Effects of pH and total organic carbon (TOC) on the distribution of trace metals in Kubanni dam sediments, Zaria, Nigeria

Abstract

The determination of Cd, Cr, Cu, Pb and Zn in the exchangeable, carbonate, Fe-Mn-oxides, organic matter and residual sediment chemical fractions of Kubanni Dam during dry and raining seasons was carried out using the spectrophotometric method after Tessiers’ sequential scheme for speciation had been carried out. The pH and Total Organic Carbon (TOC) of the sediment samples were also determined to study their effects on the distribution of metals. The results indicate that pH influenced the release or adsorption of each metal in the different sediment fractions. At low average pH of 5.21 recorded during dry season, desorption of metals from the
reducible sediment fraction into the water column occurred, which may have effect on aquatic organisms. Due to increased metal complexation at high pH, total extractable fractions of metals generally increased. Higher TOC levels during the rainy season indicated larger adsorption surfaces for Cr (19.92%) Pb (19.97%) and Zn (21.14%) on the organic matter fraction, which, under oxidizing condition, these metals may be remobilized into the aquatic environment. Cu correlated positively with the organic carbon content of the sediment samples. The positive correlation of Pb, Cd and Cr with sediment pH may reflect the tendency of cation adsorption to increase at high pH.

Key words: pH, TOC, Trace metals, Distribution, Sediments