Metals In Farmland Soils Research Articles

Pollution Characteristics, Spatial Distribution, and Evaluation of Heavy Metal(loid)s in Farmland Soils in a Typical Mountainous Hilly Area in China.

Heavy metal(loid)s pollution in farmland soil is not only a serious environmental but also a human health-related issue. Accurate understanding and evaluation of heavy metal pollution levels in the soil are very important for sustainable agricultural development and food safety. Mountainous and hilly areas have the dual functions of industrial development and agricultural production, and the farmland soil in these areas is more susceptible to heavy metal pollution. In this study, the single factor index, Nemerow index, geo-accumulation index, enrichment factor index, and potential ecological risk indices, which are mainly used to assess the contamination and risk of heavy metals in farmland soils. The sources of heavy metals in agricultural soils of the study area were analyzed using correlation analysis and principal component analysis. Finally, geostatistical methods were used to map the heavy metal contamination of farmland soils. An average concentration of all heavy metals (except As) in farmland soils of the study area exceeded the corresponding background values, as indicated by the obtained results. The results of the principal component analysis showed that the heavy metal sources in the soils of the study area can be classified into two groups. The five pollutant index methods all showed the most serious Hg pollution in the study area. The integrated pollutant mapping results showed that the risk of heavy metal pollution in the study area was mostly moderate, except for the western and central parts of the region. This study enhances understanding of the pollution levers of heavy metals in Yiyuan farmland soils, and also can facilitate the monitoring of heavy metal contaminants at the primary stage of the food chain and assess the risk of the presence of heavy metal contaminants in food, thus improving the health of the residents.

Spatial Distribution Pattern and Pollution Evaluation of Heavy Metals in Farmland Soil in Guangxi

Farmland soil is an indispensable natural resource in agricultural production. A macro analysis of the spatial distribution and pollution level of heavy metals can provide a scientific basis for future farmland pollution control. Based on the measured data of heavy metals in farmland soil in Guangxi since 2014, the spatial distribution characteristics of 6 heavy metals in farmland soil, namely Pb, As, Cd, Cr, Zn and Cu, were discussed, and the pollution status was evaluated using the geo accumulation index method. The results showed that the average values of Pb, As, Cd, Cr, Zn, Cu in farmland soil were higher than the background values of farmland soil in Guangxi. The average contents of Pb, As, Cd, Zn in farmland soil exceeded the soil environmental quality standard (GB15618-2018), and Cr and Cu did not exceed the standard; The spatial distribution characteristics of heavy metals in farmland soils in Guangxi are obviously different. Generally, the content of heavy metals in the middle and north regions is higher than that in the south regions; The land accumulation index is in the order of Zn>Pb>Cd>As>Cu>Cr, in which the average <i>I_geo</i> values of As, Cu and Cr in farmland soil are all less than 0, while affected by local mining activities, the average <i>I_geo</i> values of Zn, Pb and Cd in soil are higher.

Risk Assessment and Sources of Heavy Metals in Farmland Soils of Yellow River Irrigation Area of Ningxia

The farmland environment is directly related to the quality and safety of agricultural products. In order to understand the characteristics and main influencing factors of heavy metals in farmland soil in the Yellow River irrigation area of Ningxia, sampling and monitoring were conducted for five consecutive years from 2017 to 2021, and the distribution characteristics and correlation of heavy metals were analyzed. The pollution status and potential ecological risks of heavy metals were evaluated, and the main sources of heavy metals in farmland were analyzed. The results showed that the average values of Pb, As, Zn, Ni, Cu, Hg, Cr, and Cd in the soil of the Ningxia Yellow River irrigation area were 19.74, 11.67, 66.88, 29.09, 22.55, 0.03, 62.27, and 0.19 mg·kg-1, respectively, which were enriched to some extent compared with the background values of the soil environment in Ningxia. Among them, Hg and Cd had middle- and high-grade ecological risk points; however, none of them exceeded the control value of agricultural land soil pollution risk, and all sampling sites had no high-risk or extremely high-risk levels. The results of source analysis based on positive matrix factorization (PMF) and correlation analysis showed that there were five main sources of heavy metals in farmland soil in the study area: natural sources, mixed sources of industrial and mining activities and the production and life of residents, transportation sources, agricultural production activities sources, and industrial sources, with contribution rates of 26.54%, 25.59%, 22.52%, 15.63%, and 9.72%, respectively. On the whole, the heavy metals in farmland soil in the Ningxia Yellow River irrigation area did not exceed the standard, and there was no high-level ecological risk. The production environment of the farmland soil was good, but the contribution rate of human activities to soil heavy metals was large.

Application of Pb Isotopes and REY Patterns in Tracing Heavy Metals in Farmland Soils from the Upper-Middle Area of Yangtze River.

Farmland heavy metal pollution-caused by both human activity and natural processes-is a major global issue. In the current study, principal component analysis (PCA), cluster analysis (CA), rare earth elements and yttrium (REY) analysis, and isotope fingerprinting were combined to identify sources of heavy metal pollution in soil from different farmland types in the upper-middle area of the Yangtze River. The concentrations of Zn and Cu were found to be higher in the vegetable base and tea plantation soil compared with their concentrations in the orangery soil. On the other hand, greater accumulation of Cd and Pb was observed in the orangery soil versus the vegetable base and tea plantation soils. Influenced by the type of bedrock, REY was significantly enriched in the orangery soil and depleted in the vegetable base soil, as compared with the tea plantation soil. The Pb isotopic compositions of the tea plantation (1.173-1.193 for 206Pb/207Pb and 2.070-2.110 for 208Pb/206Pb) and vegetable base (1.181-1.217 for 206Pb/207Pb and 2.052-2.116 for 208Pb/206Pb) soils were comparable to those of coal combustion soil. The compositions of 206Pb/207Pb (1.149-1.170) and 208Pb/206Pb (2.121-2.143) in the orangery soil fell between those observed in soils obtained from coal combustion and ore smelting sites. Using the IsoSource model, the atmospheric Pb contributions of the vegetable base, tea plantation, and orangery soils were calculated to be 66.6%, 90.1%, and 82.0%, respectively, and the bedrock contributions of Pb were calculated to be 33.3%, 9.90%, and 18.1%, respectively. Based on the PCA, CA, and REY results, as well as the Pb isotope model, it appears that heavy metals in the orangery soil may be derived from atmospheric deposition and bedrock weathering, while heavy metals in the vegetable base and tea plantation soils may be derived from mining and the use of fertilizer.

Speciation Analysis and Pollution Assessment of Heavy Metals in Farmland Soil of a Typical Mining Area: A Case Study of Dachang Tin Polymetallic Ore, Guangxi

To explore the distribution characteristics and degree of pollution of heavy metals in the farmland soil around the Dachang tin polymetallic mining area in Guangxi, a total of 140 soil samples were collected around the mining area in this study. The total amount and various forms of seven heavy metals (Cu, Pb, Cd, Cr, Zn, As, and Ni) were analyzed by inductively coupled plasma mass spectrometry, and the improved continuous extraction method of heavy metal speciation analysis in the soil, the potential ecological risk index (RI), the and Nemerow evaluation index (PN) were used to evaluate pollution characteristics of the soil and the bioavailability of heavy metals. Corresponding remediation suggestions were given according to the pollution degree. The results show that the whole soil in the study area is acidic, reducing, and the content of organic matter is low. The average content of heavy metal elements is higher than the background value of Guangxi, among which Cd, Pb, and As exceed the control value and are the main elements of pollution. The speciation analysis of heavy metals in soil shows that Cd is dominated by the ion exchange form; Cu is mainly residual and in a humic acid combined form; and the rest of the elements are mainly in residual form. Among the seven heavy metals, Cd has the strongest mobility, biological toxicity, and ecological risk, followed by As, Ni, and Zn. The overall pollution level of the soil in the study area is heavily polluted (PN = 39.6), which is a very strong ecological risk level (RI = 2196.9), and the main pollutants are Pb, As, and Cd; Cd pollution is the most serious. Correlation (CA) and principal component analysis (PCA) indicate that the pollution sources of Pb, Cu, Zn, Cd, and As among the seven elements were mainly controlled by tailings accumulation, mining, and transportation, and the sources of Cr and Ni were controlled by soil-forming parent materials. Furthermore, according to the actual situation of the farmland around the mining area, two remediation suggestions are put forward: (1) use stabilization remediation technology to clean up the pollution source, such as calcium dihydrogen phosphate to reduce the bioavailability of the most polluted elements, Cd and Pb, in the soil; (2) under the concept of green environmental protection, use Typha orientalis Presl to repair the industrial and mining wasteland and some unused land.

Distribution characteristics, source analysis and health risk assessment of heavy metals in farmland soil in Shiquan County, Shaanxi Province

Soil heavy metal pollution can cause irreversible harm to the ecological environment and human health. A total of 678 surface soil samples and 60 crop samples were collected to study the contamination level, source of heavy metals and human health risk in agricultural soil in central Shiquan County. The results show that the arithmetic mean values of chromium, copper, zinc, arsenic, lead, nickel, cadmium, and mercury in the soils of the study area were 1.67, 2.17, 1.73, 1.25, 1.24, 1.86, 5.04 and 2.17 times of their background values, respectively. However, the risk control standards for agricultural soil pollution in China were not exceeded. The high-value areas of soil heavy metals Cr, Cu, Zn, Ni, Cd, and Hg are mainly distributed in the northwest-southwest area of the study region. The results of the geo-accumulation index (Igeo) showed that the pollution levels of heavy metals in soil were in the order of Cd (0.98) > Cu (0.40) > Hg (0.20) > Ni (0.19) > Zn (0.14) > Cr (0.06) > Pb (−0.30) > As (−0.81). In addition, the soil cadmium contamination factor (CF) was 5.04, the pollution load index (PLI) was 2.97, which were significantly higher than other metals contamination levels. It indicates that cadmium pollution reaches a high level. Correlation analysis and principal component analysis (PCA) showed that Cr, Cu, Zn, As, Ni, Cd and Hg in soil were mainly derived from industrial pollution, while Pb was derived from soil parent material. The soil environment in the study area will not cause non-carcinogenic effects on adults and children. It is necessary to pay attention to the high risk of cancer caused by Cr in local residents. The excessive rate of heavy metals in vegetable crops in the study area was significantly higher than that in paddy. The results can provide basic information for soil heavy metal control and crop planting planning in Shiquan County.

Risk assessment and source apportionment of heavy metalloids from typical farmlands provinces in China

Potentially toxic metals in farmland soil have recently become a significant environmental concern in China. In this study, the occurrence and distribution of eight (8) heavy metals (HMs) were investigated from 54 topsoil samples obtained across 18 provinces. Human health and ecological hazards associated with HMs were assessed through different risk characterization indices and their sources predicted. The statistically mean concentrations of HMs ranged from 0.08 to 70.05 mg kg−1, which were below the determined threshold values for agricultural lands according to the Chinese National Standard (GB 15618–2018). The respective ecological risk index (Eri) of HMs revealed that they posed a lower risk (Eri<40) but their potential cumulative ecological risk (RI) was determined as a considerable risk (300 ≤ RI < 600). Spatial distribution and heterogeneities of HMs were found to be highly concentrated in the southern parts (e.g., Yunnan, Guangdong) of China, particularly for Arsenic (As), Zinc (Zn), and Chromium (Cr). PMF model was found capable of efficiently elucidating respective sources of HMs across the studied provinces as most were impacted by geological/pedogenic and anthropogenic activities (e.g., agricultural, industrial discharge fallouts). Probabilistic health risk assessment indicated that the non-carcinogenic risk (NCR) and total carcinogenic risk (TCR) of HMs in both adults and children were low and acceptable.

A review on adsorption characteristics and influencing mechanism of heavy metals in farmland soil.

The accumulation of heavy metals in soil and crops is considered to be a severe environmental problem due to its various harmful effects on animals and plants. Soil adsorption is an essential characteristic of mud, which is the fundamental reason for soil to have a specific self-purification capacity and environmental capacity for heavy metals. The adsorption of heavy metals by soil reduces the uptake of these pollutants by crops, thereby limiting food contamination. Therefore, the adsorption of heavy metals in crop soils was taken as the primary research object. Based on the entire reading of the literature, the previous research results were compared and discussed from the four aspects of heterogeneity, physical and chemical properties, competitive adsorption, and external factors. The influencing mechanism of heavy metal adsorption characteristics in soil was reviewed. Finally, suggestions and prospects for future research on heavy metal adsorption were put forward.

Contamination, Source Apportionment, and Health Risk Assessment of Heavy Metals in Farmland Soils Surrounding a Typical Copper Tailings Pond.

Tailings resulting from mining and smelting activities may cause soil heavy-metal pollution and harm human health. To evaluate the environmental impact of heavy metals from tailings on farmland soils in the surrounding area, heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) in tailings and farmland soils in the vicinity of a typical copper tailings pond were analyzed. Contamination status, potential sources, and health risks for farmland soils were investigated. The results showed that the tailings contained a high concentration of Cu (1136.23 mg/kg). The concentrations of Cd and Cu in the farmland soils exceeded the soil quality standard. The geoaccumulation index (Igeo) indicated that the soils were moderately polluted by Cu and Cd, and slightly polluted by Ni, Cr, and Zn. The absolute principal component scores-multiple linear regression (APCS-MLR) model was applied for source apportionment. The results showed that tailings release is the main source of soil heavy-metals contamination, accounting for 35.81%, followed by agricultural activities (19.41%) and traffic emission (16.31%). The health risk assessment suggested that the children in the study region were exposed to non-carcinogenic risks caused by As, while the non-carcinogenic risk to adults and the carcinogenic risk to both adults and children were at acceptable levels. It is necessary to take effective measures to control heavy-metal contamination from tailings releases to protect humans, especially children, from adverse health risks.

Estimating the heavy metal contents in farmland soil from hyperspectral images based on Stacked AdaBoost ensemble learning

• Assessment of heavy metal pollution in soil base on hyperspectral image. • Estimating the soil heavy metal content by constructing ensemble learning model. • The estimation accuracy of heavy metal content in soil is improved. • Mapping the distribution trend of heavy metals in farmland soil. • The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Heavy metal pollution poses a huge challenge to the soil environment. With the increasing pollution level, the traditional monitoring methods cannot quickly obtain information on large-area pollution. Therefore, a large-scale mapping method with high precision is urgently needed to effectively control heavy metal pollution. This study explored a method for mapping soil heavy metal concentrations through hyperspectral images. On this basis, a new Stacked AdaBoost ensemble learning algorithm was constructed to construct the inversion model of soil heavy metal contents. The characteristic spectral bands of heavy metals were extracted as model input variables using Pearson’s correlation coefficient and successive projections algorithm. With three sets of heavy metal content data, the prediction accuracy and mapping outcomes of various machine learning methods were compared. Furthermore, the potential sources of heavy metal pollution in the study area were analyzed based on the Moran’s index. The results showed that the Stacked AdaBoost model was relatively stable with higher accuracy than traditional machine learning models. For Cr, Cu, and As, the determination coefficients ( R 2 ) of the verification set were 0.66, 0.61, and 0.74, respectively. Afterward, the results of this model were used to map the heavy metal concentration over the study area. The mapping results suggested that the heavy metal conditions of soils in the Ganhetan area were caused by nature and human activities. The As pollution in agricultural soils was the most serious, with an exceedance rate of 38.66%. Industrial areas were potential sources of soil heavy metal pollution in the study area. In summary, the Stacked AdaBoost ensemble learning model provides detailed and reliable data for agricultural ecological protection and industrial pollution control, allowing the effective management of heavy metal pollution sources.

Pollution characteristics and source identification of farmland soils in Pb-Zn mining areas through an integrated approach.

Long-term mining activities have caused serious heavy metals contamination of farmland soils. In this study, we investigated the concentrations, distributions, accumulations, potential ecological risk, and sources of eight heavy metals in farmland soils of Pb-Zn mining areas. According to the soil standard GB15618-2018, Cd was the most contaminated, followed by Pb and Zn. The geo-accumulation index showed that Pb, Zn, Cd, and Hg accumulated seriously. The potential risk index indicated that Cd, Hg, and Pb were the main environmental risk elements. An integrated approach combining multivariate statistical analysis, PMF, and GIS mapping was used to analyze the sources of heavy metals. Four main sources were identified and quantified: (1) mining activities source, the main source of Cd (71.09%) and Zn (61.88%); (2) agricultural activities source, dominated by Hg (73.01%); (3) atmospheric deposition sources, with Pb (85.11%) as the main contributor; (4) natural source, characterized by Cr (72.96%), Ni (66.04%), As (55.98%) and Cu (37.70%). This study would help us understand the pollution characteristics and sources of farmland soils in mining areas and provide basic information for the next step of pollution control and remediation.

Heavy metal pollution and risk assessment of farmland soil around abandoned domestic waste dump in Kaifeng City

In order to understand the heavy metal pollution and potential ecological risk of farmland soil around the waste dump in the eastern suburb of Kaifeng clearly and provide a scientific basis for the remediation of heavy metals in farmland soil, the single factor pollution index method, Nemero comprehensive pollution index method and Hakanson potential ecological risk method were used to evaluate the heavy metal pollution status and potential ecological risk degree of farmland in this area at the same time. The ArcGIS software was employed to map the spatial distribution of heavy metal pollution and potential ecological risks. The results show that the average values of heavy metals in this area are higher than the soil Background Value of Kaifeng City, and the problem of excessive heavy metals in the soil is significant. Of the 41 surface soil samples, Cd’s heavy and moderate pollution rates were up to 15% and 38%, respectively, and the potential ecological risk caused by Cd element was quite serious, and more than 35% of the soil samples were at higher potential ecological risk. The comprehensive review results showed that 38% of the samples were heavy pollution, and 23% of the sample soils were at higher potential ecological risk. The spatial distribution characterized by the levels of most heavy metals and the extent of potential ecological risk showed high levels in the center of the dump, with a gradual decrease towards the outward radiation zone. This means dust and leachate from waste dump are major causes of heavy metal contamination and potential ecological risks. In addition, the retrieval of the waste mound soil from landfills by villagers as soil fertilizer for rapeseed also caused, to some extent, the transfer of the waste mound contaminants.

How do controlled-release fertilizer coated microplastics dynamically affect Cd availability by regulating Fe species and DOC content in soil?

Microplastics (MPs) affect the accumulation of heavy metals by regulating the soil environment. However, studies on the dynamic effects of microplastics on the available states of heavy metals in soil are lacking. In particular, how controlled-release fertilizer coated microplastics can synergistically change the avsilable states of heavy metals in soil by affecting soil physical and chemical properties and microbial community structure is still lacking. The dynamic effect of polyurethane (PU) MPs on the effective state of soil cadmium (Cd; DGTCd), at different particle sizes and concentrations, was studied in situ by diffusive gradient in thin-films (DGT) for the first time. The bioavailability, soil chemical properties, and microbial effects of PU MPs on Cd depend on PU particle size and concentration; high-concentration (1 %) PU MPs cause a significant increase in DGT-Cd concentration. The addition of PU MPs decreased soil pH and dissolved organic carbon (DOC), while increasing the absolute zeta value, Fe(II) and Mn(II), in a manner dependent on particle size, concentration, and culture time. Correlation analysis combined with path analysis showed that PU MPs affected the effective state of Cd by changing soil properties, among which Fe(II) content and DOC were important factors controlling the activation of Cd. Meanwhile, changes in soil properties and heavy metal availability correlated significantly with microbial community composition, suggesting that PU MPs may indirectly impact heavy metal activity by affecting microorganisms and functional genes associated with C and Fe cycling. Therefore, when the concentration of PU MPs is higher than 1 %, we should strengthen ecological risk prevention and control of the compound pollution of controlled-release fertilizer coated microplastics and heavy metals in farmland soil.

Stabilization and Ecological Risk Evaluation of Heavy Metals in Farmland Soils by Addition of Attapulgite Modified with Phosphates

Purpose. Attapulgite was modified by sodium dihydrogen phosphate, oxalic acid-activated phosphate rock powder, potassium dihydrogen phosphate, calcium superphosphate, ammonium dihydrogen phosphate, and fused calcium-magnesium phosphate and used in the remediation of Cd, Zn, and Ni. Materials and Methods. Attapulgite was modified by six kinds of phosphate (ratio: 1 : 2), and the improvement effect of passivation material on soil polluted by cadmium, zinc, and nickel was determined. CaCl2-extractable and toxicity characteristic leaching procedure- (TCLP-) extractable Cd, Zn, and Ni were measured in order to estimate the bioavailability and the stabilization efficiency. Pot experiment was conducted to study the enrichment and transport ability of Cd, Zn, and Ni in corn. The ecological risk and ecological toxicity of soil environment were evaluated by calculating SEm, ERIm, CRIm, and BUF. Results and Discussion. Compared with ATP, passivation materials AAPR, AMRP, ASSP, AMAP, and AFMP can improve the stability of CD, Zn, and Ni in soil, and AAPR has the best effect. Compared with CK treatments and ATP treatments, the concentrations of TCLP-extractable Cd decreased by 30.80% and 24.72%, respectively, the concentrations of TCLP-extractable Zn decreased by 15.50% and 11.18%, respectively, and the concentrations of TCLP-extractable Ni decreased by 31.34% and 23.20%, respectively. Compared with ATP treatments, CRI, BUF-Cd, BUF-Ni, and BUF-Zn decreased by 24.67%, 52.88%, 78.73%, and 41.18%, respectively, in the AAPR treatments. Conclusions. Phosphate-modified attapulgite can effectively improve the stability of heavy metals in soil and reduce the migration of heavy metals. In the soil polluted by Cd, Zn, and Ni, the passivation effect of AAPR is the best. Therefore, AAPR can be used as an economical, safe, and effective passivation material to improve Cd-, Zn-, and Ni-contaminated soil, which would have a high utilization value in field applications.

The use of some weeds type in the disposal of heavy metals in contaminated soil

Heavy metals have much concern for communities with overpopulations due to their lack of biodegradability, which becomes contaminated to agricultural soil and agricultural products. This research employed Polyogon monospeliensis and Phalaris minor for cleanup Pb, Cd, and Co metals in farmland soils to assess their biological properties as natural accumulators. The total uptake by weed biomass ranged from 0.23 to16.86 (Pb), 0.11 to 9.31 (Cd) and 0.18 to 9.76 (Co) µg kg -1 for P. minor and 0.38 to 29.29 (Pb), 0.14 to 0.19.22 (Cd) and 0.23 to 20.76 (Co) µg kg−1 for P. monospensis respectively. These findings suggest that the concentration of heavy metals steadily increased in weed biomass with increasing pollution of the soil. The metals accumulation by weeds has a varied response to the weed species, metal type and the used concentration. The ordered sequence of tested metals remediation was ranked as follows; Pb > Cd > Co for metals. Based on bioconcentration factor (BCF) and contamination index (Ci), P. monospensis is a hyper-accumulator with appropriate growth and P. minor is a medium accumulator with negatively affected growth in a higher concentration of metals. The spreading of these weeds is widely in the winter of Egypt, thus they could be used to remediate polluted soil and protect the ecosystem with good efficiency.

Source analysis and ecological risk assessment of heavy metals in farmland soils around heavy metal industry in Anxin County

Studying the pollution status, spatial distribution characteristics, and sources of heavy metals in farmland soil in Anxin County will provide a method basis for the next step of soil remediation. This study investigates the contents of Zn, Cu, Pb, Cd, and Ni in wheat grains and soil samples. Moreover, different methods are used to evaluate soil heavy metal pollution. The results show that the soil in the study area is weakly alkaline. Cu, Zn, and Ni contents in the ground are lower than the risk screening values for soil contamination of agricultural land. In comparison, Cd and Pb contents are higher than the screening value of soil pollution risk of agricultural land, and the proportion of points lower than the control value of soil pollution risk of agricultural land are 64.58% and 16.67%, respectively. The farmland with high Cd and Pb content is mainly distributed near roads and factories and concentrated primarily on 0-20 cm topsoil. The Cd content in wheat grains meets the standard, but 4.17% of the samples are close to 0.1 mg kg−1 (more than 0.09 mg kg−1). The Pb content of 50% of the wheat grain samples exceeds the lead limit in the standard. The evaluation results of the single factor pollution index and geoaccumulation index show that the pollution degree of heavy metals in the soil is Cd > Pb > Cu > Zn > Ni. The potential ecological risk index in the study area is 288.83, and the soil heavy metal pollution is at a moderate-considerable ecological risk level. The average value of Cd's single-factor environmental risk index is 233.51, which belongs to the high environmental risk and is the main influencing factor. Cd and Pb in soil are significantly disturbed by the production activities of heavy metal processing enterprises around the farmland. It is speculated that there are two primary sources of soil heavy metal pollution in the study area. Cd, Pb, Zn, and Cu are mainly industrial and mobile sources, and Ni is primarily agricultural and natural sources.

Effects of soil properties on heavy metal bioavailability and accumulation in crop grains under different farmland use patterns

Mining activities have increased the accumulation of heavy metals in farmland soil and in food crops. To identify the key soil properties influencing heavy metal bioavailability and accumulation in food crops, 81 crop samples and 81 corresponding agricultural soil samples were collected from rape, wheat, and paddy fields. Heavy metal (copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), iron (Fe), and manganese (Mn)) concentrations in soils and rape, wheat, rice grains were determined using inductively coupled plasma atomic emission spectroscopy, and soil physicochemical properties (pH, organic matter, total nitrogen, total phosphorus, available phosphorus, and available potassium (AK)) were analyzed. Soil extractable metals were extracted using various single extractants (DTPA, EDTA, NH4OAc, NH4NO3, and HCl). The average concentrations of Cu, Zn, Pb, Cd, and Mn in the soil samples all exceeded the local geochemical background value (background values of Cu, Zn, Pb, Cd, and Mn are 43.0, 81.0, 28.5, 0.196, and 616 mg/kg, respectively), and Cd over-standard rate was the highest, at 98%. Furthermore, soil total Cd concentrations (0.1–24.8 mg/kg) of more than 86% of the samples exceeded the soil pollution risk screening value (GB 15618-2018). The sources of Cu, Zn, Pb, Cd, and Mn in soils were mainly associated with mining activities. The key factors influencing heavy metal bioavailability were associated with the types of extractants (complexing agents or neutral salt extractants) and the metals. Cd and Pb concentrations in most wheat and rice grain samples exceeded the maximum allowable Cd and Pb levels in food, respectively, and Cd concentrations in approximately 10% of the rice grain samples exceeded 1.0 mg/kg. Furthermore, rice and wheat grains exhibited higher Cd accumulation capacity than rape grains, and despite the high soil Cd concentrations in the rape fields, the rape grains were safe for consumption. High soil pH and AK restricted Cd and Cu accumulation in wheat grains, respectively. Soil properties seemed to influence heavy metal accumulation in rice grains the most.

Distribution Characteristics of Heavy Metals in Farmland Soils Around Mining Areas and Pollution Assessment

In order to explore the spatial distribution and ecological risk of heavy metals in farmland soil around Tongguan Mining area, surface soil samples from Tongguan Mining area were collected in September 2020, and the contents and distribution characteristics of eight heavy metals (Pb, Cu, Cd, Hg, Cr, Ni, Zn, and As) in the samples were analyzed. The Nemerow comprehensive pollution index and potential ecological risk index were used to evaluate soil pollution. The results showed that the contents of the eight types of heavy metal elements in this area exceeded the standard, and the exceeding rates were 97.91%, 84.79%, 100%, 95.41%, 96.87%, 98.54%, 91.45%, and 28.95%, respectively. The variation coefficients of the eight heavy metals were ranked as Hg>Pb>Cu>Cd>Zn>As>Ni>Cr. The variation coefficients of Hg, Pb, Cu, Cd, and Zn were all greater than 1. Correlation analysis showed that these five heavy metals were obviously correlated. In terms of spatial distribution, Pb, Cd, Cu, Hg, Zn, and As were distributed in patches, whereas Cr and Ni were distributed in flakes. The high values of Hg, Cd, Pb, Cu, and Zn were mainly distributed in the southern and central part of the study area. The comprehensive pollution of Nemerow showed that the severe pollution rate reached 87.91%, and the moderate pollution rate and the mild pollution rate were 9.58% and 2.5%, respectively; thus, the overall pollution was severe. The potential ecological risk index showed that Hg, Cd, Pb, and Cu were the main risk elements. The total potential ecological risk index showed that the proportion of samples with strong pollution was 97.08%, and the proportion of extremely strongly, very strongly, and strongly polluted samples were 55.63%, 27.08%, and 14.37%, respectively, indicating that the overall potential ecological risk in the study area was very strong. Combining the two pollution assessment methods, it can be seen that the heavy metal pollution around Tongguan mining area, primarily by Hg, Cd, and Pb, was serious. These results can provide data support for regional pollution control, soil remediation, and ecological protection. It is suggested that the state of soil heavy metal pollution and its transformation in various media should be monitored continuously in the future.

Pollution Properties and Ecological Risk Assessment of Heavy Metals in Farmland Soils and Crops Around a Typical Manganese Mining Area

In order to assess the ecological risks of heavy metals and explore the pattern of heavy metal migration between farmland and corresponding crops in a typical and closed manganese mining area in Hunan province, farmland soils and crops surrounding the mining area (pollution area) and away from the mining area (control area) were collected, and then the contents of Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb were analyzed. The sources and distribution of heavy metals in farmland soils were analyzed using Kriging spatial interpolation and principal component analysis, and the ecological risk was evaluated using the single factor index, comprehensive pollution index, and potential ecological risk index. The results showed that the surrounding farmland soils in the closed Manganese mining area presented serious pollution of Cd, Zn, As, and Mn, in which the average contents of the above heavy metals in the dry land soil in the polluted area were 6.22, 612.28, 37.72, and 1506.2 mg·kg-1, respectively. Compared with the soil risk screening value of agricultural land, the over-standard rates of Cd, Zn, and As were 88.41%, 94.20%, and 84.06%, respectively, and the average content of Mn in the farmland soil was three times that of the background value in the Hunan soil; however, the heavy metal pollution in the paddy field was relatively light. The principal component analysis showed that the sources of Cd, Mn, and Zn in the farmland soil were related to the manganese ore mining, whereas the source of As in the farmland soil might originate from agricultural activities. The pollution area was at a heavy pollution level, and the main pollution factors were Cd, Mn, and Zn. The Cd in the farmland soil could pose a strong potential ecological risk, but the rest of the heavy metals presented only a slight potential ecological risk. The content of Cr, Pb, and Cd in the crops in the study area exceeded the standard, and the exceeding standard rate was between 1.1% and 37.3%, where the average content of over-standard heavy metals in corn was higher than that in rice, and the average content of heavy metals in leafy vegetables was higher than that in root vegetables. The soil pollution degree of heavy metals could affect the accumulation ability of crops, and different crops had different accumulation abilities. For instance, leafy vegetables and root vegetables easily accumulated Cd and Zn; however, rice and corn separately enriched Cd and Cr, as well as Zn and Cu. The contents of heavy metals in dryland soils had a positive correlation with the content of heavy metals in corresponding crops. The contents of Cd and As in the paddy field and rice presented a positive correlation, but the remaining six heavy metal contents in rice (i.e., Cr, Mn, Ni, Cu, Zn, and Pb) did not correlate with the content of the paddy fields.

Spatial Distribution, Pollution Characteristics and Source of Heavy Metals in Farmland Soils around Antimony Mine Area, Hunan Province

Spatial Distribution, Pollution Characteristics and Source of Heavy Metals in Farmland Soils around Antimony Mine Area, Hunan Province