I gratefully acknowledge Dr. V.P. Dimri, Director of NGRI, for his constant encouragement and consent to publish this work. I wish to express my gratitude to Dr. P.K. Govil, Sri. G.L.N. Reddy and Dr. N.N. Murthy, Environmental Geochemistry Division, NGRI, for their constructive comments and useful suggestions. I owe my deep sense of indebtedness to Dr. A.S. Sudheer, Dept. of Geology and Dr. S. Srinivasulu, Dept. of Geography, S.V. University, Tirupati for their worthy guidance with their untiring initiative in completion of this work. I wish to extend my sincere thanks to Sri. A. Chakravarthi, NGRI, for his sagacious suggestions and for improving the quality of work. The financial assistance provided by the Council of Scientific and Industrial Research (CSIR), New Delhi, through the award of my Research Associate fellowship is gratefully acknowledged. I also thank anonymous reviewers for their constructive review of the manuscript and for editorial revision.