Evaluation of soil contamination status around a municipal waste dumpsite using contamination indices, soil-quality guidelines, and multivariate statistical analysis

Indiscriminate dumping of municipal solid wastes in and around most cities in Nigeria coupled with improper waste management of the available dumpsites posed a major threat of pollution in the surrounding soils. This study assesses the concentration of heavy metals and contamination status of soils around a municipal waste dumpsite located at Arufe street, Omuooke-Ekiti, SW, Nigeria using contamination indices, soil-quality guidelines, and multivariate statistical analysis. Soil samples from different depths were taken from the center of the dumpsite and surroundings at different distances and directions. The concentration of the metals in soils taken at depth of 0-50 cm (topsoil) was significantly higher than in soils taken at depth of 50-100 cm(subsoil). The mean concentrations of heavy metals in the topsoil showed the following order Fe > Cr > Mn > Zn > Pb > Cu > Ni while those of major cation followed the order Ca > K > Na > Mg. Exceptionally high concentration of the heavy metals compared with the background values were found at the center or close to the center of the dumpsite, which indicates an anthropogenic contribution. Compared with the adopted soil-quality guideline, only Cr and Pb showed concentrations well above the threshold value. The mean enrichment factor of all the heavy metals except Cr and Pb were <2. Cu, Ni, and Fe all had geo-accumulation index (I-geo) values less than zero, while the I-geo for Cr at the center of the dumpsite (topsoil) was 5. The contamination factors followed the order: Cr > Pb > Mn > Zn > Fe > Cu > Ni. The modified degree of contamination values was found to be mainly less than 1.5 except at the center of the dumpsite. The ecological risk index (ranged 4.37-505.55) implies low to considerable risk for the dumpsite. The significant positive correlations observed among heavy metals and the major cations indicate that these metals probably have similar sources and properties. The PCA reveals that the metals have a strong association and may have a similar source. The cluster analysis categorized the sampling points into three major groups of spatial similarities. The metals concentration combined with the contamination indices and soil-quality guidelines indicated that the soils in and around the dumpsite are polluted or being polluted because of the dumpsite.