3. Chromium, Cr

In 1957 chromium(Cr) was proposed as an essential element, vital for the life and normal development of animals and humans. In the natural environment, the activity of compounds containing chromium in the third and the sixth oxidation states differs substantially, Cr(III) and Cr(VI), respectively. Trivalent Cr is essential for humans and animals; it shapes the proper glucose metabolism through participation in the glucose tolerance factor (GTF) and is involved in metabolism of hydrocarbons, proteins, and lipids. Chromium supplementation brings positive results only at small doses though. Chromium-deficient nutrition impairs glucose tolerance and insulin function, alters protein metabolism, and negatively affects both growth and reproduction.

Hexavalent Cr is a strong oxidant, easily penetrating into living organisms, being reduced to Cr(III) in cells. Industrial production is a source of Cr-containing wastes, which contaminate the water and air and, in consequence, the soil. Emission of chromium to the atmosphere is mainly due to combustion of coal and other fossil fuels but also results from iron and nonferrous metal smelting. Hexavalent Cr, which acts oxidatively, is very toxic. Anthropogenic Cr soil contamination is a result of atmospheric deposition of dust but also industrial wastes discharged into the soil from paint factories, tanneries, sewage treatment plants, and chrome-steel scrap piles. Chromium is toxic to plants and accumulated in the roots and is to a limited extent transferred to overground parts of plants. In the cells of mammals and birds, Cr(VI) is reduced to Cr(III), which produces highly toxic-free radicals. Hexavalent Cr is carcinogenic to homeothermic vertebrates. Reproduction disorders were observed in mammals. In males, exposure to high Cr level deteriorates the quality of semen, leads to testicular disorders, and reduces libido. In females, Cr negatively affects fertility. A high level of Cr in the environment is mutagenic, carcinogenic, and teratogenic to birds; concentration of chromium in avian lungs increases with age, which implies equivalence of diet and air as sources of Cr intoxication. Studies show that chromium exhibits no biomagnification. On the contrary, with an increase in the trophic level, the concentration of Cr considerably decreases. This is referred to as “biominification.” In this chapter are presented the effect of exposure to hexavalent Cr and chromium content in avian and mammalian soft tissues as well as in feathers and hair.