Abstract

A study was conducted to investigate the seasonal level of heavy metals in bottom sediments of Yauri River, Northwestern Nigeria. Thirty composite samples of bottom sediments were collected at six demarcated sites along the river during the 2010/2011 raining and dry seasons. The heavy metals concentrations were determined with atomic absorption spectrometer. The mean levels range of Cd, Cr, Cu, Fe, Ni, Pb and Zn were 4.38 to 23.11, 11.08 to 74.13, 10.87 to 42.13, 100.69 to 301.02, 25.85 to 116.32, 10.11 to 34.11 and 18.91 to 109.62 µg/g for raining season and 6.25 to 13.09, 18.95 to 77.61, 17.39 to 64.05, 138.25 to 349.50, 56.13 to 91.60, 17.39 to 45.02 and 21.80 to 131.16 µg/g for dry season, respectively. The values generally were lower than the world shale values and sediment quality guidelines values. Sediments pollution assessment was carried out using enrichment factor (EF), geoaccumulation index (I_geo), contamination factor (CF) and pollution load index (PLI). The calculations of EF showed that the river is contaminated with Cd, Cu, Pb and Zn. On the other hand the I_geo values suggested that the river is polluted with Cr and Pb and moderately polluted with Cu, Ni and Zn. Contamination factor values revealed that Fe and Ni have none to medium contamination while Cd and Pb are strongly polluted. Generally, according to the pollution load index (PLI) values calculated, the river is polluted with all the elements analysed. Some of the elevated concentrations of some of the heavy metals are probably due to anthropogenic and natural sources. It can be said that the environmental or human health impact involving these metals is occurring in the river and can cause hazard to sediments dwelling organisms in the river as well as the populace in the area through food chain.

Key words: Heavy metals, Nigeria, seasonal, enrichment factor, contamination factor.