Abstract

Globally heavy metals pollutants in aquatic systems are increasing and creating major ecological disturbance(s) and direct health problems. The study on accumulation of Copper (Cu), Cadmium (Cd), Lead (Pb) and Nickel (Ni) on the bottom surface sediments of Nairobi dam was conducted between November 2012 to April 2013. Seven sampling sites were selected within the dam and sediment samples were collected once in a month during the wet and dry season. Standard methods for sampling, storage and analysing according to APHA were used; statistical analysis in form of means, independent T-test and ANOVA were used to summarize the findings. (Mean±SE) (ppm) concentrations of Pb, Cd, Cu and Ni in the dam during the dry season are: 38.01±0.26, 30.86±0.21, 21.7±0.22, 8.44± 0.15, and in wet season are: 33.73±0.22, 26.60±0.19, 19.11±0.14 and 5.94±0.12, respectively. The levels of heavy metals in the sediments at the outlet are lower compared to the other sites within the dam. These metals accumulated in the order: Pb> Cd> Cu> Ni with higher concentration during the dry than wet season. It is concluded Nairobi dam sediments are contaminated with heavy metals that are significantly higher during the dry compared to wet season (P<0.0001). Therefore it is recommended that sediments of this dam are not suitable for cultivation and or any agricultural activities.

Key words: Accumulation, heavy metals, sediments, Nairobi dam.