Identification of soil heavy metal sources from anthropogenic activities and pollution assessment of Fuyang County, China

Recent Advances in Thiourea Based Colorimetric and Fluorescent Chemosensors for Detection of Anions and Neutral Analytes: A Review

Thioureas and their derivatives are organosulfur compounds having excellent biological and non-biological applications. These compounds contain S- and N-, which are nucleophilic and allow for establishing inter-and intramolecular hydrogen bonding. These characteristics make thiourea moiety a very important chemosensor to detect various environmental pollutants. This article covers a broad range of thioureas and their derivatives that are used for highly sensitive, selective, and simple fluorimetric (turn-off and turn-on), and colorimetric chemosensors for the detection and determination of different types of anions, such as CN-, AcO-, F-, ClO- and citrate ions, etc., and neutral analytes such as ATP, DCP, and Amlodipine, etc., in biological, environmental, and agriculture samples. Further, the sensing performances of thioureas-based chemosensors have been compared and discussed, which could help the readers for the future design of organic fluorescent and colorimetric sensors to detect anions and neutral analytes. We hope this study will support the new thoughts to design highly efficient, selective, and sensitive chemosensors to detect different analytes in biological, environmental, and agricultural samples.

Soil heavy metal source apportionment and environmental differentiation study in Dulan County, Qinghai Province, using geodetector analysis

Elucidating material sources and investigating the impact of various environmental factors on material source accumulation are important for the environmental restoration of the Qinghai-Tibet Plateau. This study was conducted within the Borhan Buda Mountain Range of Dulan County, Qinghai Province, China, where 6274 surface soil samples were collected. The geoaccumulation index was employed to assess the levels of heavy metals, including As, Cr, Cu, Hg, Ni, Pb, Sb, Sn, and Zn, in the soil. A comprehensive approach combining principal component analysis (PCA) and geodetector analysis was employed to assess the spatial variation in soil heavy metal origins and the factors that influence them. The findings indicate that the mean concentrations of Pb exceed the background values for the soil in Qinghai Province, with Hg exhibiting low pollution, whereas the other elements showed no contamination. PCA indicated that the soil elements in the Borhan Buda Mountain Range were influenced by four sources, all attributed to the geological background. Geodetector analysis of the factor contributions suggested that geological factors had the strongest explanatory power for the four material sources. Furthermore, the risk detection results demonstrated significant variations in the material source contributions among most subregions when considering three environmental factors in pairs. Interaction detection revealed that the combined influence of two environmental factors on material source contributions was greater than that of the individual factors. Additionally, ecological detection demonstrated significant differences in material source contributions one, two, and three between land cover types and geological backgrounds, whereas no significant differences were observed in material source four between land cover types and geological backgrounds. This study offers valuable insights into the sources of soil elements in Dulan County and the influence of environmental factors on these sources, thereby contributing an essential knowledge base for the protection and management of soil heavy metals in the region.

Source identification and migration fate of metal(loid)s in soil and groundwater from an abandoned Pb/Zn mine

Understanding the spatial distribution, source identification, and migration fate of toxic metals is crucial for managing the potential risks associated with metal(loid)s in abandoned Pb/Zn mines. This study provides a comprehensive analysis of the heterogeneous characteristics, contamination sources, and migration fate of metal(loid)s in both mine soil and groundwater. The results reveal that the abandoned mine soil is primarily contaminated with As and Pb, whereas groundwater in the mining and smelting area is mainly contaminated with Pb. The concentrations of As and Pb in the soil reached a maximum of 37.5 mg/kg and 289 mg/kg, respectively, significantly exceeding the local background values of 13.6 mg/kg for As and 29 mg/kg for Pb. The sources of soil contamination were attributed to historical smelting activities (31.4 %) for As, Cd, Hg, and Sb, while Pb and Mn were primarily derived from the ore-deposited belt (21.5 %). Machine learning predictions indicate that the migration of As in the soil can extend up to six meters or more, predominantly influenced by the presence of grit and silt. As a significant source of groundwater contamination, both soil As and Cd can infiltrate the groundwater through convection or diffusion processes. In conclusion, it is imperative to address the long-term release of heterogeneous metal ores in the soil of abandoned mine sites, as this can severely deteriorate the quality of both soil and groundwater.

Geranium robertianum L. tolerates various soil types burdened with heavy metals

Many heavy metals (HMs) are essential micronutrients for the growth and development of plants. However, human activities such as mining, smelting, waste disposal, and industrial processes have led to toxic levels of HMs in soil. Fortunately, many plant species have developed incredible adaptive mechanisms to survive and thrive in such harsh environments. As a widespread and ruderal species, Geranium robertianum L. inhabits versatile soil types, both polluted and unpolluted. Considering the ubiquity of G. robertianum, the study aimed to determine whether geographically distant populations can tolerate HMs. We collected soil and plant samples from serpentine, an anthropogenic heavy metal contaminated, and a non-metalliferous site to study the physiological state of G. robertianum. HMs in soil and plants were determined using flame atomic absorption spectrometry. Spectrophotometric methods were used to measure the total content of chlorophylls a and b, total phenolics, phenolic acids, flavonoids, and proline. Principal component analysis (PCA) was used to investigate the potential correlation between HMs concentrations gathered from various soil types and plant samples and biochemical data acquired for plant material. A statistically significant difference was observed for all localities regarding secondary metabolite parameters. A positive correlation between Ni and Zn in soil and Ni and Zn in plant matter was observed (p<0.0005) indicating higher absorption. Regardless of high concentrations of heavy metals in investigated soils, G. robertianum displayed resilience and was capable of thriving. These results may be ascribed to several protective mechanisms that allow G. robertianum to express normal growth and development and act as a pioneer species.

Current Status and Health Risk Assessment of Heavy Metals Contamination in Tea across China

Tea is a non-alcoholic beverage popular among Chinese people. However, due to the application of chemical and organic fertilizers in the tea planting process, the environment pollutionaround the tea plantation, and the instruments used in the processing, heavy metal elements will accumulate in the tea, which brings health risks for tea consumers. This study summarized heavy metal concentrations from 227 published papers and investigated the current contamination status of tea and tea plantation soils, and, finally, the risk of heavy metal exposure to tea consumers in China is assessed, in terms of both non-carcinogenic and carcinogenic risk. The average contamination of six heavy metals in tea-arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), and lead (Pb)-were 0.21, 0.14, 1.17, 14.6, 0.04, and 1.09 mg/kg, respectively. The areas with high concentrations of heavy metals in tea were concentrated primarily in southwest China, some areas in eastern China, and Shaanxi Province in northwest China. The non-carcinogenic risks of heavy metals in tea are all within safe limits. The national average HI value was 0.04, with the highest HI value of 0.18 in Tibet, which has the largest tea consumption in China. However, the carcinogenic risks of Cd in Shaanxi Province, Anhui Province, and southwest China exceed the acceptable range, and due attention should be given to these areas.

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

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

Contamination vertical distribution and key factors identification of metal(loid)s in site soil from an abandoned Pb/Zn smelter using machine learning

Soil heterogeneity makes the vertical distribution of metal(loid)s in site soil vary considerably and poses a challenge for identifying the key factors of metal(loid)s migration in site soil profiles. In this study, a machine learning (ML) model was developed to study a typical abandoned Pb/Zn smelter using 267 site soils from 46 drilling points. Results showed that a well-trained ML model could be used to identify the key factors in determining the contamination vertical distribution and predict the metal(loid)s contents in subsurface soil. As, Cd, Pb, and Zn were the primary pollutants and their vertical migration depth arrived to 4-6 m. Based on the predictive performance of different ML algorithms, the extreme gradient boosting (XGB) was selected as the best model to produce accurate predictions for the most metal(loid)s content. Contents of As, Cd, Pb, and Zn in the heavily contaminated zones declined with an increase of soil depth. The metal(loid) contents in surface soil of 0-2 m could be readily used to predict the content of Cd, Cr, Hg, and Zn in subsurface soil from 2 m to 10 m. Based on the metal-specific XGB models, sulfur content, functional area, and soil texture were identified as key factors affecting the vertical distribution of As, Cd, Pb, and Zn in site soil. Results suggested the ML method is helpful to manage the potential environmental risks of metal(loid)s in Pb/Zn smelting site.

Assessment and mapping of total suspended particulate and soil quality around brick kilns and occupational health issues among brick kilns workers in Pakistan

Brick kilns constitute one of the major sources of environmental degradation in Pakistan. The present study was conducted to determine the soil quality and total suspended particulates (TSPs) around the brick kilns and assess the health effects on brick kiln workers. Four brick kilns were selected, two each at Sheikhupura and Pattoki city. The soil quality was assessed by analyzing pH, electrical conductivity, moisture content, nitrogen, phosphorus, potassium content, and heavy metal concentration while TSPs were measured by hand-held Microdust Pro Real time monitor. Average TSP concentration around brick kilns at Sheikhupura and Pattoki ranged between 1100 and 1200 µg/m³ and between 550 and 600 µg/m³ respectively which exceeded the Punjab Ambient Air Standards. The soil was slightly acidic (Sheikhupura: average pH = 6.41; Pattoki: average pH = 6.6) while all other analyzed parameters, except heavy metals, were lower than the required FAO Standards for good quality agriculture soil. Heavy metal accumulation in soil samples followed the general order zinc (Zn) > chromium (Cr) > nickel (Ni) > manganese (Mn) > cadmium (Cd) > copper (Cu). For assessment of occupational health and safety issues, all 440 brick kiln workers from the study areas were interviewed. Mostly, brick kiln workers suffered from chronic back pain (84%), skin issues (80.5%), dry cough (72.9%), common cold (46.1%), and shortness of breath (17.1%). The vulnerability risk varied with the nature of the work as workers engaged in brick baking were more vulnerable to respiratory issues than were those in molding task. The study concludes that brick kilns are a source of increased TSP, deteriorated surrounding soil quality, and impaired worker health. It is necessary to regulate these activities and implement requisite health and safety measures.

Identification of the factors determining the concentration and spatial distribution of Zn, Pb and Cd in the soils of the non-forest Tatra Mountains (southern Poland)

We investigated trace-metal (TM)--Zn, Pb and Cd--concentrations and spatial distributions in the uppermost layers of non-forest soils from Tatra National Park (West Carpathians). We aimed to determine the main factors affecting the distribution of TMs, as well as the risk they posed to the environment. TM concentrations were compared to the target and intervention values established by the Dutch Ministry. Principle component analysis was used to identify the potential factors affecting TM accumulation, with two-factor analysis being applied to further examine the importance of any given factor. To examine the regularity of the TM distribution, semivariograms were created. The semivariograms of Cd and Pb were similar, suggesting a moderate spatial dependence for these metal concentrations, while the Zn variogram indicated a lack of spatial continuity for this metal. We established that the Zn, Pb and Cd exceeded target levels and at some sites, Cd exceeded the intervention values, posing a strong ecological risk to the environment. Our study confirmed that the parent rock was the most important factor affecting the TM accumulation. The carbonate-free soils differed from carbonate soils in the second important factor affecting TM accumulation, for carbonate-free soils it was location when for carbonate soils-TM content in the parent material. The Zn, Pb and Cd distribution patterns indicated that Cd, but also to a lesser degree Pb and Zn, accumulation mainly resulted from long-range transport from industrialised areas, while the Zn concentrations were also affected by local sources, such as the historical mining of Zn ore.

Overview of heavy metal pollution and health risk assessment of urban soils in Yangtze River Economic Belt, China

Using national multi-purpose regional geochemical survey (NMPRGS) data, this overview systematically summarizes the pollution levels and health risks posed by 8 heavy metals (As, Cd, Pb, Zn, Hg, Cu, Cr and Ni) in urban soils of 86 cities above the prefecture level in Yangtze River Economic Belt (YREB). Meanwhile, the spatial distribution and main sources of heavy metal pollutants in urban soils of key cities are described in detail. On a regional scale, Hg and Cd contamination in urban soils of YREB is most prominent, and As, Cu, Pb and Zn contamination exists in several cities, while Cr and Ni contamination is almost not shown. The type of industrialization and the history of urbanization affect the soil heavy metal pollution in majority cities, and the influence of geological background on the content of heavy metals in urban soils cannot be ignored. Specifically, the urban pollution of Cd, As, Pb and Zn is mainly concentrated in Hunan and Hubei Provinces, which are highly developed in mining industry, especially in Zhuzhou, Chenzhou, Huangshi and Xiangtan cities, while the major soil Hg pollution occurs in Zhejiang and Jiangsu Provinces with rapid economic development, where Shaoxing, Ningbo, Suzhou and Wuxi are the key polluted cities. Heavy metals in the urban soils investigated generally posed low non-carcinogenic and carcinogenic risks to the adults. However, the non-carcinogenic risk to minors in some cities (e.g., Chenzhou and Huangshi) should be given cautious attention.

Bifunctional Amine- and Thiol-Modified Ti3C2Tx MXene for Trace Detection of Heavy Metals

Surface functionalization of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, also known as MXenes, is a powerful approach for modification of their physical and chemical properties for new applications. In this study, we demonstrate the synthesis of a bifunctional Ti₃C₂T_x MXene modified with amine and thiol groups through a facile condensation reaction. We successfully employed the resulting NH₂/SH-Ti₃C₂T_x MXene as a solid phase in the ultrasonic-assisted dispersive micro solid-phase extraction (d-μ-SPE) method for the analytical determination of heavy metals at trace levels in food and soil samples. The prepared NH₂/SH-Ti₃C₂T_x MXene showed remarkable performance in the ultrasonic-assisted d-μ-SPE method with limits of detection of 0.12 and 2.30 ng mL^-1, with linear dynamic ranges of 0.50-90 μg L^-1 and 10-120 μg L^-1 for cadmium (Cd²⁺) and lead (Pb²⁺) ions, respectively. Furthermore, the extraction efficiencies were greater than 97%, with a relative standard deviation of less than 3% for five separate batch experiments in the determination of 5.0 μg L^-1 of Cd²⁺ and Pb²⁺. This study shows that NH₂/SH-Ti₃C₂T_x can be used as a simple, rapid, reliable, selective, and sensitive material in the d-μ-SPE method for the trace determination of Cd²⁺ and Pb²⁺ in soil and agricultural products. This study demonstrates the utility of MXenes for analytical chemistry and suggests that further advances in methods for the functionalization of MXenes can open new applications for these already exciting materials.

Pollution characteristics and environmental availability of toxic elements in soil from an abandoned arsenic-containing mine

Understanding the pollution characteristics and assessing the ecological risk of toxic metals in mine soil are crucial to controlling and managing risks in abandoned mine areas. In this study, the profile soil pollution characteristics and modified ecological risk of As, Cd, Hg, Pb, Sb, and Tl for both the different mining functional areas and the downstream impacted areas at a large-scale abandoned arsenic-containing mine were studied. Results showed that both the profile soils at the mining functional areas and the surface layer in downstream sites are heavily polluted by As, Cd, Hg, Sb, and Tl. As, Hg, Sb, and Tl mainly accumulated on soils with a depth of 0-1.5 m. In contrast, these metals in the mining site were gradually increased with soil depth above the bedrock strata. Cd and Pb were mainly concentrated at depth of 2.5-3.5 m in the smelting with by-product processing site. The speciation of metals in the profile soils mainly occurred in residual fraction. However, high levels of potential mobile As and Sb were found in mining soils and smelting surface soils, as well as Tl in deep soils at mining functional sites and top soils at downstream sites, with their mean contents in these areas arrived to 2950 mg kg^-1, 9.64 mg kg^-1, and 0.98 mg kg^-1, respectively. In addition, the modified ecological risk assessment (NIRI_m) values revealed a substantial ecological risk of As, Cd, Hg, and Sb in both the entire profile soils at the mining, smelting sites and topsoil (0-1.5 m) at the adjacent downstream site. In summary, the pollution characteristics and potential ecological risk of toxic metals in profile soils from the different functional sites at arsenic-containing mine were significantly different and suitable control strategies for available toxic elements should be adopted in the different functional sites of mine.

Multivariate Statistical Analysis and Structural Sovereignty for Geochemical Assessment and Groundwater Prevalence in Bahariya Oasis, Western Desert, Egypt

The Bahariya Oasis is an example of an extremely hyperarid environment and it is characterized by an extensive nonrenewable Nubian Sandstone Aquifer System (NSAS), which is deemed the crucial provenance for agrarian and national development ventures. The present work aimed to assess the groundwater occurrences in the NSAS, and to document the main factors that control the geochemistry of the groundwater in the Bahariya Oasis. Groundwater samples were collected from 52 locations in April 2019 and were analyzed for a total of 13 water-quality physicochemical parameters. A diverse geological and structural setup has greatly impacted the groundwater flow pattern and has diverted it towards the NE by the great Bahariya anticline structure, the ENE-oriented Bahariya mid dextral strike-slip fault, and NE-striking normal faults, while NW-oriented normal faults cause the groundwater to diverge perpendicular to the groundwater flow lines. The groundwater is highly contaminated by trace metals (Fe2+ and Mn2+), which exceed the permissible limit for different purposes. Conventional graphical plots and geochemical modeling integrated with multivariate factor analysis (FA) revealed that the chemical composition of the groundwater is strongly affected by its interaction with the lithologies of the NSAS. The dissolution of aquifer host rocks (carbonates and iron oxides) and chloride salts through the infiltration of groundwater, and the incorporation of cations by the ionic exchange of Na+ by Ca2+ in clay minerals, emerged as worthy mechanisms for the groundwater development. Furthermore, the region’s rapidly increasing population, agricultural expansion, and the associated anthropogenic practices have generated a need for groundwater-quality assurance as a prime source of the water supply. Consequently, reducing the effects of the NSAS’s unsustainable extraction requires long-term monitoring and the ongoing evaluation of the groundwater.

Pollution Characteristics and Spatial Distribution of Heavy Metals in Coal-Bearing Sandstone Soil: A Case Study of Coal Mine Area in Southwest China

Soil pollution in coal mining areas is a serious environmental problem in China and elsewhere. In this study, surface and vertical profile soil samples were collected from a coal mine area in Dazhu, Southwestern China. Microscopic observation, concentrations, chemical speciation, statistical analysis, spatial distribution, and risk assessment were used to assess heavy metal pollution. The results show that the weathering of coal-bearing sandstone and mining activities substantially contributed to soil pollution. The concentrations of Fe, Ni, Cu, Zn, Mn, Cd, Hg, and Pb exceeded their background values. Cd caused the most intense pollution and was associated with heavily-extremely contaminated soils. The residual fraction was dominant for most metals, except Cd and Mn, for which the reducible fraction was dominant (Cd: 55.17%; Mn: 81.16%). Zn, Ni, Cd, and Cu presented similar distribution patterns, and Hg and As also shared similar distribution characteristics. Factor 1 represented anthropogenic and lithologic sources, which were affected by mining activities; Factor 2 represented anthropogenic sources, e.g., fertilizers and traffic pollution; and Factor 3 represented the contribution of metals from soil-forming parent material. More than half of the study area had high pollution risk and was not suitable for vegetable cultivation.

Assessment of the risks from dietary lead exposure in China

The dietary lead (Pb) risk across China was assessed based on the margin of exposure (MOE) approach by comparing the level (1.5 μg/kg/d) based on the Pb concentrations in foodstuffs from1386 published articles. The Pb averages of the 18 foods were lower than their corresponding limits enacted by the Chinese government, ranging from 0.09 to 0.30 mg/kg. Food from plants had a much higher contribution to dietary Pb intake than that from animals (86% vs. 14%), and cereals and vegetables contributed 79% of the Pb intake from plant-based food. Although each category of food contained a relatively low Pb concentration, the accumulated Pb from the total diet posed a high risk to human health. The MOE risk from dietary Pb averaged 1.57 and ranged from 0.13 to 6.18, with high risks in southern, southwestern, eastern, central, and northern China. The MOE risk from Pb could be decreased by adjusting the dietary structure, and the ratio of people categorized as high risk (MOE < 1) would decrease from 56% to 37%, 41%, or 24% if the category of cereal or vegetable or both cereals and vegetables with the lowest Pb concentration in their local areas were selected, respectively.

Source apportionment and spatial distribution of heavy metals in atmospheric settled dust of Ulaanbaatar, Mongolia

Atmospheric settled dust study was conducted with the purpose of to determine the source of heavy metal elements (As, Co, Cr, Cu, Ni, Pb, and Zn) in airborne dust from Ulaanbaatar using the multivariate analysis and spatial distribution mapping by geographic information system (GIS) with the systematic grid. A total of 57 dust samples were collected from the impervious surfaces at 2-4 m above the ground in January of 2020. The mean concentrations of heavy metals were increasing order of Co-10.4 ± 1.3 mg/kg > As-16.5 ± 5.9 mg/kg > Ni-21.3 ± 3.3 mg/kg > Pb-51.7 ± 26.4 mg/kg > Cu-65.5 ± 23.6 mg/kg > Cr-70.2 ± 18.7 mg/kg > Zn-571.3 ± 422.8 mg/kg. In terms of multivariate analysis, we used Pearson's correlation, principal component analysis (PCA), and hierarchical cluster analysis (CA). Three principal components, which are eigenvalues higher than 1, were determined accounting for 70.5% of the total variance by PCA. As a result, PC1 38.5% (As, Cr, Cu, and Ni), PC2 17.3% (Pb and Zn), and PC3 14.7% (Co and Pb) are attributable to coal combustion, vehicle exhaust emission, and resuspension of soil particles, respectively. The results of correlation analysis and CA were fairly in agreement with PCA. The spatial distribution maps of heavy metals were revealed in the downtown in which 40 covered sampling sites with about 700m intervals. In the spatial distribution mappings, generally, the southern part of the mapping area was higher concentrations of heavy metals. An increment of heavy metals concentration was presented for As, Cr, Co, and Ni with their similar trend in the southwestern part of the mapping. Besides, another trend for the distribution of the high concentrations of Cu and Zn was observed in the south and southeast parts. In terms of Pb, it had no noticeable pattern of distribution; however, a high spot was presented in the southwest part of the map.

Spatial Distribution and Source Apportionment of Soil Heavy Metals in Pearl River Delta, China

The contents of ten heavy metals (HMs) (Cu, Pb, Zn, Cd, Ni, Cr, Hg, As, Co, and Mn) in 80 surface soil samples (0–20 cm) were investigated in the Pearl River Delta (PRD), Guangdong Province, China. The average contents of Cu, Pb, Zn, Cd, Ni, Cr, Hg, As, Co, and Mn were 16.45, 40.20, 45.10, 0.09, 12.93, 47.93, 0.13, 14.44, 5.68, and 199.66 mg/kg, respectively. The soil quality was generally good, though slightly higher levels (1.17, 1.61, 1.67, and 1.62 times) of soil Pb, Cd, Hg, and As contents were observed compared with the soil background values. The spatial distribution of soil HM pollution in the PRD showed that 36% of sample sites were evaluated as sites without soil pollution, 32% as sites with slight pollution, 20% as sites with nearly moderate pollution, 9% as sites with moderate pollution, and 3% as site with serious pollution. Source apportionment analysis showed that the source of 64.33% of soil HMs in the PRD could be explained by natural and industrial sources, 24.80% by transportation, and 10.87% by agricultural activities.

Heavy metals in soils and edible tissues of Lepidium meyenii (maca) and health risk assessment in areas influenced by mining activity in the Central region of Peru

Heavy metal contamination of soil and agricultural products is an environmental problem, has an adverse effect on the quality of food crops, and is a danger to food security and public health. The concentration of arsenic (As), cadmium (Cd), lead (Pb), iron (Fe) and zinc (Zn) in surface soils and edible hypocotyls tissues of two ecotypes of Lepidium meyenii Walpers (maca) was evaluated in three districts of the Junín province, Peru. In addition, the risk to human health due to exposure to heavy metals from maca consumption was evaluated. Soil samples and maca hypocotyls were collected in areas influenced by mining and metallurgical activity. The mean concentration of Cd (0.32 ± 0.23 mg/kg) and Pb (0.20 ± 0.12 mg/kg) in maca samples exceeded the values established by the Food and Agriculture Organization and the World Health Organization. The bioconcentration factor was less than 1. The estimated daily intake of each metal was below the oral reference dose. The hazard quotient and hazard index were less than 1, it is unlikely to cause non-cancer adverse health outcome. The cancer risk for As and Cd was higher than the tolerable limit (1 × 10-6) in children and adults. In the district of Ondores, the cancer risk for As in children was higher than the acceptable limit (1 × 10-4). Residents of the Ondores district would be more exposed to As and Cd from consumption of maca hypocotyls. It is very important to carry out continuous monitoring of other toxic metals in different ecotypes of maca (red, black, yellow, purple, creamy white, pink) in order to evaluate the variation in the accumulation of heavy metals and the level of toxicity of each metal between ecotypes.

Pollution Characteristics and Associated Risk Assessment of Heavy Metals in Farmland Soils From a Typical County of Hubei Province, Central China

Knowledge from the negative impacts of the counties' anthropogenic activities on soil pollution was of great significance in China, and valuable information was urgently needed for the control and remediation of soil pollution. The current pollution levels of heavy metals (Cu, Pb, Cd, Zn, Ni, and Cr) in farmland soils were investigated in Yangxin County, Hubei Province, central China. The comprehensive results of quantitative comparison and evaluation in this study showed that Cu (144.9 ± 298.6 mg kg^-1), Cd (2.9 ± 1.6 mg kg^-1), and Ni (137.0 ± 111.0 mg kg^-1) posed higher pollution risks to public and ecosystem health, which were higher than the corresponding soil background values. The combined results of geostatistics, spatial and statistical analysis indicated that studied heavy metals were mainly attributed to agricultural, traffic and industrial induced pollution. Overall, urgent attention should be paid to the risk reduction and management of soil Cu, Cd, and Ni pollution in the study area.

Spatial distribution, risk assessment, and source identification of pollutants around gold tailings ponds: a case study in Pinggu District, Beijing, China

This work investigated heavy metal and cyanide pollution in surface soils and edible plants around Yanzhuang gold tailings ponds in the region of Yanzhuang Village in Pinggu District, Beijing. Surface soil samples were collected from 33 sites around gold tailings ponds, and concentrations of seven heavy metals (i.e., Sb, As, Cd, Cu, Pb, Zn, and Hg) and cyanide were analyzed to determine their spatial distributions, pollution degrees, and sources. The potential ecological risks of As, Cd, Cu, Pb, Zn, and Hg were preliminarily assessed. The results showed that the mean cyanide, Sb, As, Cd, Cu, and Pb concentrations were higher than the standard values. The pollutant concentrations around the tailings ponds were high and decreased with increasing distance from the ponds. The single pollution index indicated that cyanide, As, and Cd were the main pollutants. The Nemerow pollution index revealed a large region and serious degree of heavy metal pollution in soils. The potential ecological risk level of the study area was moderate, with Cd and As posing the main risks. Multivariate statistical analysis suggested that the heavy metal and cyanide pollution present mainly derived from gold tailings, with agricultural pollution also had a certain effect. However, the 12 edible plants sampled were basically not polluted.

Pollution characteristics and source identification of soil metal(loid)s at an abandoned arsenic-containing mine, China

Mining activities can result in serious contamination of soil by heavy metal(loid)s. In this study, the sources and spatial distribution of metal(loid)s, and the risks to public health from these metal(loid)s at an abandoned arsenic mine site were explored. The mean concentrations of arsenic (As), cadmium (Cd), mercury (Hg), manganese (Mn), lead (Pb), antimony (Sb), strontium (Sr), and thallium (Tl) in the soil in the mining area were higher than the mean background values. The main pollutants from the mining activities were As, Hg, and Sb. Five pollutant sources were identified using an approach that combined statistical methods, a positive matrix factorization model, and historical information analysis. As, Hg, Sb, and Tl were associated with the mining resources and related activities (37.29%); Mn (15.57%) and Sr (15.96%) were mainly from crustal origin and pedogenesis, respectively; Pb, Sb, and Tl were mainly from industrial sources (17.57%), and Cd was mainly from the production and application of phosphorous fertilizer (13.60%). Using incremental spatial autocorrelation crystallized that As, Hg, and Sb were mainly contained within 500 m of their source. There were formed existing non-carcinogenic hazards and carcinogenic risks from As, and potential carcinogenic risks from Cd, in the soil for those living locally.

Trace element contamination in urban topsoil in China during 2000-2009 and 2010-2019: Pollution assessment and spatiotemporal analysis

The Chinese government has launched a critical battle against soil pollution in recent years to establish an effective pollution prevention and control framework. This study sought to investigate the long-term pollution status of potentially toxic trace elements in urban topsoil nationwide, and to further investigate the effectiveness of pollution control over the past decade. The concentrations of 8 elements (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in urban topsoil in China between 2000-2009 and 2010-2019 were separately collected for comparative analysis. Individual and comprehensive pollution levels of the elements were evaluated at the city, provincial, regional, and national scales, and further spatially mapped using GIS. Combined with PCA, the main factors influencing these elements in soil nationwide were identified. The results revealed a severe situation in terms of potentially toxic trace element accumulation in urban topsoil, where the NNIPIs surpassed 3 in both periods. The elements As, Cd, and Hg were closely associated with industrial activity and coal burning. Hg and, in particular, Cd pollution (NPI > 3) were found to be severe in most of the cities studied. For the elements As, Cu, Pb, and Zn, pollution ranged from slight to moderate (1.0 < NPI ≤ 3.0), and Cu, Pb, and Zn were related to a significant degree with vehicle use. Soil Cr and Ni were mainly controlled by parent materials of lithogenic origin, and slight pollution was identified (1.0 < NPI ≤ 2.0). Pollution patterns showed different characteristics across the regions, and those of the same region and the nation hardly changed over time. Mercury pollution was dominant in the northern regions (NW, MYeR, NE, and NC), while Cd pollution was more severe for the south (EC, MYaR, SC, and SW). Notably, the country's comprehensive pollution level was stable across the two periods, with momentum towards improvement observed over the past decade.

Human health and ecological risk assessment of trace elements in urban soils of 101 cities in China: A meta-analysis

Urban soils pollution by trace elements arouses the growing interest in China. The aim of this study was to assess urban soil pollution by As, Cd, Cr, Cu, Hg, Ni, Pb and Zn in China and the possible impacts on urban inhabitants and urban green spaces (UGS). Data from more than 17,000 samples were applied to characterize the status of 101 cities. The pollution assessment proved that 11% of the cities are heavily polluted. According to the Hazard Index, the value of risk for the infant population in 15 cities exceed the standardly accepted tolerable levels. The carcinogenic risk assessment demonstrated the potential threat in the cities with the total population approximately 20,566,900. Cr and As were detected to be the most hazardous elements. UGS may be seriously threatened by trace elements toxicity in 38 cities. Cd was found to be the riskiest element for UGS. Ecosystem services of UGS can be significantly disrupted under the current situation in China and their status is expected to deteriorate in the future. For this reason, it is essential to alter the policy of the urbanization process and develop functional concepts of urban green infrastructures adapted to the high level of contamination which shall improve human well-being in China.

Bioavailable metal(loid)s and physicochemical features co-mediating microbial communities at combined metal(loid) pollution sites

Heavy metal contamination poses considerable threats to various ecosystems, yet little is known about the assembly and adaptation of microbial communities at sites with combined heavy metal(loid) pollution. Here, we examined metal(loid) pollutants and bacterial communities in three zones (Zones Ⅰ, Ⅱ, and Ⅲ) of an abandoned sewage reservoir with different usage years. The contamination level of multiple metal(loid)s was higher in Zone Ⅰ than in the other zones, and arsenic (As), zinc (Zn), selenium (Se), copper (Cu), tin (Sn), molybdenum (Mo), antimony (Sb), cadmium (Cd), lead (Pb), thallium (Tl), and nickel (Ni) were the major contaminants (pollution load index > 1). Bioavailable forms of titanium (Ti), chromium (Cr), Sn, and cobalt (Co) played essential roles in shaping the microbial structure, and physicochemical properties, especially organic matter (OM) and pH, also mediated the microbial diversity and composition in the metal(loid) contaminated zones. Metal-microbe interactions and heatmap analysis revealed that the bioavailability of metal(loid)s promoted the niche partitioning of microbial species. Metal-resistant species were abundant in Zone Ⅰ that had the highest metal-contaminated level, whereas metal-sensitive species prevailed in Zone Ⅲ that had the lowest pollution level. The bioavailable metal(loid)s rather than physicochemical and spatial variables explained a larger portion of the variance in the microbial community, and the homogeneous selection was the dominant ecological process driving the assembly of the microbial community. Overall, our study highlighted the importance of metal(loid) bioavailability in shaping microbial structure, future bioremediation, and environmental management of metal(loid) contaminated sites.

Improved Mapping of Potentially Toxic Elements in Soil via Integration of Multiple Data Sources and Various Geostatistical Methods

Soil pollution by potentially toxic elements (PTEs) has become a core issue around the world. Knowledge of the spatial distribution of PTEs in soil is crucial for soil remediation. Portable X-ray fluorescence spectroscopy (p-XRF) provides a cost-saving alternative to the traditional laboratory analysis of soil PTEs. In this study, we collected 293 soil samples from Fuyang County in Southeast China. Subsequently, we used several geostatistical methods, such as inverse distance weighting (IDW), ordinary kriging (OK), and empirical Bayesian kriging (EBK), to estimate the spatial variability of soil PTEs measured by the laboratory and p-XRF methods. The final maps of soil PTEs were outputted by the model averaging method, which combines multiple maps previously created by IDW, OK, and EBK, using both lab and p-XRF data. The study results revealed that the mean PTE content measured by the laboratory methods was as follows: Zn (127.43 mg kg−1) > Cu (31.34 mg kg−1) > Ni (20.79 mg kg−1) > As (10.65 mg kg−1) > Cd (0.33 mg kg−1). p-XRF measurements showed a spatial prediction accuracy of soil PTEs similar to that of laboratory analysis measurements. The spatial prediction accuracy of different PTEs outputted by the model averaging method was as follows: Zn (R2 = 0.71) > Cd (R2 = 0.68) > Ni (R2 = 0.67) > Cu (R2 = 0.62) > As (R2 = 0.50). The prediction accuracy of the model averaging method for five PTEs studied herein was improved compared with that of the laboratory and p-XRF methods, which utilized individual geostatistical methods (e.g., IDW, OK, EBK). Our results proved that p-XRF was a reliable alternative to the traditional laboratory analysis methods for mapping soil PTEs. The model averaging approach improved the prediction accuracy of the soil PTE spatial distribution and reduced the time and cost of monitoring and mapping PTE soil contamination.

Contamination, Spatial Distribution and Source Analysis of Heavy Metals in Surface Soil of Anhui Chaohu Economic Development Zone, China

Anthropogenic activities may result in the accumulation of heavy metals in the soil, especially in economic development zones with frequent industrial activities. Therefore, the investigation and assessment of soil heavy metal pollution in economic development zones is one of the important measures for soil environmental management and sustainable development. This study used Nemero evaluation, Kriging interpolation, cluster analysis, and principal component analysis to investigate the contamination degree, spatial distribution, and origin of heavy metal in Anhui Chaohu Economic Development Zone (ACED), Anhui, East China. The result showed that different land use types can cause different levels and types of soil heavy metal pollution. The maximum concentrations of heavy metals in the study area all exceeded their background value but did not exceed the guide values. The highest average concentrations were found in Zn, followed by Cr and Ni. The concentrations of As in soils have the largest coefficient of variation (CV) at 38%. The concentration of heavy metals in different functional areas was varied, the areas with higher Ni, As, Cd, Zn, and Cr concentrations were mainly distributed in Hot Springs Resort (HSR), the relatively higher concentrations of Pb, Hg, and Cu were mainly distributed in Integrated Zone (IZ), while all heavy metal (except for Ni) have relatively higher content in the surface soil of Huashan Industrial Zone (HIZ). Origin analysis showed that soil As, Cd, and Zn in HSR surface soil were predominantly influenced by agricultural activities, while Ni and Cr were mainly controlled by parent material. Pb and Hg in IZ surface soil were predominantly originated from the vehicle and domestic exhaust, and Cu was mainly controlled by industrial pollutants. Industrial activity was the main source of soil heavy metals in HIZ. Although heavy metal in ACED surface soil did not reach pollution levels, the concentration of Cd, Hg, Pb, and Cu was significantly affected by anthropogenic activities, especially in HIZ, which the necessary attention of heavy metals needs to be given.

Screening of chemical composition and risk index of different origin composts produced in Lithuania

The application of composts could be accompanied by potential hazards to soil and humans, caused by heavy metals and organic persistent pollutants. A total of 115 compost samples from four different origins (green waste composts, sewage sludge composts, mixed municipal waste composts after mechanical-biological treatment and mixed municipal waste compost) were collected to analyse the chemical composition, nutrients levels, seven heavy metals, 15 polycyclic aromatic hydrocarbons (PAHs) and seven polychlorobiphenyls (PCBs). Simulation models were used to estimate the heavy metal accumulation risk in soil and to evaluate the potential ecological risk to environment. After analysing chemical parameters of compost quality, it was found that sewage sludge composts contained the highest amounts of nitrogen (2.98%), phosphorus (4.44%) and organic matter (47.6%), and the highest potassium content (1.20%) was found in mixed municipal composts after mechanical-biological treatment. After having tested all the composts, green waste composts had the lowest content of the following nutrients: nitrogen, phosphorus, potassium and sulphur. High molecular weight PAHs dominated in green waste, sewage sludge and mixed municipal waste composts, and the opposite tendency was observed on mixed municipal waste composts after mechanical-biological treatment; low molecular weight PAHs were abundant. It was determined that, according to the total amount of 15 PAHs (16.54 mg kg^-1 d.w.) and 7 PCBs (233.53 μg kg^-1 d.w.), the most contaminated composts were produced from mixed municipal waste. As it was expected, the lowest level of PCBs (13.85 μg kg^-1 d.w.) was found in green waste composts. Monte Carlo simulations showed that the shortest period in which zinc concentration in soil could increase twice is 2 years when applying continuously mixed municipal waste compost after mechanical-biological treatment. Based on Monte Carlo simulation results from repeated application of green waste composts, mixed municipal waste compost and mixed municipal waste compost after mechanical-biological treatment could double the soil background level of copper in 6 and 3 years respectively. Reducing the content of heavy metals in composts would be of great significance for minimising the damage caused by them.

A mineralogical and chemical investigation of road dust in Philadelphia, PA, USA

Road dust was investigated within Philadelphia, a major United States city with a long history of industrial activities, in order to determine pollution levels. Almost all of the investigated minor elements were enriched relative to the continental crust. Furthermore, mean concentrations of Cr, Co, Cu, and Pb were high compared with those reported in cities in other countries. Lead pollution should be investigated further in Philadelphia, where 8 of the 30 sample sites, including those heavily trafficked by civilians, were at or above the EPA's child safety threshold for Pb in bare soil. High Spearman correlations between Zn and Cu, Zn and Cr, Cu and Cr, and Sn and V, as well as factor analysis of minor elements suggests that the primary sources of these elements were anthropogenic. Potential sources included the breakdown of alloys, non-exhaust traffic emissions, paint, smelting, and industry. We found that higher organic content in road dust may be related to higher traffic densities, which could be due to tire-wear particles. Additionally, higher mean concentrations of Fe, Cr, Cu, and Zn were found at sites with elevated traffic densities. Land use impacted some of the elements not influenced by traffic density, including Co, Sn, and Pb. Bulk mineral content was similar across different land uses and traffic densities and, thus, did not appear to be influenced by these factors. Our research emphasized the complexity of road dust and utilized a more comprehensive approach than many previous studies. This study established fundamental groundwork for future risk assessment in Philadelphia, as it identified several key pollutants in the city. Overall, this assessment serves as an informative reference point for other formerly heavily industrialized cities in the USA and abroad.

Impact assessment of metals on soils from Machu Picchu archaeological site

Machu Picchu is an archaeological Inca sanctuary from the 15th century, located 2430 m above the sea level in the Cusco Region, Peru. In 1983, it was declared World Heritage Site by UNESCO. The surroundings and soils from the entire archaeological site are carefully preserved together with its grass parks. Due to the importance of the archaeological city and its surroundings, the Decentralized Culture Directorate of Cusco-PAN Machu Picchu decided to carry out a careful monitoring study in order to determine the ecological status of the soils. In this work, elemental and molecular characterization of 17 soils collected along the entire park was performed by means of X-ray Diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) after acidic digestion assisted by microwave energy. Thanks to the combination of these analytical techniques, it was possible to obtain the mineral composition and metal concentrations of all soils from these 17 sampling points. Finally, different statistical treatments were carried out in order to confirm the ecological status of the different sampling points from Machu Picchu archaeological site concluding that soils are not impacted.

Source analysis and risk assessment of heavy metals in development zones: a case study in Rizhao, China

The effects of heavy metal pollution in parks have caused widespread concern. This study investigated the concentrations and sources of eight heavy metals in the economic and technological development zone in Rizhao City. Geo-accumulation index ([Formula: see text]) and potential ecological risk index (PERI) were used to assess the pollution level of the development zone. Sources of heavy metals were analyzed through correlation analysis (CA) and principal component analysis (PCA). Descriptive statistics showed that many types of heavy metals accumulated in the development zone. The average concentrations of Pb, Cd, Hg, Ni, and Zn in the soil exceeded the background values of soil environment in Shandong Province. [Formula: see text] showed that only Hg in the soil was at the non-pollution to moderate pollution level. Meanwhile, sediments were polluted by Hg, Cd, and Zn, with their pollution level being higher than that of the soil. PERI showed that the soil presented moderate risk level and that the river sediment showed severe risk level. Hg and Cd exhibited the highest potential ecological risk. The results of the CA and PCA showed that the main sources of heavy metal pollution in the development zone are industrial activities, followed by atmospheric factors. Focus should thus be directed toward heavy metal pollution in development zones to protect human health and the soil environment.

Heavy Metals in Agricultural Soils of the Lihe River Watershed, East China: Spatial Distribution, Ecological Risk, and Pollution Source

Concentrations of cadmium, chromium, copper, nickel, lead, and zinc in agricultural soils at 32 sites in the Lihe River Watershed of the Taihu region, East China, and their potential ecological risks and possible sources were investigated. Enrichment factor analysis demonstrated enrichment in the order Cd > Pb > Zn > Cu > Ni > Cr. The potential ecological risk index and risk assessment code analyses indicated that, of the metals studied, Cd posed the most significant ecological risk in the study area. Statistical analyses, GIS mapping, and enrichment factor analysis suggested that Cd, Pb, Cu, and Zn were derived mainly from anthropogenic sources, including agricultural, industrial, and vehicular emissions, while Cr and Ni were mainly from natural sources. Positive matrix factorization revealed that Cd, Cr, Cu, Ni, Pb, and Zn were sourced from industrial and vehicular emissions (73.7%, 21.3%, 71.4%, 20.3%, 75.0%, and 62.2%, respectively), the agricultural sector (26.3%, 36.3%, 6.8%, 38.9%, 15.7%, and 6.9%, respectively), and parent materials (0%, 42.4%, 21.8%, 40.8%, 9.2%, and 30.9%, respectively). It was recommended that strategies be implemented to reduce industrial point-source pollution.

Apportionment of sources of heavy metals to agricultural soils using isotope fingerprints and multivariate statistical analyses

Apportioning sources of environmental pollutants is key to controlling pollution. In this study, the sources of heavy metals to 234 agricultural soils from the Jianghan Plain (JHP) (∼22454 km²) in central China were discriminated between using Cd and Pb isotope compositions and multivariate statistical analyses. Concentrations of some metals in JHP soils (0.48 ± 0.2, 48.2 ± 15.9, 0.12 ± 0.23, 48.8 ± 16.4, 36.5 ± 9.8, and 96.8 ± 42.2 mg kg^-1 for Cd, Cu, Hg, Ni, Pb, and Zn, respectively) were higher than background concentrations in Chinese soil. The Cd isotope compositions for the JHP soils (δ^114/110Cd values -0.76‰ to -0.25‰) were similar to Cd isotope compositions found for smelter dust and incinerator fly ash, indicating Cd was supplied to the JHP soils by ore smelting and/or refining processes. The Pb isotope compositions for the JHP soils (²⁰⁶Pb/²⁰⁷Pb 1.182-1.195 and ²⁰⁸Pb/²⁰⁶Pb 2.078-2.124) were between the Pb isotope compositions found for Chinese coal and natural sources, which a binary isotope mixing model indicated contributed 52% and 48%, respectively, of the Pb in JHP soils. Cluster analysis and positive matrix factorization indicated that the sources of heavy metals in JHP soils may consist of smelting and/or refining activities, coal combustion, agricultural activities, and natural sources (including Han River sediment and soil parent materials). The isotope fingerprints and multivariate statistical analyses together indicated that coal combustion and smelting and/or refining activities were the main anthropogenic sources of heavy metals polluting JHP soils.

Potential effects of exploiting the Yunfu pyrite mine (southern China) on soil: evidence from analyzing trace elements in surface soil

Trace element contamination caused by mining is a serious environmental problem. The potential effects of exploiting the Yunfu pyrite mine (southern China) on soil were investigated by determining trace elements in 56 surface soil samples from the vicinity of the Yunfu pyrite mine. The samples were acid dissolved and measured by an inductively coupled plasma mass spectrometry (ICP-MS). Principal component analysis and hierarchical cluster analysis were used to identify factors influencing the trace element contents and possible sources of the trace elements. The degree of trace element pollution was determined using the geological accumulation index I_geo. Monte Carlo simulations were used to assess the health risks posed. The results show that (1) six factors (parent material, mining activities, ore composition, rainfall, terrain, and other inputs) strongly affected the trace element contents of the soil samples. (2) There were three groups of trace elements, according to their possible sources. One group (Cs, Ga, Ge, Hf, Nb, Rb, Ta, Th, Ti, U, and Zr) mainly originated in parent rocks. Another group (Cr, Ni, Sr, and V) was mainly supplied by industrial plants and traffic emissions. The third group (Ba, Co, Cu, Mn, Pb, and Zn) was mainly supplied through pyrite ore exploitation processes. (3) Some samples were slightly to moderately polluted with Cs, Ga, Ge, Nb, Rb, Ta, and Ti. Most samples were moderately to highly polluted with Ba, Co, Cu, Mn, Pb, and Zn. (4) Trace elements in soil pose strong non-carcinogenic and carcinogenic health risks to people (particularly children) living near the Yunfu pyrite mine.

Cadmium Removal from Aqueous Solutions by Strain of Pantoea agglomerans UCP1320 Isolated from Laundry Effluent

Background:

Cadmium (Cd), which is a deadly heavy metal of work-related and environmental concern, has been recognized as a substance that is teratogenic and carcinogenic for humans. Therefore, the need to develop low-cost adsorbents to remove heavy metals from aqueous solution has greatly increased. Adsorbents such as Pantoea agglomerans biomass have been used.

Aims:

We investigated the biotechnological potential of Pantoea agglomerans for the biosorption of cadmium from aqueous solution.

Patients and Methods:

Pantoea agglomerans UCP1320 isolated from the effluent of a laundry industry was used to remove cadmium from aqueous solutions. Two approaches were compared using active or thermally inactivated biomass. Three different cadmium concentrations of 1, 10 and 100 ppm were used under constant stirring at temperatures of 25°C and 35°C as was pH of 3.0, 5.0 and 7.0. Variable incubation times of 1, 6, and 24h were also studied.

Results:

The results showed that the temperature did not influence the uptake of metal by living cells nor by inactive bacterial biomass. However, increasing the pH had a positive effect on removing intermediate concentrations of cadmium. Low concentrations of cadmium were completely removed by both live and inactive biomass.

Conclusion:

Pantoea agglomerans biomass was shown to have a promising performance for the biotechnological removal of cadmium which had been dissolved in aqueous solution.

Risk Assessment and Source Identification of Toxic Metals in the Agricultural Soil around a Pb/Zn Mining and Smelting Area in Southwest China

Mining and smelting activities are the primary sources of toxic metal pollution in China. The purpose of this study was to investigate the pollution risk and identify sources of metals in the arable soil of a Zn/Pb mining and smelting district located in Huize, in Southwest China. Topsoil (346) and profile (three) samples were collected and analyzed to determine the total concentrations of eight toxic elements (Cd, Hg, As, Pb, Cr, Cu, Zn and Ni). The results showed that the mean Cd, Hg, As, Pb, Cr, Cu, Zn and Ni concentrations were 9.07, 0.37, 25.0, 512, 88.7, 239, 1761 and 90.3 mg/kg, respectively, all of which exceeded both the Huize and Yunnan soil background levels. Overall the topsoil was quite acidic, with a mean pH of 5.51. The mean geoaccumulation index (Igeo) revealed that the pollution level was in the order of Pb > Zn > Cd > Hg > As > Ni > Cu > Cr. The ecological risk index (E_i) indicated that there were serious contamination risks for Cd and Hg, high risk for Pb, moderate risk for As, and Cd and Hg were the dominant contributors to the high combined ecological risk index (E_r) with a mean parameter of 699 meaning a serious ecological risk. The Nemerow pollution index (P_n) showed that 99.1% of soil samples were highly polluted or worse. Horizontally, high concentrations of Cd, Hg, As, Pb and Zn appeared in the north and middle of the study area, while Cr, Cu and Ni showed an opposite trend. Vertically, as the depth increased, Cd, Hg, As, Pb and Zn contents declined, but Cr, Cu and Ni exhibited an increasing trend. The mobilities of the metals were in the order of Zn > Cd > Hg > As > Pb. Horizontal and vertical distribution, coupled with correlation analysis, PCA and CA suggested that Cd, Hg, As, Pb and Zn mainly came from the anthropogenic sources, whereas Cr and Ni had a lithogenic origin. The source of Cu was a combination of the presence of parent materials as well as human activities. This study provides a base for the local government to control the toxic metal pollution and restore the soil environment system and an effective method to identify the sources of the studied pollutants.

Main controlling factors and forecasting models of lead accumulation in earthworms based on low-level lead-contaminated soils

To explore the main controlling factors in soil and build a predictive model between the lead concentrations in earthworms (Pb_earthworm) and the soil physicochemical parameters, 13 soils with low level of lead contamination were used to conduct toxicity experiments using earthworms. The results indicated that a relatively high bioaccumulation factor appeared in the soils with low pH values. The lead concentrations between earthworms and soils after log transformation had a significantly positive correlation (R² = 0.46, P < 0.0001, n = 39). Stepwise multiple linear regression analysis derived a fitting empirical model between Pb_earthworm and the soil physicochemical properties: log(Pb_earthworm) = 0.96log(Pb_soil) - 0.74log(OC) - 0.22pH + 0.95, (R² = 0.66, n = 39). Furthermore, path analysis confirmed that the Pb concentrations in the soil (Pb_soil), soil pH, and soil organic carbon (OC) were the primary controlling factors of Pb_earthworm with high pathway parameters (0.71, - 0.51, and - 0.49, respectively). The predictive model based on Pb_earthworm in a nationwide range of soils with low-level lead contamination could provide a reference for the establishment of safety thresholds in Pb-contaminated soils from the perspective of soil-animal systems.

Review of Heavy Metals Pollution in China in Agricultural and Urban Soils

BACKGROUND

The concentrations of heavy metals in soil and potential risks to the environment and public health are receiving increased attention in China.

OBJECTIVES

The objective of this paper is to review and analyze heavy metals soil contamination in urban and agricultural areas and on a national scale in China.

METHODS

Initially, data on soil heavy metals concentration levels were gathered from previous studies and narratively analyzed. A further statistical analysis was performed using the geo-accumulation index (I_geo), Nemerow integrated pollution index (NIPI), mean, standard deviation (SD), skewness and kurtosis. Pollution levels were calculated and tabulated to illustrate overall spatial variations. In addition, pollution sources, remedial measures and impact of soil contamination as well as limitations are addressed.

RESULTS

The concentration level of heavy metals was above the natural background level in most areas of China. The problem was more prevalent in urban soils than agricultural soils. At the national level, the soil in most of the southern provinces and Beijing were heavily polluted. Even though the pollution condition based on I_geo was promising, the Nemerow integrated pollution level was the most worrisome. The soils in about 53% of the provinces were moderately to heavily polluted (NIPI>2). The effects were noticed in terms of both public and ecological health risks. The major sources were waste gas, wastewater, and hazardous residuals from factories and agricultural inputs such as pesticides. Efforts have been made to reduce the concentrations and health risks of heavy metals, including policy interventions, controlling contamination sources, reducing the phytoavailability of heavy metals, selecting and rearing of grain cultivars with low risk of contamination, paddy water and fertilizer management, land use changes, phytoremediation and engineering techniques.

CONCLUSIONS

China is experiencing rapid economic and technological advancements. This increases the risk of heavy metals contamination of soil. If serious attention is not paid to this problem, soil toxicity and biological accumulation will continue to threaten the sustainability of China's development.

COMPETING INTERESTS

The authors declare no competing financial interests.

Metal accumulation in populations of Calamagrostis epigejos (L.) Roth from diverse anthropogenically degraded sites (SE Europe, Serbia)

Heavy metal accumulation is recognized as a very important global pollution problem in the last decades. Plant species have been recognized as natural bioindicators of environmental pollution, especially the amount of heavy metals in soils. Moreover, only a limited number of plant species can survive in highly contaminated soils. It is also known that metal accumulation can vary greatly among different populations of the same species. This study examines the chemical composition and accumulation potential of the expansive clonal grass Calamagrostis epigejos at five localities exposed to different levels of anthropogenic pressure. Considerable differences were observed between uptake, translocation, and accumulation of total and available heavy metals, such differences corresponding to soil physico-chemical characteristics and the level of site pollution. The results indicate that Calamagrostis epigejos uptakes a significant portion of the available fraction of heavy metals in the soil and stores it in the roots, thereby exhibiting a certain potential for metal phytostabilization.

Effects of biochar addition on toxic element concentrations in plants: A meta-analysis

Consuming food contaminated by toxic elements (TEs) could pose a substantial risk to human health. Recently, biochar has been extensively studied as an effective soil ameliorant in situ because of its ability to suppress the phytoavailability of TEs. However, despite the research interest, the effects of biochar applications to soil on different TE concentrations in different plant parts remain unclear. Here, we synthesize 1813 individual observations data collected from 97 articles to evaluate the effects of biochar addition on TE concentrations in plant parts. We found that (1) the experiment type, biochar feedstock and pyrolysis temperature all significantly decreased the TE concentration in plant parts; (2) the responses of Cd and Pb concentrations in edible and indirectly edible plant parts were significantly more sensitive to the effect of biochar than the Zn, Ni, Mn, Cr, Co and Cu concentrations; and (3) the biochar dosage and surface area, significantly influenced certain TE concentrations in plant tissues as determined via correlation analysis. Moreover, the only exception in this study was found for metalloid element (i.e., As) concentrations in plants, which were not significantly influenced by biochar addition. Overall, the effects of biochar on TE concentrations in plant tissues were negative, at least on average, and the central trends suggest that biochar has a considerable ability to mitigate the transfer of TEs to food, thereby reducing the associated health risks. Our results provide an initial quantitative determination of the effects of biochar addition on multifarious TEs in different plant parts as well as an assessment of the ability of biochar to reduce TE concentrations in plants.

Heavy metals in soils of Hechuan County in the upper Yangtze (SW China): Comparative pollution assessment using multiple indices with high-spatial-resolution sampling

In order to assess heavy metals (HMs) in soils of the upper Yangtze Basin, a very high-spatial-resolution sampling (582 soil samples) was conducted from Hechuan County, an important agricultural practice area in the Southwest China. Multiple indices including geoaccumulation index (I_geo), enrichment factor (EF), sediment pollution index (SPI) and risk index (RI), as well as multivariate statistics were employed for pollution assessment and source identification of HMs in soils. Our results demonstrated that the averages of eight HMs decreased in the following order: Zn (82.8 ± 15.9) > Cr (71.6 ± 12.2) > Ni (32.1 ± 9.89) > Pb (27.6 ± 13.8) > Cu (25.9 ± 11.8) > As (5.48 ± 3.42) > Cd (0.30 ± 0.077) > Hg (0.082 ± 0.092). Averages of HMs except Cd were lower than threshold value of Environmental Quality Standard for Soils, while 43% of total samples had Cd concentration exceeding the national standard, 1% of samples for Hg and 5% samples for Ni, moreover, Cd and Hg averages were much higher than their background levels. I_geo and EF indicated that their levels decreased as follows: Cd > Hg > Zn > Pb > Ni > Cu > Cr > As, with moderate enrichments of Cd and Hg. RI indicated that 61.7% of all samples showed moderate risk, while 6.5% of samples with greater than considerable risk due to human activities should be paid more attention. Multivariate analysis showed lithogenic source of Cu, Cr, Ni and Zn, while Cd and Hg were largely contributed by anthropogenic activities such as agricultural practices. Our study would be helpful for improving soil environmental quality in SW, China, as well as supplying modern approaches for other areas with soil HM pollution.

A review of heavy metal pollution levels and health risk assessment of urban soils in Chinese cities

This study assessed literature-based data for the period 2006-2016 regarding heavy metal (As, Cd, Cr, Cu, Pb, Ni, Zn, and Hg) concentrations in soils from 32 Chinese cities and the associated human health risks. The mean concentrations of the eight metals were lower than the soil environmental quality standards in China, but were much higher than the background values for most cities. The enrichment factor (EF) and geoaccumulation index (I _geo) values showed moderate pollution levels, possibly influenced by anthropogenic activity for Cd, Hg, Pb, and Zn. The pollution levels in eastern cities were much higher than those in western cities, and heavy metals concentrations in different types of cities followed the order: industrial based cities > more developed cities > metropoles > underdeveloped cities. The human health risk assessment for heavy metals in most cities indicated that non-carcinogenic risks were within threshold values (HI < 1). The total carcinogenic risk due to As, Cr, and Ni in most urban areas was in excess of 1 × 10^-5, but was lower than 1 × 10^-4. However, in some cities (e.g., Baoji City, Tiyuan City, and Xuzhou City), Ni and Cr have potential cancer risks for both adults and children. Compared to adults, children could be more seriously threatened by heavy metal contamination in soils. In general, we recommend that Cd, Hg, and Pb are selected as priority heavy metals pollutants that require control in Chinese cities.

Indices of soil contamination by heavy metals - methodology of calculation for pollution assessment (minireview)

This article provides the assessment of heavy metal soil pollution with using the calculation of various pollution indices and contains also summarization of the sources of heavy metal soil pollution. Twenty described indices of the assessment of soil pollution consist of two groups: single indices and total complex indices of pollution or contamination with relevant classes of pollution. This minireview provides also the classification of pollution indices in terms of the complex assessment of soil quality. In addition, based on the comparison of metal concentrations in soil-selected sites of the world and used indices of pollution or contamination in soils, the concentration of heavy metal in contaminated soils varied widely, and pollution indices confirmed the significant contribution of soil pollution from anthropogenic activities mainly in urban and industrial areas.

Application of portable XRF and VNIR sensors for rapid assessment of soil heavy metal pollution

Rapid heavy metal soil surveys at large scale with high sampling density could not be conducted with traditional laboratory physical and chemical analyses because of the high cost, low efficiency and heavy workload involved. This study explored a rapid approach to assess heavy metals contamination in 301 farmland soils from Fuyang in Zhejiang Province, in the southern Yangtze River Delta, China, using portable proximal soil sensors. Portable X-ray fluorescence spectroscopy (PXRF) was used to determine soil heavy metals total concentrations while soil pH was predicted by portable visible-near infrared spectroscopy (PVNIR). Zn, Cu and Pb were successfully predicted by PXRF (R² >0.90 and RPD >2.50) while As and Ni were predicted with less accuracy (R² <0.75 and RPD <1.40). The pH values were well predicted by PVNIR. Classification of heavy metals contamination grades in farmland soils was conducted based on previous results; the Kappa coefficient was 0.87, which showed that the combination of PXRF and PVNIR was an effective and rapid method to determine the degree of pollution with soil heavy metals. This study provides a new approach to assess soil heavy metals pollution; this method will facilitate large-scale surveys of soil heavy metal pollution.

Spatial distribution of soil cadmium and its influencing factors in peri-urban farmland: a case study in the Jingyang District, Sichuan, China

Semi-agricultural ecosystems in peri-urban areas are susceptible to contamination. The spatial distribution and influencing factors of such pollution are unclear and poorly constrained in many areas worldwide. Therefore, studying the problems of soil pollution in peri-urban areas is critical for environmental management and agricultural production. In this paper, with cadmium (Cd) as the target pollutant, the spatiotemporal variations of soil cadmium pollution and the relative importance of the affecting factors were analyzed at a peri-urban area from the Jingyang District, Sichuan, China. Statistical results showed that the farmland in the study area could be considered moderately soil Cd-polluted, under the dual influence of natural factors and human activity. In particular, the soil Cd concentration in Tianyuan and Bajiaojing exceeded 0.5 mg kg^-1, for intensive industrial enterprises are distributed in these areas. Correspondingly, the geoaccumulation index also showed that the contamination of Cd in this area was moderately polluted. Moreover, the ecological risk index was 80% in the study area, indicating that the soil Cd pollution potential risk was moderate to high. High geological background values (soil Cd = 0.29 mg kg^-1), river migration, industrial enterprises, and traffic significantly influenced soil Cd pollution, with natural geological factors playing greater roles. The significant horizontal-spatial effective distances away from Shiting River, Deyang-Aba Highway, and chemical plants were 200, 400, and 100 m, respectively. These results will be useful in guiding farmland cultivation and pollution remediation effectively in the peri-urban areas.

Identification of Potential Sources of Mercury (Hg) in Farmland Soil Using a Decision Tree Method in China

Identification of the sources of soil mercury (Hg) on the provincial scale is helpful for enacting effective policies to prevent further contamination and take reclamation measurements. The natural and anthropogenic sources and their contributions of Hg in Chinese farmland soil were identified based on a decision tree method. The results showed that the concentrations of Hg in parent materials were most strongly associated with the general spatial distribution pattern of Hg concentration on a provincial scale. The decision tree analysis gained an 89.70% total accuracy in simulating the influence of human activities on the additions of Hg in farmland soil. Human activities—for example, the production of coke, application of fertilizers, discharge of wastewater, discharge of solid waste, and the production of non-ferrous metals—were the main external sources of a large amount of Hg in the farmland soil.