An evaluation of potential toxic metals in sediments of a tropical watershed in southern Benue Trough, Nigeria

This study assessed heavy metal contamination in sediments within the Anambra drainage basin in Southern Benue Trough, Nigeria. Twelve river sediments were collected from the basin upstream and downstream in two seasons-rainy and dry seasons. The control was collected from the basin source. Samples were analyzed using X-ray fluorescence (XRF) spectroscopy for common major Potential Toxic Metals (PTMs). Concentration of zinc (Zn), nickel (Ni), manganese (Mn), iron (Fe), chromium (Cr), lead (Pb), vanadium (V), molybdenum (Mo), scandium (Sc) and europium (Eu) were detected in trend: Fe>Mn>Zn>Pb >>>Cr>Ni>Mo>Eu>Sc. Contamination trend in rivers shows Adada>Oji>Ezu>Obele>Mamu>Ankpa. The rainy season and the upstream sediments had lower concentrations than the dry season and downstream, respectively. Sediments had higher PTMs concentrations than the background sediments, though most PTMs concentrations were within the recommended standards- USEPA, WHO and Consensus-Based Sediment Quality Guidelines (CBSQGs). Contamination factor (Cf), enrichment factor (Ef), and geo-accumulation index (Igeo) recorded range from 0 to 15, 0 to 6.69 and -8.43 to 3.32 respectively, signifying significant accumulation and enrichment of PTMs. Pollution load index (PLI) of the heavy metals ranges between 0.24 and 1.34, which suggest that at the different seasons, the basin was enriched with PTMs to a pollution level through anthropogenic activities. In the Anambra drainage basin, concentration and distribution of heavy metals may have been influenced by both non-anthropogenic and anthropogenic processes such as geology of the area, weathering and erosion as well as mining and agricultural activities.