SELECTED HEAVY METALS IN WATER AND SEDIMENTS AND THEIR BIOCONCENTRATIONS IN PLANT (Polygonum pulchrum) IN SOSIANI RIVER, UASIN GISHU COUNTY, KENYA

Abstract

The study was aimed to measure total concentrations of heavy metals lead, zinc and copper in water, sediment and plants samples and to assess heavy metals bioconcentration factors in plant (Polygonum pulchrum) in Sosiani River, located in Uasin Gishu County in Kenya. Sampling was done for six months between January 2010 and July 2010. Water, sediment and plant samples were collected from sampling points selected along Sosiani River extending from Naiberi to Huruma downstream using stratified sampling technique. The sediment and plant samples were dried in the oven at 50°C to constant weight and digested in a mixture of acids according to standard procedures. The water samples, digests of sediments and plants were analysed for heavy metals using Atomic Absorption Spectrophotometer (model AAS Variant 200). The results showed that the highest total heavy metals concentration in water were Cu (0.18±0.04 ppm); Pb (0.46±0.09 ppm) and Zn (0.70±0.22 ppm) at sites Kapsabet_Eldoret Bridge, MTRH and West Indies respectively. Highest recorded sediment total heavy metals were Cu (1.62±0.14 ppm); Pb (1.27±0.17 ppm) and Zn (6.73±0.88 ppm) at sites market, MTRH and Islamic Center respectively. Fractionation of heavy metals in sediments showed low percentage solubility (Cu 9.3%; Pb 8.5%; Zn 4.2%). Concentration of zinc in studied plants was highest (3.60±0.63 ppm) at Kapsabet-Eldoret Bridge, with bioconcentration factor of 15.1 times based on soluble zinc fraction and lowest at Huruma with a bioconcentation factor of 7.9. This indicates that conditions in the study area show preferential zinc metal uptake in plants compared to Cu and Pb. This may pose Zn metals health risks due to accumulation along the food chain. Suggestions are made for monitoring of heavy metals bioaccumulation in organisms such as fish in the study area.