Speciation of trace metals in chromated-copper-arsenate contaminated sediment of Ogba River

The impact of storm water run-off from a location of intensive application of CCA in wood treatment on the quality of sediment of the receiving water body was examined. Sediment samples were collected along Ogba River. Physico-chemical characteristics as well as total levels of As, Cr and Cu in sediment samples were determined. Physico-chemical analysis of composite sediment samples upstream and downstream showed pH of sediments to be neutral (6.95 upstream and 6.90 downstream). The sand content for downstream sediment was 90.52 and 87.52% for upstream sediment sample. Total levels of 3.3-14.9 mg kg(-1) As, 3.1-116.6 mg kg(-1) Cr, and 13.7-16.4 mg kg(-1) Cu were obtained for downstream sediment samples and 2.2-2.3 mg kg(-1) As, 8.1-13.1 mg kg(-1) Cr, and 6.0-7.4 mg kg(-1) Cu were obtained for upstream samples. Sequential extraction procedure involving six steps was used to evaluate the partitioning of As, Cr and Cu in the sediments. The results showed that the bioavailable fraction of sediment 20 m downstream was 10%, 100% and 20% of the total levels of As, Cr and Cu respectively in the sediment.