Accumulation of Heavy Metal Concentration and Physicochemical Parameters in Soil From Alice Landfill Site in Eastern Cape, South Africa


 Heavy metals are unique environmental and industrial pollutants scattered naturally and found almost in all phases of the environment. In certain limited areas in several parts of the world, many people and animals have suffered from several severe diseases caused by trace elements or heavy metal deficiencies and their toxicities, unaware of their existence. The compounds of Pb and Cd are classified as human carcinogens by numerous regulatory agencies. The soil samples digested using the aqua regia method, and concentration quantified through the Inductively coupled plasma mass spectrometry (ICP-MS). In this study, Pb, Cd, and Hg concentrations were recorded high on the landfill site compared to the control site. Their concentration exceeded the permissible limits from WHO. Pb concentration ranges between 0.46ppm to 1.81ppm, Cd range from 0.98ppm and 0.56ppm, and Hg has a high concentration that varies between 6.28ppm and 1.69ppm. On the contrary, the Cu concentration reportable to be lesser than accepted WHO limits compared to the other two selected elements. The mean concentration of Cu ranges from 0.41 ppm to 0.72 ppm. Soil pH for both sites ranged from slightly acidic (6.67) to neutral (7.09), which falls within the normal range suggested by WHO. High Hg and Pb concentration in this study is a thing of concern. Undertaken this study to help address the soil pollution problem due to the illegal disposal of waste that results in metal accumulation.


Introduction
Soil is a very mixed heterogeneous medium, made up of solid stages (the soil matrix) containing organic matter, minerals, and uid phases (the soil water and soil air), which are involved directly with each other as ions entering the soil system [1]. Soil serves as a sink and reservoir of metal contaminants from automobile emissions. It also functions as a natural buffer by controlling chemical elements and other environmental substances [2]. The soil quality depends on its natural composition and the anthropogenic activities caused by humans and management [3]. The contamination of soil through heavy metals has raised serious concerns in recent years regarding human health due to these metals' ability to accumulate in the environment and crop plantation. Humans could be affected by direct intake and food chain bioaccumulation [2].
Heavy metal pollution in a natural environment is a global and common problem because these metals are ineradicable, primarily if they exist in high percentages exceeding acceptable limits. Most of them are very dangerous and pose severe threats to all living organisms, including humans and plants. The concentration of heavy metals might come from vehicle exhaust since the site is situated not far from the gravel roads and tar roads from town to the surrounding areas. That results in many cars contribute to the increase of soil heavy metals [4]. The most common heavy metals are Cd, Pb, Hg, Cu, Ni, Cr, and Fe.
Some of these elements are important for all living organisms, such as Zn and Fe.
In contrast, other elements like Pb, Hg, and Cd are dangerous in living organisms even if they are present in a small amount and can generate organ abnormalities in some living organisms [5]. For example, Zinc's required amount helps maintain both the metabolic and biochemical reactions of humans' bodies [6]. These metals are non-biodegradable and dangerous because of their potential to bio-accumulate in the environment. Heavy metals have a long persistent time through contact with soil components, and as a result, they enter the food chain through plants and animals [7].
The lack of modern remediation and the latest technologies to maintain land ll sites results in waste accumulation and subsequent interaction with soil and living organisms. For this reason, there are environmental and health implications [8]. In some cases, waste is cast-off recklessly regardless of their ecological consequences, while on dumpsites, burnt debris is left in the open, and ashes are abandoned at the sites [9]. It noted that people close to this dumpsite believe that the native fertility from a waste dumpsite is high; subsequently, they collect soil to use as compost and sometimes cultivate different crops on the dumpsite's temporarily abandoned plot. On the other hand, most people become heavy metal consumption victims due to insu cient information on heavy metal levels in dumpsites, leading to these consumers' death [8].
Heavy metals are among the most important parts of environmental pollution, utilizing long-term hazardous effects on soil ecosystems and negatively in uencing biological processes in the soil. Hence there is a need for constant monitoring and regulation of their soil concentrations [10]. They commonly affect the growth, morphology, and metabolism of microorganisms, leading to decreased soil ecosystems' functional diversity [11].
A waste from municipal usually consists of papers, boxes, food waste, metal scraps, glasses, ceramics, and ashes. Improper collection and waste disposal have become one of the Alice community's most signi cant challenges every day. Some of the waste still exist in some streets despite its effort to clear them. In that case, the environment, people, and organisms are at high risk [5]. This study analyses the soil samples for their total heavy metal content in selected areas around the land ll site. Also, to evaluate the health risks posed by heavy metal pollution in soil and the effects of soil physicochemical properties on heavy metals transfer from the soil.

Sites description
The study was conducted in Alice Township under Raymond Mhlaba municipality, using two areas: the land ll site (site 1) located about 2 km outside Alice community and ≈ 3 km to the control site 2 (inside University of Fort Hare east campus). The dumpsite is situated among latitudes of 32°48'24.88"S and longitudes of 26°49'33.37"E, while the control site lies on the margins of 32°47'07.35"S to 26°57'26.10"E longitudes.
Site 1 branched into three portions: portion A (east side) got lots of broken glasses. In contrast, portion B (south side) was dominated by rusted tins and broken glasses with evidence of burnt waste, and portion C was situated outside the land ll site fence only occupied by natural vegetation. Site 2 is an undisturbed land with its soil surface covered by natural vegetation and located near hills.

collection and preparation of samples
The soil samples were randomly collected at a depth of 0-25 cm twice per week for six weeks (April to mid-May). A clean soil auger utilized in soil sampling at each portion of Site 1, and uncontaminated soils were collected from Site 2. Sampled dry soil was contained and transported to the laboratory for advanced examination. The ground soils are sieved through a 2mm mesh sieve to remove unwanted debris. The homogenized soils kept at room temperature to be analyzed further.

Moisture content
In a beaker of known mass, the soil samples were added and measured the mass. The soils were then oven-dried for 24 hours at 105°C until the constant weight obtained after heating samples were cooled in a desiccator and placed in a clean plastic bag for further analysis [7]. Calculation:

Soil pH
The soil pH was measured using a 1:2.5 ratio (soil: water by volume), where 5.0 g of sieved soil was delivered to a beaker containing 12.5 mL of deionized water and mixed well. Soil pH value is read by immersing a hand-held glass electrode pH meter into the partially settled solution, making sure the electrode doesn't touch the walls of the beaker [2].
Soil electrical conductivity (E.C.) 5.0g of homogenized soil samples were added to a beaker and mixed with 10 mL of double-distilled water. The content was shaken intermittently for 5 minutes and allowed to settle for 5 minutes. The E.C. probe curved into the solution to measure the electrical conductivity [12].

Soil Organic Matter (SOM)
In a 250 mL conical ask, 1.0g of soil sample with 10 mL K 2 Cr 2 O 7 were mixed, and the ask swirled gently to dissolve the soil. 20 mL of concentrated H 2 SO 4 has quickly added to the solution in the mixture, allowed to stand on a fume hood for 30 minutes to cool down. After that, 200 mL of distilled water added, and the formed suspension was ltered using a lter paper. 3-5 drops of ferroin indicator added, and the solution titrated with FeSO 4 . The end is reached when the solution changes from dark green to blue to reddish-brown [13,14]. 1.0g of well-mixed soil samples were digested in a hotplate using 20 mL concentrated HNO 3 . The digested mixture in a conical ask was heated until the solution was reduced to 5 mL, after which 20 mL of distilled water was added and heated until the suspension decreased to 10 mL. When digestion nished, the residue was set aside to cool at room temperature and ltered using Whatman lter paper and make up to 50 mL volumetric ask with distilled water [5]. The heavy metal concentration analysis was quanti ed using Inductively coupled plasma mass spectrometry (ICP-MS) [7]. The data was analyzed using SPSS 26, version 26.0. Tukey Post-hoc tests at p ≤ 0.05 for multiple comparisons of means from one-way ANOVA and the signi cant difference among the selected enzyme activity means. IBM Pearson's correlation will be used to analyze the relationships between the groups. This study was approved for ethical clearance by AREC University of Fort Hare, with certi cate number: Table 1 presents the soil's physicochemical properties in the land ll site and the control site.

Soil physicochemical parameters
pH: The mean concentration of hydrogen ions (pH) in all soil samples range from slightly acidic conditions (6.79 ± 0.28) to neutral soils (7.09 ± 0.37). The results revealed that the soil's pH in land ll sites stretched from slightly acidic to a neutral soil pH, whereas in the control site, the pH concentration is slightly acidic (6.67 ±0.28).
This study indicated that all collected soil samples from both sites are within the standard pH range set by WHO (6.5 to 8.5). The variation of soil pH might attribute to the topography effects, such as soils on the side of hills, which tend to be shallow due to erosional losses [15]. Also, dry environments may lead to various soil pH, where leaching and weathering are less intense, resulting in neutral and sometimes alkaline soils.
Moisture content: Soil moisture is an essential variable in the climate system. The moisture content is higher in land ll site when compared to control site soils, the mean values of moisture content on Site 1 ranges between (11.07 ± 3.39 %) and (13.48 ± 3.43 %), while in Site 2, the mean weight percentage was 10.16 ± 2.30 % respectively. The low levels of moisture in both sites may be due to these sites' topography, controlling water ow and material transport. Sites 1 and 2 were both located on hill slopes, with area 2 hillier than site A. There was a signi cant difference between all site A and site B portions.
This topography type is likely to encourage quick rainwater runoff during rainy days before the soil could absorb enough water and dry soils. Warm weather with less rain during sampling days is also contributing to a high evaporation rate of soil moisture and the resultant dry soil observed in this study.
Soil electrical conductivity (E.C.): The electrical conductivity concentration range between 606 ± 349.87 µS/cm and 72.04 ± 41.59 µS/cm. The high content of electrical conductivity practical on portion A of Site 1, followed by the control site's soils (Site 2) and the minimum values reported on portion B soils. The E.C.'s obtained data in this study is well below the earth's salinity threshold. Soil E.C. is a signi cant indicator of soil salinity, and it is a measure of the amount of salt in the soil but does not indicate the speci c salt or ions that might be present. E.C. is a good indicator of salts like sodium, potassium, chloride, or sulfate [16]. Saline soils are those with salt levels (E.C.) above 4 dS/m [17]. In the present study, the soil's E.C. indicates to be lower than the saline level.
Soil E.C. lower than 200 µS/cm has insu cient nutrients for the plants and could show a disinfected soil with little microbial activity [18].
Soil Organic matter (SOM): Organic matter means the percentage noted to range between 1.62 ± 0.93% and 0.96 ± 0.55%. In all sites, organic matter existed in meager amounts at a rate of < 2%, with the least moderate values of 1.62% observed at portion B of Site 1 and a low percentage of 0.96 reported on portion C soils. This study's low organic matter levels may be caused by decaying microorganisms' reduced existence since organic matter is considered an essential soil health component. Therefore, its reduction results in soil degradation, increasing the decomposition rate and low availability of soil vegetation. Soil organic matter is the most valuable soil property. Low and poor organic matter levels may increase soil erosion processes, while the high amount of organic matter could affect the soil pH by decreasing soil pH levels [19]. Soil organic matter improves both the soil's physical and chemical properties by promoting biological activity and maintaining environmental quality [20]. It is also known to play a signi cant role in providing nutrients and water to plants and giving a good state of plants [21].   The results reveal that the polluted soils from land ll sites hold a high Pb concentration than the soils from unpolluted sites. Lead (Pb) is a metal associated with human activities for several decades, and it is a common industrial metal that had become widespread in soil, air, and water. High Pb concentration in the dumpsites soil might be due to large deposits of used batteries, used plastics materials, lubrication oils, and automobile exhaust fumes. Areas next to the roads and in the drip lines of older housing usually contain a high Pb number [22].
Exposure to high Pb levels can cause a range of health problems such as chronic neurological disorders, especially in fetuses and children. Since they are still small, their bodies continue to grow [23]. The most common sources of Pb that might result in more Pb concentration in site B are deteriorated paint in older housing and suspended soil dust [22].

Cadmium (Cd):
Cadmium (Cd) has higher concentration levels at Site1-portion C (0.98±0.89ppm), while the lowest amounts procure at Site1-portion B (0.56±0.41ppm). The Cd levels existed in amounts way above WHO permissible limits for Site 1 and Site 2. Cd exists naturally, and it's a poisonous heavy metal that can occur as a waste product from industrial workplaces, plant soils, and smoking. The high levels may occur due to the disposal of cadmium batteries or metal scraps and metal plating, plastic stabilizers, and pesticides. It is also present as a pollutant in phosphate fertilizers, and some cigarette smoking can be a signi cant source of Cd exposure. People can have kidney failure as Cd exposure results [24]. Cd concentration has the potential to contaminate the soil at just one point. It has been noted to impact human health as it has long-term bioaccumulation, causes renal dysfunction, lung cancer, and bone defects [25].

Copper (Cu):
This metal deposit was higher on control site soils (0.72 ± 0.40ppm) than on portions of Site 1, while soils of portion B of Site1 carry shallow Cu concentration. Their concentration ranges between 0.72 ± 0.40 ppm and 0.41 ± 0.15ppm. The obtained results reveal that unpolluted soils contain higher Cu concentrations than polluted soils. For this study, Cu concentration was available below the allowed limit value from WHO, and the values were recorded less than < 1.50.
Copper is a critical element for different metabolic processes. It occurs naturally and spreads through the environment. The Cu can be free into the location through natural sources and human activities. The application of fertilizers, pesticides, and fungicides that contain copper might cause high levels of Cu in the soil. Also, the solubility of Cu decreases with the increases in soil pH [26].
Long-term Cu exposure can result in irritation of the nose, mouth, and eyes. Sometimes it can cause headaches, stomach aches, dizziness, vomiting, and diarrhea. Furthermore, high uptakes of Cu substances may lead to liver and kidney damage and death [27].
The soil contamination by Cu resulting from excessive Cu concentration has health risks that could bring about infections, anaemia, and thinning of bones [28]. Lead, copper, and Cadmium combine with the sulfhydryl (-S.H.) group, interfering with the other substances' enzymes in the body. Also, they inhibit the passage of nutrients in and out of the cell [5].

Mercury (Hg):
The mercury (Hg) concentration ranges between 6.28 ± 4.21ppm and 1.69 ± 0.62ppm. High Hg concentrations were reported on Site 1 portions, while on Site 2, soils contain small amounts. The mean concentrations of Hg for all collected soil were exceedingly above the WHO's approved limit.
WHO allows 1.0 mg/kg respectively as the maximum permissible limits of Hg on soil [29]. In South Africa, the allowable soil limit for Hg is 0.93 mg/kg [30].

Statistical results
The one-way ANOVA statistical analysis and Correlation examination results are shown in Table 3 and It also suggests that variability in Site 1 and Site 2 is not the same. They differ much more in concentration, and we are 95% con dent that the difference between the means of these two sites is not due to chance. The null hypothesis is rejected because the p-value is less than 0.05 (p < 0.05). Cd concentration (as shown in Table 4) correlated non-signi cantly negative with Hg concentration, and the correlations were positive between Cd and Cu. The concentration of Cd correlated negatively with levels of soil pH, moisture content, electrical conductivity, except for organic matter content, which signi cantly correlated with Cd at 0.05 level.
Mercury (Hg): A one-way between soil samples of two sites, ANOVA was conducted to compare Hg concentrations within these sites. There was a statistically signi cant difference in Hg concentration between soils of Site 1 and Site 2 at the p< 0.05 level for the conditions F= 8.443; p = 0.003. A negatively non-signi cant correlation has been experimented with Hg concentration and Cu, but Hg concentration correlated signi cantly positively with soil pH, moisture content, electrical conductivity, and organic matter.
Copper (Cu): The calculated one-way analysis of variance (ANOVA) on soil samples of polluted and unpolluted sites reveals a statistically signi cant difference between the two sites for Cu concentration, F= 8.443; p = 0.003. This data suggests a signi cant difference between the mean Cu concentration on two Sites (1 and 2). Cu concentration correlated negatively with pH, moisture content, organic matter, except for electrical conductivity, which correlated positively but non-signi cantly with Cu concentration.
These results indicate that physicochemical properties directly impact the concentration level of selected metals, except for Cd, which is indirectly affected by physicochemical parameters.

Discussion
The examined soil samples were moderately acidic to neutral and showing mean pH values from 6.67 to 7.09. At the same time, organic matter occurred at a low percentage < 2%, and electrical conductivity results show that the collected soils are non-saline. Soil pH and other soil properties are signi cant in soil processes responsible for heavy metals' solubility in soil and transportation [31]. At low pH, metals tend to be found as free ionic species or soluble organometals and are more bioavailable. Since low pH (acidic) metals are more soluble and more bioavailable in the soil solution, the range of pH values obtained in this study will favour plant uptake of heavy metal. Hence, toxicity problems are possible. The moderately acidic soil from the control site may rise in micronutrient solubility and mobility and signi cantly heavy metal concentration in the soil [32].
Salman et al. 2019 reported similar ndings on soil pH, resulting from low rainfall in the area. The soil organic matter occulated from below detected limits to average content of 0.76%. More than 82% of these metals Cu, Pb, and Cr reported below the upper critical limit, while Cd exceeded the allowable limits [33]. Another study said the soil pH ranged between 4.48 and 7.38. organic matter content observed from 1.59-3.36%. The obtained results indicate that Pb, Ni, and Cu levels were comparable and showed that these metals come from an inherent heterogeneity pattern. While Cd and Zn concentrations occurred more than the allowable standard values. The results show that different pollution point sources might exist in the sites [34].
This study's obtained results reveal that the soil is strongly contaminated by lead, cadmium, mercury, and copper. Their accumulation concentration order in the ground is as follows Hg > Pb > Cd > Cu.  [37].
Copper intake in plant species may increase when pH and organic fertilizers are low in the soil. Cu is one of the essential elements for all life forms but becomes toxic when it is available in large quantities. Lead concentration may occur due to fuel combustion residues accumulation from transportation and pesticides. Pb concentration is associated with organic matter colloidal in soil, which results in more Pb proportion. Pb may cause chronic emphysema because it affects the neurovegetative functions and blood hampers. Cadmium is irreversibly bound by ferric and manganese oxides in soil and clay minerals that in uence mobility [38].
Cd is one of the most phytotoxic metal pollutants because of its mobility, especially on soil with acidic soil pH. The total bioactivity richness and diversity of microorganisms decrease with the increase of heavy metal concentrations because microorganisms differ in insensitivity towards heavy metal toxicity [39].

Conclusion And Recommendations
In this study, the soil from the land ll site contains high levels of heavy metal (speci cally Pb, Hg, and Cd) concentration compared to the control site's soil. Both sites have high metal concentrations, which exceeds the permissible limits from WHO.
Due to high metal concentration, nearby farmlands are at risk of pollution in their farm products with an accumulation of these metals. The concentration of heavy metals in this land ll site appears to cause a severe problem in the surrounding environment at the moment and later may cause more danger to human health and more damage to the environment.
This study's outcomes reveal that soil from land ll sites contains more heavy metals than the soil from unpolluted areas. The soil pollution by heavy metals led to poor soil health and quality, surface and groundwater pollution, and food contamination, resulting in a hazardous risk to human health. Therefore, this study's ndings show the necessary need to monitor and manage soil pollution properly and combined working efforts from both the residing and municipality residents. This study commenced helping address the soil pollution problem due to the illegal disposal of waste to monitor waste at large garbage coming from communities. These results may have a signi cant role in helping the local authorities take severe actions for remediation processes. This report study can be an essential reference for guiding the policymakers to focus more on soil pollution caused by metals.
It is highly commended to provide proper attention to reduce the Pb and Hg pollution due to its negative in uence on human health, affecting the central nervous systems and many other disorders. Soil bioremediation, phytoremediation, and hydrometallurgy to measure Hg and Pb should be introduced as a matter of urgency. Furthermore, government managers should encourage the use of sanitary land lls.
The obtained data provides necessary information for designing and managing waste disposal around the town, also provides information on the fate of vegetables and other crops cultivated on the dumpsites.
Declarations I Maphuhla N.G, declare that this is my original work and it have never been submitted to any journal for publication. It is the rst time this work submitted for publication.

Availability of data and materials
All data analyzed in this study was collected and put together by NG Maphuhla and is available in my device, it can be requested if needed.
Con icts of Interest: The authors declare no con ict of interest. Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.