Soil Environmental Quality Standards Research Articles

Determination of soil environmental criteria for high-risk trace metals in urban park soils using improved CLEA model

The trace metals (TMs) accumulated in urban park soils can pose potential threats to human health, making the management of soil quality based on health risks critically important. Based on the human health risk assessment (HHRA) model coupled with Monte Carlo Simulation, this study improved the contaminated land exposure assessment (CLEA) model. Combined with local parameters, the Soil Environmental Criteria (SEC) for high-risk trace metals (TMs) in urban park soils were calculated. Results indicated that all the mean TCR (Total carcinogenic risk) values of seven TMs exceeded the risk threshold of 1E-06, suggesting a higher likelihood of carcinogenic risks for all populations. As and Cr presented the highest potential carcinogenic risks, and were identified as high-risk TMs in the study area. The traditional CLEA model was enhanced by incorporating region-specific data, optimizing exposure parameter calculations, and addressing parameter sensitivity and uncertainty. Using the improved CLEA model, the SEC values for high-risk TMs were calculated, revealing that the SEC values gradually increased from ages 1 to 18, while significantly decreased for individuals over 80 years old. This study effectively addresses issues of parameter uncertainty and sensitivity in the CLEA model, offering new insights for the development of soil environmental quality standards.

Cumulative characteristics and ecological risk source analysis of soil potentially toxic elements in the northern margin of the Tibetan Plateau.

To understand the soil toxic and hazardous elements content, pollution level, and ecological risk status in the northern margin of the Tibetan Plateau, we collected and analyzed 8273 sets of surface soil samples. Evaluations were conducted using the single-factor pollution index, geo-accumulation, pollution load, and potential ecological risk indices, and source identification correlation and principal component analysis. The results revealed that, compared with the background levels in China, the accumulation of soil arsenic, cadmium, nickel, and chromium was greater in the surface soil of the study area. Additionally, in comparison with Qinghai Province, more mercury accumulated in the surface soil of the study area and owing to the influence of anthropogenic activities. Benchmarking against soil environmental quality standards, the study area exhibited pollution control zones primarily dominated by arsenic and cadmium (3.9%). The spatial distribution revealed distinct zones: a ridge mountain type characterized by arsenic-cadmium-chromium-nickel, a Daban mountain type with solely cadmium presence, and a Longyangxia-Jianzha South type dominated by arsenic. Compared with the Qinghai Province soil background values, evaluations using the Pollution loading index, Geological Cumulative Index, and Potential Ecological Risk Index methods revealed varying degrees of potentially toxic element content exceedance. From an ecological risk perspective, the individual element with the highest potential ecological risk coefficients were mercury, followed by cadmium and arsenic; however, the region's overall ecological risk index was classified as low. Three distinct sources were identified: natural sources leading to high background levels of chromium, nickel, copper, zinc, and mercury; mixed natural and industrial/agricultural sources contributing to elevated cadmium levels; and human activity-related mercury enrichment. Based on the evaluation results, synergistic monitoring of soil and biota in naturally occurring risk zones is recommended to ensure the safety of agricultural and pastoral products. Additionally, ecological impact assessments and pollution source mitigation studies should be conducted in regions influenced by human activities to curb the further degradation of soil ecological quality.

Urban green space area mitigates the accumulation of heavy metals in urban soils

Despite that the heavy metals in urban soils pose a threat to public health, the critical factors that influence their concentrations in urban soils are not well understood. In this study, we conducted a survey of surface soil samples from urban green spaces in Shanghai, to analyze the concentrations of the key heavy metals. The results showed that Zn was the most abundant metal with an average concentration of 122.99 mg kg−1, followed by Pb (32.72 mg kg−1) and Cd (0.23 mg kg−1). All concentrations were found to be below the risk screening values defined by the National Environmental Quality Standards for soils of development land in China (GB36600-2018), indicating no current risk in Shanghai. However, there was a clear accumulation of heavy metals, as the mean concentrations were significantly higher than the background values. Furthermore, we explored the relationships between key heavy metals with population density, GDP and green space area. Both Spearman correlation and Random Forest analysis indicated that per capita green space area (pGSA) and population density were the most crucial factors influencing the status of heavy metals in urban soils, unlike edaphic factors e.g. SOM content in farmland soils. Specifically, there was a significantly positive linear correlation between heavy metal concentrations and population density, with correlation coefficients ranging from 0.3 to 0.4. However, the correlation with pGSA was found to be non-linear. The nonlinear regression analysis revealed threshold values between heavy metals concentrations and pGSA (e.g Zn 22.22 m2, Pb 24.92 m2, and Cd 25.92 m2), with a sharp reduction in heavy metal concentrations below the threshold and a slow reduction above the threshold. It suggests that an increase in per capita green space area can mitigate the accumulation of heavy metals caused by growing population density, but the effect is limited after the threshold. Our findings not only provide insights into the distribution patterns of heavy metals in the urban soils at the local scale, but also contribute to the urban greening at the global scale and offer guidance for city planning in the face of increasing population densities over the coming decades.

Spatio-temporal trends of mercury levels in alluvial gold mining spoils areas monitored between rainy and dry seasons in the Peruvian Amazon

Artisanal and small-scale gold mining (ASGM) in the Amazon has degraded tropical forests and escalated mercury (Hg) pollution, affecting biodiversity, ecological processes and rural livelihoods. In the Peruvian Amazon, ASGM annually releases some 181 tons of Hg into the environment. Despite some recent advances in understanding the spatial distribution of Hg within gold mine spoils and the surrounding landscape, temporal dynamics in Hg movement are not well understood. We aimed to reveal spatio-temporal trends of soil Hg in areas degraded by ASGM.,. We analyzed soil and sediment samples during the dry and rainy seasons across 14 ha of potentially contaminated sites and natural forests, in the vicinities of the Native community of San Jacinto in Madre de Dios, Peru. Soil Hg levels of areas impacted by ASGM (0.02 ± 0.02 mg kg−1) were generally below soil environmental quality standards (6.60 mg kg−1). However, they showed high variability, mainly explained by the type of natural cover vegetation, soil organic matter (SOM), clay and sand particles. Temporal trends in Hg levels in soils between seasons differed between landscape units distinguished in the mine spoils. During the rainy season, Hg levels decreased up to 45.5% in uncovered soils, while in artificial pond sediments Hg increased by up to 961%. During the dry season, uncovered degraded soils were more prone to lose Hg than sites covered by vegetation, mainly due to higher soil temperatures and concomitantly increasing volatilization. Soils from natural forests and degraded soil covered by regenerating vegetation showed a high capacity to retain Hg mainly due to the higher plant biomass, higher SOM, and increasing concentrations of clay particles. Disturbingly, our findings suggest high Hg mobility from gold mine spoil to close by sedimentary materials, mainly in artificial ponds through alluvial deposition and pluvial lixiviation. Thus, further research is needed on monitoring, and remediation of sediments in artificial to design sustainable land use strategies.

Determination of soil environment criteria for ecological safety of benzo[a]pyrene in soil based on the species sensitivity distribution approach

Benzo[a]pyrene (BaP) is a highly carcinogenic organic pollutant. Its distinct toxic effects have raised significant concerns among regulators and researchers. However, the absence of established soil environmental criteria for ecological safety of BaP has led to a lack of evidence in the current risk assessment for soil ecological security. To address this gap, we conducted a comprehensive study to investigate the toxicity of BaP using multiple soil organisms, including rice, wheat, lettuce, rape, cucumber, tomato, leonurus, and earthworm. The toxicity data obtained were applied to the species sensitivity distribution (SSD) approach, and the soil environment criteria for ecological safety of BaP under different land use types were derived. The soil environmental criteria for ecological safety of BaP were estimated to be 1.07 (Natural reserve and agricultural land), 1.63 (Parkland), 3.84 (Residential land) and 6.46 (Commercial service and industrial land) mg·kg−1, respectively. This study is the first to conduct toxicity testing and derive soil environmental criteria of BaP in terrestrial ecosystems. These findings are effective supplement for the current soil environmental quality standards and will function as the basis for ecological risk assessment of BaP.

Accumulation and Transport of Phthalic Acid Esters in the Soil-Plant System of Agricultural Fields with Different Years of Film Mulching

In this study, we investigated the accumulation and transport patterns of phthalate ester (PAEs) compounds in the soil-plant system of maize and cabbage fields under different film mulching years. The total content of five PAEs in the maize fields soil ranged from 156.19 to 566.1 μg kg−1 with film mulching for 0–20 years. The total content of five PAEs in the cabbage field soils ranged from 252.48 to 559.07 μg kg−1 with film mulching for 0–30 years. The PAEs content in cabbage and maize field soils was lower than the environmental quality standards for soil (GB 15618-2008). With the increase in film mulching years, both maize and cabbage soil PAEs contents increased significantly (p < 0.05), while among the five PAEs, the contents of di-n-butyl phthalate (DnBP) and di(2-ethylhexyl) phthalate (DEHP) increased the most significantly, and the content of DEHP in the soils was the highest. The DEHP content in soils planted with maize ranges from 134.03 to 406.79 μg kg−1 with the film mulching for 20 years; while in soil planted with cabbage, it ranges from 229.35 to 405.2 μg kg−1 with the film mulching for 30 years. The DEHP content in all of the soils has not exceed the limit value established by the USEPA in U.S. Five PAEs were detected in maize seeds and cabbage leaves, among which the DEHP content exceeded the maximum residue limit set by the National Food Safety Standard (GB 9685-2016) for DEHP in food after more than 10 years of mulching. The bioaccumulation and translocation factors in cabbage showed a significant positive correlation with the film mulching years. However, the bioaccumulation factor and translocation factor in maize have weak correlations with the film mulching years, possibly due to the lower PAEs content in the deep soil layers where maize roots are distributed. Our research revealed a significant association between the presence and distribution of PAEs in crops and mulching years. These novel discoveries provide fundamental information for controlling PAEs pollution in agricultural environments.

Remediation of large-scale model experiment for heavy metal contaminated clayey soil: An optimized mass transfer process strategy of freeze-thaw and washing

To reduce the limitations of the chemical washing method due to soil texture, the freezing technique has been used to enhance the mass transfer efficiency between the eluent and heavy metal contaminants. With the optimized water supplement and cooling conditions, a large-scale model experiment was conducted. Results show that the optimized method is prone to enhancing the eluent intake of clayey soil, leading to an increase in the amount of soil frost heave, which has a feedback effect by breaking the soil structure and enhancing the eluent intake. The synergistic effect of the two is responsible for the improvement of washing efficiency. In addition, after four freeze-thaw and washing cycles, the total removal rates of the metallic elements Pb and Cd reach 58.73% and 69.04%, respectively, satisfying the soil environmental quality standard. The soil bioavailability is effectively reduced by alternating the eluent with ethylenediaminetetraacetic acid (EDTA) and water, thereby reducing the bioavailability of Pb and Cd by 66.01% and 74.18%, respectively. This remediation strategy for heavy metals in clayey soils utilizes alternate freezing and thawing (natural cold energy) in seasonally frozen regions, which is beneficial for constructing an ecological civilization and protecting the environment.

Ecological risk evaluation and sensitivity analysis of heavy metals on soil organisms under human activities in the Tibet Plateau, China.

The Tibetan Plateau (TP), once considered a pristine environment, is now facing increased heavy metal pollution due to human activities, causing unprecedented ecological risks to soil organisms. However, little is known about the sensitivity and tolerance of different soil organisms to heavy metal toxicity in the high-altitude areas of the TP under the background of human activity intensity and future risk control priorities. In this study, we conducted an ecological risk assessment and threshold calculation for 10 heavy metals in soil for typical soil organisms, including Cd, Co, Cr, Cu, Ni, Pb, Zn, Mn, Sb, and Sn, using the species sensitivity distribution (SSD) method in the zone between Ranwu town and Renlongba glacier on the TP. The results revealed that most sampling sites had average levels of Cd, Sb and Ni exceeding their regional soil environmental background values and were the major contaminants. Impressively, the hitherto undeveloped Renlungba Glacier showed relatively high contamination levels of Sb and Ni. From the view of sensitivity differences, the toxicity risks of Cd, Cr, Cu, Ni and Pb were higher for terrestrial plants than for soil invertebrates based on the fitted heavy metal SSD curve trends. In terms of the ecological risk level, the average potentially affected fraction values of Zn and Ni reached 18.5% and 17.0%, respectively, with significant ecological risk at a few sampling sites. In terms of ecological risk thresholds, the Cd concentration at the 5% hazard concentration (HC5) control level was 0.05 mg/kg, which was the heavy metal with the highest risk in this study. Comparing the HC5 values of each heavy metal with the limit values in the current Chinese soil environmental quality standards, the existing administrative policies as a whole lack a powerful prevention of the potential ecological risk posed by heavy metals to soil organisms.

Application of Desulphurized Gypsum with Straw to Improve Physicochemical Properties of Saline-alkali Land in Yellow River Delta

In order to explore the effect of combining straw and desulphurized gypsum on improving coastal saline-alkali soil, taking the alkaline saline soil in the Yellow River Delta as the research object, six treatments including the control (CK), desulphurized gypsum (DG), medium straw amount (MS), desulphurized gypsum+low straw amount (DGLS), desulphurized gypsum+medium straw amount (DGMS), and desulphurized gypsum+high straw amount (DGHS) were set up through a field location experiment. Combined with the aggregate classification method, the changes in bulk density, total porosity, pH, soluble salt content, microbial biomass carbon, dissolved organic carbon, new carbon, and aggregate organic carbon of coastal saline alkali soil under different treatments were compared. The results showed that the MS and DGHS treatments significantly reduced soil bulk density and increased soil total porosity, water content, and average weight diameter. The pH and exchange sodium percentage decreased significantly under all treatments, and there was no significant difference. DG treatment significantly reduced the soil sodium adsorption ratio. Compared with that in the MS treatment, the soil sodium adsorption ratio of DGLS, DGMS, and DGHS showed a further decreasing trend, with a decrease range of 57%-66%. Compared with MS, soil soluble Na+ decreased by 27.92%, 32.23%, and 20.15% under the DGLS, DGMS, and DGHS treatments, whereas the soil soluble Ca2+ and SO42- contents increased significantly. Compared with that in CK, all treatments could significantly reduce Cl- content, and there was no significant difference among all treatments. Compared with that in MS, microbial biomass carbon and dissolved organic carbon were significantly increased by 113% and 147% by DGMS and 22.81% and 28.24% by DGHS, respectively. The new carbon formation of DGLS, DGMS, and DGHS was 67%, 114%, and 175% higher than that of MS, respectively. The average size proportion of fine aggregates treated by DGLS, DGMS, and DGHS was 29.12% higher than that treated by MS. Straw returning and application of desulfurized gypsum increased the organic carbon content of coarse aggregates and fine aggregates in salinized soil. The average value of new carbon formation in coarse aggregates and fine aggregates treated by DGMS and DGHS was 233% and 142% higher than that treated by MS, respectively. Desulphurized gypsum applied to soil did not lead to soil heavy metal pollution, and the soil heavy metal content of different treatments was lower than the secondary standard of the soil environmental quality standard. These results can provide scientific basis for the improvement and utilization of coastal saline-alkali soil and the comprehensive utilization of industrial and agricultural wastes in the Yellow River Delta.

Non-Carcinogenic Risk Assessment for Heavy Metals in the Soil and Rice in the Vicinity of Dabaoshan Mine, South China

Heavy-metal pollution has attracted wide attention in recent years. The problem of heavy-metal pollution in the vicinity of the Dabaoshan mine, the largest polymetallic mine in South China, has attracted widespread attention. In this study, 38 samples of rice and paddy soil near the Dabaoshan mine were collected. The physical and chemical properties of the soil, including Cu, Cd, Zn, Pb, and Ni levels in the soil and rice, were analyzed. The heavy-metal baseline in paddy soil was analyzed by a normal Q–Q plot. The bioaccumulation factor of the rice was calculated. The non-carcinogenic risk of heavy metals was evaluated by calculating the hazard quotient (HQ). Threshold values of Cu, Cd, Zn, Pb, and Ni were 35.01, 0.51, 70.94, 59.78, and 16.34 mg/kg, respectively. The threshold values of Cu, Zn, and Pb were higher than the background value and lower than the secondary value of China’s soil environmental quality standard. The threshold value of Cd was higher than both the background value and the secondary value of China’s soil environmental quality standard. There was no significant threshold value for Ni in soil. The bioaccumulation factors of Cd, Zn, and Ni were straw > rice > husk. The bioaccumulation factors of Cu and Pb were straw > husk > rice. The HQ of Cd showed that the values for both adults and children were greater than 1, and the HQ for children was higher than that for adults. The HQs of Cu, Pb, Zn, and Ni were all less than 1. This indicated that Cu, Cd, Zn, and Pb pollution had occurred in the area, and that the Cd pollution was more serious. Therefore, it is necessary to strengthen land management, carry out the treatment of soil heavy metal pollution, and reduce the health risks of heavy metals in the study area.

Changes in soil Cd contents and microbial communities following Cd-containing straw return

Contamination of soil with cadmium (Cd) threatens food safety and human health. In general, crop straws from contaminated soils could accumulate considerable amounts of Cd. The addition of Cd-containing rice straw can have negative effects on soil environment. In this study, straws varying in Cd concentration were added to soil at a rate of 5% (w/w) to investigate the effects of Cd-containing straw on soil Cd dynamics and soil microbial communities. Results showed that large amounts of Cd, especially bioavailable Cd, were released into soil during the decomposition of Cd-containing straws. The addition of straws with 10, 20 and 40 mg kg−1 Cd increased total Cd in soils from 0.31 mg kg−1 to 0.89, 1.39 and 2.09 mg kg−1, respectively, exceeding the screening value of total Cd < 0.4 mg kg−1 for paddy soils of pH 5.5–6.5 according to Chinese Soil Environmental Quality Standards. Moreover, the addition of Cd-containing straw decreased alpha-diversity of bacterial and fungal communities compared to the clean straw. Indeed, changes in soil factors including pH, Eh, dissolved organic C and Cd level jointly reconstructed soil microbial communities. The addition of Cd-containing straw increased the relative abundance of bacterial species Acidobacteria and Proteobacteria but decreased that of Firmicutes. Meanwhile, it increased the relative abundance of fungal species Basidiomycota and Fusarium which were considered Cd-tolerant. This study revealed the potential environmental risk and the variation of microbial communities caused by increasing soil Cd bioavailability after direct application of Cd-containing rice straw to the field.

Assessment of Soil Heavy Metal Pollution and Health Risks in Different Functional Areas on the Northern Slope of the Eastern Tianshan Mountains in Xinjiang, NW China.

In typical semi-arid areas, the timely and effective monitoring and evaluation of soil heavy metal pollution are of critical importance to prevent soil deterioration and achieve the sustainable use of soil resources. To further understand the degree of soil heavy metal pollution in different functional areas, we studied the soil heavy metal pollution on the northern slope of the eastern Tianshan Mountains in Xinjiang. We collected 104 surface soil samples from typical commercial (A), industrial (B), and agricultural (C) areas with different land-use patterns. The contents of Zn, Cu, Cr, Pb, As, and Hg in the soil of different functional areas were evaluated using the geo-accumulation index, the single-factor pollution index, and potential ecological risk. The results showed that the contents of Pb, As, and Hg in soils of different functional areas exceeded 4.47, 8.03, and 1.5 times the background values of Xinjiang soil, respectively. The average contents of Zn, Cu, and Cr were lower than the background values of Xinjiang soil. Except for As in different functional areas, the contents of the other elements in the different functional areas reached the level of soil environmental quality standards in China (GB15618-2018). The geo-accumulation index of heavy metals in different functional areas was in the order of Area C > Area A > Area B, indicating that Area C was the most polluted. The results of the single-factor pollution index showed that the pollution levels of Pb, As, and Hg were higher, and the pollution levels of Cr, Cu, and Zn were lower. The results of the potential ecological risk index showed that the northwest of Area A was higher, the southeast of Area B was more polluted, and the central and eastern parts of Area C were more polluted. From the perspective of spatial distribution, the spatial distribution characteristics of Zn and Cr elements in different functional areas are consistent, but the spatial distribution characteristics of Cu, Pb, As, and Hg in different functional areas are quite different. The high values of these four elements are mainly distributed in residential areas, factories, and metal smelters. It is necessary to divide the functional areas based on different land-use patterns, and the prevention of soil single-element and heavy metal pollution in different functional areas is reasonable for land resources and provides a scientific basis for the effective planning of quality assurance.

Distribution Characteristics and Influencing Factors of Organochlorine Pesticides in Agricultural Soil from Xiamen City.

The concentration and distribution of 15 organochlorine pesticides in the soil of Xiamen City were determined. Overall, among the 15 selected target pesticides, 14 organochlorine pesticides (OCPs) were detected (hexachlorobenzene was not). The range of detected pesticides was undetected-10.04 ng/g, the total detection rate was 35.2%, and the three pollutants with the highest detection rate in all samples were Heptachlor (66.7%), δ-Hexachlorocyclohexane (60.0%), and p, p'-Dichlorodiphenyldichloroethane (58.3%). The degree of pollution in descending order was Tong'an > Xiang'an > Jimei > Haicang. Linear regression analysis of soil properties and OCP concentration distribution revealed that OCPs were positively correlated with water content, dissolved organic carbon, and pH and negatively correlated with cation exchange capacity. The origin of OCPs was evaluated using the relationship between the parent compound and its metabolites, with possible new hexachlorocyclohexane and isomer (HCHs) input. By comparing the risk screening values of ΣHCHs and ΣDDTs in "Soil Environmental Quality Standards", the concentrations in all soil samples were lower than the standard values, which indicated that the OCP residues in Xiamen were very low.

Variation in pollution status, sources, and risks of soil heavy metals in regions with different levels of urbanization

Soil heavy metal (HM) pollution is an increasing threat to ecosystem integrity and human health with rapid urbanization. Nevertheless, how soil HMs vary with the process of urbanization remains unclear. Here we used index evaluation, spatial analysis, and a positive matrix factorization (PMF) model to determine the pollution characteristics and sources of eight soil HMs (Mn, Cr, Cu, Zn, As, Cd, Pb, and Ni) among regions with different urbanization levels (urban area, suburb, and ecoregion) in Baoding City, Northern China. We also assessed the risks posed to the ecosystem and human health using risk assessment models. The results indicated that the mean levels of Cu, Zn, As, Cd, and Pb in the study area exceeded the soil environmental quality standards by 10.7 %, 10.7 %, 12.5 %, 23.2 %, and 3.57 %, respectively. A pronounced regional spatial distribution was discovered with high levels in suburban areas. Both the geo-accumulation index and potential ecological risk index revealed significantly higher HM contamination in suburban areas than in urban or ecoregion areas. Source apportionment based on the PMF model and correlation analysis showed that soil HMs in suburban areas primarily originated from agricultural activity, industrial sources, and natural sources. Those in urban soils originated from industrial sources, urban traffic, and natural sources, whereas those in ecoregions derived from natural sources and agricultural activity. The complex sources of soil HMs in suburban areas resulted in the highest carcinogenic risks to children health, followed by the ecoregion, but not in urban areas. This study identified the differences in pollution levels, sources, and risks of soil HMs among regions with different urbanization levels and can guide future efforts to mitigate and manage soil HM pollution during urbanization.

Tracing and quantifying the source of heavy metals in agricultural soils in a coal gangue stacking area: Insights from isotope fingerprints and receptor models

Historic coal gangue stacking probably brings heavy metals (HMs) into the surrounding agricultural soil, posing potential harm to human and environmental health. For better controlling and preventing agricultural soil HMs pollution, the screening of priority pollutants and identification of their pollution pathways are urgent in coal gangue stacking areas. Thus, this study selected a coal gangue stacking area in Chongqing, China as the research object and conducted the pollution evaluation, spatial distribution and source apportionment of the HMs (Cd, Cr, Ni, Cu, Zn, As, Pb and Hg) in surrounding agricultural soil. Results showed that the soil was moderately to heavily contaminated by Cd with average concentrations of 1.23 mg/kg, which were 4.1 times higher than the Environmental Quality Standards for Soils of China. Cd was considered as the soil precedent-controlled pollutant in this study area and subsequent soil δ114/110Cd values indicated that Cd in surface soils primarily originated from the leachate of coal gangue stacking, which contributed about 89.9 % and 85.47 % to the total soil Cd according to the absolute principal component scores-multiple linear regression model (APCS-MLR) and positive matrix factorization model (PMF), respectively. In addition, other HMs mainly resulted from the leachate of coal gangue, natural and agricultural mixed pollution as well as traffic pollution. Therefore, this study provided basic information for pollution control of the HMs in agricultural soil in the coal gangue stacking area.

Do tillage systems affect the cadmium threshold in farmland soil for environmental quality standard setting?

Tillage systems may change the cadmium (Cd) threshold of farmland soil. However, there have been few studies on this topic. Therefore, this study aimed to explore the influence of tillage systems on Cd threshold. The study conducted 2-year field experiments under different tillage systems (early rice-fallow, early rice-late rice and early rice-vegetable) at three typical Cd-polluted sites in China. The species sensitivity distribution (SSD) method was used to construct the SSD curves for the calculation of the Cd threshold by analyzing the experimental data. The sensitivity analysis results based on the SSD curves revealed that the sensitivities to Cd in rice varieties under the same tillage system were substantially different but almost the same under different tillage systems. These results can help select rice varieties with low Cd sensitivity for crop safety. Different tillage systems at the same site varied in their influence on Cd threshold values. Cd threshold values under early rice-late rice (e.g., 0.27, 0.28 mg/kg in Xiangtan City) and early rice-vegetable (e.g., 0.26, 0.31 mg/kg in Xiangtan City) tillage systems were roughly lower than that under the early rice-fallow tillage system (e.g., 0.33, 0.35 mg/kg in Xiangtan City). Notably, the influence of tillage systems resulted in Cd threshold values being generally lower than the Cd risk screening values of the current Chinese soil environmental quality standard. Analysis of the influence of different tillage systems on the Cd threshold is beneficial for the optimization of farmland soil environmental quality standards.

Spatial Distribution and Sources of Heavy Metals in Soil of a Typical Lead-Zinc Mining Area, Yangshuo

Taking a typical lead-zinc mining area in Yangshuo county, Guangxi as the research object, the contents of 10 metal elements (Cr, Mn, Ni, Cu, Zn, As, Cd, Sb, Hg, and Pb) in the surface soil of Sidihe River basin in Yangshuo were analyzed and determined. Pearson correlation analysis, principal component analysis (PCA), positive definite matrix factorization (PMF), and other methods were comprehensively used to quantitatively analyze their contributions and identify pollution sources. In total, 168 surface soil samples were collected across the study area. The mean concentrations of Zn, Cd, Hg, and Pb in the soils were higher than the National Environmental Quality Standards for Soils in China. The mean contents of Sb, Cd, Cu, Pb, and Zn were higher than their corresponding local background values by approximately 1.01, 5.50, 3.29, 9.11, and 10.67 times, respectively, indicating that heavy metals have been enriched in topsoil. The Igeo showed that the major pollutant element in the soils was Hg, followed by Pb, Zn, and Mn. Correlation analysis and principal component analysis showed that the sources of metal pollution in surface soil in the study area were complex and mainly from human activities. Cu, Zn, Cd, Sb, As, and Pb were mainly derived from mining activities; Hg, Cr, and Ni were controlled by soil parent material sources; and Mn and Cd were mainly derived from mining activities and agricultural activities. PMF model analysis results showed that the metal pollution sources in the surface soil were jointly affected by these three sources. Mining activities, natural sources, and a mixed source of mining activities and agricultural activities were the main sources of heavy metal pollution in the soils, accounting for 58.0%, 13.5%, and 28.6% of the total heavy metal accumulation, respectively. Ni, Cu, Zn, As, Sb, Hg, and Pb were derived mainly from mining activities. Cr, Ni, and Hg were mainly attributed to natural sources, such as soil parent materials and rainfall erosion (44.6%, 23.2%, and 21.0%, respectively), and Mn and Cd were associated with a mixed source of mining activities and agricultural activities (75.4% and 70.4%).

Health risk assessment of heavy metals in soils and food crops from a coexist area of heavily industrialized and intensively cropping in the Chengdu Plain, Sichuan, China.

Environmental pollution caused by rapid industrial activities are becoming increasingly drastic, particularly its impact on soil and plant health. The present study was conducted to investigate the heavy metal (loid) (As, Cd, Cu, Hg, Pb, and Zn) concentrations in soils and food biomass crops and estimate the potential health risks of metals to humans via consumption of contaminated food biomass crops from Shifang, a periurban agricultural areas in the Chengdu Plain, Sichuan, China. Results revealed that the soils have been experiencing a substantial accumulation of heavy metals, especially for Cd, with a mean of 0.84 mg kg−1, about six times higher than the background values, of which 98% exceeded the pollution warning threshold of the China Soil Environmental Quality Standards. A total of 78% of all the grain part failed the national food standard for Cd. No significantly positive relationships between metal levels in food biomass crops and in the corresponding soils, indicated metals enrichment in soils were not entirely reflected to crops contaminant burdens. Estimated daily intake (EDI) of all the metals except for Pb, exceeded the oral reference dose (RfD) or the minimal risk levels recommended by USEPA and ATSDR. Target hazard quotients (THQs) of all the metals except for Cd was less than one indicated that potential health risk to the local inhabitant originated mainly from Cd exposure via cereals consumption. Mitigation strategies to curtail Cd-contaminated soils and crops Cd burdens need careful tailoring to meet the needs of health and safety in this region.

Distribution characteristics and potential ecological risk assessment of heavy metals in soils around Shannan landfill site, Tibet.

At present, sanitary landfill is mainly used for domestic waste treatment in Shannan City, Tibet. However, there are few studies on heavy metals in the soil around the landfill in Shannan city. Therefore, the surrounding soil of Luqionggang landfill in Shannan City, Tibet Autonomous Region, is taken as the research object. In the study, the geo-accumulation index method, Nemerow comprehensive pollution index method and potential ecological risk index method are mainly used to evaluate the pollution and risk of heavy metals in the soil around the landfill site. The main results are as follows: The average pH value of the soil around the landfill site is 9.37, belonging to the strong alkaline range. The average values of heavy metals Hg and Ni in soil exceeded the background content, and the average contents of other heavy metals Cu, Pb, Zn, Cr, As and Cd did not exceed the background content. The average content of these eight heavy metals did not exceed the screening value of the national soil environmental quality standard. In the horizontal direction, the average content of heavy metal elements Cu, Cr, Cd, Hg and Ni is relatively high in the west. The average content of heavy metals As, Zn and Pb in the north, east and south is slightly higher than that in the west. And the farther away from the landfill, the less the soil is affected by heavy metals. The evaluation results of geo-accumulation index show that heavy metal Hg is the most affected. The average value of the comprehensive pollution index is 2.969, which is between 2 and 3, belonging to the moderate pollution level. And the west side of the landfill (downstream area) is greatly affected. The evaluation results of potential ecological hazard pollution index show that the potential risk index of single pollutants of heavy metals Cu, Pb, Zn, Cr, Ni, As and Cd belongs to low ecological hazard level, and the potential risk index of single pollutants of heavy metal Hg belongs to relatively heavy ecological hazard level. On the whole, the total potential risk coefficient belongs to medium pollution hazard degree. According to the correlation analysis, there is no significant correlation between heavy metal elements As and Hg and the other six heavy metal elements. In addition, the pollution source of heavy metal As may be mainly soil forming factors and the pollution source of Hg may be mainly human factors.

Probabilistic risk assessment of heavy metals in urban farmland soils of a typical oasis city in northwest China

Previous studies lacked quantitative evaluation studies of the probability of ecology and human health risks from soil heavy metals. This study assessed heavy metal risk level by collecting topsoil samples from a typical oasis city (Wuwei) in northwest China and then quantitatively evaluating the ecological risk from heavy metals by incorporating the uncertainty of health risk model parameters into the risk assessment. This study found that anthropogenic activities have influenced the accumulation of heavy metals in the study area and that the risk of contamination of soil heavy metals was characterized as light to moderate contamination and low ecological risk. On this basis, the species sensitivity distribution curves of heavy metals were constructed using species acute toxicity data, the predicted no effect concentrations of heavy metals were derived, and a probabilistic ecological risk evaluation was conducted. The results show that the current soil environmental quality standards in China are not effective in protecting species diversity. In addition, the probability of ecological risk for Cr, Ni and As in the study area was 63.3%, 23.8% and 7.1%, however, traditional pollution assessment methods underestimate the hazard of Cr. Monte Carlo simulations have shown that the probability of the carcinogenic risk of Cr (adults: 79.4%; children: 94.5%) and As (adults: 78.9%; children: 94.0%) is high, the probability of the total carcinogenic risk exceeding 1E-06 is 99.0%, the probability of the non-carcinogenic risk is low, and the slope factor and reference dose can significantly affect the evaluation of human health risks.