Assessment of Potential Ecological Risks Associated with Heavy Metals in Soil of Waste Disposal Site at Khulna: A Spatial and Temporal Appraisal

Abstract

Most of the ecological and health risk occurs due to the emission of heavy metal from contaminated soil of waste disposal site. The main focus of this study was to assess the ecological risk associated with heavy metals present in soil of waste disposal site. To these endeavors, sixty soil samples were collected from different locations of a selected waste disposal site at Rajbandh, Khulna, Bangladesh. This study period covered both, dry season (March to May, 2016) and rainy season (June to August, 2016). In the laboratory, metal elements of Aluminium (Al), Arsenic (As), Barium (Ba), Calcium (Ca), Cadmium (Cd), Cobalt (Co), Chromium (Cr), Copper (Cu), Iron (Fe), Mercury (Hg), Potassium (K), Manganese (Mn), Sodium (Na), Nickel (Ni), Lead (Pb), Antimony (Sb), Scandium (Sc), Strontium (Sr), Titanium (Ti), Vanadium (V) and Zinc (Zn) in soil was measured through standard test methods. In this study, to assess the ecological risks associated with heavy metals various indices such as potential contamination index (Cp), contamination factor (CF), contamination load index (PLI), modified contamination degree (mCD), numerical integrated contamination factor (NICF), enrichment factor (EF), geo-accumulation index (Igeo), ecological risk index (ER) and potential ecological risk index (PERI) were used. In addition, Pearson’s correlation and principal component analysis (PCA) was performed using SPSS and XLSTAT. The results of skewness and kurtosis revealed that the heavy metals in soil were normally distributed for both seasons. The soil sample collected from center of disposal site showed comparatively the higher concentration than the other soil samples from larger distances with respect to center of the disposal site for both seasons. Results indicated the level of contamination for soil was severe or very severe based on Cp for Cd and Sb for both seasons as well as Pb and As for dry season. In addition, CF for Cd and Sb showed very high level of contamination in both seasons. Additionally, CF for Pb and As showed moderate to considerable contamination in dry season; where, CF for same elements showed moderate to low contamination in rainy season. The results of EF for Pb, Zn, Cd, As, Hg, Co and Sb contributed the class of extremely severe enriched for dry season. Mainly, EF for Sb and Cd indicated the soil was extremely severe enrichment for dry and rainy season. Besides, ER for Cr, Cu, Pb, Zn, Ni, As, Hg and Co; and ER for Cd indicated the slightly ecological risk and extremely strong ecological risk, respectively, for dry season. Moreover, PERI for entire soil samples indicated the extremely strong ecological risk. It was observed that the soil sample of the central point of the disposal site showed comparatively the higher potential ecological risk than other soil samples collected from larger distances with respect to center of the disposal site for both seasons. Results of Pearson’s correlation and PCA indicated that most of the heavy metals were found to correlate significantly with each other indicating close association of these parameters in both seasons. The spatial distribution of heavy metals represented the same pattern for both seasons but the intensity of heavy metals decreases in relation to the increasing of lateral distance from the center of disposal site. Finally, it can be concluded that the outcome of this study will help to know the degree of contamination of soil as well as the ecological risk from the contaminated soil of a selected waste disposal site.