Analytical Profiling of Heavy Metals Contamination in soils, Dismantling Dust, and Rubber Samples in Karachi City Using AAS, WD-XRF, and SEM Technique

The concentrations of Cd, Cr, Cu, Fe, Ni, Pb, & Zn were determined in the samples of soil, dismantling dust and rubber collected from the electronic waste dumping site of Shershah market and rubber from the Local market of Karachi city Pakistan. The city e-waste dumping and dismantling sites toxicity were not conducted before using modern techniques. The subsequent data of the heavy metals concentration were obtained using Atomic Absorption Spectrometry (AAS), Scanning Electron Microscopy (SEM), and Wavelength Dispersive- X-Ray Fluorescence Spectrometry (WD-XRF). Cu, Pb, and Zn were found as 133.17, 104.53 & 113.26 in soil, whereas in dismantling dust Pb & Zn were remained 10.56 and 12.65 mg/kg similarly. The China toy particle analysis by SEM was resulting metallic trend as Fe > Zn > Pb > Cd > Ni > Cr. The estimated data were compared with the levels allowed by the Pakistan Environmental Protection Agency (Pak-EPA) and the United States Environmental Protection Agency (USEPA). The maximum allowable limit for Cd is 3; Cr, Cd, and Pb are 100 for Ni is 50 and 300 mg/kg for Zn. The presence of these heavy metals from e-waste dumping would become soon a significant reason to cause serious health problems for the nearby residents and as well as city too. It has been concluded that the dumping of e-waste is the major source of contamination of heavy metals in the studied media. It is recommended that the e-waste must be recycled formally to prevent the soil from being polluted.
.


INTRODUCTION
Discarded electronic and electrical appliances generate e-waste. These include computers, televisions, mobile phones, digital music recorders or players, refrigerators, washing machines, etc (Patil & Ramakrishna, 2020) (Iqbal et al., 2015a). The presence of a mixture of various plastics and chemicals in e-waste can cause harmful impacts on humans and the environment owing to improper treatment of the waste (Singh, Duan, & Tang, 2020) (Liu et al., 2018). The composition of the waste varies in products having different categories. The substances have been categorized into 'hazardous' and 'non-hazardous' substances and their number are more than 1000 (Perkins, Brune Drisse, Nxele, & Sly, 2014). Among the hazardous substances in e-waste, there are heavy metals like Lead (Pb), inhabitants. Almost 2 million people pass from this area daily (Iqbal et al., 2015a) (Rafeeq et al., 2020) (Umair, Anderberg, & Potting, 2016) (Umair, Björklund, & Petersen, 2015). Therefore, it is essential to determine the composition of the ewaste generated and dumped in the market. Analysis of the contaminants in e-waste dumpsites can be done by collecting the samples of dumpsite soil. The study of heavy metals in these significant environmental wastes can confer data in the atmosphere of the site (Iqbal et al., 2015a) (Mostafaii et al., 2021).
Workers in dismantling sites and their children are exposed to heavy metals through drinking of contaminated water, ingestion of contaminated food, inhalation of polluted air and dermal absorption. These metals can cause acute and chronic toxicity in the people, for example, the presence of Pb in the blood affects IQ of the children (Xu, Zeng, Boezen, & Huo, 2015) (Olafisoye, Adefioye, & Osibote, 2013). Studies have demonstrated that children and workers in ewaste dumpsites were contaminated with heavy metals and persistent organic substances (Liu et al., 2018) (Zeng, Xu, Boezen, & Huo, 2016) (Imran, Haydar, Kim, Awan, & Bhatti, 2017). Furthermore, surface water and plants have also been polluted with e-waste toxic substances (Olafisoye et al., 2013) (Michelle et al., 2016).
Literature reveals that Printed Circuit Boards (PCB) of CPU and monitor of computers are polluted with Cu and Pb and their concentrations were 50 folds more than the Toxicity Threshold Limit Concentration (TTLC) for the metals in electrical and electronic equipment in the developed countries (Singh, Duan, Ogunseitan, Li, & Tang, 2019). Consequently, this equipment containing Cu and Pb are hazardous wastes. The disposal of the ewaste will cause health and environmental issues (Shaikh, Thomas, Zuhair, & Magalini, 2020) (Li & Achal, 2020). The purpose of the present work was to take initiative against e-waste contamination. This study will provide a quantitative analysis based on primary data to address the subsequent e-waste effects. The heavy metals in WEEE contaminated soil and groundwater were assessed using different Latest techniques like AAS, WD-XRF and SEM collected from the Shershah market area, Karachi.

Study Area
The E-waste dumping site focused in this study is located (24°52'52.7"N and 66°59'40.0"E) in Karachi, Sindh Provence in southeastern Pakistan. This dumpsite is mainly located to the second-hand goods supply market. Huge stuff of old material is available for purchase, considered as the largest reusable material market in Asia. E-waste recycling business is not older than 15-20 years in Pakistan (Iqbal et al., 2017). The specific recycling area and dumpsite were focused, where mostly the poor peoples and their children or hired children are involved in e-waste related activities. Since this area is closest to the seaport in Pakistan. Therefore, became the main receiver of e-waste. The main (50-60%) recycling was carried out on this site. Another site was also selected for reference sampling where none of these types of activities were observed. Any difference in population, traffic density, lifestyle, rainfall, and socioeconomic status did not exist between the involved and controlled sites. The study was conducted from April to August in 2015-2018. A large no of soil samples was collected from the dumpsite and from control for reference (Umair et al., 2016) (Rafeeq, 2019).

Collection of soil samples
Soil samples were collected in April at various points of the e-waste dumpsite located (north to south) within the premises of Lyari expressway wall. 150-meter length of dumpsite was considered as an active site. The dumpsite was classified into A, B, C, D, and E points to determine the profile of the heavy metal in the soil. Designated point A covers about a fifty-meter wide (east to west) and thirty-meter long (north to south). The Lyari River cuts up the e-waste along with market waste dumping sites and opposite residential waste sites. The river let falls into the Arabian Sea.
Furthermore, the total area (150-meter long) was also divided into points A, B, C, D, and E to get comparative data. The marked areas were further subdivided such as A-1. A-2, A-3, A-4 and A-5. Uniform sampling was carried out from all areas. Stainless steel scale was used to drawn samples of burning ash from the areas keeping a depth up to 10 cm. The five core samples were randomly collected and homogenized. A composite sample was taken as a representative sample of the whole soil point area. The composite sample was air-dried, crushed, and sieved through 2 mm sieve. The sample was stored in a polythene bag and labeled accordingly. A reference sample was also collected from the Nazimabad Cricket Playground 6.7 miles away from the dumpsite. In 2015-2018 (when the study was conducted for yearly monitoring) from the same dumping site, the surface and depth samples were collected by dividing the dumpsite into two parts A & B. The surface samples were marked as AS and BS while the depth samples were AD and BD (Rafeeq, 2019).

Collection of e-waste surface dust samples
The amount of dumping activity was investigated by the analysis of soil heavy metals. The heavy metals containing dust can become part of the human body through ingestion, inhalation, and dermal absorption (Ohajinwa, van Bodegom, Vijver, & Peijnenburg, 2018). Weather conditions especially the dry season increase the prevalence of heavy metals in the dust (Juneng, Latif, & Tangang, 2011) (Adaramodu, et el., 2012) (Olafisoye et al., 2013). Therefore, the samples of dust were analyzed from the dismantling sites. The sampling was carried out from three main units of the dismantling from streets no 08, 09, and 10, where about 1000 kg per day e-waste is processed in each. The plastic brush and dustpans were used to collect fine particulates from 150-200 g dust by gentle sweeping motion. The auxiliaries were clean with tissue papers. Three composite samples of the dust were analyzed from the Shershah market and a control sample from Nazimabad playground. The samples were stored in plastic bags before the laboratory analysis. The samples were dried by keeping in the desiccators for 3 hrs, sieved using mesh (less than 2mm), and eventually homogenized. About 25 g of dust sample was grounded into a fine powder of 100 mesh size using a mini-mill (II), a ball mill before the chemical analysis (Rafeeq et al., 2020) (Rafeeq, 2019).

Collection of Rubber samples
The rubber sample was collected from the local market available in the form of china toys. Forty-four samples were selected and purchased from different local markets in Karachi. Samples were randomly picked from local market stalls; mall stores, bargain stores, roadside vendors, retail toy shops, and Imtiaz supermarket Gulshan e Iqbal Karachi. All samples were separated into two respective categories with code and labeled properly.

Soil and Dust Sample Preparation for AAS Analysis
The samples of soil and dust were digested with conc.HNO 3 and extracted with concentrated HCl (Rafeeq et al., 2020) Osoh, 2012). The wash glass and flask were washed with the deionized water and filtered into a 250 mL volumetric flask using a Whatman No. 42 filter paper, the filtrate was diluted up to the mark with the deionized water. A blank solution and a series of CRM sample were also prepared (Rafeeq, 2019) (Guo et al., 2010.

Soil Samples Preparation for WD-XRF Analysis
Soil samples were pounded by mixing with wax to get the homogenization by using a mini ball mill (a zirconium-based balls mill). The sample rotation in the machine was set clockwise and counters clockwise for 2 minutes at 240 rpm. Herzog press pellet machine was used to prepare the hard, flat, and smooth surface by applying 25 KN force. Boric Acid was used as a binder to prevent the breaking or dispersion of samples during bombarding of high-intensity X-Rays (Ahmed, Hassan, Akhter, & Mumtaz, 2019).

Soil and Rubber Sample Preparation for SEM Morphological Analysis
Soil (AS, AD, BS, and BD) and Rubber (10×10) mm samples were bombarded with the Gold (Au) particles. The Ion sputter coater machine was used to make the samples electrical conductor to avoid the building up charges during SEM analysis, which is necessary to analyze the sample with more sensitivity on SEM so that clear images should receive. Ion sputter coater machine is used to deposit metal coating that has a thickness of few nanometers, which is a very thin layer (Ahmed et al., 2019) (Hassan & Naseem, 2020          . SEM image of rubber sample particle at a magnification of 66X with Graph of SEM-EDX analysis of elements of a selected particle in rubber sample image-point 1 Figure 17. SEM image of rubber sample particle at a magnification of 66X with Graph of SEM-EDX analysis of elements of a selected particle in rubber sample image-point 2 Figure 18. SEM image of rubber sample particle at magnification of 66X with Graph of SEM-EDX analysis of elements of selected particle in rubber sample image-point 3   (Rafeeq et al., 2020). The higher concentrations within the samples were found to be 508 mg/kg of Cu, 154 mg/kg of Pb, 137 mg/kg of Zn,8 mg/kg of Ni, and 4.5 (mg/kg) mg /kg of Cr, respectively in samples A-E. The decreasing concentration order were as Cu > Pb > Zn > Ni > Cr for assessment level in 2015. The dumpsite soil and reference sample concentration indicate a clear difference between controlled and active sites for ewaste and non-e-waste activities. Furthermore, the average concentration of heavy metals for a single point with some statistical analysis is tabulated in (Table 1). The graphical representation is depicted in (Figure 1).

Results of Scanning Electron Microscope (SEM) analysis of depth soil and control sample marked as R in 2019
The detailed summarized comparison presented in table 2 from the year 2015-2018 with their respected acceptable values in soil by USEPA and Pak-EPA (Rafeeq et al., 2020) (Alam et al., 2015). Two elements Fe and Cd were added to the study. The overall concentrations for metal were found higher in 2015 than subsequent years, while in 2018 analysis was again increased than preceded two years. This may be the effect of low level of rain than the previous years. The order of metallic contamination was Cu > Zn > Pb > Fe > Ni > Cr > Cd. Maximum value for Cu, Zn, Pb, Fe. Ni, Cr and Cd were observed as 332. 41, 125.35, 111.95, 5.90, 5.74, 2.91 and 0.58 mg/kg respectively. WD-XRF analysis was also carried out for the surface and depth soil samples in 2017 from the same dumpsite (shershah) Karachi. The maximum concentrations were found for Cu in sample BS, Zn in AS, Pb in AS, Fe in BS, Ni in BS, and Cr in AS, as 122. 86, 101.85, 94.79, 4.57, 3.27, and 0.82 mg/kg respectively, while Cd was not detected in either for surface or depth composite samples shown in table 4. The corresponding typical CRM was not confirmed as the instrument is purely installed for furnace refractory materials.
Another confirmation of the presence of metals in soil was carried out by SEM-imaging and SEM-EDX for the samples collected in 2017. Fig 5, 8, 10, 13,16 were the images of samples AS, BS, AD, BD, and R. Fig 6 & 7 were showing in AS particle selection with its EDX . Fig 7 for BS, Fig 9 & 10 highlighting AD Fig 14 & 15 representing BD, similarly reference sample connected with Fig 15. Maximum two images were confirming the focused metal in the soil as can be seen in EDX of the images. The morphological study confirmed the presence of metals in the soil. An evaluated concentration in mg/kg on particle basis on different zooming power for the soil of surface and depth were presented in table 5 serial 1-8 with percentage absolute error at 1 sigma, and percentage relative error at 1 sigma.
The dust samples were also collected from dismantling sites in Karachi. The concentration of heavy metals such as Cd, Cr, Cu, Fe, Ni, Pb, and Zn was determined as given in Table 3 and graphically presented in Fig 2. The concentration of the metals was higher than the referenced sample values, indicating the pollutants difference in dismantling and control site, containing the nature of the samples. The pH of the samples was 7-8, showing the alkaline nature of the samples.
Rubber from the toy (China toy) was analyzed for heavy metals using SEM-imaging & SEM-EDX at 66X. Three different points were considered to report which were showing the metallic presence. Figures 18, 19 & 20 are the images of these sample points with their EDXs. The metallic concentration in mg/kg with percent absolute error at 1 sigma & percent relative error at 1 sigma were tabulated in Table 6. Although the results in mg/kg were higher for selected metals but the absolute and relative error indicating the level of significance of the results, as lowest the error higher will be the accuracy. The fact is also that the SEM-EDX is not known for accurate quantitative analysis but for the qualitative study, SEM could be a primary tool (Zadora & Brozek-Mucha, 2003) (Batista, Melo, Gilkes, & Roberts, 2018).   (Fig 18, Table 6).
A comparison of the whole study has also been tabulated in Table 7. In which dumping site profiling, four-year detailed study, dismantling dust and rubber sample results were compared by their range values. Either the results were evaluated from AAS, WD-XRF, or SEM-EDX. All of the tabulated results are alarming for the e-waste activities as Cu & Pb are touching the maximum allowable limits of USEPA 300 & 100 mg/kg for soil (Ofudje, 2014) (USEPA, 1997). Despite the mathematical expression and comparison with recommendations, the contamination level is the clear image as increased. Dismantling dust contamination directly impacts on the workers and the surrounding residential, as the lower level of Cd, 0.07 mg/kg, and Pb, 10.56 mg/kg could directly pose a serious chronic threat to inhalers (USEPA, 1997). Rubber sample concentration for heavy metals are also threatened as the circle of contact for rubber or plastic is general public especially children from 0.5 -6 years old, rather than the workers for e-waste. The metals in rubber also indicate the route map of EoL (end of life) product to recycled product (Dimitrakakis, Janz, Bilitewski, & Gidarakos, 2009) (Vehlow et al., 2000) (Nnorom & Osibanjo, 2009).

CONCLUSION
In this study, a complete analytical profile of heavy metals in soil, dismantling dust, and rubber (recycled product) was carried out in various samples collected from the electronic waste dumpsite and dismantling site of the Shershah market, and from the local market in Karachi. In the samples of soil, the higher average concentrations were found to be 373.87 mg/kg of Cu, 112.11 mg/kg of Pb, 125.41 mg/kg of Zn, 6.31 mg/kg of Ni and 2.44 mg /kg of Cr, respectively. The dust samples were analyzed for heavy metals such as Cd, Cr, Cu, Fe, Ni, Pb, and Zn collected from dismantling sites. The metallic trend in dismantling dust was observed as Zn > Pb >Fe > Cu > Cr > Ni > Cd with lead concentration of 10.56 mg/kg and Cd of 0.069mg/kg. Nearly the same results were also observed through WD-XRF for an alternate route of verification. The soil and rubber particle analysis by SEM-EDX was also indicating the presence of heavy metals. The concentration of the metals in soil and dust was higher than the controlled reference sample values, indicating the metallic pollutants containing the nature of the samples. The pH of samples was 7-8, showing the alkaline nature of the samples. This study will be valuable for selecting appropriate mitigation for the e-wasteimpacted deteriorated environments and to safeguard the environment and people from potential hazards. This quantitative analysis-based study would be helpful in future socio-economic indications if a deep medicated investigation is performed by anyone or any means.