Physico-chemical Characteristics And Pollution Levels Of Trace Metals In The Little Akaki And Big Akaki Rivers

In the present work, physico-chemical variables (temperatures, pH, TDS, and conductivity) andrnsome selected trace metals (Cd, Cu, Co, Ni, Pb, and Zn) analysis of the water and surfacernsediments from river Big Akaki and Little Akaki were conducted with a view to asses the qualityrnof the rivers as well as to identify the potential contaminated areas. The results of physicochemicalrnparameters revealed that the mean values of temperature reading, pH, conductivity, andrnTDS along LAR varied between 19 to 21 oC, 6.59 to 7.71, 661 to 1790 μS/cm and 317 to 881rnmg/L, respectively and the ranges of these values along BAR are 17 to 21 oC, 369 to 749 μS/cm,rn176 to 316 mg/L. Trends of these variables showed an intimate relation with anthropogenicrnactivities along both rivers. Trace metals in sediment and water samples were determined byrnFAAS. The levels of dissolved trace metals in these rivers were found to be below the detectionsrnlimit of the method except for Zn and indeed Ni and Co in some sampling sites of the rivers. Thernlevels of dissolved metals in both rivers are below the South Africa guidelines fixed forrnirrigational, domestic and livestock watering purposes. In contrast to water samples significantrnamount of metals were found in both river sediment samples at all sampling stations. Thernconcentration ranges of the metals in LAR sediments were: 0.43 to 1.45,30 to 89, 18.32 to 44.02,rn119 to 73, 55.73 to 320, and 205 to 730 mg/L for Cd, Cu, Co, Ni, Pb, and Zn, respectively also thernmean range of these metals in BAR sediments are 0.31 to 0.59, 30.5 to 89.41, 18.33 to 30.47, 119rnto 62, 35.67 to 71.75, 172.89 to 288 mg/L, respectively. Levels of Cd and Co were found to be lowrnin both river sediments and they are below EPA sediment quality guidelines (SQG). Cu in bothrnriver sediments was found to be below SQG except at one site along LAR. Both rivers sedimentsrnwere found to be enriched with Ni and all sampling sites of LAR and 80% of BAR sites surpassed SQG for Ni. The levels of Zn and Pb along BAR sediments are below SQG while 30% of sitesrnalong LAR contain Pb above SQG and one site along LAR surpassed the SQG for Zn content.rnPair wise comparison of the two rivers revealed that generally the levels of trace metals and thernvalues of physico-chemical variables in LAR are higher than that of BAR. The levels of Cd, Pbrnand Zn in the sediments of LAR showed a significant positive correlation with each other.rnKey words:

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