[4] Barman S C, Kisku G C, Bhargava S K. Journal of Environmental Biology, 1999, 20: 1.
[5] Prasad M N V, Freitas H. Environmental Pollution, 2000, 110: 277.
[6] Haritonidis S, Malea P. Environment al Pollution, 1999, 104: 365.
[7] Ho Y B. Hydrobiology, 1990, 203: 73.