ECOLOGICAL RISK ASSESSMENT AND POLLUTION LOAD OF HEAVY METALS IN SOILS WITHIN BORI URBAN, RIVERS STATE, NIGERIA.

Abstract

The study assessed the ecological risk and polluting load of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in surface soils within Bori Urban. The composite soil samples collected from different locations were prepared and atomic absorption spectrophotometer (AAS) was used for the analysis of the heavy metals. From the results of the analysis, the mean concentrations (mg/kg) of the heavy metals decreased in the order Cu (37.42) > Ni (34.06) > Cr (28.66) > Zn (7.75) >Pb (2.03) > Cd (0.89). The mean concentrations of Cd, Cu, and Ni were above USEPA soil guidelines and world unpolluted soil average, while those of Pb and Zn were below. The mean concentrations of the heavy metals from the study locations were all above that of the control location. The findings indicated that the urban soils of the study were loaded with heavy metals due to anthropogenic activities. The anthropogenic percentage input was in the range of 63.92 - 89.13 above 50% indicating anthropogenic origin of the heavy metals in soils of the study area. The results of ecological risk index (Er) indicated that Cd with Er (467.40) contributed up to 94.51% to the potential ecological risk index (RI) while Zn (0.78) contributed 0.16%. The heavy metals under study posed highly strongly potential ecological risk with RI value of 494.56 to the Bori urban soil due to anthropogenic activities. The ANOVA result of FCal 6.42 > [F(5.30) = 2.53, P< 0.05)] revealed significant differences between the soil sample mean values due to different anthropogenic pollution sources with different loads of heavy metals as pollutants. The Omega Squared (w2) value of 0.52 > 0.14 showed very strong interactive relationship among the heavy metals to bring about high level of ecological potential risk of the urban soils in the study area. Based on the findings, the surface soils have elevated load of heavy metals thereby posing ecological potential risk to Bori urban soils. Therefore, there should be periodic monitoring and environmental audit by relevant authorities to ensure good soil quality of Bori urban soil. Keywords: Potential ecological risk, pollution load, Bori Urban, Anthropogenic Percentage input, contamination Factor.