Assessment of Potential Ecological Risks Associated with Heavy Metals in Soil at the Khulna Waste Disposal Site: A Spatial and Temporal Assessment. The main focus of this study was to assess the ecological risk associated with heavy metals in the soil of the waste disposal facility.
61 Figure 4.4: Comparison of Cd concentration in the present study with the permitted limits from different sources.
Nomenclature
- Background Information
- Soil and Its Contamination
- Problem Statement and Justification
- Objectives of the Study
- Specific Objectives
- Contribution to Knowledge
- Significance of the Study
- Scope and Limitations
- Outline of the Study
This study was conducted to assess the ecological risks associated with metallic elements in the soil of a waste dump. Assessing the potential ecological risks associated with heavy metals in the soil of a waste dump.
Chapter I describes general knowledge on the background of waste disposal sites, challenges of MSW management and dumping facilities, contaminated soil, metal element
As a final point, the results of this study will provide a protective approach for the ecological restoration of landfills worldwide. The study has been presented in five separate chapters which include different aspects of this study.
The study can inform the environmental management authorities about the level of metal element pollution in the Khulna region and thus provide a reference for future studies of the same. There are many metal elements, but this study considered only 21 metal elements, which from related literature are prevalent in soil at selected waste disposal sites.
General
The indices used in this study to assess ecological risk are also presented in detail in this chapter. Finally, the concept of Pearson correlation, principal component analysis (PCA) and the geostatistical technique of ordinary kriging are also highlighted in this chapter.
Municipal Solid Waste
In addition, this chapter also provides a comprehensive literature review that includes characteristics of metal elements, soil contamination with metal elements at the disposal site, soil quality standard, sources of metal elements, ecological risk assessment of soil associated with metal elements. The major sources of MSW in Khulna city are residences, wholesale and retail marketplaces including shopping malls, streets, hotels and restaurants, private clinics and hospitals, educational institutions, cinemas, railways, buses and launch/steamer ghats, slaughterhouses, etc.
Dumping Facilities of Municipal Solid Waste
- Open Dumping Facilities
There are two general methods for the final disposal of MSW, one is open dumping and the other is sanitary landfill (Visvanathan and Trankler, 2003). In South and Southeast Asia, the open dumping approach is the most predominant waste disposal option (Ali et al., 2014).
Environmental Effects of Waste Disposal Site
The occurrence of uncontrolled landfills affects not only health and the environment, but also the quality of life. Because the presence of landfills not only degrades the quality of the environment, but also violates human rights by affecting community pride.
Exposure Pathways of Waste Disposal Sites
These adverse effects then affect human health and the natural environment (aquatic, terrestrial flora and fauna) (Butt et al., 2008). Ecological and health risk assessments are an essential tool to recognize and illustrate the hazard of landfill to the environment (Butt et al., 2008).
Approaches and Challenges of MSW Management
Most developing countries follow the practice of open dumping of solid waste which causes environmental and health risks (Ali et al., 2014).
Effects of MSW on the Environment
Landfills can transfer significant levels of toxic and persistent metals to the soil environment (Udosen et al., 2006). The rate of metal uptake by a plant can be influenced by factors such as metal species, plant species, plant age and plant part (Singh et al., 2010).
Environmental Risk of Metal Elements Mobility in Waste Disposal Sites
Metallic elements and persistent organic contamination are of concern because of their potential harmful effects on humans and the environment. Therefore, for these reasons, waste dumps commonly produce leachate with concentrations of metallic elements.
Soil Contamination
Since the sulfur content is not sufficient to immobilize all deposited metals, organic materials retain a large proportion of metals in landfills. Over the years, the intrusion of oxygen into landfills increases, and as a result, oxidized material increases the risk of metal release.
Sources of Metal Elements and Its Effect
The metallic elements Cd, Hg and Pb have not been shown to be essential for either plants or animals (Misra and Mani, 2009). Metallic elements are not biodegradable and once they enter an environment, they will stay there for a long time.
Mechanism of Action of Metal Elements
In this regard, the compilation of past and present catalogs of atmospheric metal element concentration is an activity of great importance (Shrivastav, 2001).
Soil Contamination by Metal Elements
According to some research conducted on landfill soils, soil contains different types of concentrations of metal elements depending on age, content and location (Mustafa et al., 2015). Field investigations and soil column studies reported rapid leaching of significant concentrations of zinc, copper, chromium, and cadmium (Sukkariyah et al., 2005).
Key Concepts in Understanding Soil Contamination
At elevated concentrations of metal elements, it is toxic to soil microorganisms and plants and can have a negative effect on soil fertility and yield. Many authors have shown that the activity of metal ions in the soil solution is a key factor in determining the bioavailability of an element and its toxicity to various organisms.
Indices and Methods for the Assessment of Soil Contamination
The ecological risk assessment of soil and sediment pollution associated with heavy metals has received increasing attention in both developing and developed countries in recent decades. CF is the ratio of the metal content in the sediment to the background value of the metal.
Background Soil Quality Standards used in this Study
Potential Ecological Risk Assessment
In addition, the potential ecological risk index (PERI) is a method used for risk assessment of metal elements. In this study, the principle of pearson's correlation was carried out using XLSTAT to investigate the correlation between metal elements in the soil at the waste disposal site.
Principal Component Analysis
The Pearson correlation technique is a parametric measure developed by Karl Pearson from a related idea introduced by Francis Galton in the 1880s (Galton, 1886; Pearson, 1895). Pearson's correlation produces a sample correlation coefficient, r, which measures the strength and direction of linear relationships between pairs of continuous variables.
Geostatistical Interpolation Technique
A typical interrelationship between PCA and hierarchical cluster analysis (HCA) as well as the performance of these interpolation techniques is shown in Figure 2.13. The interpolation technique of OK produced a prediction surface (map) that indicated the level of contamination by different colors in Figure 2.15.
General
Present Condition of the Selected Waste Disposal Site
- Geological Setting of Study Area
- Soil and MSW Condition of Waste Disposal Site
Collection of soil samples from various selected locations of waste disposal sites in Rajbandh, Khulna, Bangladesh. In this study, sixty soil samples were collected from various selected waste dump locations, shown in Figure 3.5.
Laboratory Investigations
- Acid Digestion
- Analysis of Metal Elements with AAS
Soil samples were taken at a depth of 0-30 cm from the existing soil surface of the waste disposal site. Soil samples were collected from the bottom of the borehole by manually excavating the soil with hand shovels.
Assessment of Soil Contamination using Various Indices
- Potential Contamination
- Contamination Factor
- Contamination Load Index
- Nemerow Integrated Contamination Factor
- Potential Ecological Risk Index
The contamination factor (CF) of a specific metal element is the ratio of metal element concentration in soil and the background value of the same metal element. The degree of contamination (CD) is an index to estimate the contamination extent of soil by metal elements in soil.
Statistical and Geostatistical Analysis
- Descriptive Statistical Analysis
- Pearson’s Correlation Analysis
- Principal Component Analysis
- Geostatistical Interpolation Techniques
The sign of the correlation coefficient indicated the direction of the correlations, while the magnitude of the correlation indicated the strength of the correlation (Patil and Patil, 2010). These loading factors give a new set of variables that explain the variability in the original data set; the first computers retained a greater proportion of the total variance, which consequently led to effective and.
General
Basic Statistical Analysis
The descriptive statistical data for the concentration of metal elements in soil at the waste disposal site for dry season and rainy season are given in table 4.1 and table 4.2, respectively. In addition, this consequence for the concentration of Fe was also supported by Islam et al. 2012) in the soil of the waste disposal site in Gazipur, Bangladesh.
Evaluation of Soil Quality Comparing with Allowable Limit
Figure 4.3 illustrates the comparison of the soil Pb concentration in this study with permissible limits from different countries available in the literature. Figure 4.4 illustrates the comparison of the Cd concentration in this study and the maximum permissible limits from different countries available in the literature.
Variation of Metal Content in Soil
- Iron
- Copper
The comparison of soil Fe concentration for dry and rainy seasons in the present study with other researchers for similar cases is shown in Figure 4.6 and Figure 4.7, respectively. Moreover, the concentration of Cu in the dry season was found to be approximately 2.0, 2.3, and 4.0 times higher than that in the rainy season for the sampling distances of 30, 180, and 300 meters, respectively (Figure 4.11).
Spatial Distribution of Metal Concentration in Soil
- Iron
- Chromium
- Zinc
- Cadmium
- Arsenic
- Mercury
- Titanium
- Antimony
The magnitude of Zn concentration for the soil sample from the center (about 0 m) varies from 46 to 48 mg/kg, while for the soil sample from the farthest point (390 m from the center) it varies from 23 to 26 mg/kg for the dry season . The magnitude of Sb concentration for the soil sample from the center (approximately 0 m) ranges from 11 to 12 mg/kg, and for the soil sample from the farthest point (390 m from the center) from 2 to 3 mg/kg for the dry season.
Analysis of Various Indices
- Potential Contamination Index
- Contamination Factor
- Nemerow Integrated Contamination Factor
- Contamination Load Index
- Enrichment Factor
- Potential Ecological Risk Index
- Overall Risk identified by Indicies in this Study
The values of Igeo were calculated based on the concentration of metal elements in soil. In addition, the value of ER for heavy metals in dry season soil is illustrated in Figure 4.44.
Spatial Distribution of Various Indices
- Contamination Factor
- Iron
- Chromium
- Zinc
- Cadmium
- Arsenic
- Titanium
- Antimony
- Enrichment Factor
- Manganese
- Chromium
- Lead
- Cadmium
- Arsenic
- Mercury
- Antimony
- Ecological Risk Index
- Chromium
- Copper
- Lead
- Zinc
- Nickel
- Cadmium
- Mercury
The spatial distribution of EF for the metal elements Cd in the soil for the dry season and the rainy season is demonstrated in Figure 4.61 (a) and Figure 4.61 (b), respectively. The spatial distribution of ER for Hg metal elements in soil for the dry and rainy season is shown in Figure 4.72(a) and Figure 4.72(b), respectively.
Concluding Remarks
In dry season, the magnitude of PERI for whole soil samples indicated the extremely strong ecological risk due to the presence of heavy metals in soil for all the soil sampling points (boreholes) of the selected waste disposal site. The magnitude of PERI for whole soil samples indicated the extremely strong ecological risk due to the presence of heavy metals in soil for all the soil sampling points (boreholes) of the selected waste disposal site for dry season.
Recommendations for Future Study
The results of Pearson correlation and PCA showed that most of the heavy metals were found to have statistically significant correlation with each other in the soil of the selected waste disposal site, indicating close relationship of these parameters with each other in both seasons. The spatial distribution of heavy metals in the soil represented the same pattern of distributions in both seasons, but the intensity of heavy metals decreases with increasing lateral distance from the center point of the waste disposal site.
Problems in the assessment of heavy metal levels in estuaries and the formation of a pollution index”. Assessment of the potential ecological risk of heavy metals in reclaimed soil at an open pit coal mine”.
Appendicies
A new window named “Explore” is appeared. Then desired field is selected in
Results are appeared in a new window named “Output”
In a excel sheet required data was tabulated and launched XLSTAT by clicking the add-in “XLSTAT” on the sheet
Results are appeared in a new window named “PCA”
Data added clicking “File” > “Add XY data” then the excel sheet previously added by
Then the borehole appears in the "Data View" window as points and a new layer in it.
Step 4: The new layer projected through “Projected coordinated system” through clicking
Toolboxes"> "System Toolboxes" > "Data Management Tollboxes.tbx" > "Projection and Transformation" > "Raster" > "Project". Then the window named "Project" appeared and click the required field containing "Projected Coordinate System" as output coordinate system.
Spatial analysis done through clicking “Toolboxes”> “System Toolboxes” > “Spatial
Spatial and seasonal variation of the concentrations of metallic elements in the soil of a waste dump.
