1. Environmental Geochemistry Group, LGIT-OSUG, University of Grenoble, BP 53, F-38041 Grenoble, Cedex 9, France
2. Department of Chemistry, University of Kalyani, Kalyani 741 235, West Bengal, India
3. Institute of Physics, Bhubaneswar 751005, India
4. Current address: BRGM, BP 6009, F-45060 Orléans, Cedex 2, France