Impact of repeated single-metal and multi-metal pollution events on soil quality

Identification of the pollution sources and hidden clustering patterns for potentially toxic elements in typical peri-urban agricultural soils in southern China

Peri-urban agricultural soils are often contaminated by potentially toxic elements (PTEs) due to rapid urbanization, industrial activities, and agricultural practices. In this study, two advanced analytical methods including positive matrix factorization (PMF) model and K-means clustering algorithm were integrated to explore the potential sources and concealed contamination patterns of 8 PTEs in peri-urban soils in county Gaoming, China. Descriptive statistics showed average concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn) as 19.11, 0.18, 35.69, 20.31, 18.26, 151.7, 67.75, and 0.29 mg/kg, respectively. The PMF model identified three primary sources: geogenic (Cr, Ni), industrial and traffic-related (Pb, Hg, Zn), and agricultural (As, Cd and Cu). The contribution of each source was quantified: geogenic sources contributed 55.6% to Cr and 52.3% to Ni, industrial sources accounted for 41.8% of Pb, 58.4% of Hg, and 41.9% of Zn, while agricultural practices contributed 88.1% of As, 77.9% of Cu, and 70.7% of Cd. Subsequently, K-means clustering classified the soil samples into three distinct clusters based on the derived factor contribution from PMF model, reflecting their clear spatial associations with different types of land use: large-scale agricultural areas (Cluster 1), natural vegetation (Cluster 2), and urbanized zones (Cluster 3). Furthermore, boxplots showed that the highest PTE concentrations were found in the third cluster, confirming the significant impact of human activities, while the lower concentrations in the second cluster indicated more natural conditions. These results underscored the dual influences of agriculture and urbanization on PTE contamination, which highlighted the need for targeted soil management strategies. Moreover, the integration of PMF and K-means clustering effectively reveals potential sources and concealed pollution patterns, providing insights for managing pollution and safeguarding environmental health in rapidly urbanized areas.

Long-Term Trends and Ecological Risks of Heavy Metal Accumulation in Cultivated Land of Songnen Plain, China

Heavy metal pollution in agricultural soils poses a serious threat to food security. Therefore, it is crucial to conduct risk assessments and issue early warnings about high levels of metal contamination for the sustained prosperity of agriculture. To assess the risks, identify the sources, quantify the amounts, and determine the extent of pollution from seven heavy metals, as well as to provide early warnings, 78 soil samples were collected from farmed lands in the Songnen Plain of Jilin Province. The average concentrations of Zn, Cu, Mn, Pb, Cd, Ni, and As were found to be 2.05, 1.5, 0.2, 1.09, 2.68, 1.53, and 1.17 times higher than the background values of Chinese soils, respectively. Source analysis indicated that toxic Pb originates from vehicle exhaust emission, while Cd, Cu, and Ni are attributed to industrial activities. Zn and As are likely associated with agricultural practices, and Mn predominantly stems from natural environmental sources. The geo-accumulation index suggests relatively high, accumulation levels for Zn, Cu, Mn, and Pb. Meanwhile, the single-factor pollution index indicates elevated pollution levels of Zn, Cu, and Cd. Potential ecological risk assessment reveals that certain areas within Changchun and Baicheng cities exhibit higher ecological risks. Notably, Cd has the highest potential ecological risk index (RI) of the seven heavy metals and warrants special attention. By analyzing annual pollutant accumulations, predictions can be made about the heavy metal content in four cities within the Songnen Plain, enabling the issuance of early warnings regarding soil heavy metal risks. The findings suggest that without proactive measures to mitigate heavy metal accumulation in soils, Changchun and Songyuan will reach severe pollution levels by 2031 and 2029, respectively.

Enrichment and sources of major and trace elements in the Qinghai-Tibetan Plateau: a case study of the Golog Prefecture

The Qinghai-Tibet Plateau (QTP) is a vital region for global atmospheric circulation and biodiversity. This study aims to evaluate the contents and enrichment status of 25 soil elements, namely Al, As, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, S, Sc, Si, Sn, Sr, Fe, Ti, V, and Zn, in the plateau region. Specifically, our analysis revealed that As exhibited significant enrichment near fault zones and intrusive rocks, while Ca was mainly enriched due to the dissolution of carbonate rocks. Additionally, Principal Component Analysis and Multiple Linear Regression (PCA-MLR) were used to examine the origins of these elements. The potential ecological risk posed by Cd and Pb was evaluated and found to be negligible. Soil element enrichment in the QTP was mainly influenced by lithology, and high spatial variability was observed in As, Ca, and S, which were mainly affected by geological processes and grazing activities. Six sources of elements in the plateau region were identified, namely geological mixed sources, grazing activities, alkaline granite, ultrabasic rocks, fault zones and intrusive rocks, as well as atmospheric deposition. Among these, geological mixed sources and grazing activities were determined to be the priority contributors. Although grazing activities on the QTP as well as atmospheric deposition at long distances caused the enrichment of elements in the area, the ecological risk was negligible. The outcomes of this work can be used as a theoretical basis for prospective investigation on the stability of high-altitude ecosystems, species diversity, and geochemical background.

Machine learning-driven source identification and ecological risk prediction of heavy metal pollution in cultivated soils

To overcome challenges in assessing the impact of environmental factors on heavy metal accumulation in soil due to limited comprehensive data, our study in Yangxin County, Hubei Province, China, analyzed 577 soil samples in combination with extensive big data. We used machine learning techniques, the potential ecological risk index, and the bivariate local Moran's index (BLMI) to predict Cr, Pb, Cd, As, and Hg concentrations in cultivated soil to assess ecological risks and identify pollution sources. The random forest model was selected for its superior performance among various machine learning models, and results indicated that heavy metal accumulation was substantially influenced by environmental factors such as climate, elevation, industrial activities, soil properties, railways, and population. Our ecological risk assessment highlighted areas of concern, where Cd and Hg were identified as the primary threats. BLMI was used to analyze spatial clustering and autocorrelation patterns between ecological risk and environmental factors, pinpointing areas that require targeted interventions. Additionally, redundancy analysis revealed the dynamics of heavy metal transfer to crops. This detailed approach mapped the spatial distribution of heavy metals, highlighted the ecological risks, identified their sources, and provided essential data for effective land management and pollution mitigation.

Quantitative assessment of ecological risk from pollution source based on geostatistical analysis and APCS-MLR model

The safety of human health and agricultural production depends on the quality of farmland soil. Risk assessment of heavy metal pollution sources could effectively reduce the hazard of soil pollution from various sources. This study has identified and quantitatively analyzed pollution sources with geostatistical analysis and the APCS-MLR model. The potential ecological risk index was combined with the APCS-MLR model which has quantitatively calculated the source contribution. The results revealed that As, Cr, Cd, Pb, Zn, and Cu were enriched in soil. Geostatistical analysis and the APCS-MLR model have apportioned four pollution sources. The Mn and Ni were attributed to natural sources; As and Cr were from agricultural activities; Cu and Zn were originated from natural sources; Cd and Pb were derived from atmospheric deposition. Atmospheric deposition and agricultural activities were the largest contributors to ecological risk of heavy metals in soil, which accounted for 56.21% and 36.01% respectively. Atmospheric deposition and agricultural activities are classified as priority sources of pollution. The combination of source analysis receptor model and risk assessment is an effective method to quantify source contribution. This study has quantified the ecological risks of soil heavy metals from different sources, which will provide a reliable method for the identification of primary harmfulness sources of pollution for future studies.

Tracing and source fingerprinting of metals from the southern coastal sediments in Bangladesh

Trace element pollution from anthropogenic sources is increasingly widespread. This pollution in terrestrial environments threatens agricultural crop production, while in aquatic environments, it threatens fish cultivation. The contamination of these crucial food sources raises significant concerns regarding food safety, security, and its potential adverse effects on human health. Coastal areas are particularly vulnerable to heavy metal pollution due to their proximity to industrial and urban centres, as well as their susceptibility to contamination from marine sources. In attempting to identify the sources of heavy metals (As, Cu, Cr, Cd, Fe, Hg, Mn, Ni, Pb, and Zn) and measure their contributions, we collected soil samples from thirty sites along the three coastal districts (Patuakhali, Barguna, and Bhola) in Bangladesh. Using atomic absorption spectroscopy, heavy metal concentrations in soil samples were measured and three receptor models (PMF, PCA-MLR, and UNMIX) were applied to detect their sources. Pairwise correlation analysis of metal concentrations in 30 sites across 3 coastal districts showed all possible patterns, including both significant and insignificant positive and negative relationships between different metals, except for As and Hg which did not display any significant relationships with other metals. The concentrations of Cu, Fe, Mn, Ni, and Zn exceed the US-EPA sediment quality standard. The applied PCA-MLR, PMF, and UNMIX models identified several sources of heavy metal contamination, including (i) mixed anthropogenic and natural activities: contribution of 59%, 37%, and 43%, and (ii) vehicle emissions: contribution of 23%, 26% and 29%. The recognized metal sources should be prioritised to avoid the discharge of poisonous pollutants from anthropogenic factors and any possible future exposure. This study's findings have implications for ongoing monitoring and management of heavy metal contamination in coastal environments to mitigate potential health and ecological impacts and can inform policy development and management strategies.

Heavy metals pollution from smelting activities: A threat to soil and groundwater

Throughout the literature, the word "heavy metal" (HM) has been utilized to describe soil contamination; in this context, we characterize it as those elements with a density greater than 5 g per cubic centimeter. Contamination is one of the major global health concerns, especially in China. China's rapid urbanization over the past decades has caused widespread urban water, air, and soil degradation. This study provides a complete assessment of the soil contamination caused by heavy metals in China's mining and smelting regions. The study of heavy metals (HMs) includes an examination of their potential adverse impacts, their origins, and strategies for the remediation of soil contaminated by heavy metals. The presence of heavy metals in soil can be linked to both natural and anthropogenic processes. Studies have demonstrated that soils contaminated with heavy metals present potential health risks to individuals. Children are more vulnerable to the effects of heavy metal pollution than adults. The results highlight the significance of heavy metal pollution caused by mining and smelting operations in China. Soil contaminated with heavy metals poses significant health concerns, both carcinogenic and non-carcinogenic, particularly to children and individuals living in heavily polluted mining and smelting areas. Implementing physical, chemical, and biological remediation techniques is the most productive approach for addressing heavy metal-contaminated soil. Among these methods, phytoremediation has emerged as a particularly advantageous option due to its cost-effectiveness and environmentally favorable characteristics. Monitoring heavy metals in soils is of utmost importance to facilitate the implementation of improved management and remediation techniques for contaminated soils.

Source-sink response analysis of heavy metals and soil pollution assessment in non-ferrous metal industrial agglomeration areas based on decision unit

Soil heavy metals (HMs) pollution is a worldwide concern. In this study, decision units based on "source-sink relationship" were established using multi-source data. The source-sink response of heavy metals in agricultural soils at the regional scale was analyzed using machine learning methods, receptor models, and geospatial analysis. The comprehensive pollution risk score (CRS) was proposed by integrating a variety of key evaluation indicators to evaluate the pollution degree of each decision unit. We divided the study area into 193 decision units, the proportions of sites with concentrations of Cd, Hg, As, Pb, and Cr exceeding the most stringent risk screening values were 16.4 %, 2.2 %, 4.0 %, 7.6 %, and 0.2 %, respectively. Agricultural activities (livestock manure, fertilizer, sewage irrigation), industrial activities (rare earth ore and tungsten‑molybdenum mining and smelting), and soil parent material are the dominant pollution sources of HMs in the study area. The risk of contamination of each element is ranked from largest to smallest according to the CRS as Cd > Hg > Pb > As > Cr. The western and southwestern water pollution decision units are the areas with the highest risk of soil HMs contamination. This quantitative evaluation framework can provide a relatively accurate decision basis for soil pollution management.

Cadmium reduced methane emissions by stimulating methane oxidation in paddy soils

Flooded rice paddy fields are a significant source of anthropogenic methane (CH4) emissions. Cadmium (Cd) is one of the most common and toxic contaminants in paddy soils. However, little is known about how the soil microbial communities associated with CH4 emissions respond to the increasing Cd-stress in paddies. In this study, we employed isotopically 13C-labelled CH4, high-throughput sequencing analysis, and gene quantification analysis to reveal the effect and mechanism of Cd on CH4 emissions in paddy soils. Results showed that 4.0 mg kg-1 Cd addition reduced CH4 emissions by 16-99% in the four tested paddy soils, and significantly promoted the transformation of 13CH4 to 13CO2. Quantitative polymerase chain reaction (qPCR) demonstrated that Cd addition increased the abundances of pmoA gene, the ratios of methanogens to methanotrophs (mcrA/pmoA) showed a positive correlation with CH4 emissions (R2 = 0.798, p < 0.01). Furthermore, the composition of the microbial community containing the pmoA gene was barely affected by Cd addition (p > 0.05). This observation was consistent with the findings of a pure incubation experiment where methanotrophs exhibited high tolerance to Cd. We argue that microbial feedback to Cd stress amplifies the contribution of methanotrophs to CH4 oxidation in rice fields through the complex interactions occurring among soil microbes. Our study highlights the overlooked association between Cd and CH4 dynamics, offering a better understanding of the role of rice paddies in global CH4 cycling.

The multi-media environmental behavior of heavy metals around tailings under the influence of precipitation

Precipitation can lead to significant leaching of heavy metals from abandoned tailings，resulting in a decline in the quality of the surrounding environment. This study aimed to simulate and quantify the migration patterns and fate of heavy metals in tailings caused by precipitation in various environmental media (tailings, air, water, soil, and sediments) using leaching tests, source apportionment, and a fugacity model. Results revealed that the average contents of Cd, Cu, As, Pb, Zn, and Cr in the un-weathered tailings were 3.43, 495.56, 160.70, 138.94, 536.57, and 69.52 mg/kg, respectively. The ecological risk factors in the tailings as well as in sediments and soils, were in the following order: Cd >Cu >As >Pb >Zn >Cr. A fugacity model based on the mass-balance methods was established, achieving a good agreement between simulation and measured values. The total amounts of Cd, Cu, As, Pb, and Zn leached from abandoned tailings over the 30-year evaluation period were estimated to be 1.09, 62.44, 0.16, 0.94, and 102.12 t, respectively. Soil and sediments are important reservoirs for heavy metals. The sum of the As, Cd, Cu, Pb, and Zn storage capacities in the soil and sediment accounted for 77.28%, 75.63%, 73.94%, 69.39%, and 57.80% of the total storage capacity, respectively. This study could provide the means for the establishment of a targeted pollution control plan, a guide for restoration projects, and will aid in controlling pollution risk and improving the surrounding environment.

The technique of arsenic elimination from contaminated soil with enhanced conditions by electro-kinetic remediation

Remediation of arsenic-contaminated soil by the technique of electro-kinetic using various enhanced conditions is the thrust of this study. Many tests were performed with different operating conditions, such as the electrodes solution (tap water) with a variable pH at (2, 5, and 8). Cyclodextrin (10% hydroxypropyl-beta-cyclodextrin, or HPCD) has been used as an activating agent that helps enhance this process of soil arsenic clean-up. Agricultural wastes (pomegranate peels) were used after treating them as an adsorbent to impede the return of pollutants to the soil as a result of reverse osmosis. The results obtained after the remediation's completion indicated that the best elimination capacity was 72% at a pH of 2. This indicates that the elimination capacity increases with the decreasing pH of the electrodes solution. Mixing the HPCD solution with soil as an enhanced solution increased the solubility and desorption of arsenic from the soil. Then, arsenic-containing HPCD micelles readily moved to the cathode electrode by electro-osmotic flow, and the elimination capacity increased (84%). It was concluded that pomegranate peels are a good adsorbent for arsenic returning to the soil during the treatment process as a result of reverse osmosis. Hence, the application of this material in this research gave a perfect impression of its use as an inexpensive, environmentally friendly adsorbent and an alternative to commercial absorbents.

Spatial patterns and the associated factors for breast cancer hospitalization in the rural population of Fujian Province, China

BACKGROUND

Despite the known increasing incidence of breast cancer in China, evidence on the spatial pattern of hospitalization for breast cancer is scarce. This study aimed to describe the disparity of breast cancer hospitalization in the rural population of Southeast China and to explore the impacts of socioeconomic factors and heavy metal pollution in soil.

METHODS

This study was conducted using the New Rural Cooperative Medical Scheme (NRCMS) claims data covering 20.9 million rural residents from 73 counties in Southeast China during 2015-2016. The associations between breast cancer hospitalization and socioeconomic factors and soil heavy metal pollutants were evaluated with quasi-Poisson regression models and geographically weighted Poisson regressions (GWPR).

RESULTS

The annual hospitalization rate for breast cancer was 101.40/100,000 in the studied area and the rate varied across different counties. Overall, hospitalization for breast cancer was associated with road density (β = 0.43, P = 0.02), urbanization (β = 0.02, P = 0.002) and soil cadmium (Cd) pollution (β = 0.01, P = 0.02). In the GWPR model, a stronger spatial association of Cd, road density and breast cancer hospitalization was found in the northeast regions of the study area while breast cancer hospitalization was mainly related to urbanization in the western regions.

CONCLUSIONS

Soil Cd pollution, road density, and urbanization were associated with breast cancer hospitalization in different regions. Findings in this study might provide valuable information for healthcare policies and intervention strategies for breast cancer.

Ecological risk assessment of potentially toxic elements in selenium-rich soil with different land-use types

Dashan Village area is one of the representative areas in China with high selenium concentration in the natural environment. A total of 133 topsoil samples have been collected in the Dashan Village area to explore the potential toxic elements (PTEs) background concentrations in soils under different land-use types for a comprehensive PTEs risk assessment (arsenic, cadmium, chromium, copper, mercury, nickel, lead, selenium and zinc). The results show that the geometric mean concentrations of As, Cr, Cu, Hg, Ni, Pb, Se and Zn found in the soil of the Dashan Village area were lower than the control standard for soil contamination risk in agricultural land. However, the geometric mean concentrations of Cd exceeded their corresponding standard values. For different land-use types, geometric mean concentrations of As, Cd, Cu, Hg, Ni and Pb in the arable soils were higher than in woodland soils and tea garden soils. Based on the potential ecological risk assessment, the woodland, arable and tea garden were at low-risk levels. Cadmium posed the highest ecological risk, while the other PTEs were of low risk in soils. Multiple statistical analyses and geostatistical analysis indicated that the concentrations of Cr, Ni, Pb, Cu, Zn and Se originated mainly from natural sources, while the concentrations of Cd, As and Hg could be influenced by anthropogenic activities. These results provide scientific support for the safe utilization and ecological sustainability of selenium-rich land resources.

Risk Assessment of Heavy Metals in Soils from Four Different Industrial Plants in a Medium-Sized City in North China

Laboratory experiments were carried out to analyze 39 soil samples collected from four industrial areas in Xuzhou City using inductively coupled plasma mass spectrometry and atomic fluorescence spectrometry. The descriptive statistics of heavy metals (HMs) in the soil profiles showed that the HM content at three depths was highly variable, and most coefficients of variation (CVs) showed moderate variability. The enrichment of Cd at all depths exceeded the risk screening value, and Cd pollution occurred in four plants. The enrichment of the other HMs at three depths was mainly concentrated in the pharmaceutical plant A and chemical plant C. It was found that the different HMs had different vertical distribution characteristics. For the different industrial plants, the raw materials and products not only made the spatial distribution characteristics of the HMs different, but also caused the HM types and contents to differ. The average single pollution indices of Cd in plant A, iron-steel plant B, and plant C indicated a slight pollution level. The other seven HMs in A, B, and C and all HMs in chemical plant D belonged to the safe category. The mean values of the Nemerow pollution index in the four industrial plants belonged to the warning category. The analysis showed that none of the HMs posed potential noncarcinogenic health risks, and only the carcinogenic health risks of Cr in plants A and C were unacceptable. The carcinogenic effect of Cr through the inhalation intake of resuspended soil particulates and that of Cd, Ni, and As via direct oral ingestion were the main exposure pathways.

The potential ecological risk assessment of soil heavy metals using self-organizing map

Heavy metal pollution control zoning aiming at the health maintenance of watershed soil ecosystem has become an important means of soil environmental protection and governance. Based on the self-organizing map (SOM), this study classifies the data sets of eight heavy metals such as Co, Cd, Zn, Cr, Cu, Pb, Ni, and Tl in 354 samples, calculates the potential ecological risk value of soil heavy metals in combination with the potential Hakansom Risk index (HRI), and uses the geographic information system (GIS) for visualization. In the research results, SOM has divided five soil ecological risk categories. The highest average ecological risk value of 85.95 is found in cluster IV, which is clustered and distributed in urban development areas in the upper reaches of the river. The average ecological risk values of cluster I and cluster V are relatively close at 79.64 and 79.19, respectively. Cluster I and cluster V are distributed in the north of the river in a linear and cluster manner, respectively, and are located on a concave bank with a relatively gentle slope. The average ecological risk of soil pollution in cluster II is 77.59, which is linearly distributed on both banks of the river. The ecological risk of soil pollution in cluster III is the lowest (74.39), mainly scattered in the south of rivers with less human activities. The study further identified the environmental factors that affect the soil ecological risk value in different cluster units and put forward the classified and differentiated management and control strategies for different cluster units. The research shows that SOM can cluster the data sets of heavy metals with high sensitivity and low threshold through competitive learning to effectively provide the distribution information of abnormal soil ecological risk areas. This information is helpful for urban environmental management departments and planning departments to take targeted management and recovery measures to avoid the health risks related to soil heavy metal pollution.

Insights into the spatiotemporal differences in tailings seepage pollution by assessing the diversity and metabolic functions of the soil microbial community

The formation of tailings ponds depends on the long-term accumulation of tailing and high terrain. Its seepage pollution characteristics may have gradient variations on spatiotemporal scales. Used three nearby metal tailings ponds with different service times, we aimed to reveal seepage pollution trends on spatiotemporal scales and the response of soil microbial community. The results showed that the degree of seepage pollution was negatively correlated with the distance from the tailings pond on the spatial scale, while the seepage pollution showed higher levels in tailings ponds with longer service times on the temporal scale (RI = 248.04-2109.85). The pollution effect of seepage persisted after the tailings pond was discontinued (RI = 226.72). Soil microbial diversity increased with spatial scale expansion. The proportion of Actinomyces gradually increased and Proteobacteria decreased. Cr (r = 0.21) and Fe (r = 0.22) contributed more to the microbial community changes. Functional predictions showed that pathways related to signal transduction and energy metabolism were more abundant in the tailings pond. In contaminated areas, the proportion of nitrate respiration and cellulolysis functional communities had decreased, and some potentially pathogenic human taxa had accumulated. These results emphasized that there was pollution accumulation on temporal scale and pollution dispersion on spatial scale around tailings ponds, and the response of the microbial community further illustrated these trends.

The sources risk assessment combined with APCS/MLR model for potentially toxic elements in farmland of a first-tier city, China

With the rapid economic development, potentially toxic elements (PTEs) are continuously migrating, transforming, and enriching in farmland through atmospheric deposition and other media, posing threats to food security and human health. At present, there are few quantitative studies on the health risks of PTEs sources in farmland. In this study, absolute principal component score-multiple linear regression (APCS-MLR) receptor model was used to quantify the pollution sources of PTEs in farmland in Suzhou of Yangtze River Delta Economic Zone, China. Combined with geoaccumulation index (I_geo) and health risk assessment model, the source risk of PTEs was further quantified. The results show that Cd has reached the level of unpolluted to moderate polluted (0 < I_geo < 1); the total hazard index (THI) and total carcinogenic risk (TCR) index of PTEs are acceptable for adults, but not for children (THI > 1, TCR > 1 × 10^-4). The results of APCS-MLR source apportionment were industrial sources (25.65%), agricultural sources (20.00%), traffic sources (16.81%), and domestic pollution sources (9.71%). The I_geo values of all pollution sources were less than 0, and no ecological risk was caused. The contribution patterns of pollution sources to THI and TCR in adults and children are similar. Industrial pollution sources pose the greatest non-carcinogenic risk to humans, accounting for 47.35% and 47.26% of adults and children, respectively; for carcinogenic risks, domestic pollution sources contribute the most among all identified pollution sources, accounting for 27.71% and 27.73% of adults and children, respectively. In general, this study emphasizes the need to strengthen the supervision of industrial pollution sources and domestic pollution sources in the study area to reduce the health risks to children.

Advances in the application of immobilized enzyme for the remediation of hazardous pollutant: A review

Nowadays, ecofriendly, low-cost, and sustainable alternatives techniques have been focused on the effective removal of hazardous pollutants from the water streams. In this context, enzyme immobilization seems to be of specific interest to several researchers to develop novel, effective, greener, and hybrid strategies for the removal of toxic contaminants. Immobilization is a biotechnological tool, anchoring the enzymes on support material to enhance the stability and retain the structural conformation of enzymes for catalysis. Recyclability and reusability are the main merits of immobilized enzymes over free enzymes. Studies showed that immobilized enzyme laccase can be used up to 7 cycles with 66% efficiency, peroxidase can be recycled to 2 cycles with 50% efficiency, and also cellulase to 3 cycles with 91% efficiency. In this review, basic concepts of immobilization, different immobilization techniques, and carriers used for immobilization are summarized. In addition to that, the potential of immobilized enzymes as the bioremediation agents for the effective degradation of pollutants from the contaminated zone and the impact of different operating parameters are summarized in-depth. Further, this review provides future trends and challenges that have to be solved shortly for enhancing the potential of immobilized systems for large-scale industrial wastewater treatment.

Microbial Interventions in Bioremediation of Heavy Metal Contaminants in Agroecosystem

Soil naturally comprises heavy metals but due to the rapid industrialization and anthropogenic events such as uncontrolled use of agrochemicals their concentration is heightened up to a large extent across the world. Heavy metals are non-biodegradable and persistent in nature thereby disrupting the environment and causing huge health threats to humans. Exploiting microorganisms for the removal of heavy metal is a promising approach to combat these adverse consequences. The microbial remediation is very crucial to prevent the leaching of heavy metal or mobilization into the ecosystem, as well as to make heavy metal extraction simpler. In this scenario, technological breakthroughs in microbes-based heavy metals have pushed bioremediation as a promising alternative to standard approaches. So, to counteract the deleterious effects of these toxic metals, some microorganisms have evolved different mechanisms of detoxification. This review aims to scrutinize the routes that are responsible for the heavy metal(loid)s contamination of agricultural land, provides a vital assessment of microorganism bioremediation capability. We have summarized various processes of heavy metal bioremediation, such as biosorption, bioleaching, biomineralization, biotransformation, and intracellular accumulation, as well as the use of genetically modified microbes and immobilized microbial cells for heavy metal removal.

Research Progress on Heavy Metals Pollution in the Soil of Smelting Sites in China

Contamination by heavy metals is a significant issue worldwide. In recent decades, soil heavy metals pollutants in China had adverse impacts on soil quality and threatened food security and human health. Anthropogenic inputs mainly generate heavy metal contamination in China. In this review, the approaches were used in these investigations, focusing on geochemical strategies and metal isotope methods, particularly useful for determining the pathway of mining and smelting derived pollution in the soil. Our findings indicate that heavy metal distribution substantially impacts topsoils around mining and smelting sites, which release massive amounts of heavy metals into the environment. Furthermore, heavy metal contamination and related hazards posed by Pb, Cd, As, and Hg are more severe to plants, soil organisms, and humans. It's worth observing that kids are particularly vulnerable to Pb toxicity. And this review also provides novel approaches to control and reduce the impacts of heavy metal pollution. Hydrometallurgy offers a potential method for extracting metals and removing potentially harmful heavy metals from waste to reduce pollution. However, environmentally friendly remediation of contaminated sites is a significant challenge. This paper also evaluates current technological advancements in the remediation of polluted soil, such as stabilization/solidification, natural attenuation, electrokinetic remediation, soil washing, and phytoremediation. The ability of biological approaches, especially phytoremediation, is cost-effective and favorable to the environment.

Integrated assessment of the impact of land use types on soil pollution by potentially toxic elements and the associated ecological and human health risk

The impact of land use type on the content of potentially toxic elements (PTEs) in the soils of the Qinghai-Tibet Plateau (QTP) and the associated ecological and human health risks has drawn great attention. Consequently, in this study, top- and subsurface soil samples were collected from areas with four different land uses (i.e., cropland, forest, grassland, and developed area) and the total contents of Cr, Cd, Cu, Pb and Zn were determined. Geostatistical analysis, self-organizing map (SOM), and positive matrix factorization (PMF), ecological risk assessment (ERA) and human health risk assessment (HRA) were applied and used to classify and identify the contamination sources and assess the potential risk. Partial least squares path modeling (PLS-PM) was applied to clarify the relationship of land use with PTE contents and risk. The PTE contents in all topsoil samples surpassed the respective background concentrations of China and corresponding subsurface concentrations. However, the ecological risk of all soil samples remained at a moderate or considerable level across the four land use types. Developed area and cropland showed a higher ecological risk than the other two land use types. Industrial discharges (32.8%), agricultural inputs (22.6%), natural sources (23.7%), and traffic emissions (20.9%) were the primary PTE sources in the tested soils, which indicate that anthropogenic activities have significantly affected soil PTE contents to a greater extent than other sources. Industrial discharge was the most prominent source of non-carcinogenic health risk, contributing 37.7% for adults and 35.2% for children of the total risk. The results of PLS-PM revealed that land use change associated with intensive human activities such as industrial activities and agricultural practices distinctly affected the PTE contents in soils of the Qinghai-Tibet Plateau.

Heavy Metal, Waste, COVID-19, and Rapid Industrialization in This Modern Era—Fit for Sustainable Future

Heavy metal contamination, waste, and COVID-19 are hazardous to all living things in the environment. This review examined the effects of heavy metals, waste, and COVID-19 on the ecosystem. Scientists and researchers are currently working on ways to extract valuable metals from waste and wastewater. We prefer Tessier sequential extraction for future use for heavy metal pollution in soil. Results indicated that population growth is another source of pollution in the environment. Heavy metal pollution wreaks havoc on soil and groundwater, especially in China. COVID-19 has pros and cons. The COVID-19 epidemic has reduced air pollution in China and caused a significant reduction in CO2 releases globally due to the lockdown but has a harmful effect on human health and the economy. Moreover, COVID-19 brings a huge amount of biomedical waste. COVID-19’s biomedical waste appears to be causing different health issues. On the other hand, it was discovered that recycling has become a new source of pollution in south China. Furthermore, heavy metal contamination is the most severe ecological effect. Likewise, every problem has a remedy to create new waste management and pollution monitoring policy. The construction of a modern recycling refinery is an important aspect of national waste disposal.

Combination of UNMIX, PMF model and Pb-Zn-Cu isotopic compositions for quantitative source apportionment of heavy metals in suburban agricultural soils

Quantitative identification of heavy metals (HM) sources in soils is key to prevention and control of heavy metal pollution. In this study, UNMIX, PMF (Positive matrix factorization) model and Pb-Zn-Cu isotopic compositions were combined to quantitatively identify heavy metal sources in a suburban agricultural area of Kaifeng, China. Using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) and ICP-MS, we measured Pb, Zn and Cu stable isotopic compositions, HM concentrations and HM chemical fractions in studied soils, as well as potential sources around the highly polluted site, including total suspended particle, compound fertilizer, irrigated river water and sediments. The results showed that total contents and chemical fractions of heavy metals, as well as Pb-Zn-Cu isotopic compositions presented great variation in different sites, which implied that heavy metal accumulation was obviously affected by local anthropogenic pollution source. UNMIX and PMF presented good agreement on source apportionment that industrial and agricultural activities (61.74% and 60.75% for UNMIX and PMF, respectively) were the major contributors to heavy metal accumulation in the study area. Especially, sewage irrigation and atmosphere deposition accounted for a large proportion (28.14% and 41.03% for UNMIX and PMF, respectively). Moreover, isotopic compositions of Pb, Zn and Cu in highly polluted soils and environment media gave further confirmation that sewage irrigation and atmosphere deposition were primary anthropogenic source. Therefore, combination of UNMIX, PMF model and Pb-Zn-Cu isotopic compositions showed good coordination in quantitative and specific source identification of heavy metals in agricultural soils.

The Effect of Sample Preparation and Measurement Techniques on Heavy Metals Concentrations in Soil: Case Study from Kraków, Poland, Europe

Accurate and reliable laboratory results are an extremely important and integral part of conducting scientific research. Many factors influence the results obtained, including the type of determination method, accuracy and precision of measurements, and laboratory equipment used for the tests. This paper presents the results of measurements of heavy metal concentration in soil using two methods for adding soil components into solution and different laboratory methods and types of measuring equipment. The first method used was hot digestion of soil samples with a mixture of concentrated HNO3 and HClO4, after prior ashing of organic matter (IUNG method). The second method was a two-stage decomposition, where soil samples were hot digested, initially with oxidizing acid (HNO3) and subsequently with non-oxidizing acid (HF) (two-stage decomposition). The concentrations of selected heavy metals (Cr, Cu, Fe, Mn, Ni, Pb and Zn) were determined in solutions obtained by both digestion methods. The solutions obtained from soil decomposition were determined twice using atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP MS) methods in different laboratories using different types of spectrometers. In most cases, the measured concentrations of heavy metals are the highest for the two-stage solution samples and the measurements of their concentrations carried out using ICP. The exceptions are the measurements of Cu and Ni concentrations. In the case of Cu, lack of significant differentiation in concentrations of this metal may result from different forms of occurrence of Cu in soil than in the case of other metals. For Ni, however, a reversal of the trends seen for the other metals is observed and the type of spectrometer used for measurements is important. There may be an interference of the spectrometric spectrum of Ni with the spectra of the other determined metals. However, this is not clear at the present stage of the study. In conclusion, the results of this study indicate that the choice of soil sample preparation and the type of spectrometer used for measurements can, in many cases, determine the value of laboratory results, even if it is in an expected range of standard material. Research of published papers proved that most of them show only results based on one selected course of methodology without comparison with others. The novelty of the paper is the comparison of the measurements of heavy metal concentration in soil using two methods for adding soil components into solution and different laboratory methods and types of measuring equipment. Additionally, the article includes a discussion of the importance of methodology. We believe that the conclusions may help to better understand how sample preparation and measurement methods applied may influence the results obtained.

Impacts of corn stover management and fertilizer application on soil nutrient availability and enzymatic activity

Corn stover is a global resource used in many industrial sectors including bioenergy, fuel, and livestock operations. However, stover removal can negatively impact soil nutrient availability, especially nitrogen (N) and phosphorus (P), biological activity, and soil health. We evaluated the effects of corn stover management combined with N and P fertilization on soil quality, using soil chemical (nitrate, ammonium and Bray-1 P) and biological parameters (β-glucosidase, alkaline phosphatase, arylsulfatase activities and fluorescein diacetate hydrolysis—FDA). The experiment was performed on a Mollisol (Typic Endoaquoll) in a continuous corn system from 2013 to 2015 in Minnesota, USA. The treatments tested included six N rates (0 to 200 kg N ha⁻¹), five P rates (0 to 100 kg P₂O₅ ha⁻¹), and two residue management strategies (residue removed or incorporated) totalling 60 treatments. Corn stover management significantly impacted soil mineral-N forms and enzyme activity. In general, plots where residue was incorporated were found to have high NH₄⁺ and enzyme activity compared to plots where residue was removed. In contrast, fields where residue was removed showed higher NO₃⁻ than plots where residue was incorporated. Residue management had little effect on soil available P. Soil enzyme activity was affected by both nutrient and residue management. In most cases, activity of the enzymes measured in plots where residue was removed frequently showed a positive response to added N and P. In contrast, soil enzyme responses to applied N and P in plots where residue was incorporated were less evident. Soil available nutrients tended to decrease in plots where residue was removed compared with plots where residue was incorporated. In conclusion, stover removal was found to have significant potential to change soil chemical and biological properties and caution should be taken when significant amounts of stover are removed from continuous corn fields. The residue removal could decrease different enzymes related to C-cycle (β-glucosidase) and soil microbial activity (FDA) over continuous cropping seasons, impairing soil health.

Assessment of the Heavy Metal Contamination of Roadside Soils Alongside Buddha Nullah, Ludhiana, (Punjab) India

The present study was carried out to determine the physico-chemical characteristics and heavy metal contents in roadside soil samples collected during 2 sampling periods (September 2018 and April 2019) from 8 different roadside sites lying parallel to the Buddha Nullah, an old rivulet, flowing through Ludhiana, (Punjab) India. The contents (mg/kg) of seven metals (cadmium, chromium, cobalt, copper, lead, nickel and zinc) were estimated using a flame atomic absorption spectrophotometer. Among the metals analyzed, the contents of Cd, Co, Cu, Pb and Zn were found above the permissible limits. The results of the index of geoaccumulation (Igeo), contamination factor (CF), contamination degree (Cdeg), modified contamination degree (mCdeg), the Nemerow pollution index (PI) and pollution load index (PLI) indicate a moderate to high heavy metal contamination of the analyzed soil samples. The results of the potential ecological risk factor (ERi) and potential ecological risk index (RI) indicate a low to moderate risk of heavy metals in the studied soil samples. The Pearson correlation analysis revealed that most of the variables exhibited a statistically significant correlation with one or more variables during the two samplings. Multivariate analysis demonstrates that contents of heavy metals in the study area are influenced by anthropogenic and geogenic factors.

Sweet sorghum for phytoremediation and bioethanol production

As an energy crop, sweet sorghum (Sorghum bicolor (L.) Moench) receives increasing attention for phytoremediation and biofuels production due to its good stress tolerance and high biomass with low input requirements. Sweet sorghum possesses wide adaptability, which also has high tolerances to poor soil conditions and drought. Its rapid growth with the large storage of fermentable saccharides in the stalks offers considerable scope for bioethanol production. Additionally, sweet sorghum has heavy metal tolerance and the ability to remove cadmium (Cd) in particular. Therefore, sweet sorghum has great potential to build a sustainable phytoremediation system for Cd-polluted soil remediation and simultaneous ethanol production. To implement this strategy, further efforts are in demand for sweet sorghum in terms of screening superior varieties, improving phytoremediation capacity, and efficient bioethanol production. In this review, current research advances of sweet sorghum including agronomic requirements, phytoremediation of Cd pollution, bioethanol production, and breeding are discussed. Furthermore, crucial problems for future utilization of sweet sorghum stalks after phytoremediation are combed.

Graphical Abstract

Pollution and Risk Assessment of Heavy Metals in the Sediments and Soils around Tiegelongnan Copper Deposit, Northern Tibet, China

The surface sediments of the Rongna River and the surface soils around the Tiegelongnan copper deposit were collected, and the heavy metals Cu, Zn, Pb, Cr, Cd, As, Hg, and Ni were measured for their concentrations and health risk assessment. When the Rongna River passed through the Cu deposit area, the concentrations of Cu, Zn, As, Cd, Ni, and Hg in the surface sediments increased significantly, and the concentrations of Cu, Zn, and As exceeded the corresponding Grade II environmental quality standard. The heavy metals in the soil of the mining area were greater than the background value of the soil in Tibet. The geoaccumulation index indicated that the sediments of the river entering the mining area were very highly polluted by Cu and moderately polluted by Cd and Zn, and the soils in the mining area were moderately polluted by Cu. The potential ecological risk (PER) indices revealed that the sediments of the river entering the mining area had significantly high ecological risks, while the PER of the sediments away from the river section of the mining area was low, and the PER of the soils around the Cu deposit was moderate. The results of the health risk assessment indicated that the noncarcinogenic risks of heavy metals in sediments and soil of the mining area were within the acceptable range for adults and children. However, the carcinogenic risk of As and Cd in the sediment and As in the soil exceeds the relevant national standards, which may pose a certain risk to human health.

A questionnaire based probabilistic risk assessment (PRA) of heavy metals in urban and suburban soils under different land uses and receptor populations

The choice of receptor populations is crucial for assessing the health risk posed by heavy metals in soil. A total of 457 questionnaires were conducted on 10 sensitive receptor populations, which were exposed to potentially contaminated soil under four land uses, to determine their exposure frequency (EF) and exposure time (ET) values. The exposure risk (ER: the probability of being exposed to target soil) varied between the receptor populations because of their different EF and ET values. Green maintenance workers in park soil, who had fixed outdoor working hours (6 or 7 days per week and 8 h per day), had the highest EF and ET values, while adults and children who visited parks only at weekends had the lowest EF values. Green maintenance workers, sanitation workers, and children faced the highest hazards (i.e., hazard index (HI) values) from heavy metals in soil in parks and residential areas, roadsides, and farmland, and were found to be the most sensitive receptor populations (MSRPs) for these land uses. The 90th percentile of the HI value for the four land uses based on MSRPs followed the order of roadsides (0.48) > parks (0.44) > residential areas (0.21) > suburban farmlands(0.18), and all were lower than 1, indicating a virtually safe level. Washing hands immediately and wearing shoes when working on farmland considerably reduced the HI values by 56.6%. The EF, ET, and body weight (BW) values were the most sensitive parameters in the health risk assessment. The results suggested that the type of receptor population will greatly affect the results of a health risk assessment for soil pollutants. It is necessary to select the risk receptors carefully based on the land use types.

Risk assessment and ecotoxicological diagnosis of soil from a chemical industry park in Nanjing, China

Soil pollution due to the activities of industrial parks, is becoming an increasingly serious issue, particularly throughout China. Therefore, it is essential to explore the soil pollution characteristics and its ecotoxicological effects on model species, such as higher plant species, in typical industrial areas. In this study, concentrations of heavy metals and polycyclic aromatic hydrocarbons (PAHs) were examined in the soil collected from 10 sampling sites at a chemical industry park in Nanjing, China. The pollution index was used to assess the heavy metal pollution level of soils, while the hazard index (HI) and carcinogenic risk index (RI) were calculated to assess the human health risk of soil PAHs. In addition, wheat (Triticum aestivum L.) was used as the model species to evaluate the ecotoxicological effects of polluted soil in pot experiments. Results showed that the content of heavy metals and PAHs varied greatly in soil samples, among which the heavy metal pollution at S1, S2 and S3 was the most serious. The health risk assessment of PAHs indicated that non-carcinogenic and carcinogenic values for all soil samples were below the threshold levels. Statistical analysis of the correlation between contaminated soil and toxic effects in wheat found that the significance values of regression equations were all less than 0.05 for chlorophyll content, peroxidase (POD) and amylase (AMS) activity. This indicates that the chlorophyll content, POD and AMS activity in wheat leaves could be suitable biomarkers for evaluation of the combined toxicity of multiple pollutants. This study provides a reference for future research on the risk assessment of soil containing multiple pollutants from industrial chemical parks.

Cadmium Pollution Impact on the Bacterial Community Structure of Arable Soil and the Isolation of the Cadmium Resistant Bacteria

Microorganisms play an important role in the remediation of cadmium pollution in the soil and their diversity can be affected by cadmium. In this study, the bacterial community in arable soil samples collected from two near geographical sites, with different degrees of cadmium pollution at three different seasons, were characterized using Illumina MiSeq sequencing. The result showed that cadmium is an important factor to affect the bacterial diversity and the microbial communities in the high cadmium polluted area (the site H) had significant differences compared with low cadmium polluted area (the site L). Especially, higher concentrations of Cd significantly increased the abundance of Proteobacteria and Gemmatimonas whereas decreased the abundance of Nitrospirae. Moreover, 42 Cd-resistant bacteria were isolated from six soil samples and evaluated for potential application in Cd bioremediation. Based on their Cd-MIC [minimum inhibitory concentration (MIC) of Cd²⁺], Cd²⁺ removal rate and 16S rDNA gene sequence analyses, three Burkholderia sp. strains (ha-1, hj-2, and ho-3) showed very high tolerance to Cd (5, 5, and 6 mM) and exhibited high Cd²⁺ removal rate (81.78, 79.37, and 63.05%), six Bacillus sp. strains (151-5,151-6,151-13, 151-20, and 151-21) showed moderate tolerance to Cd (0.8, 0.4, 0.8, 0.4, 0.6, and 0.4 mM) but high Cd²⁺ removal rate (84.78, 90.14, 82.82, 82.39, 81.79, and 84.17%). Those results indicated that Burkholderia sp. belonging to the phylum Proteobacteria and Bacillus sp. belonging to the phylum Firmicutes have developed a resistance for cadmium and may play an important role in Cd-contaminated soils. Our study provided baseline data for bacterial communities in cadmium polluted soils and concluded that Cd-resistant bacteria have potential for bioremediation of Cd-contaminated soils.

Bioavailability, distribution and health risk assessment of arsenic and heavy metals (HMs) in agricultural soils of Kermanshah Province, west of Iran

Kermanshah Province as an agricultural hub exports food crops to neighboring countries. In this study, contamination status, bioavailability, spatial distribution, and ecological and human health risk of arsenic and heavy metals (HMs) in soil were investigate. For this purpose, 121 agricultural soil samples were collected and analyzed using ICP-MS. The data were studied by calculating some geochemical indices, and using geographical information system and statistical analysis. Results showed that Cd has the highest bioavailability, following by Cu and As. Also, Cu was severely associated with organic matter. Enrichment factor (EF) followed the order of As > Cu > Pb > Se > Cd > Zn > Ni > Cr, and the soil pollution index (SPI) ranged from 0.82 to 2.65. Low potential ecological risk was measured for most of the samples. However, Kermanshah County and Eastern parts of the Province showed the highest HMs enrichment and ecological risk. Moreover, high carcinogenic risk of Cr and Ni threatens the children. Cr showed also high non-carcinogenic hazard index (HI) for children. Principal component analysis (PCA) indicated the anthropogenic origins for As, Cd, Cu, Pb, Se and Zn, while Cr and Ni originated mainly from a geogenic source. Furthermore, Kruskal-Wallis H test revealed that As, Cd, Cr, Cu, Ni, Pb, Se and Zn concentrations were significantly different (p < 0.05) between 16 Counties of the Kermanshah Province. Overall, the management of urban and industrial contamination sources is required to minimize the concentration of bioavailable portion of HMs and preventing residents of the area from being exposed to contaminants.

Insights into Persistent Toxic Substances in Protective Cases of Mobile Phones: Occurrence, Health Risks, and Implications

Despite the popularity of smartphones worldwide, persistent toxic substances (PTSs) in protective cases of mobile phones (PCMPs) and their health risks via direct skin contact have been ignored. This study investigated PTSs in PCMPs made in China with different materials and sales territory and their potential harm to human health. Polybrominated diphenyl ethers (PBDEs, 6.40 ng/g), new brominated flame retardants (NBFRs, 144 ng/g), organophosphate esters (OPEs, 10.1 μg/g), short-chain chlorinated paraffins (SCCPs, 3.58 μg/g), medium-chain chlorinated paraffins (MCCPs, 3.17 μg/g), and heavy metals (HMs, 72.3 μg/g) were detected. It was found that the different concentrations and compositions depend on the material, region, and use. Moreover, the raw materials used to fabricate PCMPs are of variable quality and may include recycled plastic waste. There are no standard quality specifications for PCMPs, and different materials have different properties, including specific surface area and adsorption ability. The risk assessment performed by Monte Carlo simulations indicated that the PTSs evaluated pose no health risks to the general population and may have adverse effects on individual high-exposure populations. According to the results of this work, it is suggested that more stringent global specifications for the selection of raw materials should be established, including the content and structural characteristics of PTSs, limitations on the use of additives in the production process, and the handling after use.

Bioaugmented Phytoremediation of Metal-Contaminated Soils and Sediments by Hemp and Giant Reed

We assessed the effects of EDTA and selected plant growth-promoting rhizobacteria (PGPR) on the phytoremediation of soils and sediments historically contaminated by Cr, Ni, and Cu. A total of 42 bacterial strains resistant to these heavy metals (HMs) were isolated and screened for PGP traits and metal bioaccumulation, and two Enterobacter spp. strains were finally selected. Phytoremediation pot experiments of 2 months duration were carried out with hemp (Cannabis sativa L.) and giant reed (Arundo donax L.) grown on soils and sediments respectively, comparing in both cases the effects of bioaugmentation with a single PGPR and EDTA addition on plant and root growth, plant HM uptake, HM leaching, as well as the changes that occurred in soil microbial communities (structure, biomass, and activity). Good removal percentages on a dry mass basis of Cr (0.4%), Ni (0.6%), and Cu (0.9%) were observed in giant reed while negligible values (<100‰) in hemp. In giant reed, HMs accumulated differentially in plant (rhizomes > > roots > leaves > stems) with largest quantities in rhizomes (Cr 0.6, Ni 3.7, and Cu 2.2 g plant^–1). EDTA increased Ni and Cu translocation to aerial parts in both crops, despite that in sediments high HM concentrations in leachates were measured. PGPR did not impact fine root diameter distribution of both crops compared with control while EDTA negatively affected root diameter class length (DCL) distribution. Under HM contamination, giant reed roots become shorter (from 5.2 to 2.3 mm cm^–3) while hemp roots become shorter and thickened from 0.13 to 0.26 mm. A consistent indirect effect of HM levels on the soil microbiome (diversity and activity) mediated by plant response (root DCL distribution) was observed. Multivariate analysis of bacterial diversity and activity revealed not only significant effects of plant and soil type (rhizosphere vs. bulk) but also a clear and similar differentiation of communities between control, EDTA, and PGPR treatments. We propose root DCL distribution as a key plant trait to understand detrimental effect of HMs on microbial communities. Positive evidence of the soil-microbe-plant interactions occurring when bioaugmentation with PGPR is associated with deep-rooting perennial crops makes this combination preferable over the one with chelating agents. Such knowledge might help to yield better bioaugmented bioremediation results in contaminated sites.

Compost and Sewage Sludge for the Improvement of Soil Chemical and Biological Quality of Mediterranean Agroecosystems

Conventional fertilization practices in agroecosystems concern the supply of bioavailable nutrients, such as mineral fertilizers. A consolidated alternative to restoring the long-term fertility of agricultural soils is their amendment with organic fertilizers. Soil amendment with biowaste compost or sewage sludge represents a sustainable strategy to avoid the landfilling of organic matter derived from urban waste and sewage sludge. This study aims at validating the use of quality biowaste compost and sewage sludge from secondary sedimentation (alone or in combination with mineral fertilizers) in a Mediterranean agroecosystem and their effects on soil chemical and biological quality, with a view to verifying the maintenance of soil fertility and functionality. In particular, the dynamics of soil organic matter, pH, potentially toxic elements and microbial community functionality were assessed, in experimental mesocosms, during 6 months of incubation. The research showed that, while soil amendment with biowaste compost induces positive effects on soil organic matter and phosphorous concentrations, as well as on microbial community functionality, the amendment with the selected sewage sludge does not determine any benefit to the microbial community or any danger in relation to soil potentially toxic element concentrations and toxicity. The quantity of sewage sludge employed, chosen according to regional directives, was thus not enough to stimulate the edaphic microflora activity.

Physiological and genetic effects of cadmium and copper mixtures on carrot under greenhouse cultivation

The exposure to combinations of heavy metals can affect the genes of vegetables and heavy metals would accumulate in vegetables and thereby indirectly affecting human health. Exploring the links between genetic changes and phenotypic changes of carrot under the combined pollution of Cd and Cu is of great significance for studying the mechanism of heavy metal pollution. Therefore, this study examined the effects of mixtures of cadmium (Cd) and copper (Cu) on physiological measures (malondialdehyde (MDA), proline, and antioxidant enzyme) and expression of growth-related genes (gibberellin gene, carotene gene, and glycogene) in carrot under greenhouse cultivation. The results showed in the additions with mixtures of Cd and Cu at higher concentration, the MDA content increased significantly (p < 0.05), whereas the proline content was not significantly different from those in the control. In the mixed treatments with high Cd concentrations, the activity of superoxide dismutase (SOD) was significantly lower than that in the control (p < 0.05); whereas the activity of peroxidase (POD) increased to different degrees compared to the control. In the additions with mixtures of Cd and Cu, compared with the control, the expression of the gibberellin gene was downregulated from 1.97 to 20.35 times (not including the 0.2 mg kg^-1 Cd and 20 mg kg^-1 Cu mixture, the expression of gibberellin gene in this treatment was upregulated 1.29 times), which lead to decreases in the length and dry weight of carrots. The expression of the carotene gene in mixed treatments downregulated more than that in single treatments, which could reduce the ability of carrots to resist oxidative damage, as suggested by the significant increase in the MDA content. In the addition with mixtures of Cd and Cu, compared with the control, the expression of the glycogene was downregulated by 1.42-59.40 times, which can cause a significant reduction in the sugar content in carrots and possibly further reduce their ability to resist heavy metal damage. A cluster analysis showed that in the additions with mixtures of Cd and Cu, the plant phenotype was affected first, and then with increases in the added concentration, the expression of genes was also affected. In summary, in the additions with mixtures of Cd and Cu, plants were damaged as Cd and Cu concentrations increased.

Application of Geostatistical Analysis and Random Forest for Source Analysis and Human Health Risk Assessment of Potentially Toxic Elements (PTEs) in Arable Land Soil

Arable land soil is one of the most precious natural resources of Earth, it provides the fundamental material and numerous resources essential for the development of human society. To determine the pollution of potential toxic factors in the surface soil of cultivated land and its risks to human health, concentrations of five different potentially toxic elements (PTEs) were detected in 1109 soil samples collected in Xiangzhou, China, in 2019. In this study, health risk assessment was used to judge the degree of pollution in the study area, the result of Geographic Information System (GIS) was as used to research the spatial distribution characteristics of PTEs, and random forest (RF) was used to assess the natural and man-made influencing factors. We investigated the sources of PTEs through quantifying the indicators, which gave further insights. The main results are: (1) In arable land soil, the average content of PTEs is 0.14 mg/kg cadmium (Cd), 0.05 mg/kg mercury (Hg), 12.89 mg/kg arsenic (As), 29.23 mg/kg lead (Pb), and 78.58 mg/kg chromium (Cr), respectively. The content of As and Pb outpaced the background value of Hubei soil. (2) The human health risk assessment in Xiangzhou indicates that the most important exposure pathway is soil ingestion, occupied about 99% to health risks of PTEs; non-carcinogenic risk from exposure to As, Pb and Cr in soil was higher than the limit (overall potential risk index, HI > 1) for both children and adults. Moreover, carcinogenic risk postured by Cd, Cr, and As was higher than the limit (10^-4) through soil exposure for both children and adults, indicating that Cd, As, Pb and Cr in soil have significant effect on people's health through exposure. (3) We found that the increased PTEs in the arable land soil mainly originated from potential water sources, air and soil pollution sources, breeding farms, and mining areas.

Comprehensive assessment of heavy metals pollution of farmland soil and crops in Jilin Province

As a major agricultural province in China, it is necessary to study the content of heavy metals in farmland soil and crop in Jilin Province and to evaluate the risks to ecology and human health. This study presented the work completed on 79 soil samples, 10 rice samples, 66 maize samples and 15 soybean samples collected from Jilin Province farmland and evaluated six heavy metals (Zn, Cu, Pb, Cd, Hg and As) concentrations. The results showed that the concentrations of the six heavy metals in farmland soil and crop samples from Jilin Province basically met the soil standards and food health standards of China. The agricultural soil pollution spatial distribution was the most serious in the south of Jilin Province and the lightest in the west. The non-carcinogenic risks faced by children eating crops were higher than those of adults, but the carcinogenic risks were lower than those of adults. Both of the two health risks to adults and children from eating crops were very limited. The results would help determine the heavy metals pollution in farmland soil in Jilin Province efficiently and accurately and helped decision makers to achieve a balance between production and environmental regulation.

Potentially toxic elements in the Middle East oldest oil refinery zone soils: source apportionment, speciation, bioaccessibility and human health risk assessment

In this research, fifteen potentially toxic elements (PTEs) (Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Sc and Zn) were analysed and quantified in samples collected at 44 sites in an urban area of Iran. Sources were apportioned using enrichment factors (EFs), modified pollution index (MPI), principal component analysis (PCA), multivariate linear regression of absolute principal component scores (MLR-APCS) and speciation, with a focus on anthropogenic PTEs in the urban and industrial soils of the Arvand Free Zone area, an oil-rich zone in the country. Furthermore, the bioaccessibility and the human health risks of PTEs were investigated. The EF revealed a significant enrichment for elements such as Cd, Cu, Hg, Mo, Pb, Sb and Zn. Values of MPI showed that Abadan industrial district and Abadan petrochemical complex are the most polluted sites in the study area.The PCA/MLR analysis revealed four main sources: natural sources, fossil fuel combustion, traffic and oil derivatives and petroleum waste. The relative contribution of each source to PTE concentration varied from 32.3% of the natural sources to 30.6% of traffic and from 20.1% of petroleum waste to 17% of fossil fuel combustion. The source apportionment of metals generated using MLR-APCS receptor modelling revealed that 85.0% of Hg was generated by oil products. Chemical speciation results were compatible with the results obtained from PCA. Bioaccessibility of PTEs decreased from gastric to intestinal phase except Mo and Sb due to their different geochemical characteristics. Hazard index (HI) for non-cancer risk of PTEs for both children and adults based on total element concentrations was estimated to range from 2-fold to more than 10-fold higher than that of bioaccessible phases.

Comprehensive Urumqi screening for potentially toxic metals in soil-dust-plant total environment and evaluation of children's (0-6 years) risk-based blood lead levels prediction

Environmental contaminations by potentially toxic metals (PTMs) are associated with energy exploitation and present a significant problem in urban areas due to their impacts on human health. The PTMs status in Urumqi total environment inevitably impacted by extensive development of coal and oil industries has been lack of understanding comprehensively. A series of PTMs (As, Ba, Ce, Co, Cr, Cu, Ga, La, Mn, Ni, Pb, Rb, Sr, Th, U, V, Y, Zn, Zr) in the soil-dust-plant (foliage of Ulmus pumila L.) system of Urumqi (NW China) were screened by XRF and ICPMS. Multivariate statistics, risk models, GIS-based geostatistics, Positive Matrix Factorization (PMF) receptor modelling and blood lead levels of 0-6 aged children evaluated by IEUBK model are used to determine the priority pollutants, sources and health effects of the investigated elements. The spatial distribution of PTMs in soil-dust-plant system significantly coincides with coal combustion, traffic emission, and industrial activity. Although all PTM toxicants in soil, dust and tree foliage show some effects, the priority contaminants are observed for Cu, Pb and Zn as single element. The total carcinogenic and non-carcinogenic risks from PTMs are beyond the tolerance range of 0-6 year's old children, and the dust (TCR = 1.07E-04) PTMs pose approximatively equivalent carcinogenic risk to soil PTMs (TCT = 1.09E-04). The predicted BLLs (75-83 μ g·L^-1) of 1-2 years children are most strongly influenced by Pb in soil and dust, and therefore more attention should be focused on sources of Pb to support the primary health care of the toddlers in Urumqi.

Assessment of Anthropogenic Sources of Potentially Toxic Elements in Soil from Arable Land Using Multivariate Statistical Analysis and Random Forest Analysis

In order to study the spatial distribution and anthropogenic sources of potentially toxic elements in Xiangzhou, soil samples were collected from arable land and were analyzed for five different potentially toxic elements: Cd, Hg, As, Pb, and Cr. Inverse distance weighting (IDW) was used to study the spatial distribution of potentially toxic elements in the soil, while principal component analysis (PCA) and random forest analysis (RFA) were applied to examine the anthropogenic sources. It was shown that the combination of multiple analysis tools provides an effective way of delineating multiple potentially toxic elements from anthropogenic sources. The results showed that the average contents of Cd, Hg, and Cr in soils were lower than the background values of Hubei, whereas the average concentrations of As and Pb in soils were higher than the background values of Hubei. Through PCA, it was concluded that human activities contributed more than 60% of the As, Pb, and Cr concentrations in Xiangzhou soils, which was verified by a random forest simulation methodology. Through random forest analysis, Pb, As, and Cr in the soil were found to originate from factories and enterprises, livestock farms, mining areas, and traffic; Cd in the soil was found to originate from mining and the processing of minerals, human production and construction activities, and agricultural irrigation; and Hg in the soil was found to originate from livestock manure, mining and processing of minerals, and human industrial production. The results of this study could provide support for better management of soil pollution through prevention practices such as specific industrial governance and layout optimization.

Spatiotemporal modeling of soil heavy metals and early warnings from scenarios-based prediction

Prediction of soil heavy metal concentrations based on continuous site specific investigation can provide reference for soil metal contamination prevention and early warning of soil environmental quality. In this study, the spatiotemporal variations of soil heavy metals (Cd, Ni, Zn, Pb and Cu) in Wenling were analyzed with 132 and 169 soil samples gathered in 2011 and 2016. In addition, we adopted a scenario-simulation model to predict future dynamic concentrations of soil heavy metals under optimistic (the pollution inputs are zero under strict environmental policy) and default (the pollution status maintain constant) conditions. Results indicated that the paddy soil was contaminated mainly by Cd and Cu. Spatiotemporal maps revealed distinct patterns in the joint area, where soil Cd, Ni, Zn, Pb and Cu all increased in northwest. Soil heavy metal concentrations as well as the associated ecological risks would decline gradually under optimistic scenario, while sharply increase when no control acts are taken over long term in default condition. The percentages of soil Cd and Cu that exceeding their corresponding risk screening value (RSV) under the default condition would be 1.6 and 1.3 times higher than those under optimistic scenario 10 years later. The probability of high potential ecological risk in default condition would be twice higher than that under optimistic scenario in 2026. Overall, strengthening the control of pollution sources and strict environmental policy are very important for soil heavy metals contamination prevention and control.

Environmental Risk Evaluation and Source Identification of Heavy Metal(loid)s in Agricultural Soil of Shangdan Valley, Northwest China

To understand the environmental quality and heavy metal(loid) pollution of farmlands in Shangdan Valley, the contents of macroelements (Na, K, Si, Mg, Ca, Al, Fe, Ti, P, S, Cl, Br) and heavy metal(loid)s (Cu, Pb, Zn, Mn, Ni, V, Co, Cr, As) were surveyed by the X-ray fluorescence method. The pollution degree and ecological risk of the heavy metal(loid)s were judged by the Nemerow synthetic pollution index, geo-accumulation index, and potential ecological risk index, and their sources were identified by the multivariate statistic method. The mean contents of nine heavy metal(loid)s in Shangdan Valley farmland soil exceeded their corresponding reference values. Soils were not contaminated with As, Cr, Mn, and Ni but were slightly contaminated with Co, Cu, Pb, V, and Zn. Their comprehensive pollution levels were moderate to serious. The ecological risk index of single heavy metal(loid) decreased in the sequence As > Pb > Co > Cu > Ni > V > Zn > Cr > Mn. The source analysis results indicated that Cu, Pb, Zn, and As were highly affected by anthropogenic inputs, e.g., metal smelting and agricultural activities, while Mn, Ni, Cr, and V were principally derived from a natural source. As for Co, it was affected by a mixture source of nature, fossil fuel combustion, and fertilizer.

Dose and time-dependent response of single and combined artificial contamination of sulfamethazine and copper on soil enzymatic activities

The widespread contamination of antibiotics and heavy metals results in imbalance in the ecosystem. However, the effect of the interaction between sulfamethazine (SM2) and copper (Cu) on soil enzymatic activities is unclear. Therefore, this study investigated the effect of single and combined artificial contamination of SM2 and Cu (0, 1.6 mmol kg^-1 Cu and 0, 0.05, 0.2, 0.8 mmol kg^-1 SM2) on soil enzymatic activities (urease, sucrose, phosphatase, and RubisCO). A single application of Cu at a concentration of 1.6 mmol kg^-1 inhibited the urease, phosphatase and sucrase activities, while a stimulating effect on RubisCO activity was observed on day 7, 21, and 28 of incubation. The individual application of SM2 at higher concentration exhibited significant inhibition of sucrase, phosphatase, and urease activities while a stimulatory effect on RubisCO activity was observed on day 14 and 21 of incubation. The combined contamination of SM2 and Cu significantly inhibited the activities of urease, sucrase, and phosphatase. The effect of combined contamination of SM2 and Cu on the activity of RubisCO was different. The analysis results of interaction types show that there are synergistic or antagonistic effects between Cu and SM2, and these effects can amplify or reduce the effect of Cu or SM2 on soil enzyme activities. Integrated biological responses version 2 (IBRv2) analysis showed that the combined contamination of Cu and SM2 had a greater inhibitory or stimulatory effect on soil enzyme activities than the single contamination of Cu and SM2, depending upon dose and time.

Commercial and farm fermented liquid organic amendments to improve soil quality and lettuce yield

The anaerobic decomposition of organic wastes might lead to the formation of organic-byproducts which can then be successfully used as organic fertilizers. This study evaluated the impact of the application of two fermented liquid organic amendments (commercial vs. farm-made) at two doses of application (optimal vs. suboptimal), compared to mineral fertilization, on lettuce growth and soil quality. To this purpose, two experiments were conducted at microcosm- and field-scale, respectively. In the microcosm experiment, organically amended soils resulted in lower lettuce yield than minerally fertilized soil but, in contrast, they enhanced microbial activity and biomass, thus leading to an improvement in soil quality. The fertilization regime (organic vs. inorganic) significantly affected soil microbial composition but did not have any significant effect on structural or functional prokaryotic diversity. In the field experiment, at the optimal dose of application, organically-amended soils resulted in comparable lettuce yield to that displayed by minerally fertilized soils. The application of organic amendments did not result in an enhanced microbial activity and biomass, compared to mineral fertilization, but led to a higher soil prokaryotic diversity. Among the organically-amended plots, the optimal application dose resulted in a higher lettuce yield and soil microbial activity and biomass, but led to a decline in soil prokaryotic diversity, compared to the suboptimal application dose. Our results indicate that commercial and farm-made fermented liquid organic amendments possess the potential to ameliorate soil quality while sustaining crop yield. Given the strong influence of other factors (e.g., type of soil, dose of application) on the effects exerted by such amendments on soil quality and fertility, we recommend that an exhaustive characterization of both the amendments and the recipient soils should be carried out prior to their application, in order to better ensure their potential beneficial effects.

Aided phytostabilisation over two years using iron sulphate and organic amendments: Effects on soil quality and rye production

An outdoor macrocosm experiment using Fe-based and organic amendments over 2 years was set up to evaluate the effectiveness of aided-phytostabilisation. For that, a soil contaminated with As- and Cu-rich waste material (∼13000 mg As kg^-1 and ∼500 mg Cu kg^-1) was treated with combinations of iron sulphate (Fe) with lime, paper mill sludge (PS), holm-oak biochar (BC), olive mill waste compost (OMWC) or green waste compost (GWC). Rye (Secale cereale L.) was grown in the treated and non-treated soils 16 months after addition of the amendments. Arsenic and Cu dynamics in soil were assessed throughout the experiment and soil quality parameters (soil nutrients, organic matter and soil biology) were measured almost two years after addition of the amendments. All treatments resulted in a reduction of soluble and extractable Cu during the experiment and, despite the increase in soil pH (from 5 to 68) and DOC (from 10 up to 50 mg DOC L^-1) provoked by the amendments, As was not significantly mobilised in the treated soils. Treatments combining Fe sulphate with the organic materials, especially biochar and both composts, resulted in an increase in soil available nutrients and enhanced rye growth. In this semi-field scale experiment, the combination of Fe sulphate with holm-oak biochar showed the most promising results in terms of soil fertility (nutrient availability), plant As and Cu uptake and soil C sequestration. Further research should focus on monitoring long-term effects of the soil amendments on crops, following repeated applications.

Source analysis and risk assessment of heavy metals in development zones: a case study in Rizhao, China

The effects of heavy metal pollution in parks have caused widespread concern. This study investigated the concentrations and sources of eight heavy metals in the economic and technological development zone in Rizhao City. Geo-accumulation index ([Formula: see text]) and potential ecological risk index (PERI) were used to assess the pollution level of the development zone. Sources of heavy metals were analyzed through correlation analysis (CA) and principal component analysis (PCA). Descriptive statistics showed that many types of heavy metals accumulated in the development zone. The average concentrations of Pb, Cd, Hg, Ni, and Zn in the soil exceeded the background values of soil environment in Shandong Province. [Formula: see text] showed that only Hg in the soil was at the non-pollution to moderate pollution level. Meanwhile, sediments were polluted by Hg, Cd, and Zn, with their pollution level being higher than that of the soil. PERI showed that the soil presented moderate risk level and that the river sediment showed severe risk level. Hg and Cd exhibited the highest potential ecological risk. The results of the CA and PCA showed that the main sources of heavy metal pollution in the development zone are industrial activities, followed by atmospheric factors. Focus should thus be directed toward heavy metal pollution in development zones to protect human health and the soil environment.

Pollution Assessment and Source Apportionment of Trace Metals in Urban Topsoil of Xi'an City in Northwest China

Sixty-two topsoil samples were collected within the third ring road of Xi'an City in Northwest China and analyzed by X-ray fluorescence spectrometry for the concentrations of As, Ba, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn. The pollution levels of trace metals were assessed by pollution index (PI) and Nemerow pollution index (NPI). Meanwhile, the sources of trace metals were apportioned by receptor models, including positive matrix factorization (PMF), UNMIX, and principal component analysis-multiple linear regression (PCA-MLR). The average concentrations of the trace metals analyzed in the urban soil exceeded the corresponding soil element background values of Shaanxi Province, especially for Co, which was 2.38 times higher than the corresponding background value. The mean of PI was 2.38 for Co, reflecting a moderate pollution level, and ranged from 1.07 to 1.72 for other trace metals, presenting slight pollution levels. The NPI of trace metals varied between 1.20 and 3.50 with an average of 2.00, indicating that trace metals presented slight pollution in 62.90% of soil samples, moderate pollution in 30.65% of soil samples, and heavy pollution in 6.45% of soil samples, respectively. Three sources of trace metals apportioned by the three receptor models were mixed nature and anthropogenic source, traffic exhaust, and industrial emissions. The contributions of them were 38.58%, 32.72%, and 28.70% from the PMF, 65.36%, 17.76%, and 16.88% through the UNMIX and 49.16%, 38.90%, and 11.94% via the PCA-MLR, respectively. Meanwhile, the study results suggested that the combined usage of multiple receptor models is a good method to apportion the source compositions and contributions of trace metals in urban soil.

Potential Benefits and Risks for Soil Health Derived From the Use of Organic Amendments in Agriculture

The use of organic amendments in agriculture is a common practice due to their potential to increase crop productivity and enhance soil health. Indeed, organic amendments of different origin and composition (e.g., animal slurry, manure, compost, sewage sludge, etc.) can supply valuable nutrients to the soil, as well as increase its organic matter content, with concomitant benefits for soil health. However, the application of organic amendments to agricultural soil entails a variety of risks for environmental and human health. Organic amendments often contain a range of pollutants, including heavy metals, persistent organic pollutants, potential human pathogens, and emerging pollutants. Regarding emerging pollutants, the presence of antibiotic residues, antibiotic-resistant bacteria, and antibiotic-resistance genes in agricultural amendments is currently a matter of much concern, due to the concomitant risks for human health. Similarly, currently, the introduction of microplastics to agricultural soil, via the application of organic amendments (mainly, sewage sludge), is a topic of much relevance, owing to its magnitude and potential adverse effects for environmental health. There is, currently, much interest in the development of efficient strategies to mitigate the risks associated to the application of organic amendments to agricultural soil, while benefiting from their numerous advantages.