 0.64–1.56 μg/mL. Extreme hypocupremia could produce Menkes disease, known as Menkes kinky hair syndrome, a genetic disorder, characterized by steely hair, due to a mutation of the transport protein mediating the copper uptake from the intestine, but also by progressive neurological deterioration and early childhood death [10].

## **3.8 Toxicity of zinc (Zn)**

Another trace element, zinc, is involved in over 200 enzymes, with action in immune system, catalytic and structural structures, but also, in processes like synthesis and degradation of some components, including lipids, proteins, carbohydrates, nucleic acids, transcription and translation of polynucleotide, genetic expression, cell proliferation and differentiation, normal growth and development during pregnancy, childhood, adolescence, reduced growth rate and impaired resistance to infection [10].

Exposure to zinc of human is made by inhalation of zinc vapors and ingestion of a large overdose of zinc supplements, which contain zinc sulfate, overusing denture cream, but also by consumption of contaminated food and water [75, 76].

Zinc poisoning, at intakes higher than 100 mg/day, has been associated with abdominal pain, vomiting, diarrhea, nausea.

Long term exposure can cause malabsorption of copper and in case of diabetics, it can affect immune function associated with diabetes mellitus [10]. Severe toxicity present symptoms like kidney injury, pancreatic function damage, liver failure, dehydration and acute gastrointestinal bleed, septic shock, lethargy, sideroblastic anemia and dizziness [74, 76]. Zinc inhalation could produce dyspnea, airway inflammation and acute respiratory distress symptom, especially in case of occupational exposure [76].

Because this metal could interfere in copper absorption in the gastrointestinal tract, leading to copper deficiency [10], chronic exposure can cause polyneuropathy and can affect bone marrow [76].

#### **3.9 Toxicity of nickel (Ni)**

Nickel is an essential trace element for plant, animals and human, but also a chemical pollutant which exist in several oxidation states, but most common is Ni2+. In the body, it is involved in activation of some enzymes, in protein structure and function, in prolactin production [3, 10].

Environmental contamination with nickel comes from natural sources, like volcanic emissions, weathering of soils, but also from industry, being used in catalysts for automobile, electroplating, electroforming, jewelry production, medical prostheses, production of nickel-cadmium batteries, cast coins [19].

This metal can reach the body through ingestion of contaminated water and food, inhalation of dust or smoking cigarettes and dermal contact, leading to increases level of Ni in blood, urine and body tissues. However, less than 10% of ingested nickel is absorbed by gastrointestinal tract [3, 10].

It can pass through plasma membrane through diffusion, calcium transport channels and phagocytosis, is circulated to various tissues, where bind with albumin, histidine and macroglobulin. In case of nickel, the target organs are kidneys, bons, lungs, liver, brain and glands of endocrine system, but it is not accumulated in those, being excreted outside [3].

Nickel exposure can produce disorders of liver, kidney, spleen, brain and tissues, but also vesicular eczema, nasal and lung cancer. Also, it interferes in iron resorption, which lead to anemia, disturb the incorporation of calcium into skeleton, causing parakeratosis damage [10]. On reproductive system, this metal affects the quality of semen and cause abnormalities in it, including the tail of sperms [3].

Occupational exposure can cause allergic dermatitis, known as "nickel allergy". In case of dermal contact, skin rash or allergic dermatitis appear, due to wearing of nickel-plated jewelry. Women are more sensible to nickel than men, especially in pregnant women which work in metallurgic industry and their babies hence structure abnormalities [3, 10].

At cellular level, it can produce breaking of DNA strands, cross linking of DNA protection, DNA oxidation, nucleotides removal, genes mutations, modifications of chromatids, binding to enzymes involved in DNA repair and degradation of protein, generation of ROS, enhances lipid peroxidation, affecting calcium and sulfhydryl homeostasis, degradation of glutathione [3].
