1. Ackefors, H., Hilge, V. and Lind�n, O.: 1990, Contaminants in Fish and Shellfish Products. European Aquaculture Society, Aquaculture Europe 1989. Business Joins Science, De Pauw, N. and Billard R. Bredene (eds.), Belgium. Special Publication no. 12, 306?315.
2. Asplund, J.: 1979, Heavy Metals in Natural Waters, A Literature Survey. (In Swedish, English Summary). National Swedish Environmental Protection Board, Solna. 197 pp.
3. Balon, E. J.: 1978, Ambio 7, 39?48.
4. Balon, E. K. and Coche, A. G.: 1974, Lake Kariba. A Man-Made Tropical Ecosystem in Central Africa, Junk, The Hague.
5. Beadle, L. C.: 1981, The Inland Waters of Tropical Africa, Longman Group Ltd., Longman House.