The world production of Cr is in the order of 10 7 tons per year 60–70% is used in alloys, including stainless steel, and 15% is used in chemical industrial processes, mainly leather tanning, pigments and electroplating. Soils may contain between μg of chromium per gram. Cr abundance in Earth’s crust ranges from 100 to 300 μg g −1. Ĭr is the seventh most abundant element on earth and 21st in the crustal rocks.

In addition, Cr(III) may be also oxidized to Cr(VI) in the presence of an excess of oxygen, being transformed again to the more toxic form. However, high levels of Cr(VI) may overcome the reducing capacity of the environment and thus persist as a pollutant. Cr(VI) is a strong oxidizing agent and in the presence of organic matter is reduced to Cr(III) this transformation is faster in acid environments such as acidic soils. In contrast, Cr(III) in the form of oxides, hydroxides or sulfates, is much less mobile and exists mostly bound to organic matter in soil and aquatic environments.

Cr(VI), considered the most toxic form of Cr, is usually associated with oxygen as chromate (CrO 4 2−) or dichromate (Cr 2O 7 2−) ions. Although it is able to exist in several oxidation states, the most stable and common forms are the trivalent Cr(III) and the hexavalent Cr(VI) species, which display quite different chemical properties. Chromium transport, Chromium toxicity, Chromate reduction, Chromium resistance, Bioremediation 1 IntroductionĬhromium is a transition metal located in group VI-B of the periodic table.

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