Contamination Indices and Ecological Risk Assessment of Trace Metals in Soil from Selected Dumpsites in Uyo Metropolis, Nigeria

Abstract

The contamination indices and ecological risk assessment of trace metals in soil from five different dumpsites in Uyo metropolis and their control site was assessed using models stipulated by Hakanson (1980) while the mean concentrations of some trace metals in soil from the investigated dumpsites were determines using Flame atomic absorption spectrophotometer.  The range for the result of trace metals in soil from the study locations in both seasons were as follows: Lead (Pb) (0.160-7.336), Cadmium (Cd) (0.096-21.098), Zinc (Zn) (0.311-50.090), Iron (Fe) (0.100-62.150), Copper (Cu) (0.279-79.490). All the concentrations were reported in mg/kg. The range for the contamination indices in both seasons were as follows: Contamination Factor (CF),- (0.528-29.520), Degree of Contamination (CD), (5.733-73.410), Pollution Load index (PLI),- (1.141-7.999), Enrichment factor (EF), (0.215-4.928). The grading for the ecological Risk index (ERI) and Potential Ecological Risk index (PERI) was from low ecological risk to high Ecological risk. The result for the dry season was significantly higher than the result for the wet season (P < 0.05) and the concentrations in the dumpsite were also higher than the concentration from the control sites. The concentrations of all the investigated metals in both seasons were lower than the WHO and EU limit except Cd and Cu for at Idoro and Mbak Etoi dumpsites in the dry season. The pollution load index (PLI) value for all the dumpsites were greater than one for both seasons indicating progressive deterioration of soil from the dumpsites.  The contribution of Lead and Cadmium to the contamination factor and the degree of contamination was higher than Cu, Fe and Zn. The degree of contamination for most of the dumpsites indicated high degree of contamination for most of the sites in both wet and dry seasons. The enrichment factor revealed that Cd and Pb from Idoro and Ifa Atai in the wet season and Zn, Cu at Ifa Atai were from anthropogenic sources while in the dry season; Cu, Cd, Fe and Zn were mostly from crustal sources except Pb at Idoro road and Ifa Atai village dumpsites. The result for ERI and PERI revealed that Cd and Pb were major contributors to the ecological risk of the soil ecosystem. Due to human health concern, dumping of municipal wastes at open waste dumpsites closed to agricultural farmland should be discouraged.