DETERMINATION OF SELECTED HEAVY METALS POLLUTANTS AND

Abstract

The study set out to evaluate the effect of industrial activities by analyzing selected heavy metals and physicochemical parameters of water. Chemical survey was conducted in 9 selected sites (potential polluting sites) along Athi river to determine the levels of heavy chemical elements; lead (Pb), Copper (Cu), chromium (Cr), Nickel(Ni) Cadmium(Cd) and to asses water quality based on physicochemical parameters. The variation in concentration of these metals in the water and sediments as well as other water quality parameters was a key factor to establish the pollution levels in different parts of the river. The recommended WHO procedures of water sampling and analyses were followed. Atomic absorption spectrometry analytical technique was used in the determination of the heavy metal levels dissolved in the water and sediments samples. The results obtained in water samples ranged from Pb( 0.23-0.54mg/L),Cu(0.0082-0.0163mg/L), Ni(0.00810.0284mg/L), Cr(0.1363-0.3255mg/L), Cd(0.0117-0.0240mg/L) and for sediment samples Pb(0.1277-0.3513mg/L), Cu(0.0607-0.1386mg/L),Ni(0.0191-0.0498mg/L), Cr(0.0692-0.1329mg/L) and Cd(0.0108-0.0428mg/L). The values recorded for physicochemical parameters were pH(6.5-7.4), TDS(109-136mg/L), COD(66-102mg/L), BOD(6-15mg/L) and conductivity(155-206 µs/cm). From the results it was evident that the water was heavily polluted and not fit for domestic, agricultural and industrial purposes. Four of the analyzed heavy metals Pb, Cr, Cd and Ni surpassed the recommended WHO maximum permissible limits (0.01mg/L), (0.01mg/L), (0.003mg/L) and (0.001mg/L) respectively. Lead and chromium had the highest levelss in both sediments and water while Cd and Ni had the lowest concentrations. A Kruskal-Wallis test which, was conducted for the mean heavy metal concentrations, BOD, pH, Conductivity, TDS and COD to determine the significant difference of these water quality parameters in the nine different sampling locations showed significant differences between heavy metals in water and sediments and heavy metals in different stations(p<0.05). ANOVA test on pH did not reveal any significant difference (p<0.05) between the means of the various locations sampled and all results obtained fell within national and international standards of ESEPA/WHO. The BOD values were all higher than the normal BOD for unpolluted water of ≤ 2mg/L. The variation of electrical conductivity and TDS gradually decreased downstream with a slightly sharp rise at the middle of the sampling points; with observed TDS levels falling below the EPA's recommended maximum of TDS(500mg/L) in water. The COD values obtained were weak < 400mg/L.However, comparing all the observed values with the EPA regulations, the waters of this river is unsafe for domestic, industrial or agricultural use.