Bioaccumulation of zinc, lead, cadmium in water hyacinth, hippo grass and papyrus reed as water quality indicator in River Kisat in Kisumu County, Kenya

Abstract

River Kisat in Kenya is increasingly being polluted serving as a sink for waste receiving effluent from sewerage, industrial waste and agricultural pesticide residues leading to heavy metal contamination. This has led to the contamination of the aquatic ecosystem and water used by communities for consumption and farming. Little information is available on the bio-indicative aspects of water quality using bioaccumulation factor by macrophytes. This study aimed at determining concentrations of Zn, Pb and Cd in water, (Eichhornia crassipes (water hyacinth), Vossia cuspidata (hippo grass), Cyperus papyrus (papyrus reed) and bioaccumulation factors (BAF) in River Kisat, Kisumu County. This was determined following laboratory standard procedures using Atomic Absorption Spectrophotometer (AAS). Results showed mean concentrations (mg/L) of Cd (Below detectable limit), Zn (0.2 -0.15) and Pb (0.03-0.03) in water. Mean values were within allowable WHO drinking water limits except for Pb which was above acceptable limits. Zn recorded highest accumulated levels in E. crassipes (72.43mg/L), C. papyrus (70.13mg/L) and V. cuspidate (71.03mg/L). E. crassipes was observed to bioaccumulate the highest concentration of the heavy metals with C. papyrus bioaccumulating the lowest (E. crassipes > V. cuspidata> C. papyrus). Pearson matrix correlation analysis showed positive significant correlations (r = 0.621; p = 0.027) between Zn and Pb in water and the macrophytes which reflected a common source of pollution and indication of accumulation. BAF recorded for all macrophytes ranged from 2.45 to 6.85, above value of 1, indicating significant bioaccumulation for Zn and Pb. The findings from this study showed higher concentrations of Zn and Pb in the macrophytes in comparison to the water in River Kisat with BAF values >1 indicating bioaccumulation which represented poor water quality. The study recommends local authorities employ monitoring processes with incorporation of BAF as a water quality indicator where low metal concentrations in water are recorded, introduce penalties for polluters and sensitize local inhabitants on detrimental health effects of heavy metal and avoid use of River Kisat water for agricultural activities.