Özet:

Heavy metals contamination is a global environmental concern because it is difficult to remove these contaminants from the environment, unlike other pollutants. Chromium (Cr) is one of the most important heavy metals used extensively in various industries, out of which the tanning industry deserves special mention. There are more than 2500 tanneries in the country and nearly 80% of the tanneries are engaged in the chrome tanning process. Massive amounts of Cr waste are discharged annually in the environment as a result of industrial and manufacturing activities. Cr, a highly reactive element with an oxidation state of 6 exhibits stability as Cr (III) and Cr (VI). Hexavalent chromium is actually more toxic in effect to living organisms than its trivalent form. USEPA has classified Cr (VI) as a group A carcinogen, based on its chronic effects. Prolonged exposure to Cr (VI) is found to cause cancer in the digestive tract and lungs and in other cases epigastric pain, nausea and vomiting. Cr (VI) exposure has severe impacts on aquatic species also. In the present study chromium (VI) tolerant bacterial strains were isolated from the tannery effluent of Park Circus area. Most of the bacterial isolates were Gram-negative while few were Gram-positive. 6 bacterial strains were tested for their Cr tolerance capacity of which S6 showed maximum Cr tolerance of 0.4-0.5 mg/ml. The growth responses to different concentrations of Cr (VI) by the bacterial isolates, were also studied. The responses of the bacteria depended on the time of incubation and Cr (VI) concentration. Keywords: Chromium, tolerance, bacteria, growth response.      

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