%0 Journal Article
%T Chromium as an Environmental Pollutant: Insights on Induced Plant Toxicity
%A Helena Oliveira
%J Journal of Botany
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/375843
%X In the past decades the increased use of chromium (Cr) in several anthropogenic activities and consequent contamination of soil and water have become an increasing concern. Cr exists in several oxidation states but the most stable and common forms are Cr(0), Cr(III) and Cr(VI) species. Cr toxicity in plants depends on its valence state. Cr(VI) as being highly mobile is toxic, while Cr(III) as less mobile is less toxic. Cr is taken up by plants through carriers of essential ions such as sulphate. Cr uptake, translocation, and accumulation depend on its speciation, which also conditions its toxicity to plants. Symptoms of Cr toxicity in plants are diverse and include decrease of seed germination, reduction of growth, decrease of yield, inhibition of enzymatic activities, impairment of photosynthesis, nutrient and oxidative imbalances, and mutagenesis. 1. Introduction Chromium (Cr) is the 17th most abundant element in the Earth¡¯s mantle [1]. It occurs naturally as chromite (FeCr2O4) in ultramafic and serpentine rocks or complexed with other metals like crocoite (PbCrO4), bentorite Ca6(Cr,Al)2(SO4)3 and tarapacaite (K2CrO4), vauquelinite (CuPb2CrO4PO4OH), among others [2]. Cr is widely used in industry as plating, alloying, tanning of animal hides, inhibition of water corrosion, textile dyes and mordants, pigments, ceramic glazes, refractory bricks, and pressure-treated lumber [1]. Due to this wide anthropogenic use of Cr, the consequent environmental contamination increased and has become an increasing concern in the last years [3]. Chromium exists in several oxidation states, but the most stable and common forms are Cr(0), the trivalent Cr(III), and the hexavalent Cr(VI) species. Cr(0) is the metallic form, produced in industry and is a solid with high fusion point usually used for the manufacturing of steel and other alloys. Cr(VI) in the forms of chromate ( C r O 4 2 £¿ ), dichromate ( C r O 4 2 £¿ ), and CrO3 is considered the most toxic forms of chromium, as it presents high oxidizing potential, high solubility, and mobility across the membranes in living organisms and in the environment. Cr(III) in the forms of oxides, hydroxides, and sulphates is less toxic as it is relatively insoluble in water, presents lower mobility, and is mainly bound to organic matter in soil and aquatic environments. Moreover, Cr(III) forms tend to form hydroxide precipitates with Fe at typical ground water pH values. At high concentrations of oxygen or Mn oxides, Cr(III) can be oxidized to Cr(VI) [4, 5]. As Cr(VI) and Cr(III) present different chemical, toxicological, and
%U http://www.hindawi.com/journals/jb/2012/375843/