BiocatalysisBacillus sp.
IntroductionHexavalent chromium [Cr(VI)] compounds are used in a wide variety of commercial processes and unregulated disposal of chromium containing effluents has led to the contamination of soil, aquatic sediments, and surface and groundwater environments. Chromium, a steel-grey, lustrous, hard and brittle metal, occurs in nature in the bound form that constitutes 0.1-0.3 mg/kg of the Earth's crust. It has several oxidation states ranging from (ÀII) to (þVI), the trivalent and hexavalent states being the most stable. A maximum acceptable concentration of 50 mg/L for Cr(VI) in drinking water has been established on the basis of health considerations (Kiilunen, 1994). In some American states, the exposure limit for Cr(VI) is as low as 15 mg/L for humans and 10 mg/L for aquatic organisms (Levitskaia et al., 2008) which is below the detection limit for most low cost colorimetric methods. Cr(VI) concentrations above the allowable limit cause cancer in humans and aquatic fauna, and is acutely toxic at much higher concentrations (U.S. EPA, 1978; Federal Register, 2004 A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w a t r e s
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