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Trace Elements in Abiotic and Biotic Environments
tops, 458 mg/kg. Also plants grown in sludged soils may contain increased Zn levels,
up to 85 mg/kg in oat grains, and up to 114 mg/kg in soybean seeds. However, plants
grown in Zn-contaminated soils accumulated a great proportion of the metal in roots
(Kabata-Pendias 2011). Plants grown on Zn–Pb waste deposits containing Zn up to 171,790
mg/kg, have this metal, in top parts, up to 902 mg/kg (Wójcik et al. 2014). Some bacteria
species (e.g., Rhizobium leguminosarum) may promote the growth of plant, Brassica
juncea, on Zn-contaminated sites, due to an impact on Zn speciation and its accumulation in roots (Adediran et al. 2013). Some Zn-hyperaccumulating plants (e.g., Thlaspi
caerulescens, Brassicaceae) contain this metal, in top parts, up to 10,000 mg/kg.
Mushrooms easily absorb Zn from aerial deposits. Common chanterelles
(Cantharellus cibarius) grown in mountains of Poland contain higher amounts of
Zn, from 74 to 130  mg/kg, than those grown in the Baltic Sea coast, from 52 to
67 mg/kg (Falandysz et al. 2012).
55.6 HUMANS
Zinc is one of the most abundant trace metals in humans and its total content of the
body (70 kg) is in the range 2–3 g, of which about 7 mg/L is in the blood, 70–100
in the bones, and 50 mg/kg in the muscle (Emsley 2011). Zinc is an essential nutrient for human health and is vital for many biological functions, supporting normal
growth and development in pregnancy, childhood, and adolescence.
Sources of exposure to Zn include ingestion of food, drinking water, polluted air,
tobacco products, and occupational exposure. Food is its primary source. Humans are
currently exposed to various levels of Zn, as food supplements and additives, medicines,
and disinfectants, and in antiseptic and deodorant preparations, and dental cement.
After ingestion, Zn in humans is initially transported to the liver and then distributed throughout the body. Zinc is absorbed at about 20%–30% of ingested quantities. The highest concentrations of Zn in humans are in the liver, kidney, pancreas,
prostate, and eyes. Zinc is also present in plasma, erythrocytes, and leukocytes. It is
mostly bound to albumin (60%–80%), and to a lesser extent to α-2-macroglobulin
and transferrin (WHO 2001d).
Zinc plays specific and important catalytic, cocatalytic, and structural roles in
enzymes, and in many other proteins and biomembranes. Over 300 Zn metalloenzymes have been identified, including alkaline phosphatase, lactate dehyrogenase,
carbonic anhydrase, carboxypeptides, and DNA and RNA polymerases. It is vital for
enzymes, activating growth (height, weight, and bone development), growth and cell
division, immune system, fertility, taste, smell and appetite, skin, hair and nails, and
vision (WHO 2001d).
Zinc deficiency in the humans is associated with numerous health effects. Its
deficiency, especially in infants and young children under 5 years of age, has
received global attention. Zinc deficiency is the fifth leading cause of death and
disease, in the developing world. According to the WHO, about 800,000 people die
annually, due to Zn deficiency, of which 450,000 are children under the age of 5.
Globally, around 2 billion people are affected by Zn deficiency. It is also estimated
that 60%–70% of the population in Asia and Sub-Saharan Africa could be at risk of
low Zn intake (Prasad 2006).