Metals In Farmland Soils Research Articles

Multivariate and geostatistical analyses of heavy metal pollution from different sources among farmlands in the Poyang Lake region, China

Intensive urbanization and industrialization activities have caused the continuous discharge of heavy metals into the soils of China’s Poyang Lake region, where they pose a major threat to human health. Yet, the spatial characteristics of these heavy metals in farmland soils and their pollution sources in this region remain unclear. We collected 115, 84, 26, and 987 farmland soil samples with heavy metal pollution from different sources (industrial and mining enterprises, sewage irrigation, urban, and general farming) in the Poyang Lake region, respectively. Descriptive statistics revealed that 1.1% of As, 7.3% of Cd, 0.3% of Pb, and 0.2% of Hg concentrations did surpass China’s Soil Environmental Quality Management Standard (GB 15618-2018). In addition, 32.8% of As, 74.4% of Cd, 89.2% of Pb, 45.0% of Cr, and 13.7% of Hg concentrations of soil samples exceeded the background soil concentrations of heavy metals in this region, notably Cd and Pb, whose maximum values were respectively 11.64- and 21.47-fold the background values. Compared with general farming areas, the other three pollution sources had significantly higher concentrations of As, Cd, Pb, Cr, or Hg in their soils. The results of principal component (PC) and geostatistical analyses showed that PC strongly related to mainly As and Cr was mainly influenced by natural characteristics while PC closely related to mainly Cd, Pb, and Hg was driven by mainly human activities in farmland soils from the four sources. Factor loadings for the different sources showed As and Cr on the same PCs, and Cd, Pb, and Hg on the other PCs, confirming the association of the heavy metal pollution with its sources.

Characteristics of PCDD/Fs and metals in surface soil around an iron and steel plant in North China Plain

In this study, the level of 18 species of metals and 17 species of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were monitored in surface soil samples around an iron and steel plant in the North China Plain. The concentration of PCDD/Fs and metals in the soil ranged from 0.16 to 4.5 ng I-TEQ/kg and 1.2 to 24,182.2 mg/kg, respectively. Furthermore, the prevailing winds were confirmed to influence the spatial distribution of PCDD/Fs and metals concentrations. The highest concentration of PCDD/Fs was located in downwind soil sample 4 (S4), which showed more than 50% of PCDFs in the total PCDD/Fs, and high levels of lower chlorinated PCDFs. Moreover, the highest Cd and Zn concentrations of 18.1 and 2647.8 mg/kg, respectively, were observed in soil collected from S4, which were significantly above the government guidelines for metals in farmland soil. Our results show that a group of metals (Mg, Al, K, Fe, Cu, Zn, Se, Cd, Sb and Pb) was well correlated with all PCDD/Fs except three (OCDD, 1,2,3,4,6,7,8-HpCDD and 1,2,3,7,8,9-HxCDD), which likely originated from iron and steel processes. Additionally, Pb, Zn, Cd and all polychlorinated dibenzofurans showed a good correlation and grouped in one cluster, suggesting anthropogenic sources from sintering process. Therefore, the metallic characteristics in soil, especially the Pb, Zn and Cd tracers, implied evidence of the accumulation of PCDD/Fs from sinter plants.

Analysis of Characteristics and Sources of Heavy Metals in Farmland Soils in the Xijiang River Draining of Guangxi

In order to determine the distribution characteristics of heavy metal pollution in farmland soils and related influencing factors in the Xijiang River Basin, 2187 farmland soil samples were collected and their heavy metal contents were tested. The spatial structure and distribution characteristics of heavy metal elements were studied using a combination of geostatistics theory and GIS spatial interpolation. The potential ecological risk index was employed for risk assessment. Multivariate statistical methods, such as correlation analysis and principal component analysis, were used to analyze heavy metal sources. Results showed that farmland soils in the Basin were enriched with seven kinds of heavy metal to some extent, with Cd accumulation being the most evident. T-test independent samples results showed significant differences in heavy metal content between dry and field paddy soils (P<0.05). Cd content in paddy soils was significantly higher than in corresponding dry land soils. Cd in farmland soils in Xijiang River exhibited higher potential ecological risk. Correlation analysis and principal component analysis showed that enrichment of Pb, Zn, As, Cd, and Cu in soil was due to anthropogenic factors such as mining activities, traffic, and sewage irrigation, while Ni and Cr were influenced by natural factors, such as soil parent material. High-content areas of As, Cd, Pb, Zn, and Cu in the upper reaches of the basin are all distributed in the Diaojiang River basin and the Dahuanjiang River basin. Cd was most widely distributed. The most intensive sampling sites indicated that mining activities have caused some degree of heavy metal pollution in local farmland soils.

Pollution and Ecological Risk Assessment of Heavy Metals in Farmland Soils in Yanqi County, Xinjiang, Northwest China

A total of 50 farmland soil samples were collected from the Yanqi County, Xinjiang, China, and the concentrations of eight heavy metal elements (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn) were determined by standard methods. The spatial distribution, pollution level and ecological risk status of heavy metals were analyzed based on GIS technology, the Geo-accumulation Index (Igeo), the Pollution Load Index (PLI) and the Potential Ecological Risk Index (RI). Results indicated that: (1) The average contents of Cd, Cr, Ni, Pb, and Zn of farmland soils exceeded the background values of irrigation soils in Xinjiang by 1.5, 1.40, 1.33, 2.63, and 4.92 times, respectively. Cd showed a no-pollution level, Zn showed a partially moderate pollution level, Pb showed a slight pollution level, and Cr, Cu, As, Mn, and Ni showed no-pollution level, compared to the classification standard. The PLI values of heavy metal elements of farmland soils varied from 0.83 to 1.89, with an average value of 1.29, at the moderate pollution level. (2) The Individual Potential Ecological Risk Index for heavy metals in the study area was ranked in the order of: As > Ni > Cu > Cd > Pb > Cr> Zn. The RI values of heavy metals of farmland soils varied from 3.45 to 11.34, with an average value of 6.13, at the low ecological risk level. (3) Cu and Mn of farmland soils were mainly originated from the soil parent material and topography of the study area. As, Cd, Ni and Pb were mainly originated from human activities, and Cr and Zn may originated from both natural and anthropogenic factors in the study area.

A Portable Electrochemical System for the On-Site Detection of Heavy Metals in Farmland Soil Based on Electrochemical Sensors

In this paper, a portable electrochemical system for the on-site detection of heavy metals (HMs) in farmland soil is developed, characterized, and evaluated. The system has a three-electrode configuration and includes a signal acquisition and processing device and a computer, which integrates a microcontroller-based potentiostat to implement square-wave anodic stripping voltammetry at a bismuth-film-modified glassy carbon electrode. In addition, three analysis methods, namely, the standard addition method, the bivariate regression model, and double-stripping voltammetry, were integrated into this system for the on-site detection of HMs to meet different analysis requirements. One unique characteristic of the system is its custom software, which enables calculations based on all three analysis methods. Moreover, stripping peak currents and background currents can be identified and acquired automatically by two of the developed algorithms. The system was assessed by applying it to detect Pb(II) and Cd(II) in an acetate buffer solution and acetic acid soil extracts. The interference of Cu(II) can be inhibited by adding 0.1-mM ferrocyanide to the real sample exacts by complexation. The results indicate that the system was sensitive, effective, and reliable and has broad application prospects in the field of on-site analysis. In addition, the system can be used by non-specialist personnel.

Principal Component Analysis and Ecological Risk Assessment of Heavy Metals in Farmland Soils around a Pb-Zn Mine in Southwestern China

The farmland soil around a Pb-Zn mine in southwestern China was studied. One hundred forty-nine surface soil samples were taken from 0-20 cm depth, and the contents of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were tested. The correlations among these heavy metals were studied with multivariate analysis, and the potential sources of the metals were identified. The environmental risk of the metals was evaluated with the Potential Ecological Risk Index method. The results showed that the amounts of Cd, Pb, and Zn were at relatively high level, with average concentrations of 15.56, 419.4, and 933.4mg·kg-1 respectively, indicating the soil was heavily polluted. The average concentrations of Hg and As were 0.13 and 37.3mg·kg-1, suggesting moderate soil pollution. The average concentrations of Cu, Ni, and Cr were lower than Yunnan soil background values. The multivariate analysis suggested that the sources of Cd, Pb, Zn, Hg, and As were similar and came mainly from smelting activities in the mining area. The sources of Cu, Ni, and Cr were similar and can be attributed to natural sources. The comprehensive potential ecological risk index was 2294.8, which suggested a high potential ecological risk. In general, the farmland soils in the research area were polluted seriously by the mining and industrial activities.

Using sequential indicator simulation method to define risk areas of soil heavy metals in farmland.

The heavy metals in soil have serious impacts on safety, ecological environment and human health due to their toxicity and accumulation. It is necessary to efficiently identify the risk area of heavy metals in farmland soil, which is of important significance for environment protection, pollution warning and farmland risk control. We collected 204 samples and analyzed the contents of seven kinds of heavy metals (Cu, Zn, Pb, Cd, Cr, As, Hg) in Zengcheng District of Guangzhou, China. In order to overcame the problems of the data, including the limitation of abnormal values and skewness distribution and the smooth effect with the traditional kriging methods, we used sequential indicator simulation method (SISIM) to define the spatial distribution of heavy metals, and combined Hakanson index method to identify potential ecological risk area of heavy metals in farmland. The results showed that: (1) Based on the similar accuracy of spatial prediction of soil heavy metals, the SISIM had a better expression of detail rebuild than ordinary kriging in small scale area. Compared to indicator kriging, the SISIM had less error rate (4.9%-17.1%) in uncertainty evaluation of heavy-metal risk identification. The SISIM had less smooth effect and was more applicable to simulate the spatial uncertainty assessment of soil heavy metals and risk identification. (2) There was no pollution in Zengcheng's farmland. Moderate potential ecological risk was found in the southern part of study area due to enterprise production, human activities, and river sediments. This study combined the sequential indicator simulation with Hakanson risk index method, and effectively overcame the outlier information loss and smooth effect of traditional kriging method. It provided a new way to identify the soil heavy metal risk area of farmland in uneven sampling.

Source Apportionment of Heavy Metals in Farmland Soils Around Mining Area Based on UNMIX Model

Forty-two farmland soil samples were collected from the mining area of Huize City, Yunnan Province, to identify the sources of metals in the farmland soils, and 14 selected elements in farmland soils were detected. The UNMIX model was applied to identify the sources of the metals. The inverse distance weighted interpolation method of statistical analysis in ArcGIS was used to develop a spatial distribution map of the six severely polluted metals to validate the source apportionment results of the UNMIX model. The results indicated that:① the metals, Pb, Zn, and Cd, in the studied farmland soils were seriously polluted according to the soil background values of Yunnan Province and the Chinese environmental quality standard; ② there were three potential sources of metals according to UNMIX model:source 1 was the anthropogenic sources caused by industrial activities with a source contribution rate of 16.32%; source 2 was the anthropogenic sources caused by coal combustion and fertilization with a source contribution rate of 68.26%; and source 3 was the combined sources caused by mining related activities and soil parent materials with a source contribution rate of 15.42%; and ③ the spatial distribution of selected metals was in accordance with the local land-use and the results of the UNMIX model. Therefore, the UNMIX model can be effectively applied to the source apportionment of heavy metals in farmland soils around the mining area.

The occurrences of heavy metals in farmland soils and their propagation into paddy plants.

In this research, heavy metal accumulation pattern was investigated using the data measured from the soil, paddy plants, and irrigation water samples in Jessore district in Bangladesh with the aid of principal component analysis. A total of 28 samples representing farmland soil and irrigation water along with paddy plant were collected from 28 locations in the Jessore district in November 2016. In agricultural soil, arsenic (As) and nickel (Ni) were found 2.78 and 1.11 times more concentrated than their background values. In addition, 89% of the sample sites exhibited enhanced As concentrations relative to the background value. Principal component analysis (PCA) of soil data showed strong homogeneity in many species (e.g., Ni, Cu, Fe, and As) to reflect intense agricultural activities. In contrast, Pb showed no such homogeneity in soil accumulation pattern. In plant samples, Cu, Fe, and As were strongly correlated and homologous. This homology of pollution was in agreement with the pollution homology in the agricultural soil in which the plants were grown. In irrigation water, Cu and Ni were homologous. Observation of spatial distribution and other variables indicated that the accumulation of any particular metal in paddy plants was correlated with its content in soil and irrigation water, which was influenced by the soil organic matter, soil/water pH, and other metals present in that environment.

Characteristics of Heavy Metals Pollution of Farmland and the Leaching Effect of Rainfall in Tianjin

The leaching effect of the rainfall process for removing heavy metals from farmland soils is a critical physical process. To study the leaching effect of the rainfall process on heavy metals in soil, the pollution characteristics of seven heavy metals in farmland soil have been investigated in the suburban Tianjin region by combining the current data with previously reported runoff data in the same region. There is a large difference for these tested heavy metals in soils, with Zn having the highest concentration at 106.61±56.24 mg·kg-1 and Cd having the lowest concentration at 0.31±0.31 mg·kg-1. Compared with the background value in Tianjin, only the content of Cd is at higher levels (a four-fold increase). The results from a single factor pollution index and comprehensive pollution index analysis indicate that the comprehensive pollution index ranking is Cd > Cu > Ni > Zn > As ≈ Cr > Pb. Cd, Cu, Ni, and Zn are in the moderate pollution, mild pollution, and alert level categories, respectively. Except for As, the results from a correlation analysis, the principal component analysis (PCA), and the cluster analysis indicate the possible similar origins of Cr, Ni, Cu, Zn, Cd, and Pb. The multivariate statistical analysis indicates that Cd is mainly derived from human activities, Zn, Cu, Cr, Ni, and Pb are affected by anthropogenic and natural sources, and As is mainly influenced by natural conditions. By comparing the ratios of individual heavy metals to Cr in soils and runoffs, the leaching behaviors have been studied, with the leaching capacity ranked as Cd > As > Cu ≈ Pb > Ni > Cr ≈ Zn. In summary, Cd pollution in soil is more prominent than pollution from other metals and should receive attention.

Bioavailability and soil-to-crop transfer of heavy metals in farmland soils: A case study in the Pearl River Delta, South China.

Soil-bound heavy metals are of great concern for human health due to the potential exposure via food chain transfer. In the present study, the occurrence, the bioavailability and the soil-to-crop transfer of heavy metals in farmland soils were investigated based on data from two agricultural areas, i.e. Sihui and Shunde in South China. Six heavy metals (As, Cu, Hg, Mn, Ni and Pb) were quantified in the farmland soils. The mean single pollution level indices (PI) were all lower than 1 except for Hg in soils from Shunde (PI = 1.51 ± 0.46), suggesting the farmland soils were within clean and slightly polluted by heavy metals. As, Cu, Ni and Pb were found to be mostly present in the non-bioavailable form. The majority of Hg was considered potentially bioavailable, and Mn was found to be largely bioavailable. Soil pH was an important factor influencing bioavailability of soil-bound heavy metals. The concentrations of heavy metals in vegetables from Sihui and Shunde were within the food hygiene standards, while the rice grain from Sihui was polluted by Pb (PI = 10.3 ± 23.4). Total soil concentrations of heavy metals were not correlated to their corresponding crop concentrations, instead, significant correlations were observed for bioavailable concentrations in soil. The results supported the notion that the bioavailability of the investigated heavy metals in the soil was largely responsible for their crop uptake. The soil-to-crop transfer factors based on bioavailable concentrations suggested that Cu, As and Hg in soils of the study area had greater tendency to be accumulated in the vegetables than other heavy metals, calling for further human health assessment by consuming the contaminated crops.

新疆焉耆盆地辣椒地土壤重金属污染及生态风险预警

PDF HTML阅读 XML下载 导出引用 引用提醒 新疆焉耆盆地辣椒地土壤重金属污染及生态风险预警 DOI: 10.5846/stxb201611302449 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41561073）；新疆杰出青年科技人才培养项目（qn2015jq003） Soil heavy metal pollution and ecological risk warning assessment of pepper field in Yanqi Basin, Xinjiang Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:从新疆加工辣椒主产地（焉耆盆地）采集105个辣椒地典型土壤样品，测定其中As、Cd、Cr、Cu、Mn、Ni、Pb和Zn等8种重金属元素的含量。采用污染负荷指数（Pollution load index，PLI）、潜在生态风险指数（Potential ecological risk index，RI）和生态风险预警指数（Ecological risk warning index，IER）对辣椒地土壤重金属污染及生态风险进行评价。结果表明：（1）焉耆盆地辣椒地土壤Cd、Cr、Ni、Pb和Zn含量的平均值分别超出新疆灌耕土背景值的1.65、1.40、1.32、3.21、6.42倍。辣椒地土壤Pb和Zn呈现重度污染，Cd、Cr和Ni轻度污染，As、Mn和Cu无污染。（2）土壤PLI平均值为1.40，呈现轻度污染。各重金属元素单项生态风险指数从大到小依次为：Cd、Ni、As、Cu、Pb、Cr、Zn。土壤RI平均值为18.40，属于轻微生态风险态势，IER平均值为-4.78，属于无警态势；博湖县辣椒地污染水平、潜在生态风险程度与生态风险预警等级最高，焉耆县污染水平、潜在生态风险程度与生态风险预警等级最低。（3）辣椒地土壤As、Cd、Pb与Zn主要受到人类活动的影响，Cr、Cu、Mn和Ni主要受到土壤地球化学作用的控制。Cd是焉耆盆地辣椒地生态风险等级最高的重金属元素，研究区农业生产过程中要防范Cd的污染风险。 Abstract:Heavy metals have long been recognized as pollutants that are potentially harmful to human health. In recent decades, research on heavy metals in soil environments has become a hotspot in environmental research. Under normal conditions, heavy metal concentrations in soils are several orders of magnitude higher than that in the background value of soils. Thus, the concentrations and potential ecological risks of heavy metals in farmland soils are important reference indicators for evaluating farmland soil environmental quality. Human activities are known to result in heavy metal pollution of farmland soils. Recent research in this field in China has focused on the sources, distribution, pollution, and ecological risk of heavy metals in farmland soils in the eastern or central parts. However, there has been limited research on soil contamination of farmland, particularly pepper fields, in the arid regions of northwest China. Therefore, we collected a total of 105 soil samples from pepper field in the main pepper production area (Yanqi Basin) in Xinjiang, China, and determined the content of eight heavy metals (As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn) by standard methods. The heavy metal pollution of pepper field soils was analyzed based on pollution load index (PLI), potential ecological risk index (RI), and ecological risk warning index (IER). The results indicated that the average content of Cd, Cr, Ni, Pb, and Zn exceeded 1.65, 1.40, 1.32, 3.21, and 6.42 times, respectively, that of the background values for irrigation soil in Xinjiang. High levels of Pb, and Zn pollution, low levels of Cd, Cr and Ni pollution, and no As, Mn, or Cu pollution were detected in pepper field soils. The average value of PLI was 1.40, which showed a light pollution level; the average RI for each heavy metal in decreasing order was as follows:Cd, Ni, As, Cu, Pb, Cr, and Zn. The average value of RI of soil was 18.40, which indicated light ecological risk. The average value of IER of soil was -4.78, which indicated a no warning situation. The pollution level, potential ecological risk, and ecological risk warming of Bahrash county were the highest, whereas those of Hejing county were the lowest in Yanqi Basin. As, Cd, Pb, and Zn pollution in pepper field soil were mainly affected by the human activities, and Cr, Cu, Mn, and Ni pollution were mainly affected by the geochemical background of soils. Cd was the main pollutant of farmland soil with strong influence on the PLI, RI, and IER. The pollution risk of Cd should be a major concern during the process of agricultural production in Yanqi Basin. 参考文献 相似文献 引证文献

Analysis on the distribution characteristics and sources of soil heavy metals in suburban farmland in Xiangtan City

The rapid development of the economy will inevitably have an impact on the farmland soil environment. The content of heavy metal is increasing day by day, and the heavy metal can enter people's body through different channels and endanger people's health. Based on agricultural land and crop types in accordance with the regional land use classification, using the method of the Single Factor Index and Comprehensive Pollution Index, the pollution status of heavy metals in farmland soil in the suburbs of Xiangtan city was studied and evaluated. At the same time, we use SPSS software to analyze the four heavy metal elements (Cu, Zn, As and Pb) and analyze their possible sources. The results showed that the farmland soils in Erhuan Road and Zhubu Port were polluted, and the farmland soil in Shuangma (an old industrial district) was not polluted; for different crop lands, orchards and vegetable lands were not contaminated, but rape and rice lands were contaminated. Pearson correlation analysis showed that Cu, As and Pb might come from the same pollution source, while Zn might come from other sources. Waste water from a chemical plant, crop types, automobile exhaust and other human factors may be important sources of soil pollution in agricultural fields.

Watershed soil Cd loss after long-term agricultural practice and biochar amendment under four rainfall levels

Some heavy metals in farmland soil can be transported into the waterbody, affecting the water quality and sediment at the watershed outlet, which can be used to determine the historical loss pattern. Cd is a typical heavy metal leached from farmland that is related to phosphate fertilizers and carries serious environmental risk. The spatial-vertical pattern of Cd in soil and the vertical trend of Cd in the river sediment core were analyzed, which showed the migration and accumulation of Cd in the watershed. To prevent watershed Cd loss, biochar was employed, and leaching experiments were conducted to investigate the Cd loss from soil depending on the initial concentration. Four rainfall intensities, 1.25 mm/h, 2.50 mm/h, 5.00 mm/h, and 10.00 mm/h, were used to simulate typical rainfall scenarios for the study area. Biochar was prepared from corn straw after pretreatment with ammonium dihydrogen phosphate (ADP) and pyrolysis at 400 °C under anoxic conditions. To identify the effects of biochar amendment on Cd migration, the biochar was mixed with soil for 90 days at concentrations of 0%, 0.5%, 1.0%, 3.0%, and 5.0% soil by weight. The results showed that the Cd leaching load increased as the initial load and rainfall intensity increased and that eluviation caused surface Cd to diffuse to the deep soils. The biochar application caused more of the heavy metals to be immobilized in the amended soil rather than transported into the waterbody. The sorption efficiency of the biochar for Cd increased as the addition level increased to 3%, which showed better performance than the 5% addition level under some initial concentration and rainfall conditions. The research indicated that biochar is a potential material to prevent diffuse heavy metal pollution and that a lower addition makes the application more feasible.

Determination of some total and bioavailable heavy metals in farmland soil around Rivers Niger and Benue in Lokoja, Nigeria

The work assessed the distribution of Cd, Cu, Mn, Ni, Pb and Zn in the farmland soils around Rivers Niger and Benue and beyond the confluence in Lokoja, Nigeria. The samples were collected in the dry and rainy seasons of 2013 and 2014, digested with aqua regia and analysed for heavy metals using atomic absorption spectrophotometry. The soil pH ranged from 6.4 to 7.2 for the farmland soils collected 50 m away from the bank of the rivers and each point 10 m apart (n=72). There was no significant difference in the mean values of the organic matter, organic carbon and moisture contents of the soils across the seasons. Cd concentration (mg/kg)in the soil samples collected in March 2013, June 2013, January 2014 and May 2014 at 0 – 15 cm depth ranged from 3.95 - 8.4; Cu 11.6 - 20.2 ; Mn 150.3 - 211.5; Ni 177.0 - 281.0 ; Pb 20.3 - 34.2 and Zn 40.5 - 77.8. The levels of the metals in the soil follow the ranking: Ni > Mn > Zn > Pb > Cu > Cd; with Cd and Ni being above European Union permissible limits. The order of the percentage of extracted metal by EDTA to the total metal content was Pb>Zn>Cu>Ni>Mn>Cd. I-geo pollution index showed that the farmland soils were moderately contaminated with Ni and Cd. Hence, there is the need to enforce environmental laws that borders on proper solid waste and effluent disposals. Key Words : Heavy Metals– Pollution index – River Niger and Benue – Soils – Season

Effects of Continuous Application of Sewage Sludge Compost on Heavy Metals Accumulation and Mobility Characteristics in Soil Profile and on Heavy Metals Uptake of Wheat

The use of sewage sludge compost(SSC)as fertilizer may cause increased leaching due to its high content of heavy metals and thus pose a threat to groundwater quality. The effect of SSC application on heavy metals leaching in calcareous soils has been studied in field trials, which provides basis for determining heavy metals environmental capacity and preventing metal pollution in farmland soil scientifically. The results indicated that the contents of Cu, Zn elevated obviously with the increase of the age and the dosage of SSC utilization in the topsoil(0-15 cm) under 4-year continuous application of SSC. Under higher levels of the compost treatment, the heavy metals Cu and Zn were found to migrate into the 15-30 cm soil and 60-90 cm soil under the experimental condition. Nevertheless, the majority of Cu and Zn from SSC accumulated in topsoil and the highest accumulation rates could reach 75.3% for Cu and 85.9% for Zn. The contents of Cd, Pb increased significantly in topsoil after 4-year continuous application of SSC, and their increases could reach 57.2%-165.2% for Cd and 13%-34% for Pb compared with CK. At 60-90 cm soil, the contents of Cr, As and Pb were also significantly higher than those in CK treatment. Application of SSC not only caused accumulation of some heavy metals in topsoil but also leached heavy metals located in the subsurface soil down in this experiment. Continuous utilization of SSC increased Zn concentration of wheat grain, and the increase could reach 13.3%-47.9%. For the concentrations of Cr and Pb in wheat grain, the values exceeded the national food and healthy standards value (GB 2762-2012) in part of compost treatments. The cumulative ratio of heavy metals carried out by wheat were all below 10% after 4-year experiment, wheat grain carried much more Cu, Zn out than wheat straw, but it was opposite for Cr, As, Cd, Pb. The cumulative ratio of heavy metals carried by wheat decreased with the increasing level of SSC utilization. The amounts of heavy metals migrated to deeper soil should be considered when determining the environmental capacity of heavy metals in farmland soil.

Current status and temporal trend of heavy metals in farmland soil of the Yangtze River Delta Region: Field survey and meta-analysis

While the spatial distributions of heavy metals in farmland soil of China have been comprehensively delineated, their temporal trends are rarely investigated but are important for environmental risk management. In this study, the current status and temporal trends of heavy metals in the farmland soil of Yangtze River Delta (YRD) were evaluated through field survey and meta-analysis. The field survey conducted in 2014 showed that the concentrations of Cd, Pb, Cu, Zn, and Ni in the farmland topsoil were 0.23 ± 0.14, 37.63 ± 15.60, 25.83 ± 41.62, 88.38 ± 43.30, and 29.21 ± 12.41 mg kg−1 (mean ± standard deviation), respectively. The heavy metals showed relatively higher concentrations on the borders among Zhejiang, Jiangsu, and Shanghai. In the meta-analysis, we selected 68 published studies related to heavy metal pollution in farmland topsoil of YRD from 2000 to the year (2014) when the field survey was conducted. The results show an increasing trend for Cd (p < 0.05; 0.0081 mg kg−1 year−1), a decreasing trend for Cu (p < 0.05; -0.80 mg kg−1 year−1), and no significant trend for Pb (p = 0.155), Zn (p = 0.746), and Ni (p = 0.305). The increasing rate of Cd from the meta-analysis is consistent with the rate (0.0013 mg kg−1 year−1) derived from the mass balance calculation for Cd, where atmospheric deposition originated from intensive coal combustion is considered as the main source of Cd in the topsoil. The decreasing trend of Cu is likely due to largely reduced application of copper-based agrochemicals. Environmental regulation and soil remediation are needed to protect food safety and ecosystem from heavy metal pollution, especially Cd.

Heavy Metal Detection in Soils by Laser Induced Breakdown Spectroscopy Using Hemispherical Spatial Confinement

Spatial confinement has great potential for Laser Induced Breakdown Spectroscopy (LIBS) instruments after it has been proven that it has the ability to enhance the LIBS signal strength and repeatability. In order to achieve in-situ measurement of heavy metals in farmland soils by LIBS, a hemispherical spatial confinement device is designed and used to collect plasma spectra, in which the optical fibers directly collect the breakdown spectroscopy of the soil samples. This device could effectively increase the stability of the spectrum intensity of soil. It also has other advantages, such as ease of installation, and its small and compact size. The relationship between the spectrum intensity and the laser pulse energy is studied for this device. It is found that the breakdown threshold is 160 cm−2, and when the laser fluence increases to 250 J/cm2, the spectrum intensity reaches its maximum. Four different kinds of laser pulse energy were set up and in each case the limits of detection of Cd, Cu, Ni, Pb and Zn were calculated. The results show that when the laser pulse fluence was 2.12 GW/cm2, we obtained the smallest limits of detection of these heavy metals, which are all under 10 mg/kg. This device can satisfy the needs of heavy metal in-situ detection, and in the next step it will be integrated into a portable LIBS instrument.

Analysis of spatial variations and sources of heavy metals in farmland soils of Beijing suburbs.

To understand the effect of intense human activities in suburbs on environmental quality, we obtained 758 measurements of the heavy metals in certain farmland soils of the Beijing suburbs. Multivariate statistical analysis and geostatistical analysis were used to conduct a basic analysis of the heavy metal concentrations, the distribution characteristics and the sources of pollution of the farmland soils in these suburbs. The results showed the presence of eight heavy metals in the agricultural soils at levels exceeding the background values for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn. In particular, all the measured Cr concentrations exceeded the background value, while As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were present at 1.13, 1.68, 1.95, 1.43, 1.63, 0.79, 0.92 and 1.36 times their background values, respectively. The results of correlation, factor and spatial structure analyses showed that Cd, Cu, Pb and Zn were strongly homologous, whereas Cr and Hg showed a degree of heterogeneity. The analysis further indicated that in addition to natural factors, Cd, Cu, Pb and Zn in the soil were mainly associated with distribution from road traffic and land use status. Different agricultural production measures in the various areas were also important factors that affected the spatial distribution of the soil Cr concentration. The major sources of Hg pollution were landfills for industrial waste and urban domestic garbage, while the spatial distribution of As was more likely to be a result of composite pollution. The regional distribution of the heavy metals indicated that except for Cr and Hg, the high heavy metal levels occurred in districts and counties with higher organic matter concentrations, such as the northwestern and southeastern suburbs of Beijing. There was no significant Ni pollution in the agricultural soils of the Beijing suburbs.

Status of metal accumulation in farmland soils across China: From distribution to risk assessment

Increasing metal pollution has drawn broad public attention in China due to severe environmental quality deterioration. However, so far, there has been no study to survey metal accumulation in Chinese farmland soil at the national scale. In this study, we determined 11 metals in farmland soils across the Mainland China. Our results indicated the concentrations of Pb, Cd, Zn, and Cu (10.1–184.2, 0.082–1.31, 20.2–321.9, 8.2–515.9 mg/kg, respectively) were elevated above their reference values. Moreover, these metals followed a similar geochemical distribution pattern. The accumulation of Pb, Cd, Zn, and Cu in soils may be associated with human activities for soil fertility. Cadmium had the highest pollution index (PI) of 5.28, and the average hazard quotients (HQs) for all the metals were below 1. Hence, except for Cd, the metals in Chinese arable soils are comparatively safe. Results from this study may provide valuable information for agricultural soil management in China.