Pollution assessment of heavy metal accumulation in the farmland soils of Beijing's suburbs

The binding effects and mechanisms of dissolved organic matter (DOM) on the fate of mercury in sludge anaerobic digestion combined with thermal hydrolysis

Dissolved organic matter (DOM) plays an important role in regulating the fate of mercury (Hg), e.g., mobility, bioavailability, and toxicity. Clarifying the role of DOM in binding Hg in the treatment processes of sewage sludge is important for relieving Hg contamination risks in land applications. However, the impacts of DOM on Hg binding in sewage sludge are still unclear. In this study, we investigated the evolution of Hg and its speciation in full-scale sludge anaerobic digestion (AD) with thermal hydrolysis. The role of DOM in binding Hg(II) was further analyzed. The results showed that AD with thermal hydrolysis led to an increase in the Hg content in the sludge (from 3.72 ± 0.47 mg/kg to 10.75 ± 0.16 mg/kg) but a decrease in Hg mobility (the mercury sulfide fraction increased from 60.56 % to 79.78 %). Further adsorption experiments revealed that at equivalent DOM concentrations, DOM with a low molecular weight (MW<1 kDa) in activated sludge, DOM with a medium molecular weight (1 kDa 5 kDa) in both anaerobically digested sludge and conditioned sludge showed high binding amounts of Hg(II), with 1372.54, 535.28, 942.09 and 801.51 mg Hg/g DOM, respectively. Parallel factor analysis (PARAFAC) and fluorescence quotient (FQ) results showed that tryptophan-like and tyrosine-like substances had high binding affinities for Hg(II). Furthermore, X-ray photoelectron spectroscopy (XPS) indicated that the reduced organic sulfur contained in the DOM was potentially bound to Hg through the interactions of Hg-S and Hg-O. These results indicated that DOM may play special roles in regulating Hg speciation. The association between DOM and Hg(II), such as the significant positive correlation (p < 0.05) between the dissolution rate of Hg(II) and release of tryptophan-like substances during thermal hydrolysis, suggested the potential way for removing Hg from sludge.

Geochemical baseline establishment, pollution level and health risk assessment of soil heavy metals in the upper Xiaowen River Basin, Shandong Province, China

This study analyzed the distribution and content of eight heavy metals (Cu, Pb, Zn, Ni, Cr, As, Cd, and Hg) in 221 surface soil samples from the upper reaches of the Xiaowen River. Environmental geochemical baselines were established for the eight heavy metals, and the pollution status was assessed on the basis of these baselines and the soil background value of Weifang City. The calculation results of Nemerow pollution index and the potential ecological hazard index (PEHI)-Ri showed that the overall pollution degree and ecological hazard in the study area were at a slight level. 49% (calculated by baseline value) and 24% (calculated by background value of Weifang City) samples were at moderate or above pollution level. 9% (calculated by baseline value) and 42% (calculated by background value) samples were at the level of moderate potential ecological hazards or above. According to the calculation results of Igeo and PEHI-Ei, the main pollutant in the study area was Hg, followed by Cd. 3% (calculated by baseline value) and 12% (calculated by background value) of Hg samples were at moderate or above contamination levels. 5% (calculated by baseline value) and 38% (calculated by background value) of Hg samples were at the level of strong potential ecological hazard or above. The western, central, and eastern parts of the study area were mainly the primary areas of pollution and ecological hazards. The non-carcinogenic risk was at an acceptable level, the carcinogenic risk was at a tolerable level, and the main risk pathway was oral intake, with Cr being the main contributor. Source apportionment indicated that soil heavy metals primarily originate from soil parent material, transportation, agricultural fertilization, and industrial emissions (waste gas, waste water and solid waste).

Risk assessment and source identification of soil heavy metals: a case study of farmland soil along a river in the southeast of a mining area in Southwest China

To investigate the heavy metals (HMs) contamination of surface farmland soil along the river in the southeast of a mining area in southwest China and identify the contamination sources, 54 topsoil samples were collected and the concentrations of seven elements (Zn, Ni, Pb, Cu, Hg, Cr, and Co) were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and atomic fluorescence spectrometry (AFS). The geo-accumulation index ([Formula: see text]) and comprehensive potential ecological risk index ([Formula: see text]) were used for analysis to determine the pollution degree of HMs and the risk level of the study area. Meanwhile, the Positive Matrix Factorization (PMF) model was combined with a variety of statistical methods to determine the sources of HMs. To explore the influence of the river flowing through the mining area on the concentrations of HMs in the farmland soil, 15 water samples were collected and the concentrations of the above seven elements were determined. The results showed that the concentrations of Pb, Cu, and Zn in soil all exceeded the risk screening value, and Pb in soil of some sampling sites exceeded control value of "Agricultural Land Soil Pollution Risk Control Standard".[Formula: see text] showed that Pb was heavily contaminated, while Cu and Zn were moderately contaminated. RI showed that the study area was at moderate risk. PMF and various statistical methods showed that the main source of HMs was the industrial source. In the short term, the river flowing through the mine has no significant influence on the concentration of HMs in the soil. The results provide a reference for the local government to control contamination and identify the sources of HMs.

Pollution evaluation and source identification of heavy metals in soil around steel factories located in Lanshan District, Rizhao City, eastern China

More than 40 enterprises have settled in the constructed steel-supporting industrial park adjacent to the Yellow Sea in Lanshan District, Rizhao City, eastern China. The concentration of heavy metals in the soil around steel factories often exceeds the limit specified by the national environmental agency. In this study, nine metals (Cu, Zn, Pb, Cd, Cr, Ni, Mn, Fe, and Mg) in the soil around the steel-supporting industrial park were examined, and 100 soil samples were analyzed. The pollution characteristics and sources of these heavy metals were obtained via pollution index analysis, potential ecological risk evaluation, geostatistical analysis, and multivariate statistical analysis combined with a positive matrix factorization (PMF) model. The results indicated that the heavy metals showed varying accumulation levels, among which Cd, Ni, and Pb were the major heavy metals greatly influencing the soil quality. The area around the steel factories exhibited heavy pollution and a high ecological risk, and Ni and Cd were the main risk factors. The soil at the steel factories and that in the southeastern and southwestern parts of the study area attained higher heavy metal element contents than those in the soil in other parts. PMF analysis confirmed that Cu, Pb, and Cd originated from mixed agricultural and traffic sources. Mn was related to natural sources. Cr and Ni likely resulted from atmospheric deposition, and Zn, Cd, Fe, and Mg were mainly associated with industrial materials, with these four sources accounting for 32.68%, 12.2%, 27.57%, and 27.54%, respectively, of the total metal content. This study could facilitate the investigation, evaluation, and source identification of soil heavy metal pollution in industrial regions and surrounding areas of Lanshan District, Rizhao City.

Associations of metals and metals mixture with lipid profiles: A repeated-measures study of older adults in Beijing

Metals inevitably and easily enter into human bodies and can induce a series of pathophysiological changes, such as oxidative stress damage and lipid peroxidation, which then may further induce dyslipidemia. However, the effects of metals and metals mixture on the lipid profiles are still unclear, especially in older adults. A three-visits repeated measurement of 201 older adults in Beijing was conducted from November 2016 to January 2018. Linear Mixed Effects models and Bayesian kernel machine regression models were used to estimate associations of eight blood metals and metals mixture with lipid profiles, including total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), Castelli risk indexes I (CRI-1), Castelli risk indexes II (CRI-2), atherogenic coefficient (AC), and non-HDL cholesterol (NHC). Cesium (Cs) was positively associated with TG (β_Cs = 0.14; 95% CI: 0.02, 0.26) whereas copper (Cu) was inversely related to TG (β_Cu = -0.65; 95%CI: -1.14, -0.17) in adjusted models. Manganese (Mn) was mainly related to higher HDL-C (β_Mn = 0.14; 95% CI: 0.07, 0.21) whereas molybdenum showed opposite association. Metals mixture was marginally positive associated with HDL-C, among which Mn played a crucial role. Our findings suggest that the effects of single metal on lipid profiles may be counteracted in mixtures in the context of multiple metal exposures; however, future studies with large sample size are still needed to focus on the detrimental effects of single metals on lipid profiles as well as to identify key components.

A Comprehensive Evaluation System for the Stabilization Effect of Heavy Metal-Contaminated Soil Based on Analytic Hierarchy Process

Stabilization technology is widely used in the remediation of heavy metal-contaminated farmland soil. However, the evaluation method for the remediation effect is not satisfactory. To scientifically evaluate the remediation effect, this study constructed a comprehensive evaluation system by bibliometric analysis and an analytic hierarchy process (AHP). Ultimately, 16 indicators were selected from three aspects of the soil, crops, and amendment. The 16 indicators are divided into three groups, namely indicators I that can be evaluated according to the national standards of China, indicators II that can be evaluated according to the classification management of farmland and Indicators III that are the dynamic change indicators without an evaluation criterion. Comprehensive scores for 16 indicators were calculated using three response models, respectively. According to the difference between the scores before and after the remediation, the remediation effect is divided into five levels, which are excellent, good, qualified, poor, and very poor. This study provides a theoretical basis and insightful information for a farmland pollution remediation and a sustainable utilization.

Health risk assessment of heavy metal(loid)s in the farmland of megalopolis in China by using APCS-MLR and PMF receptor models: Taking Huairou District of Beijing as an example

The quality of agricultural soils is important for agricultural production and food safety. The contamination of agricultural soils by heavy metal(loid)s (HMs) has aroused global attention. Fifty-two topsoil samples with 8 HMs were gathered to assess the health risks of farmland soil in Huairou District, Beijing. As a significantly enriched pollutant, the results revealed that Hg had greater ecological risks relative to other HMs. We found that the positive matrix factorization (PMF) model appears to be more physically plausible in identifying complex pollution sources compared to the absolute principal components score-multiple linear regression (APCS-MLR) model, which had a higher fit coefficient (r² = 0.69-0.99). Five HMs from pollution sources, including agricultural activities, traffic source, natural source, fuel burning, and industrial production, were identified by integrating the PMF model with Pearson's correlation analysis, revealing corresponding contribution rates of 29.40%, 22.54%, 20.16%, 15.20%, and 12.70%, respectively. The probabilistic health risk evaluation results showed an absence of non-carcinogenic risks in all populations, but the carcinogenic risk could not be ignored, especially in children. In addition, the source-oriented health risks showed that agricultural activities made the largest contribution to the health risks of all populations. This research provides scientific evidence for preventing HMs contamination and control of farmland.

Discharge Patterns of Potentially Harmful Elements (PHEs) from Coking Plants and Its Relationship with Soil PHE Contents in the Beijing–Tianjin–Hebei Region, China

The Beijing–Tianjin–Hebei (BTH) region in China is a rapid development area with a dense population and high-pollution, high-energy-consumption industries. Despite the general idea that the coking industry contributes greatly to the total emission of potentially harmful elements (PHEs) in BTH, quantitative analysis on the PHE pollution caused by coking is rare. This study collected the pollutant discharge data of coking enterprises and assessed the risks of coking plants in BTH using the soil accumulation model and ecological risk index. The average contribution rate of coking emissions to the total emissions of PHEs in BTH was ~7.73%. Cross table analysis indicated that there was a close relationship between PHEs discharged by coking plants and PHEs in soil. The accumulation of PHEs in soil and their associated risks were calculated, indicating that nearly 70% of the coking plants posed a significant ecological risk. Mercury, arsenic, and cadmium were the main PHEs leading to ecological risks. Scenario analysis indicated that the percentage of coking plants with high ecological risk might rise from 8.50% to 20.00% as time progresses. Therefore, the control of PHEs discharged from coking plants in BTH should be strengthened. Furthermore, regionalized strategies should be applied to different areas due to the spatial heterogeneity of risk levels.

A GIS study to rank Irish agricultural lands with background and anthropogenic concentrations of metal(loid)s in soil

Heavy metal pollution may cause a serious threat to human health and is a global problem. The bio-availability of metals and metalloids (metal (loid)s) in the soil is a dominating parameter for metal (loid) uptake by plants, and which may subsequently be ingested by individuals through the food pathway. This study aimed to develop a novel approach based on a semi-quantitative probability-impact (P-I) matrix with the help of a GIS mapping tool. ArcGIS was used for data analysis, classification, and reclassification of parameters of the model. Nine influencing parameters were selected for a semi-quantitative risk ranking. These are soil pH, soil organic carbon (SOC), soil texture class, slope, field/soil drainage class, Integrated Risk Quotient (IRQ), proximity to mines, urban activity, and potential biosolids application areas. The results revealed that certain areas (including Co. Louth, Co. Wicklow, Co. Wexford) along the East coast of Ireland pose a higher relative risk. Therefore, in-depth quantitative human health risk assessment is proposed considering the potential bioaccumulation of metal (loid)s if the crops are grown on land with elevated levels of metal (loid)s. Furthermore, this work reveals the usefulness of the GIS mapping techniques in risk assessment to rank areas of elevated levels of potential pollutants.

Soil heavy metal pollution source analysis based on the land use type in Fengdong District of Xi'an, China

The soil environment imposes a great influence on human health. Soil heavy metal pollution caused by human activities is an important part of environmental problems in urban areas. Due to an inadequate infrastructure, imperfect management, and intensive human activities, the sources of heavy metals in urban fringe areas are often more complicated than those in other areas, such as mining areas and agricultural irrigation areas. To solve this problem, the first step is to locate the source of pollution. However, the traditional methods of source analysis, such as principal component analysis and positive matrix factorization, always require correlations between elements. This study examined the Hg, Cd, Pb, and Cu contents in the Fengdong District of Xi'an, China, and found that these elements are not correlated in this area. Hence, traditional source analysis methods are not applicable in the study area. In response to this problem, this research proposed a new source analysis method based on Pearson's correlation analysis. The Nemerow index, geoaccumulation index, and ecological risk index were adopted to evaluate soil heavy metal pollution in the study area. Via comparison to the actual situation, it was concluded that the geoaccumulation index is more suitable for source analysis in this area. Through Pearson's correlation analysis, it was found that the geoaccumulation index is significantly correlated with the various land use types. Among them, transportation land exerted a greater impact on Pb pollution, and industrial land exerted a significant impact on the Hg distribution. The Cu distribution was related to construction land, while the Cd distribution was mainly related to urban land and cultivated land. In addition, the demolition of residential areas and abandoned farmlands imposed significant effects on Pb and Cd pollution, respectively.

Environmental burden of unprocessed solid waste handling in Enugu State, Nigeria

Improper waste management has assumed a worrisome dimension in cities across many developing countries. One of its commonest features is open dumps. Open dumps in Enugu and Nsukka were investigated in this study. Waste samples were collected from ten dumps located in low-income, low-to-middle income, and high-income zones of the study area. The composition of waste was determined following standard methods and results obtained subjected to statistical analyses. Selected open dumps were subjected to detailed inspection in order to identify possible environmental impacts. Soil samples were also collected from the top soil and subsoil (15 cm) of selected dumps and analyzed for As, Cd, Cr, Cu, Hg, Mn, Pb, Ni, Cd, and Zn. The sources of contamination were determined using the principal component analysis (PCA) and cluster analysis (CA). Results of heavy metal analyses were used to determine extent of soil pollution. Food waste ranged from 29.6 to 56.5% with an average of 42.2%. Analysis along income line showed a decline in the proportion of food and rubber waste from lower to high income. The order of heavy metals concentration in waste dump soils investigated was as follows: Mn > Zn > Cu > Cr > Pb > As > Ni > Cd > Hg. The pollution indices (PI) of the dumpsites ranged from 1.87 for Ni to 1634.6 for Cu in the topsoil, and 0.62 for Ni to 1354.74 for Cu in the subsoil, indicating a severe level of pollution. Pollution load index (PLI) ranged from 25.38 to 75.07 with a mean of 60.75 for the dump surface and from 51.46 to 21.7 with a mean of 33.86 below the dump soil. Forty-three percent (43%) of the topsoil and 40% of the subsoil exhibited ecological risk index values greater than 320, indicating extreme degree of ecological risk. The first principal and second principal components with 36% and 28.2% variance respectively represent the growing impact of electronic waste disposal, specifically mobile phones, personal computers, and other potable electronic devices with short life span on waste dumps. The third principal component (10.2%) represents input from households and other forms of chemicals such as insecticides, paints, and detergents.

Quantitative analysis of the main sources of pollutants in the soils around key areas based on the positive matrix factorization method

Quantitative identification of the main sources of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in soils around multiple types of key areas is of great significance for blocking pollution sources. However, there is a lack of more comprehensive relevant research. In this study, Beijing was taken as the research area and four main sources were identified using the positive matrix factorization (PMF) method. The concentration of Pb, PAHs, Cr, and Hg in soils was significantly affected by the presence of landuse type, road traffic, natural factor, and industrial production, respectively, and the farmland, distance to main road, Proterozoic Changcheng-Jixian parent material and cinnamon soil type, and the gross industrial production make greater contributions to these four factors respectively than other variables. Moreover, the uncertainty of the PMF indicates that this four-factor PMF solution is stable and appropriate. These results provide support for the comprehensive control of soil environmental risks.

Spatio-temporal variation and source changes of potentially toxic elements in soil on a typical plain of the Yangtze River Delta, China (2002-2012)

The spatio-temporal variation and temporal changes in the sources of Cr, Pb, Cd, Hg, and As in soil on the Hangzhou-Jiaxing-Huzhou (H-J-H) Plain were analysed based on 4,359 soil samples collected in 2002 and 2012. Geostatistical and spatial analysis methods were used to explore the spatio-temporal variation in the pollution levels and 'pollution hotspots' for potentially toxic elements (PTEs), and the positive matrix factor model was used to quantitatively appoint and analyse temporal changes in PTE sources. The results indicated that the PTE content in most parts of the survey area were at a safe level in both 2002 and 2012, but a clearly upward trend was detected for Cr, Pb, and Cd. Moreover the pollution index for Cr, Pb, Cd, and the Nemerow composite pollution index increased in the west but decreased in the east of the H-J-H Plain from 2002 to 2012. The pollution index for Hg and As presented the opposite spatial pattern. It is obvious that there have been changes in the spatial pattern of pollution hotspots for PTEs on the H-J-H Plain from 2002 to 2012. Four sources of PTEs in soil were quantitatively appointed. In 2002, 2012, the dominant sources of Cr, Cd, Hg, and As were soil parent materials, industrial activities, atmospheric deposition and agricultural inputs, respectively. The dominant source of Pb in the soil changed from traffic emissions to soil parent materials, indicating the benefit of banning the use of leaded gasoline in China. This study highlights the importance of monitoring soil environmental quality and highlights the significance of spatio-temporal variation in PTEs in suburban zones or transitional areas undergoing rapid industrialization and urbanization, like the H-J-H Plain.

Concentrations, Spatial Distributions, and Sources of Heavy Metals in Surface Soils of the Coal Mining City Wuhai, China

Various studies have shown that soils surrounding mining areas are seriously polluted by heavy metals. In this study, 58 topsoil samples were systematically collected throughout the coal mining city Wuhai, located within the Inner Mongolia Autonomous Region of China. The concentrations of As, Hg, Cr, Ni, Cu, Zn, Cd, and Pb in these samples were measured and statistically analyzed. The mean concentrations of all heavy metals were lower than their Grade I values defined by the Chinese Soil Quality Standard. However, the mean concentrations of individual heavy metals in many samples exceeded their background values. The spatial distribution of heavy metals was analyzed by the ordinary kriging interpolation method. The positive matrix factorization model was used to ascertain contamination sources of the eight heavy metals and to apportion the contribution of each source. The most severely polluted area was the Wuhushan mine site in the Wuda district of Wuhai. Our results showed that coal mining strongly affected heavy metal contamination of the local soils. Results of source apportionment indicated that contributions from industrial activities, atmospheric deposition, agricultural activities, and natural sources were 31.3%, 26.3%, 21.9%, and 20.5%, respectively. This clearly demonstrates that anthropogenic activities have markedly higher contribution rates than natural sources to heavy metal pollution in soils in this area.

Pollution status and ecological risk of heavy metals in the soils of five land-use types in a typical sewage irrigation area, eastern China

Sewage irrigation has been widespread in the water shortage area of eastern China and inevitably tends to result in heavy metal accumulation in soils. A total of 148 surface soil samples from five land-use types were collected in Longkou, a typical sewage irrigation area of China, and As, Cd, Cu, Pb, and Zn concentrations were determined. The Nemerow index method and improved fuzzy comprehensive evaluation method were used to examine the pollution status of heavy metals. The potential ecological risk was evaluated by the Hakanson model by adjusting the assessment threshold, and its spatial distribution was interpolated using geostatistical techniques. As, Cd, Cu, Pb, and Zn accumulated in different amounts in the five land-use types. Urban industrial land and mining land were moderately polluted, irrigated land was slightly polluted, orchards were minimally polluted, and bare land was at a safe level of pollution. Cd exhibited high percentages of strong and severe levels of potential ecological risks. For Cd, irrigated land, orchard, and bare land mainly presented moderate risks, whereas urban industrial land and mining land mainly presented high risks. The comprehensive ecological risk of the five heavy metals was at a severe level for all tested land-use classes except for bare land.

Soil heavy metal contamination assessment in the Hun-Taizi River watershed, China

The Hun-Taizi River watershed includes the main part of the Liaoning central urban agglomeration, which contains six cities with an 80-year industrial history. A total of 272 samples were collected from different land use areas within the study area to estimate the concentration levels, spatial distributions and potential sources of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn) with a geographic information system (GIS), principal component analysis (PCA) and canonical correspondence analysis (CCA). Only the concentration of Cd was over the national standard value (GB 15618–2018). However, the heavy metal concentrations at 24.54%, 71.43%, 63.37%, 85.71, 70.33%, 53.11%, and 72.16% of the sampling points were higher than the local soil background values for As, Cd, Cr, Cu, Hg, Ni, Pb and Zn, respectively, which were used as standard values in this study. The maximal values of Cd (16.61 times higher than the background value) and Hg (12.18 times higher than the background value) had high concentrations, while Cd was present in the study area at higher values than in some other basins in China. Cd was the primary pollutant in the study area due to its concentration and potential ecological risk contribution. The results of the potential ecological risk index (RI) calculation showed that the overall heavy metal pollution level of the soil was considerably high. Three groups of heavy metals with similar distributions and sources were identified through PCA. The results of the CCA showed that the distribution of mines was the strongest factor affecting the distributions of Ni, As, Zn, Pb, and Cd. However, Cu was strongly influenced by the distance to the nearest river. These findings can provide scientific support for critical planning and strategies for soil pollution control and removal to support the sustainable development of the study area.

Ecological risk assessment and source identification of heavy metal pollution in vegetable bases of Urumqi, China, using the positive matrix factorization (PMF) method

Heavy metal pollution is a widespread problem and strongly affects human health through the food chain. In this study, the overall pollution situation and source apportionment of heavy metals in soil (Hg, Cd, As, Pb, Ni, Zn, Cu and Cr) were evaluated using various methods including geo-accumulation index (Igeo), potential ecological risk index (RI) and positive matrix factorization combined with Geographical Information System (GIS) to quantify and identify the possible sources to these heavy metals in soils. The results of Igeo showed that this farmland top soil moderate contaminated by Hg, other selected elements with noncontamination level. And the average RI in the top soil was 259.89, indicating a moderate ecological risk, of which Hg and Cd attributed 88.87% of the RI. The results of the PMF model showed that the relative contributions of heavy metals due to atmospheric depositions (18.70%), sewage irrigations (21.17%), soil parent materials (19.11%), industrial and residential coal combustions (17.43%) and agricultural and lithogenic sources (23.59%), respectively. Of these elements, Pb and Cd were came from atmospheric deposition. Cr was attributed to sewage irrigations. As was mainly derived from the soil parent materials. Hg originated from industrial and residential coal combustions, and most of the Cu, Zn and Ni, except for Pb, were predominantly derived from agricultural and lithogenic sources. These results are important in considering management plans to control the aggravation of heavy metal pollution and ultimately to protect soil resources in this region. In addition, this study enhances the understanding of heavy metal contamination occurrence in agroecosystem that helps predicting and limiting the potential of heavy metal exposure to people and ecosystem.

Heavy-Metal Pollution Characteristics and Influencing Factors in Agricultural Soils: Evidence from Shuozhou City, Shanxi Province, China

Although soil quality can be highly altered by mining activities, there are few reports on soil pollution in mining cities. We systematically characterized the heavy metals (HMs) pollution, risks, sources, and influencing factors in the surrounding soils of Shuozhou. Specifically, 146 samples were collected, and the potential ecological risk index (RI) and the single-factor index were jointly used to understand the environmental risk of HMs. Meanwhile, correlation analysis was applied to find the influencing factors of HMs. The results of the soil pollution risk assessment in the entire area of Shuozhou were compared with those in the open-pit mine area. (1) The mean concentrations of Cr, As, Cd, Pb, and Hg in our study were found to be higher than the background value. The RI results indicated that most soil samples (82.88%) in Shuozhou had a low potential ecological risk. Compared with the Pingshuo open-pit mine (average RI value: 200.07), the potential ecological RI was lower. (2) The HM correlation indicated that Cr and As were associated with the parent rock, whereas Cd, together with Hg and Pb, were associated with anthropic activities. (3) There was no significant correlation between HM concentrations and farmland slope. Located in the Datong Basin, the terrain of Shuozhou is relatively flat and open and has little impact on the distribution of HMs. (4) Only Hg and Pb have a negative correlation with pH. This suggests that soil with a lower pH value may be beneficial to the accumulation of Hg and Pb in soil. (5) Among the eight industry types examined, the pollution capacity level of the leather, fur, feather, and footwear industries is the strongest, indicating that HMs around LI industry sites represent the maximum level among the eight types.

Temporal-spatial trends in potentially toxic trace element pollution in farmland soil in the major grain-producing regions of China

Pollution from potentially toxic trace elements (PTEs) is becoming serious and widespread in farmland soils in China, threatening food security and human health. Few large-scale studies systematically analyzed their temporal-spatial trends over vast spatially elaborate sites. The soil health status of the main grain producing areas was first announced based on a total of 3662 spatially elaborate farmland topsoil sites from the 1980s to the 2000s. Nearly 21.5% of sites were polluted, although only slightly. Pollution from the Cd, Ni, Cu, Zn, and Hg was more serious. Pollution was more extensive in the south than in the north. There was an increasing trend in the PTE concentrations, especially Cd with a growth of 21–25%, and in the proportion of mixed pollution at the sites (19.3%), Cd (21.5%), Pb (3.6%), Zn (5.7%), Cu (7.0%), and Hg (3.1%). Furthermore, temporal variations in severe Cd pollution and mixed-level Hg pollution in the north are severer. This study may provide guidance for policymakers regarding the protection and high-risk area of PTE contamination in the soils.

Impact of Non-Agricultural Employment and Environmental Awareness on Farmers’ Willingness to Govern the Heavy Metal Pollution of Farmland: A Case Study of China

Heavy metal pollution of farmland is a significant issue affecting the quality of agricultural products and human health. Farmers’ behaviors can have a direct impact on the level of heavy metal pollution affecting farmland in China. Whether the heavy metal pollution of farmland can be effectively governed at a low cost depends on the farmers. This paper analyzes the mechanism by which the extent of non-agricultural employment and environmental awareness influences farmers’ willingness to govern the heavy metal pollution of farmland using microdata for farmers in China and conducts an empirical analysis via a logit model. The results show that farmers in China display low willingness to govern the heavy metal pollution of farmland and that the increase in non-agricultural income will not significantly improve this willingness. Environmental awareness and farmers’ willingness to govern the heavy metal pollution of farmland are closely related: the higher the environmental awareness of farmers is, the stronger their willingness to govern heavy metal pollution, and the higher the probability of their participating in fallow land treatment. The government can introduce incentives to improve farmers’ environmental awareness of the heavy metal pollution of farmland. In addition, the government should strengthen publicity about the positive effects of fallow land treatment and encourage farmers to participate in the governance of heavy metal pollution of farmland. Given increasing non-agricultural employment opportunities and the transformation of agricultural production modes, agricultural technical training provided by governmental departments can enable them to be more scientific and rational in their agrochemical selection and application, thus reducing or avoiding the heavy metal pollution of farmland at the source. Attention should be paid to the differences between farmers to ultimately reduce the cost and improve the efficiency of treatment.