Spatial distribution, pollution characteristics and risk assessment of heavy metals in soils: A case study in the desert city of India

The rapid urbanization in China may lead to heavy metal pollution in urban soil, threatening the health of residents. By collecting literature data published in the last 15 years, the characteristics and risks of heavy metals in the urban soils of 52 cities in China were analyzed. The results showed that the average ω(Pb), ω(Cd), ω(Cu) and ω(Zn) in the urban soils of China were 58.5, 0.49, 42.1, and 156.3 mg·kg-1, respectively, and the average Igeo values were ordered as follows Cd(1.10) > Zn(0.36) > Pb(0.28) > Cu(0.13). The high concentrations of heavy metals in the urban soils were mainly found in cities located in coastal economically developed provinces (such as Jiangsu, Zhejiang, etc.) and resource-based provinces (such as Hunan, Henan, Inner Mongolia, etc.). The cities of Kaifeng, Yangzhou, Hohhot, Taiyuan, and Xiangtan had relatively high Igeo values for heavy metals in the soils. The concentrations of heavy metals in soils from industrial areas and roadsides were significantly higher than those from residential areas and parks, suggesting that heavy traffic and developed heavy industry were the main causes of heavy metal accumulation in the urban soils. No significant correlations between the average concentrations of heavy metals in urban soil and urban economic and environmental indicators[such as permanent population, GDP, ρ (PM10), ρ(PM2.5), and SO2 emissions] were found. The concentrations of heavy metals in urban soils showed large spatial heterogeneity, and hence the average concentrations may not reflect the overall accumulation level in a city. The non-carcinogenic risks for children posed by heavy metals in urban soils were generally low, and the main risk contributor was Pb. However, the exposure to heavy metals in soils in cities with developed smelting industries is worthy of attention.

Chemical speciation, vertical profile and human health risk assessment of heavy metals in soils from coal-mine brownfield, Beijing, China

Spatial distribution and ecological risk assessment of soil heavy metals in a typical volcanic area: Influence of parent materials

A causation-based method developed for an integrated risk assessment of heavy metals in soil

In order to comprehensively understand the content, source, speciation characteristics, and risk of heavy metals in cultivated soil of Pingshui Village, Zhaoping County, Hezhou City, this study conducted measurements on the total amounts of Cr, Ni, Cu, Zn, As, Cd, Pb, and Hg in 34 soil samples within the study area. Correlation analysis and principal component analysis were employed to investigate their sources. An improved BCR sequential extraction procedure was utilized to analyze the occurrence forms of eight heavy metals in soil samples. Ecological risks were evaluated using the geo-accumulation index (Igeo), potential ecological risk index (RI), and risk assessment code (RAC). The findings revealed that: (1) The soil heavy metals in the study area exhibited varying degrees of enrichment, primarily attributed to anthropogenic activities. (2) There was no significant difference in the speciation characteristics of the eight heavy metals in the soil of each sampling site in the study area, and the main components were all residual fraction, and the mild acid-soluble fraction of Cd and Zn accounted for a relatively high proportion in individual sampling sites, which should be paid attention to. (3) Through the results of three risk assessment methods, it is concluded that the heavy metal pollution of soil in the study area is serious, and continuous attention should be paid to the corresponding pollution prevention measures.

Taking a city in Guangdong Province as the research area, the concentration and spatial distribution characteristics of heavy metals in the surface soil were studied to clarify the situation of soil heavy metal pollution and priority control factors, providing basic data for the prevention and control of soil heavy metal pollution in the city. The content characteristics of heavy metals in 221 soil samples in the city were analyzed, and the potential health risk assessment and source analysis were carried out through the Monte Carlo model, the potential health risk assessment (HRA) model, and the PMF receptor model. It was found that heavy metals ω(As), ω(Hg), ω(Cd), ω(Pb), ω(Cr), ω(Cu), ω(Ni), and ω(Zn) in the soil of the city were 18.16, 0.43, 1.46, 68.57, 98.34, 64.19, 26.53, and 257.32 mg·kg-1, respectively, with a moderate to high degree of variation. Except for Ni concentration, the soil concentrations of other heavy metal elements exceeded the background values of soil in Guangdong Province to a certain extent, and the concentrations of Cd and Zn exceeded the national secondary standards, resulting in severe heavy metal pollution; the main sources of heavy metals were industrial sources, and natural parent materials, lead battery manufacturing, transportation, artificial cultivation, and pesticide and fertilizer inputs also had an undeniable impact on the accumulation of heavy metals in the soil. Heavy metals in the soil had a certain degree of tolerable carcinogenic health risk for both children and adults, whereas non-carcinogenic risks could be ignored. The potential health risk of children was greater than that of adults, and the main exposure route was through oral intake. The input sources of pesticides and fertilizers and As should be the main controlling factors for the health risks of heavy metals in the city's soil, followed by mixed sources and Cr. There were differences in the spatial distribution characteristics and relative pollution levels of heavy metals, and it is necessary to deepen zoning monitoring and control, strengthen soil pollution prevention and control, and reduce human input of heavy metals in soil.

Soil heavy metals in karst areas have obvious high background value characteristics. Conducting county-level soil heavy metal ecological risk assessment and identifying heavy metal sources in karst areas are of great significance for soil pollution control and land resource management. Taking Pingguo City, a typical karst county in Guangxi Province, as the study object, 3 151 surface and deep soil samples were collected using the grid method and combined to form 785 analytical samples. The contents of eight heavy metal elements, including As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, were determined. The content characteristics and sources of heavy metals were analyzed using statistical analysis, interpolation analysis, factor analysis, and the absolute principal component-multiple linear regression model （APCS-MLR）. Using the content of heavy metal elements in deep soil （150-200 cm） as background values, the ecological risk assessment of heavy metals in surface soil （0-20 cm） in the study area was conducted using the geo-accumulation index （Igeo） and potential ecological risk index （RI） methods. The results showed that the average content of heavy metal elements in the deep soil of the study area was significantly higher than the background value of the C layer soil in Guangxi Province, and the average content of heavy metal elements in the surface soil was significantly higher than the background value of the A layer soil in Guangxi Province. The spatial distribution of soil heavy metal element content generally showed the characteristics of high in karst areas and low in non-karst areas. The main sources of As, Cr, Ni, Pb, and Zn were soil parent materials, with contribution rates of 74.36%, 84.59%, 93.69%, 79.67%, and 78.17%, respectively. The main sources of Cd were soil parent material sources and unknown sources, with contribution rates of 37.33% and 31.05%, respectively. The main sources of Cu were soil parent materials and unknown sources, with contribution rates of 59.07% and 40.23%, respectively. The main sources of Hg were tectonic activity and mineralization, as well as unknown sources, with contribution rates of 52.49% and 30.65%, respectively. The geo-accumulation index （Igeo） showed that the surface soil was mainly polluted by Cd, with mild or above pollution accounting for 47.78%. The potential ecological risk index （RI） showed that the proportion of surface soil heavy metal comprehensive potential ecological hazards with mild, moderate, strong, and very strong levels was 80.78%, 14.97%, 2.51%, and 1.64%, respectively.

Combining random forest and XGBoost models for source apportionment and health risk assessments of heavy metals in suburban farmland soils.

To study the sources and potential risks of heavy metals in soils of characteristic agricultural product producing areas is of great significance for the scientific management and safe utilization of soil and crop resources. The contents of heavy metals As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the 254 surface soil samples collected from the Heze oil peony planting area were determined. The content characteristics and correlation of heavy metals were analyzed using multivariate statistical methods. The sources of heavy metals in topsoil were analyzed using Igeo, PMF, and PCA/APCS. The ecological risks of the eight heavy metals were assessed through the potential ecological risk index (PERI). The results showed that the average contents of seven heavy metals in the soil were basically consistent with the background values of soil elements in Heze City, except that the average value of Cd was 1.44 times higher than the background value in Heze City. Correlation analysis and cluster analysis revealed that Pb, Hg, and Cd elements in the soil were greatly affected by human activities in the later period. The sources of eight heavy metals in the study area were natural sources, agricultural fertilizer sources, industrial coal sources, and domestic transportation sources, with the contribution rates of 81.31%, 15.45%, 2.74%, and 0.50%, respectively; 84.25% of the sites in the study area were at slight ecological risk, whereas the moderate risk and strong risk sites accounted for 14.96% and 0.79%, respectively. Among them, Cd and Hg were the dominant elements of ecological risk in the study area.

Using the case of Ulaanbaatar, Erdenet, and Darkhan cities from Mongolia, the study aimed to assess the contamination level and health risk assessment of heavy metals (As, Cr, Pb, Ni, and Zn) in urban soil. A total of 78 samples was collected from a variety of functional areas. The geoaccumulation index (Igeo) and integrated pollution index (IPI) were used in pollution assessment, while the health risk was scored using a hazard quotient (HQ) and health index (HI) for non-carcinogenic heavy metals, as well as a lifetime average daily dose (LADD) for carcinogenic heavy metals. The results show that the concentration of heavy metals in the soil samples taken from Darkhan city, which presented “uncontaminated” values in terms of Igeo for all metals, was relatively lower than other cities within the contamination assessment. Furthermore, the Igeo value signified “uncontimated to heavily contaminated” soil in the Ulaanbaatar and Erdenet cities. Typically, as for the IPI that observed similar trends with Igeo, the mean IPI values in Ulaanbaatar, Erdenet, and Darkhan were 1.33 (moderate level of pollution), 1.83 (moderate level of pollution), and 0.94 (low level of pollution), respectively. In terms of the assessment of potential health risk, there was a particular or different level of ingestion, dermal contact, and inhalation exposure pathway for human health. Among these three different pathways, the ingestion was estimated by the main contributor for health risk. Each value of HQ and HI indicated that soil heavy metals of studied cities were at a safe level (<1) or had the absence of a significant health risk there. In addition, the potential health risk for children was greater than for adults, where heavy metal values of HI for children had a high value compared to adults. We estimated carcinogenic risks through the inhalation exposure, and as a result, there were no significant risks for human health in the studied cities from three elements (As, Cr, and Ni).

Lalu wetland is the world’s largest plateau urban wetland. It was designated as a national-level nature reserve in China in 2004 and is often called “the lung of Lhasa”. It serves as a vital recreational area for urban residents. Concerns have arisen about the potential harm to human health due to heavy metals (HMs) in the wetland soil. This study assessed the ecological risk of HMs in Lalu wetland soil by using the potential ecological risk index and geo-accumulation index techniques. The findings showed that the Lalu wetland’s overall risk level is low risk. with Cd being the primary pollutant. Through the absolute principal component scores–multiple linear regression (APCS-MLR) model and Pearson correlation analysis, three sources of HMs were identified, including traffic sources, soil parent material sources, and geothermal sources, contributing 51.13%, 32.35%, and 16.52%, respectively. The results of the probabilistic health risk assessment based on Monte Carlo simulation indicate that non-carcinogenic risks are absent for both adults and children. However, acceptable carcinogenic risks are present. For adults, the main exposure mode is through dermal contact, while children are primarily exposed through ingestion. Children manifest a heightened vulnerability to these risks compared to adults, with As being the primary contributing element. The source-oriented health risk assessment (HRA) highlights geothermal sources as the primary contributors to health risks. The research results provide insights into the current status of HMs in Lalu wetland soil, offering a scientific basis for restricting and managing contamination by HMs in wetlands.

To investigate the distribution characteristics and hazard levels of eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) in karst soil with a high geological background of heavy metals, 32 and 40 surface soil samples were collected from limestone and clastic rock areas, respectively, in the northern part of Mashan County, Guangxi Province, a typical mountainous county dominated by primary industries in China. Geostatistical methods, Pearson’s correlation analysis, the geo-accumulation index, and the potential ecological hazard index were applied to explore the influencing factors of those heavy metals and evaluate their potential contamination risks. The results show that (1) the levels of the eight heavy metal elements in the surface soils of karst areas exceeded the background values of soil for Mashan County, the background value of soil (layer A) in China, and abundance value of upper crust. According to the soil pollution risk screening values specified in the Soil Environmental Quality: Risk Control Standard for Contamination of Agricultural Land, the proportions of heavy metals in the soils of karst areas were ranked as Cd (100%) &gt; As (90.6%) &gt; Cr (84.4%) &gt; Zn (68.8%) &gt; Ni (37.5%). Meanwhile, the heavy metals in the soils of non-karst areas did not exceed the overall values for Mashan County, and Ni, Pb, and Zn did not exceed the overall national soil values. One-quarter of Cd in non-karst samples exceeded the risk-threshold screening value. There was a high degree of variation and a significant difference in the contents of heavy metal elements between karst and non-karst areas. (2) The element combinations of As-Cd-Cu-Hg-Ni-Pb-Zn and Cr in karst areas were characterized by the influence of carbonate rock parent material. The non-karst areas were characterized by Ni-Cu-Pb-Zn, As-Cr-Hg, and Cd assemblages, which were mainly influenced by the mixture of laterite parent materials, sand shale parent materials, and basic-rock residual materials, and that may be affected by element migration caused by soil erosion and anthropogenic activities. (3) Analysis of the geo-accumulation index showed that karst areas were generally found to be at the clean to light pollution level, except for in the areas whose samples exhibited medium/high pollution levels for Cd and Cr, with the Cd pollution being the more serious of the two. Small amounts of Cd and Cu were present in the non-karst areas at a light contamination level, while other elements were at the level of no pollution. (4) The results of the potential ecological risk index showed that Cd and Hg were the main ecologically hazardous heavy metal elements in the soils of the study areas. The potential ecological risk level in karst areas was much higher than in non-karst areas, especially for Cd, and was mainly influenced by the carbonate rock parent material.

In order to understand the spatial distribution, influencing factors, ecological risk characteristics, and sources of heavy metals in the soil profile （0-1 m） of farmland in the Guanzhong Plain, soil samples of 0-1 m were collected from 124 sites in the Guanzhong Plain. The contents of heavy metals （As, Cd, Cr, Cu, Ni, Pb, and Zn） in soil were analyzed at different depths （0-10 cm, 10-20 cm, 20-40 cm, 40-60 cm, and 60-100 cm）. The study generated the spatial distribution characteristics of soil heavy metals based on geostatistics and investigated the influencing factors of heavy metals based on structural equation modeling （SEM）. In addition, the ecological environmental risks of soil heavy metals were evaluated using the methods of index of geo-accumulation （Igeo）, single factor contaminant index （Pi）, and potential ecological risk index （Ei）. Finally, the sources of soil heavy metals were analyzed using the PMF model. The results showed that the average heavy metal content of ω（As）, ω（Cd）, ω（Cr）, ω（Cu）, ω（Ni）, ω（Pb）, and ω（Zn） in the 0-10 cm were 19.57, 0.71, 69.65, 21.91, 28.67, 17.54, and 73.77 mg·kg-1, respectively. The average values of As, Cd, Cr, Pb, and Zn exceeded the background values. With the increasing soil depth, all heavy metals showed a decreasing trend except for Cd and Ni. The spatial distribution indicated that different heavy metals in the same soil layer had different spatial distributions, and the spatial distribution of heavy metals also varied at different depths. The structural equation model showed that the factors affecting the distribution of heavy metals at different depths were deeply dependent. The ecological risk assessment showed that Cd at different depths had higher ecological risks, while the rest were considered minor risks. The sources of 0-40 cm soil layer were consistent, and the main sources were pesticides and herbicides, organic fertilizers and fertilizers, natural sources, and traffic-induced atmospheric subsidence and industrial sources； the sources of 40-100 cm were consistent, and the main sources were pesticides and herbicides, organic fertilizers and fertilizers, natural sources, and traffic-induced atmospheric subsidence.

The enrichment of heavy metals in soil is a consequence of both natural processes and anthropogenic activities. Conducting source analysis and ecological risk assessment of heavy metals in soil is a necessary approach for serving the prevention and control of soil heavy metal pollution. To identify the sources and ecological risk characteristics of heavy metals in the soil of Yifeng County， Jiangxi Province， surface soil samples were collected， and the heavy metal content and pH value were analyzed. The absolute principal component score-multiple linear regression （APCS-MLR） receptor model was applied to analyze the sources of heavy metals in the soil， and the contribution rates of each source were quantitatively calculated. The ecological risk of heavy metals in the soil was evaluated based on the geo-accumulation index method and the potential ecological risk index method. Meanwhile， GIS was utilized to explore the spatial distribution pattern of heavy metals in the soil. The results showed that the average values of ω（As）， ω（Cd）， ω（Cr）， ω（Cu）， ω（Hg）， ω（Ni）， ω（Pb）， and ω（Zn） in the soil of the Yifeng County were 9.7， 0.211， 68， 25， 0.113， 24， 37， and 87 mg·kg-1， respectively， which were higher than the soil background values of the Jiangxi Province. Controlled by geological settings， the high content areas of As， Cr， Cu， and Ni were consistent with the distribution of the Qingbaikou metamorphic rock formations in the area， and the spatial distribution of Cd， Hg， Pb， and Zn showed significant differences from the distribution of rock formation types due to anthropogenic activities. The ecological risk assessment found that the risk of soil heavy metal pollution in the Yifeng County was relatively low on the whole， but there were local occurrences of slight pollution and moderate risk mainly caused by As， Cd， and Hg. The APCS-MLR receptor model identified three sources of heavy metals. Arsenic， Cr， Cu， and Ni were predominantly derived from natural sources， with contribution rates of 80.06%， 69.92%， 80.49%， and 94.27%， respectively. Lead and Zn primarily originated from transportation activities， contributing 74.73% and 66.99% to the overall contamination. Furthermore， Cd and Hg were predominantly influenced by industrial and agricultural sources， with respective contribution rates of 43.62% and 58.09%. The above research can provide data and theoretical support for soil pollution prevention and control in the Yifeng County.

Pollution status and health risk assessment of heavy metals in the soil of Sahibzada Ajit Singh (SAS) Nagar district of Punjab, India and its source apportionment