Distribution of Cr, Pb, Cd, Zn, Fe and Mn in Lake Victoria sediments, east Africa.

The presence of many metals at trace or ultra-trace levels in the human environment has received increased global attention (WHO 1977; Hutton 1982; IRPTC 1984). Surveillance of concentrations of heavy metals in the environment is of global interest since elements like cadmium, lead and mercury are listed as environmenta]ly dangerous chemical substances. Sediments as a sink for pollutants are widely recognized pollution sources and diagenesis and biochemical transformations within the sediment may mobilize pollutants posing a threat to a wider Diological community. The natural (Dackground) concentrations of heavy metals in lake sediments can be estimated either by analysis of surface sediments in non-polluted regions or by analysis of core samples antedating m0dern pollution. The degree of contamination of selected rivers and lake sediments by lead, zinc and cadmium bas been reviewed by W4rren (1981) . Tne distribution pattern of heavy meta]s in tropical freshwater systems has been little studied. Kilham (1972) studied the biogeochemistry of African lakes and rivers. Onyari (19~5) round increased concentrations of lead and other trace metals in Lake Victoria. Thus this study was initiated in order to further investigate the distribution patterns of lead and other metals in Lake Victoria.