Level and ecological risk assessment of heavy metals in old landfill in Bayelsa state, Nigeria

This study assessed the ecological fate of heavy metals within the vicinity of an area formally used as dump site in Igbogene, Bayelsa state. Soil auger was used to collect samples at 0 - 20 cm depth at 50, 100 and 150 m distances from the four cardinal points viz: North east and west and south east and west. The soil samples were sieved, ashed, digested and analyzed using atomic adsorption spectrometry. The heavy metals results ranged from 646.73 to 715.33 mg/kg (iron), 59.30 to 73.05 mg/kg (manganese), 83.20 to 114.18 mg/kg (zinc), 10.67 to 15.95 mg/kg (copper), 7.70 to 9.64 mg/kg (chromium), 11.56 to 14.48 mg/kg (cadmium), 10.09 to 13.86 mg/kg (lead), 4.57 to 6.33 mg/kg (nickel) and 3.52 to 4.92 mg/kg (vanadium). Statistically there was no significant variation (p>0.05) across the various distances for each of the metals studied, but apparent decline in values exist as the distance away from the landfill increased. In addition, each of the metals showed positive significant correlation with each other at p<0.01. Cluster analysis revealed two main clusters. These are samples from each of the latitude directions, southern direction (east and west) and northern direction (east and west).  Pollution indices were higher in sample obtained from the southern direction (west and east) compared to northern area (west and east) but generally it ranged from no pollution to moderate pollution. Positive quantification of contamination indicates that pollution due to anthropogenic activities occurred in few instances. The ecological risk index showed low risk/fate of the heavy metals studied area. Key words: Environmental risk, heavy metals, dumps site, pollution indices, wastes.