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Assessment of heavy metal pollution in the urban stream sediments and its tributaries
Sekabira, K.; Origa, H. Oryem; Basamba, T.A.; Mutumba, G. & Kakudidi, E.
Abstract
Globally, aquatic ecosystems are highly polluted with heavy metals arising from anthropogenic and
terrigenous sources. The objective of this study was to investigate the pollution of stream sediments and possible
sources of pollutants in Nakivubo Channel Kampala, Uganda. Stream sediments were collected and analysed for heavy
metal concentration using flame atomic absorption spectrophotometer. The degree of pollution in Nakivubo channelized
stream sediments for lead, cadmium, copper, zinc, manganese and iron was assessed using enrichment factor, geoaccumulation
index and pollution load index. The results indicated that (1) the sediments have been polluted with lead,
cadmium and zinc and have high anthropogenic influences; (2) the calculation of geo-accumulation index suggest that
Nakivubo stream sediments have background concentration for copper, manganese and Fe (Igeo ≤ 0); (3) factor analysis
results reveal three sources of pollutants as explained by three factors (75.0 %); (i) mixed origin or retention phenomena
of industrial and vehicular emissions; (ii) terrigenous and (iii) dual origin of zinc (vehicular and industrial). In conclusion,
the co-precipitation (inclusion, occlusion and adsorption) of lead, cadmium and zinc with manganese and iron hydroxides,
scavenging ability of other metals, very low dissolved oxygen and slightly acidic to slightly alkaline pH in stream water
could account for the active accumulation of heavy metals in Nakivubo stream sediments. These phenomena may pose
a risk of secondary water pollution under sediment disturbance and/or changes in the geo-chemistry of sediments.
Keywords
Anthropogenic; Channelized; Factor analysis; Geo-accumulation; Vehicular
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