Recent Influences of Anthropogenic Activities and Seasons on Heavy Metal Distribution in Shoreline Sediments in Lake Victoria Near Kisumu City, Kenya

Abstract

The Winam Gulf on Lake Victoria around Kisumu city has seen increase in anthropogenic activities. The activities discharge pollutants, especially heavy metals into the lake. The heavy metals sink into sediments, which slowly release them into the lake water. The objective of this study was to evaluate the distribution and sources of heavy metals into Winam Gulf sediments near Kisumu city during wet and dry seasons. Sediments were sampled from sites at Molasses Plant, Coca-Cola Plant, Rivers Kisat and Kisian discharge points at intervals of 50 m from the shoreline into the lake. The metal level (µg/g) ranges obtained were: 0.90-1.20 (Cd), 2.60-36.00 (Cr), 71.40-122.90 (Cu), 1283.40-1468.70 (Fe), 792.30-1631.20 (Mn), 61.80-181.00 (Pb) and 100.10-187.60 (Zn) with River Kisat discharge point recording the highest levels for all metals. The metal levels were different (p ≤ 0.05) in all sites. River Kisat discharge point had the highest heavy metals concentration due to the dense anthropogenic activities within the adjacent environment. Metal levels varied (p ≤ 0.05) with seasons in all sites with higher levels recorded during wet season an indication of surface runoff. In all sites, the levels decreased (p ≤ 0.05) with increased distances from the shore into the lake suggesting a dilution effect. The results confirm that the anthropogenic activities cause metal pollution. It is necessary to control activities that discharge heavy metals into the lake water and continuously monitor the heavy metal levels. This will enable enforcement agencies to formulate regulations to safeguard human and aquatic life within the gulf.