Remediation Of Polluted Soils Research Articles

Patent mining on soil pollution remediation technology from the perspective of technological trajectory

Recent years have seen a marked growth in soil environmental problems, however, the research & development (R&D) direction of soil pollution remediation technology (SPRT) for addressing related challenges to the global ecosystem is still unclear. Patent is the most effective carrier of technological information. Therefore, this study investigates the status and future direction of SPRT through the analysis and mining of 14,475 patents from 1971 to 2020. In 2006–2020, 14,435 SPRT patents (79% of the total) were published, which is in the development stage. By measuring the proportion of high-value patents, determined by the ratio of the number of patent families containing two or more patents (PF2) to that containing at least one patent (PF1), we found that United States (PF2/PF1 = 0.711), Japan (PF2/PF1 = 0.500), and South Korea (PF2/PF1 = 0.431) hold a monopoly. International patent organizations serve as a bridge for technology transfer. Patent CN101947539-A measured by structural hole index (Effective size = 98.194, Efficiency = 0.926) has the most significant technological influence. Therefore, in order to accomplish the technological transition and improve the soil remediation capacity, more attention should be paid to the microbial-assisted phytoremediation technology related to inorganic pollutants, hyperaccumulators and stabilizers. Additionally, patents CN102834190-A (Effective size = 23.930, Efficiency = 0.855, Constraint = 0.141, Hierarchy = 0.089) and CN105855289 (Effective size = 21.453, Efficiency = 0.795 Constraint = 0.149, Hierarchy = 0.086) are both at the location of structural holes. So, more research should be carried out on green and cost-effective solutions for reducing organic pollutants in soil remediation. The current study identifies opportunities for innovations and breakthroughs in SPRT and offers relevant information on technological development prospects.

Enhanced Fluoride Stabilization by Modified Layered Double Hydroxides for the Remediation of Soil Pollution: Performance and Mechanism

Enhanced Fluoride Stabilization by Modified Layered Double Hydroxides for the Remediation of Soil Pollution: Performance and Mechanism

Integrating Biochar, Bacteria, and Plants for Sustainable Remediation of Soils Contaminated with Organic Pollutants.

The contamination of soil with organic pollutants has been accelerated by agricultural and industrial development and poses a major threat to global ecosystems and human health. Various chemical and physical techniques have been developed to remediate soils contaminated with organic pollutants, but challenges related to cost, efficacy, and toxic byproducts often limit their sustainability. Fortunately, phytoremediation, achieved through the use of plants and associated microbiomes, has shown great promise for tackling environmental pollution; this technology has been tested both in the laboratory and in the field. Plant-microbe interactions further promote the efficacy of phytoremediation, with plant growth-promoting bacteria (PGPB) often used to assist the remediation of organic pollutants. However, the efficiency of microbe-assisted phytoremediation can be impeded by (i) high concentrations of secondary toxins, (ii) the absence of a suitable sink for these toxins, (iii) nutrient limitations, (iv) the lack of continued release of microbial inocula, and (v) the lack of shelter or porous habitats for planktonic organisms. In this regard, biochar affords unparalleled positive attributes that make it a suitable bacterial carrier and soil health enhancer. We propose that several barriers can be overcome by integrating plants, PGPB, and biochar for the remediation of organic pollutants in soil. Here, we explore the mechanisms by which biochar and PGPB can assist plants in the remediation of organic pollutants in soils, and thereby improve soil health. We analyze the cost-effectiveness, feasibility, life cycle, and practicality of this integration for sustainable restoration and management of soil.

Effective immobilization of Cd(II) in soil by biotic zero-valent iron and coexisting sulfate

In this work, zero-valent iron (ZVI) combined with anaerobic bacteria was used in the remediation of Cd(II)-polluted soil under the mediation of sulfate (SO42−). Owing to hydrogen-autotrophic sulfate reduction, serious corrosion occurred on sulfate-mediated biotic ZVI in terms of solid phase characterization as massive corrosive products (e.g., goethite, magnetite and green rust) were formed, which were crucial in the immobilization of Cd(II). Thus, this integrated system achieved a 4.9-fold increase in aqueous Cd(II) removal and converted more than 53% of easily available Cd(II)-fractions (acid-extractable and reducible) to stable forms (oxidizable and residual) based on the sequential extraction results as compared to the sulfate-mediated ZVI system. Increasing SO42− concentration and ZVI dosage both demonstrated positive correlation to Cd(II) immobilization, which further reflected that hydrogenotrophic desulfuration acted an essential role in improving Cd(II) immobilization. It indicated that hydrogenotrophic desulfuration could accelerate iron corrosion and promote reactive mineral formation through biomineralization, as well as generate cadmium sulfide precipitates (CdS) to achieve excellent immobilization performance for Cd(II). Besides, this reaction was favorable under neutral pH condition. Our results highlighted the promoted effect of hydrogen-autotrophic desulfuration on ZVI corrosion to immobilize Cd(II) and offered a practicable technique in Cd(II)-polluted soil remediation.

Assessment of Polluted Soil Remediation Using Bacterial Community Tolerance to Heavy Metals as an Indicator

The assessment of remediation on metal-polluted soils is usually focused on total and/or bioavailable metal content. However, these chemical variables do not provide direct information about reductions in heavy metals pressure on soil microorganisms. We propose the use of bacterial communities to evaluate the efficiency of three remediation techniques: crushed mussel shell (CMS) and pine bark (PB) as soil amendments and EDTA-washing. A soil sample was polluted with different doses of Cu, Ni, and Zn (separately). After 30 days of incubation, the remediation techniques were applied, and bacterial community tolerance to heavy metals determined. If bacterial communities develop tolerance, it is an indicator that the metal is exerting toxicity on them. Soil bacterial communities developed tolerance to Cu, Ni, and Zn in response to metal additions. After remediation, bacterial communities showed decreases in bacterial community tolerance to Cu, Ni, and Zn for all remediation techniques. For Cu and Ni, soil EDTA-washing showed the greatest reduction of bacterial community tolerance to Cu and Ni, respectively, while for Zn the soil amendment with PB was the most effective remediation technique. Thus, bacterial community tolerance to heavy metals successfully detect differences in the effectiveness of the three remediation techniques.

A mechanism of microbial sensitivity regulation on interventional remediation by nanozyme manganese oxide in soil heavy metal pollution

Studies have found that nanozyme materials can be an potential solution for microorganisms with insufficient enzyme activities to meet habitat requirements, bringing new application prospects for the remediation of soil pollution via inoculation with exogenous microorganisms. However, few studies have investigated the mechanism of microbial sensitivity regulation when using nanozyme materials. In this study, we attempt to fill this gap by investigating the microbial sensitivity regulation mechanism (MSRM) on typical paddy field heavy metal pollution (As3+ and Cr6+) using nanozyme nanoMn3O4-coated microbial populations (NMCMP). Analysis of maintained enzyme activity, changes in microbial community structure and heavy metal content showed that the sensitivity of microbial community composition can be significantly altered by adding nanoMn3O4-coated microbial communities via 16s DNA and metagenomic analyses. Flavisolibacter and Arthrobacter were confirmed as two main bacteria species relevant to the remediation of the heavy metal pollution (As3+ and Cr6+). In addition, we also found that NMCMP could enhance the reduction of Cr6+ level and inhibit the release and rapid oxidation of As3+ from As2H2S3 during the process of remediation. This study will provide important research value for the remediation of soil heavy metal pollution by microbial methods.

Valorization of agriculture waste biomass as biochar: As first-rate biosorbent for remediation of contaminated soil

Each year, Asia produces an estimated 350 million tonnes of agricultural residues. According to Ministry of Power projections, numerous tonnes of such waste are discarded each year, in addition to being used as green manure. The methodology used to convert agricultural waste into the most valuable biochar, as well as its critical physical and chemical properties, were described in this review. This review also investigates the beneficial effects of bio and phytoremediation on metal(lloid)-contaminated soil. Agriculture biomass-based biochar is an intriguing organic residue material with the potential to be used as a responsible solution for metal(lloid) polluted soil remediation and soil improvement. Plants with faster growth and higher biomass can meet massive remediation demands. Recent research shows significant progress in agricultural biomass-based biomass conversion as biochar, as well as understanding the frameworks of metal(lloid) accumulation and mobility in plants used for metal(lloid) polluted soil remediation. Biochar made from various agricultural biomass can promote native plant growth and improve phytoremediation efficiency in polluted soil with metal(lloid)s. This carbon-enriched biochar promotes native microbial activity by neutralising pH and providing adequate nutrition. Thus, this review critically examines the feasibility of converting agricultural waste biomass into biochar, as well as the impact on plant and microbe remediation potential in metal(lloid)s polluted soil.

Photocatalytic nanomaterials: Applications for remediation of toxic polycyclic aromatic hydrocarbons and green management

Nanomaterials (NMs) have piqued the attention of scientists and researchers across many biomedical sciences due to their superior physical, chemical, and magnetic properties. The efficacy and efficiency of NMs depend on adapting to specific site conditions and soil composition. NMs have lately received much attention in the context of polycyclic aromatic hydrocarbons (PAHs) polluted soil remediation and water mitigation because of their unique properties resulting from their nanoscale sizes. The remediation of hazardous PAHs in water and soil is a hot research subject. Because the exposure of PAHs in water and soil results in pollution, which raises major human health concerns. The current review reports novel advancements in NMs that subsidize enhancement for degradation of PAHs. Challenges to the fabrication of high activity-based photocatalytic materials are also discussed. Furthermore, this review delivers exclusive and wide-ranging perspectives on the fabrication of nanomaterial-based photocatalytic systems. The knowledge of both soil remediation and water mitigation is also updated.

Comparison of Pb and Cd in wheat grains under air-soil-wheat system near lead-zinc smelters and total suspended particulate introduced modeling attempt

The excessive accumulation of wheat grain metals and metalloids caused by ambient air contamination has drawn an increasing concern. However, at present, the differences in the pathways of cadmium and lead accumulation in wheat grains in an air-soil-wheat system are not clear. In this study, wheat was grown around a lead‑zinc smelting area and exposed to different soil Pb and Cd levels and different ambient air Pb and Cd levels. Lead and Cd accumulation in wheat grains was examined in this study. Two models of wheat grain Pb and Cd concentrations were established based on the 3 variables including soil Pb and Cd concentration, ambient air Pb and Cd concentration, and soil pH. The results showed that total suspended particulate (TSP), soil, and wheat grains exhibited different degrees of Pb and Cd contamination in the study area, and the contamination of Cd is more serious than Pb contamination. The Pb in wheat grains was more likely to derive from ambient air than from soil, whereas the impact of ambient air on the accumulation of Cd in wheat grains might be very limited. This speculation was confirmed by the results of the predictor variable relative weight method based on the multiple regression analysis. Introduction of ambient air factor (TSP Pb and Cd) greatly improved the modeling effect of wheat grains Pb, while the modeling of grain Cd was more dependent on soil pH and total soil Cd. This research suggests that the reduction in wheat grain Pb is likely to be achieved by the control over ambient air Pb, whereas the reduction in the wheat grain Cd by the remediation of soil pollutants.

Ozonation for remediation of pesticide-contaminated soils at field scale

This work is the first ever study under field conditions for the removal of different classes of pesticides from soil using ozonation as a remediation technique. Initial assays were conducted with three different soil matrices to assess the effectiveness of the methodology under lab conditions. Field scale experiments were carried out on plots located in a greenhouse during the winter of 2020. The polluted soil was exposed to different treatments to test the effect of the mode of ozone application on pesticide degradation (S: polyethylene film covering, SOS: polyethylene film + surface ozone application, SOD: polyethylene film + deep application, SODS: polyethylene film + dual application, and C: no treatment). Ozonation impact was also assessed by variations on physical–chemical characteristics of the soil. Higher degradation was detected in ozonized soils, particularly in the SODS treatment, where ozone was dually applied on the surface and deep. During monitoring of remediation experiments, 15 of the main transformation products (TPs) were found. The results suggest that ozonation has favourable prospects to be considered a credible alternative technology for remediation of pesticide polluted soils.

Effects of lead pollution on soil microbial community diversity and biomass and on invertase activity

Lead (Pb) pollution is one of the most widespread and harmful environmental problems worldwide. Determination of changes in soil properties and microbial functional diversity due to land use is needed to establish a basis for remediation of soil pollution. This study aimed to investigate soils contaminated by Pb from different sources and to analyze the functional diversity and metabolism of soil microbial communities using Biolog technology. Pb pollution (>300 mg kg−1) significantly influenced the diversity and metabolic functions of soil microbial communities. Specifically, Pb contamination significantly reduced soil microbial biomass carbon (C) and nitrogen (N) levels and catalase activity while increasing invertase activity. Furthermore, Biolog EcoPlate assays revealed that Pb pollution reduced the general activities of soil microorganisms, suppressing their ability to utilize C sources. In Pb-contaminated areas lacking vegetation cover, Shannon, Simpson, and McIntosh diversity indices of soil microorganisms were significantly reduced. The microbial diversity and biomass C and N levels were affected by land use and soil properties, respectively, whereas soil enzyme activity was primarily affected by the interaction between land use and soil properties. Our results provide a reference and a theoretical basis for developing soil quality evaluation and remediation strategies.

Dual Ions Neutralized and Stabilized Red Mud for Chromium(VI) Polluted Soil Remediation

Dual Ions Neutralized and Stabilized Red Mud for Chromium(VI) Polluted Soil Remediation

Stabilization of Pb, Cd, and Zn in soil by modified-zeolite: Mechanisms and evaluation of effectiveness

As a type of soil stabilization material, zeolite has good cation exchange ability and synchronous stabilization potential for multiple active heavy metal cations in soil. However, natural zeolite contains relatively high amounts of impurities, and has a single heavy metal stabilization mechanism, which limits its capacity to stabilize heavy metals in soil. To develop a stabilization material that could efficiently stabilize several heavy metals simultaneously, in the present study, modified zeolite (MZEO) was prepared via NaCl pretreatment, chitosan modification, modified chitosan loading, and CaSiO3 modification to enable Pb, Cd, and Zn stabilization in soil. The aim of the present study was to explore zeolite modification technologies, reveal the stabilization mechanism of polymetallic contaminated soil and evaluate the stabilization effects of MZEO. According to the results, the modification treatment increased the cation exchange capacity of MZEO nearly 8-fold, the specific surface area 3.4-fold, and its internal pore structure was richer, with more adsorption sites. The appearance of a -NH2 absorption bands confirmed the loading of chitosan successfully, and the modification enhanced the heavy metal stabilization mechanism. Upon the addition of MZEO to Baiyin soil, the chemical morphologies of heavy metals changed, which reduced the weak acid extracted forms of Pb, Cd, and Zn in the soil by 21%, 10%, and 19%, respectively. The potential mechanisms of free heavy metal reduction were ion exchange with Na in MZEO, heavy metal mineral formation by Al replacement in the crystal lattice, and bonding with SiO32− formed by the hydrolysis of MZEO-loaded synaptic CaSiO3 particles, to form silicate precipitation. MZEO application minimized heavy metal leaching risk in the soil and heavy metal biological/plant accessibility, with potential economic benefits. MZEO has promising applications in polluted soil remediation.

Analysis of Soil Pollution Remediation Technology and Soil Ecological Protection Measures

Analysis of Soil Pollution Remediation Technology and Soil Ecological Protection Measures

A novel chitosan-urea encapsulated material for persulfate slow-release to degrade organic pollutants

A novel eco-friendly material (CS-U@PS) for persulfate slow-release to effectively degrade organic pollutants (methyl orange and pyrene) was synthesized using chitosan and urea as the encapsulated framework materials via an emulsion cross-linking method for the first time. The obtained CS-U@PS exhibits spherical shapes with a uniform size of approximately 2–3 µm according to the particle-size distribution and SEM image results. The slow-release mechanism was proposed through a kinetics model study and the Ritger–Peppas model fit well (r2 = 0.9699) to indicate that the slow-release process is non-Fickian diffusion. The influences of urea and PS dosages and oxidative conditions on methyl orange degradation were studied, and all the results suggested that urea played an important role in PS slow-release and can also catalyze the activation of PS by iron to further produce radicals and improve the removal efficiency of pollutants. A pyrene removal rate of 90.53% was achieved in aqueous solutions and an above 80% removal rate was obtained in weakly acidic or neutral soil environments by CS-U@PS activated by Fe2+ with citric acid as the chelating agent. Therefore, the fabricated slow-release oxidation materials exhibit application potential for the remediation of organic polluted groundwater and soil.

Effect of γ-Fe2O3 nanoparticles on the composition of montmorillonite and its sorption capacity for pyrene

Fe content and distribution on montmorillonite would probably enhance its sorption capacity for hydrophobic organic pollutants. Thus, Fe modified montmorillonites with different ratios of FeSO4·7H2O and Ca-montmorillonite were prepared. The results indicated that γ-Fe2O3 nanoparticles were not only generated at the montmorillonite surfaces, but that the γ-Fe2O3 also extended the edges of montmorillonite surfaces. The sorption capacities for pyrene were enhanced and even reached 834.79 μg g−1 with increase in ferrous iron content, but were then suppressed due to aggregation of γ-Fe2O3 on montmorillonite surfaces. Furthermore, pyrene was directly observed on γ-Fe2O3-montmorillonite surfaces with a lattice spacing parameter of approximately 0.27 nm, indicating that a new phase that mainly contained pyrene was generated during the sorption process. Additionally, after regenerating the γ-Fe2O3-montmorillonite composites, they could be reused for at least 5 cycles. It is therefore proposed that the prepared γ-Fe2O3-montmorillonite could be exploited as a potential green composite for remediation of hydrophobic organic pollutants in soil and sediment.

A bibliometric analysis of permeable reactive barrier enhanced electrokinetic treatment for sustainable polluted soil remediation

Research on soil remediation continues to develop, one of which is electrokinetic remediation combined with a permeable reactive barrier as a medium to prevent the migration of metals removed from the anode and cathode spaces. Thus, it is hoped that there is no need for reprocessing the residue resulting from electrokinetic remediation. This study aims to conduct a bibliographical analysis related to electrokinetic remediation coupled by permeable reactive barriers for heavy metal contaminated soil and to examine the effect of using various types of reactive barrier materials and their placement on the pollutants removal in the soil. Based on the results of bibliographic analysis, 26 relevant scientific articles were obtained, and the most publications in 2020 with 27% additional article publications are found. China and Environmental Science and Pollutant Research are the countries and journals that contribute the most to publications related to EK-PRB on heavy metal polluted soils.

BIOREMEDIATION OF CONTAMINATED SOIL WITH PETROLEUM PRODUCTS

Petroleum products are recognized as one of the most environmentally hazardous soil contaminants. The sources of this pollution are the enterprises of petroleum and chemical industry, transport, landfills. Soil has the ability to absorb many chemicals and retain them in the surface, fertile layer. Petroleum products change the mechanical, chemical, biochemical and physico-chemical characteristics of the soil, which can lead to the destruction of plants and microorganisms and affects on the soil self-cleaning. The degree of petroleum products impact on plants and microorganisms depends on many factors: temperature and humidity of the air and soil, the amount of nutrients, soil type, the concentration of pollutants. The effect of petroleum products on plants is due direct toxic effects and transformation of the soil environment. At the cellular and physiological level, the effect of petroleum hydrocarbons on plants is appeared in the violation of the structure of chloroplasts and photosynthesis. Hydrocarbons damage the membranes of chloroplasts, mitochondria, root cell membranes. Plants that grow in conditions of petroleum pollution of the soil contain more substances with stress-protective properties. The impact of soil contamination on plants can be direct and indirect. Direct impact - is the impact of petroleum components on plants, indirect impact - are changes in morphological, physicochemical and biological properties of the soil. Moreover, petroleum pollution can have negative and stimulating effects on plants. Therefore, determination the phytotoxic effect in soils contaminated with petroleum products, for selection the optimal methods of soil remediation is relevant today. The question of probiotics uses for remediation contaminated soil is not enough studied in Ukraine. Wide use of probiotic is prevented by insufficient study of this area: deficiency of scientific and scientific-practical base, comparative studies of different probiotics, methods of calculating the required doses to obtain a given cleansing effect and more. Thus, there is a need for further studies of effects of petroleum products on plants and methods of remediation of contaminated soils with probiotics. The article evaluates the phytotoxicity of contaminated soil with petroleum products before and after cleaning with probiotics. To assess the phytotoxic effect of petroleum products were used indicators: seedling height, root length, phytomass of seedlings and phytomass of plants root system. In the experiment were used test-plants: peas (Pisum sativum), oats (Avéna satíva). Remediation of contaminated soil was performed by biological method using probiotic Sviteko-Agrobiotic-01 (dilution 1: 100). The probiotic was applied on the second day after petroleum contamination. The obtained results showed that petroleum products pollution has a different effect on peas and oats in different periods from the moment of pollution. Contaminated soil with petroleum products hadn’t significant phytotoxic effect on Pisum sativum seeds on the 2nd day after contamination. Оn the 30th day after contamination research results showed clear toxic effect on Pisum sativum seeds by concentration of petroleum products of 5000 and 10000 mg/kg; Оn the 180 days after contamination research results showed toxic effect on Pisum sativum seeds at all research concentrations. Contaminated soil with petroleum products had phytotoxic effect on Avéna satíva seeds on the 2nd day after contamination starting from the concentration of petroleum products 5000 mg/kg (such as decreasing the length of the roots and the ground part of plants). On the 30th and 180 th day after contamination petroleum products hadn’t toxic effect on Avéna satíva seeds in the all range of the studied concentrations. It was found that contaminated soil for Pisum sativum becomes toxic mostly on 30th day after the introduction of petroleum products and soil toxicity increase over the time. For Avéna satíva, the soil becomes toxic from the moment of contamination at concentrations of petroleum products 5000 mg/kg and the toxicity of the soil decreases over time. The research results confirmed the effectiveness of biological method (use probiotics) of cleaning the soil from petroleum products. It is established that probiotics clean the soil up to the 5th class of toxicity (no toxicity) at almost all concentrations of petroleum products. Only in the variant with Pisum sativum at concentration of petroleum products 20,000 mg/kg the phytotoxic effect was more than 20% (low toxicity). The average value of the efficiency of soil remediation from petroleum products by probiotics at sowing Pisum sativum was 75%, at Avéna satíva - 74%. Therefore, the experiment showed high efficiency of bioremediation from petroleum products in comparison with soil self-cleaning. On the basis of research results it is planned to develop methodical bases of complex system of remediation of technogenic polluted soils by the way of application of newest environmentally benign methods (using probiotic).

Transferring waste red mud into ferric oxide decorated ANA-type zeolite for multiple heavy metals polluted soil remediation

Herein, a novel "waste reclamation for soil remediation" strategy has been developed for both alkaline waste red mud (RM) recycling and heavy metal (HM) polluted soil remediation. Through a direct one-pot hydrothermal reaction process, the Al, Si, alkali, and Fe2O3 components in waste RM have been transferred into ferric oxide decorated ANA-type zeolite (Fe2O3-ANA). As tested by the HMs polluted soil remediation and oilseed rape planting experiment, when 25 g/kg Fe2O3-ANA is added into the Pb2+, Cu2+, Cr3+ and anionic AsO2- polluted soil (HM concentration: 100–200 mg/kg), it can effectively suppress the HMs mobility in soil and reduce the bio-accumulation concentrations of HMs in the harvested oilseed rape (reduce ratio: 37.9–69.5%). The detailed mechanism study using energy dispersive X-ray energy spectroscopy, in-depth X-ray photoelectron spectroscopy and density function theory calculation concludes that the Cu2+, Pb2+ and Cr3+ in soil have been adsorbed and trapped in the framework structure of ANA in Fe2O3-ANA mainly via the cation exchange process. While the anionic AsO2- species are mainly caught by the Fe2O3 component in Fe2O3-ANA via surface adsorption. Overall, this work firstly transforms waste RM into Fe2O3-ANA for soil remediation, which is valuable to waste resource recycling and environmental conservation.

Pollution Characteristics and Associated Risk Assessment of Heavy Metals in Farmland Soils From a Typical County of Hubei Province, Central China

Knowledge from the negative impacts of the counties' anthropogenic activities on soil pollution was of great significance in China, and valuable information was urgently needed for the control and remediation of soil pollution. The current pollution levels of heavy metals (Cu, Pb, Cd, Zn, Ni, and Cr) in farmland soils were investigated in Yangxin County, Hubei Province, central China. The comprehensive results of quantitative comparison and evaluation in this study showed that Cu (144.9 ± 298.6mgkg-1), Cd (2.9 ± 1.6mgkg-1), and Ni (137.0 ± 111.0mgkg-1) posed higher pollution risks to public and ecosystem health, which were higher than the corresponding soil background values. The combined results of geostatistics, spatial and statistical analysis indicated that studied heavy metals were mainly attributed to agricultural, traffic and industrial induced pollution. Overall, urgent attention should be paid to the risk reduction and management of soil Cu, Cd, and Ni pollution in the study area.