Heavy metals are pollutants of river sediments, and their concentration varies depending on parental material and anthropogenic inputs, thus important to distinguish between the natural and anthropogenic inputs. The objective of this study is to use different types of indexes to assess the current pollution status in Ogbere River sediment and select the best index to describe the sediment quality. The indexes used in this study were enrichment factor (EF), geoaccumulation index (Igeo) and principal component analysis (PCA). The PCA has an advantage over other index analyses as it reduces the dimensionality of the data set and thus used to support multivariate cluster analysis. From the study, a total of 12 sediment samples were collected in both seasons across six sampling location and pollution indexes indicated three things: firstly, the metal distribution profile in the sediment showed that the heavy metals analysed for were lower than the maximum allowable limits stipulated by Department of Petroleum Resources (DPR); secondly, minor to extremely severe significant levels of enrichment and thirdly, practically uncontaminated to a moderately contaminated degree of contamination in Ogbere River during the study period. The PCA is considered more sensitive in the analysis of benthic changes and as well as sediment quality. However, the heavy metal assessment indices are not only used for sediment quality. Biological testing and ecological analysis of existing community related to sediment contamination are further recommended in River Ogbere.

Rivers in Nigeria are faced with increasing contamination of both solid and liquid wastes that enter the surrounding water bodies, and some of these are toxic pollutants that settle onto the riverbed (the ultimate sink of contaminants in the aquatic environment). These toxic pollutants are released into the aquatic environments and inadvertently pose serious public health risks and hazards. This study aims to assess the level of potentially toxic element in River Ogbere water in the city of Ibadan. A total of 12 surface water samples collected from River Ogbere in Ibadan during the dry and wet season of 2019 was analysed for pH, EC, Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Cadmium (Cd), Chromium (Cr), Lead (Pb) and Nickel (Ni). The pH was found in the alkaline range (7.40 -7.83) while the conductance was obtained in the range of 236.67 -353.3 µs/cm in both seasons. Fe, Mn, Zn, Cu, Cr, Pb, and Ni were detected in all the samples in the range 0.10 -5.44 mg/L, 3.20 -5.03 mg/L, 0.12 -1.27 mg/L, 0.03 -0.51 mg/L, 0.03 -0.68 mg/L, 0.01 -0.75 mg/L and 0.01 -0.03 mg/L in both seasons respectively, whereas Cd was detected only in 75% of the samples (0.00 -0.07 mg/L). Overall seasonal variation was significant for Fe, Mn, Pb, Cd, and Cr. The maximum mean concentration of Fe (5.44 mg/L), Mn (5.03 mg/L), Zn (1.27 mg/L), Cu (0.68 mg/L), Pb (0.75 mg/L) and Ni (0.03 mg/L) were all observed during the dry season. The heavy metals also varied with the change of sampling locations. The dominance of these toxic element in the surface water of River Ogbere followed the sequence: Mn > Fe > Zn > Cu > Cr > Pb > Ni > Cd. The anthropogenic activities around the study area were observed to have increased the influx of toxic metals at both upstream and downstream sections of the river. In view of the high human activities along the river, River Ogbere appeared to have been polluted visibly. The constant water quality monitoring and development of River Ogbere safety plans is recommended.