Types Of Heavy Metals Research Articles

Insight into different removal behaviors and mechanism of heavy metals via sulfate-loaded layered double oxide

Sulfur-containing materials with high affinity toward heavy metals have recently aroused great research enthusiasm. Yet the removal differences and mechanisms for various heavy metals remain unclear in view of rarely systematical reports. In this regard, a sulfate-loaded adsorbent (MgAl-LDO@S) synthesized by precursor-calcination strategy was employed for investigating the removal differences of heavy metals (i.e., Pb(Ⅱ), Cd(Ⅱ) and Ni(Ⅱ), typical heavy metals in wastewater). As predicted, a diverse adsorption capability for metals on MgAl-LDO@S was observed, following the order of Pb(Ⅱ) (631.90 mg g−1) > Cd(Ⅱ) (208.27 mg g−1) > Ni(Ⅱ) (119.02 mg g−1). Both adsorption isotherm and kinetic demonstrated that the monolayer, heterogeneous-homogeneous, and multilayer adsorption occurred in Pb(Ⅱ), Cd(Ⅱ) and Ni(Ⅱ), respectively, which were controlled by chemisorption. Furthermore, the removal differences were deeply exploded via the combination of XRD, FT-IR and XPS analyses and contribution calculation. The ion exchange was the main adsorption mechanisms for Pb (II) with 44.77%, while complexation dominated in Cd(II) and Ni(II) removal, with the proportion of 53.36% and 55.89%, respectively. Besides, the solubility constant (Ksp) of precipitate, affinity of sulfate group, as well as the self-characteristic properties contributed to various removal ability for heavy metal ions (e.g., ionic radius, electronegativity, and hard-soft-acid-base attribute) as well.

A facile one-pot synthesis of ionic liquid@porous organic frameworks for rapid high-capacity removal of heavy metal ions, pesticides and aflatoxin from two non-food bioactive products

Without inert gas protection and extra assistance by energy field, a green, facile, and catalyst-free strategy to synthesize ionic liquid@porous organic frameworks (IL@POFs) with high efficiency was developed for the first time. Besides, they have high specific surface area, stability and sustainability. As the brutal facts, many industrial crops are easily polluted and then cause safety risks. Among above IL@POFs, 1-butyl-3-methylimidazolium proline salt@porous organic framework ([C4mim][L-pro]@POF) exhibits rapid removal performance for typical heavy metal ions from Poria cocos (removing 100% Pb2+ within 5 min; 207.47 mg/g for Pb2+ and 62.85 mg/g for Cu2+). The separation mechanisms are coordination, accompanied by ion exchange and electrostatic interaction. Moreover, 1-butyl-3-methylimidazolium hexafluorophosphate@porous organic framework ([C4mim][PF6]@POF) could remove 85% triazophos and 93% aflatoxin B1 (AFB1) effectively from Radices trichosanthis within 5 min, and multiple intermolecular interactions contribute to its adsorption capacity and selectivity. Above sorbents can be reused after effective elution. The proposed strategy not only provides valuable reference for the high-efficient synthesis of IL@POFs but also opens up a new pathway to recycling contaminated industrial crops.

Multifaceted evaluation of distribution, occurrence, and leaching features of typical heavy metals in different-sized coal gasification fine slag from Ningdong region, China: A case study

The coal gasification fine slag (CGFS) from the entrained-flow coal gasification unit faces the challenge of safe disposal and clean utilization in the Ningdong region, China. This study aims to provide complete and thorough understanding of the distribution features, chemical speciation, environmental impact, and leaching behavior of typical heavy metals (i.e., V, Cr, Mn, Ni, Cu, Zn, Ba, and Pb) in the CGFS with different size fractions. The results show that the distribution of selected heavy metals in the CGFS has evident particle size dependence. Except for Zn, the other heavy metals in different size fractions mainly exist in chemical speciation of residual form with the ratio of 50.11–86.69 wt%. Moreover, it is found that the heavy metals in the different-sized CGFS show different RAC (risk assessment code) environmental risk levels and TCLP (Toxicity Characteristic Leaching Procedure) leaching concentrations. Especially, Zn in SGFS-C and SGFS-D posed a high-risk level to the environment, while the heavy metal elements of Cr, Mn, Ni, Zn, and Ba in other size fractions are classified as a medium environmental risk. In addition, the TCLP test results indicate that the leaching concentration of Cr, Mn, Ni, Zn, Ba, and Pb exceeds the groundwater-related regulatory limit in China. The pH-dependent leaching experiments suggest that Pb shows the amphoteric behavior, while the leaching mode of other heavy metals seems to be the cationic pattern. Furthermore, the leachability of the selected heavy metals in small-size fractions of the CGFS should be given more consideration at both acid and alkaline pH ranges. The leaching kinetic results demonstrate that the most effective mechanism to describe the leaching process of Cr, Ni, Zn, and Pb in different CGFS size fractions is the diffusion-controlled theory, which is supported by the different morphological traits of spherical mineral particles and carbon particles in the CGFS.

The fate of heavy metals in the co-processing of solid waste in converter steelmaking

The improper disposal of large amounts of solid waste (SW) has led to serious ecological and environmental problems, especially heavy metal (HM) pollution. Converter steelmaking has the potential to co-process SW, but the distribution of heavy metals (HMs) during converter steelmaking is unclear. In this study, the effects of smelting temperature and slag alkalinity on the distribution of typical HMs in the SW of steel samples, steel slag, and the gas phase were investigated in a specially-made induction furnace. The results showed that upon increasing the smelting temperature, As (As2S3) was mainly distributed in the steel sample, and the HM-containing compounds Cr2O3, CrCl3, ZnCl2, ZnS, ZnO, PbCl2, PbS, and PbO were mainly distributed in the gas phase. Upon increasing the alkalinity within a certain range, the distribution of HMs in steel samples and steel slag increased gradually, while their distribution in the gas phase decreased. Thermodynamic calculations, Eh-pH diagrams, XRD patterns, and XPS spectra indicated that impurity elements in the hot metal and the CaO content affected the chemical reactions by which HM-containing compounds in the steel sample formed elemental HMs and those in steel slag existed as oxides; therefore, it is necessary to choose a suitable temperature and alkalinity for slag when disposing of different types of SW.

Heavy Metals in Soils From Intense Industrial Areas in South China: Spatial Distribution, Source Apportionment, and Risk Assessment

Heavy metal pollution from various industrial activities has raised global concern. The present study collected 71 surface and 67 subsurface soils from the area with intensive industrial activities in South China. The typical heavy metals, including Cd, As, Hg, Cu, Ni, Pb, Zn, and Cr concentrations, were detected for studying their spatial distribution patterns. Sources apportionment and risks were analyzed using geographical information system and combined approach, including principal component analysis (PCA), positive matrix factorization (PMF), and geo-accumulation index. The concentrations of Cd, As, Hg, Cu, Ni, Pb, and Zn (except Cr) were higher than relevant background levels while exhibiting different pollution degrees in surface and subsurface soils. The PMF results showed that agriculture, industry, transportation, and nature were the four primary contributing sources of heavy metals in soils from the study area. In general, anthropogenic activities were the dominant factors, significantly influencing heavy metal distributions in surface and subsurface soils. Health risks of heavy metals in soil to the population via soil inhalation, skin contact, and ingestion indicated the non-carcinogenic and carcinogenic risks were at an unacceptable level. Each exposure route contribution is higher for adults than for children, whereas there is a relatively high risk of cancer for adults than for children. Therefore, increasing attention shall be needed for monitoring the heavy metal pollution in soils in the areas with dramatic economic development, e.g., South China.

Eco − utilization of silicon − rich lye: Synthesis of amorphous calcium silicate hydrate and its application for recovering heavy metals

During sustainable high-value utilization of coal-based solid wastes, a kind of characteristic silicon-rich lye (SRL) generated, and its comprehensive recovery and recycling remains an important subject. Through a simple and facile strategy of mild caustic-crystallization method, SRL was favorably utilized through calcium silicate hydrate (C − S − H) synthesis with silicon conversion efficiency over 97.33%. The micro-morphology of C − S − H presented a typical “honeybee hive”−like porous structure with numerous exchangeable activity cations and combination sites in the silicate chain structure. The amorphous C − S − H products possessed marvelous recovery abilities for typical heavy metals as Cu (II), Zn (II), and Cr (III) in industrial wastewater with recovery efficiency all above 99.6% in quite a short period. The recovery mechanism of C − S − H toward heavy metals was revealed as calcium ions exchange and interlayer structure combination with SiO4 and AlO4 tetrahedron through the analysis of characterization technologies and DFT simulation calculation. C − S − H synthesized in SRL contributes to achieving valuable resources conversion and recycling for guiding sustainable development of coal-based solid waste comprehensive utilization.

Effect of Soil Aggregate Separation Methods on the Occurrence Characteristics of Typical Pollutants

To study the distribution characteristics of typical pollutants in soil aggregates using different sieving methods, urban and arable soils were collected from Beijing and separated to different sizes by dry and wet sieving methods, to analyze present concentrations of inorganic chlorine and nine typical heavy metals (Cr, Mn, Co, Ni, Cu, Zn, Cd, As, and Pb). Results revealed that the distribution of wet-sieved aggregates was biased towards microaggregates (<250 μm), while the contrary result was found for the dry sieving method. Inorganic chlorine was more likely to be enriched in <53 μm fractions attained by both sieving methods. However, the content of inorganic chlorine in wet-sieved aggregates was significantly lower than in those that were dry sieved, which means the water’s effect on soluble ions was more pronounced. Heavy metals in urban soils were preferentially enriched in microaggregates no matter what kind of sieving method was applied. As for Mn and As found in agricultural soils using the dry sieving method, they were preferentially enriched in the fractions of 1000–2000 μm and 250–1000 μm, while the other seven heavy metals were preferentially enriched in <53 μm fractions, indicating that Mn and As in agricultural soils were easily transferred in aggregates with different particle sizes. Samples with particle sizes <53 μm showed the highest distribution factors for all heavy metals when the wet sieving method was applied. The dry sieving method resulted in a higher mass loading of heavy metals in coarser fractions and lower proportions in finer fractions. Results of a potential ecological risk analysis showed that the ecological risk (Eri) value of Cd found in aggregates by the different sieving methods was significantly different (p < 0.05). The findings suggest that different sieving methods could result in different occurrence patterns of pollutants in the soil aggregates of different land use types.

Characteristics of dissolved organic matter in surface water and sediment and its ecological indication in a typical mining-affected river-Le'an River, China.

Dissolved organic matter (DOM) plays an important role in the cycling and toxicity of heavy metals in aquatic systems. However, most studies have focused only on DOM in either water or sediments. This study aimed to analyze the source, composition, and structural characteristics of DOM in both surface water and bottom sediments of the Le'an River and its major tributaries. In addition, the potential ecological risks of three typical heavy metals (Cu, Pb, and Zn) were quantitatively evaluated based on the characteristics of DOM and in situ data. The results showed that sediment DOM is more aromatic and hydrophobic than surface water DOM. Although humic-like components dominated the DOM pool in both surface water and sediments, their sources were different. Surface water DOM is mainly autochthonous, while sediment DOM is controlled by both autochthonous and allochthonous sources. Risk prediction results based on DOM characteristics show that surface water has a higher potential risk of heavy metal release than sediments. Comprehensively considering the ecological risk of water and sediments, high-risk areas were found to be mainly distributed in the upper and middle reaches of the Le'an River. This distribution is attributable to the developed mining and smelting industries in these areas and consistent with the risk assessment results of measured concentrations of heavy metals. This study established a new technique for predicting the ecological risk of aquatic systems based on the characteristics of DOM in surface water and sediments.

Potential threat of antibiotics resistance genes in bioleaching of heavy metals from sediment

Bioleaching is considered a promising technology for remediating heavy metals pollution in sediments. During bioleaching, the pressure from the metals bioleached is more likely to cause the spread of antibiotic resistance genes (ARGs). The changes in abundance of ARGs in two typical heavy metal bioleaching treatments using indigenous bacteria or functional bacteria agent were compared in this study. Results showed that both treatments successfully bioleached heavy metals, with a higher removal ratio of Cu with functional bacteria agent. The absolute abundances of most ARGs decreased by one log unit after bioleaching, particularly tetR (p = 0.02) and tetX (p = 0.04), and intI1 decreased from 106 to 104 copies/g. As for the relative abundance, ARGs in the non-agent treatment increased from 3.90 × 10−4 to 1.67 × 10−3 copies/16S rRNA gene copies (p = 0.01), and in the treatment with agent, it reached 6.65 × 10−2 copies/16S rRNA gene copies, and intI1 relative abundance was maintained at 10−3 copies/16S rRNA gene copies. The relative abundance of ARGs associated with efflux pump mechanism and ribosomal protection mechanism increased the most. The co-occurrence network indicated that Cu bioleached was the environmental factor determining the distribution of ARGs, Firmicutes might be the potential hosts of ARGs. Compared to bioleaching with indigenous bacteria, the addition of functional bacteria agent engendered a decrease in microbial alpha diversity and an increase in the amount of Cu bioleached, resulting in a higher relative abundance of ARGs. Heavy metal pollution can be effectively removed from sediments using the two bioleaching treatments, however, the risk of ARGs propagation posed by those procedures should be considered, especially the treatment with functional bacteria agents. In the future, an economical and efficient green technology that simultaneously reduces both the absolute abundance and relative abundance of ARGs should be developed.

Study on the occurrence of typical heavy metals in drinking water and corrosion scales in a large community in northern China

Excessive heavy metal content in drinking water could lead to red water and acute and chronic diseases. A field study in combination with batch experiments using pipe scales of drinking water distribution systems (DWDS) in the study area, was used to determine the content distribution and migration of As, Cd, Cr, Mn, Pb, and V in DWDS. In the field study, As, Cd, Cr, Pb, and V contents in pipe scales and drinking water were extremely low and did not exceed the Chinese drinking water standards. However, Mn concentrations at the end of the DWDS with aged and corrosive pipes were relatively high, which presented a risk of excessive release. The batch experiment showed that As in pipe scales would not be released into water under static immersion conditions; however, pipe scales would release excessive Cd, Cr, Mn, Pb, and V in the initial reaction stage, and the heavy metal contents released by tubercle scales in the initial release stage were at least twice as much as those released by loose scales. The mass percentage of four metals (excluding Cd and Pb) released from pipe scales was extremely low. The field study and batch experiment data both suggested a strong correlation between Cr and V released into the water, indicating a synergistic effect. There were differences in heavy metals released in the field research and the batch experiment. The amount of Cd, Cr, Pb, and V released were not consistent with its proportion in pipe scales. As release did not occur under static conditions, but may be promoted by the water flow in the actual network. The effect of water flow on heavy metal release in DWDS should be considered.

Toxicity of coal fly ash and coal gangue leachate to Daphnia magna: Focusing on typical heavy metals

To identify potential toxicity of heavy metals (HMs) in coal fly ash (FA) and coal gangue (CG), this study measured Cd, Cr, Cu, Zn, Pb and Ni in two FAs and two CGs, and assessed their leachates' toxicity to Daphnia magna (D. magna). The results showed that the selected HMs in material and their leachates were low. However, under simplified Elendt M7 medium exposure system, the added leachates inhibited the survival and reproduction of D. magna. The HMs in D. magna increased as leachate increased, and D. magna mortality increased as the HMs in D. magna increased overall. The Cr and Ni in D. magna both showed significant linear positive correlation with the mortality. These indicated that HMs in leachate dilutions were important reason to inhibit D. magna. Moreover, the HMs in leachate also changed the biomarkers and caused oxidative stress in D. magna. Antioxidant system and cell structure of D. magna were further destroyed as leachates increased. The leachates’ inhabitation (mortality and living offspring) to D. magna depended on the properties of FA and CG, and the chemical composition of their leachates. Element level (e.g., C, S and N) and their chemical speciation (e.g., S2− and NH4+) likely impacted the leaching rate and toxicity of HMs.

Leaching and solidification behavior of Cu2+, Cr3+ and Cd2+ in the hydration products of calcium sulfoaluminate cement

Utilization of industrial solid wastes such as aluminum dust, carbide slag, red mud and flue gas desulfurization gypsum (FGD gypsum) as raw materials for the production of calcium sulfoaluminate cement (CSA) is an effective way for solid waste recycling. However, the heavy metals in these industrial solid wastes may affect the cement hydration and environment, limiting the application of CSA from solid wastes. In this work, to clarify the interaction between heavy metals and CSA, as typical heavy metals, Cu2+, Cr3+ and Cd2+ were introduced with different contents. The study found that Ca2+ in ettringite crystalline can be exchanged with Cu2+/Cd2+, and Al3+ can be exchanged with Cr3+, and this chemical capture method can prevent the leaching of heavy metals. The ICP-OES results show that the retention ratios of Cu2+, Cr3+ and Cd2+ with 2 wt% dopant were above 99.99%. Besides, the proper amount of heavy metals makes CSA hydration to maintain an alkaline environment to facilitate the crystallization and growth of ettringite. However, when content of Cr3+ was excessive (more than 2%), the pH value declined severely, which was unfavorable to the stability of ettringite. The XPS results indicated that the Cu2+, Cr3+ and Cd2+ could weaken the binding energy of Ca–O and Al–O bond, decreasing the stability of ettringite crystal, resulting to weaken the compressive strength of CSA, but all are acceptable. The hydration kinetics indicate that the Cr3+ ions make the activation energy barrier to the hydration reaction drop drastically, resultantly, accelerating the hydration process, while Cu2+ and Cd2+ delayed the hydration process, maybe the origin of variation of setting time.

Non-linear associations between metabolic syndrome and four typical heavy metals: Data from NHANES 2011–2018

Previous studies have found that heavy metals are associated with metabolic syndrome (MetS), although findings are inconsistent. Further, investigations into potential associations that consider age- or gender-specific effects and dose-response associations for metal exposure and MetS are rare. In this study, we explore the associations between blood levels of typical heavy metals [lead (Pb), cadmium (Cd), mercury (Hg) and manganese (Mn)] and MetS among adults using logistic regression analysis and restricted cubic splines (RCS) logistic analysis using data from the US National Health and Nutrition Examination Survey 2011–2018. After adjusting for covariates, higher levels of blood Pb, Cd and Hg were associated with lower risks of MetS in participants overall, and in all subgroup analyses, by logistic regression analysis (all P-values <0.05); in contrast, higher levels of blood Mn had a higher risk of MetS only in the age group of 30–49 years (P-values <0.05). We also found non-linear associations of heavy metal levels in blood with risk of MetS in participants overall, in specific age groups and in both genders, using RCS logistic regressions (all P-values <0.05). In addition, the non-linear associations of Pb and Hg we observed in different subgroups differed. In conclusion, blood levels of four heavy metals were associated with the risk of MetS through a variety of non-linear patterns.

Ecological Risk Assessment of Heavy Metals Contamination in Lower Klang River

Estuarine and coastal environments are known to be major sinks for heavy metals. This ecosystem and its sustainability should be secured using the ecological as indicators. This study is conducted to quantify the heavy metal concentration and to assess the potential ecological risk levels of heavy metals in the sediments from Klang River Estuary. Three typical heavy metals such as cadmium (Cd), lead (Pb) and zinc (Zn) were identified. The surface sediment samples were collected from three sampling stations. The concentration of heavy metals in the sediments were arrange in a decreasing sequence of Pb > Zn > Cd. A range of pollution indicators based on single pollution indices such as Contamination Factor, Contamination Degree, Pollution Load Index and Geoaccumulation Index were considered for ecological risk analysis. In conclusion, the ecological risk levels of heavy metals in the sediments from Lower Klang River were low and unpolluted. However, an overall assessment regarding to the heavy metals’ concentrations, spatial distribution and their potential sources need to be monitored for a better understanding of the water-sediment interaction.

Analysis on the effect of large-scale compound ecological engineering system on pollution control of the estuary of a lake

Abstract The quality of the water and the water environment in the estuary of a lake directly affect the water quality and ecological functions of the entire lake. Multi-technology systems, which integrate biotechnological analysis of a lake estuary and restoration of the ecological functions of the water in situ, have gradually been adopted for lake management and restoration. The Xielugang Estuary is located north of the Yangcheng Middle Lake and always exhibits a certain degree of eutrophic phenomena. To ensure the safety of the ecological environment in Yangcheng Lake, a multi-level purification and ecological system with ‘intercept precipitation–ecological restoration–coupled biological treatment’ was developed. Water quality monitoring results for the inlet and outlet of different units in the system from October 2020 to May 2021 showed that the system was effective. We also found that the purification capacity of the composite system was high and the system could significantly enhance the reduction of total nitrogen, total phosphorus, potassium permanganate index and total suspended solids. The average removal rates for these components were 41.34, 61.76, 35.21 and 67.21%, respectively, and the removal rate for typical heavy metals (Zn, Cu, Cd, and Pb) was 30.4–48.9%. The composite system substantially improved the water quality of the estuary and the wetland ecological function, demonstrating its effectiveness and significance.

Investigation of the variations in dissolved organic matter properties and complexations with two typical heavy metals under the influence of biodegradation: A survey of an entire lake

Biodegradation is a key factor determining the properties and metal binding behaviour of dissolved organic matter (DOM). In this study, the contributions of biodegradation to DOM properties and metal binding behaviour in Dongping Lake were explored by using synchronous fluorescence (SF) spectroscopy, two-dimensional correlation spectroscopy (2D-COS) excitation-emission matrix and parallel factor analysis (EEM-PARAFAC). According to the ratio of the fluorescence intensity of different materials to the entire fluorescence intensity (%Fmax), protein-like substances were the main substances of DOM in this lake. The reduction of protein-like substances and the enhancement of humification could be found in the whole lake under the influence of biodegradation. 3 areas (Area A, Area B and Area C) were obtained by principal component analysis (PCA), however, PCA results suggested that DOM properties and sources had some differences in the 3 areas, and DOM bioavailability in Area C was stronger than that in the other 2 areas. With copper (Cu2+) and lead (Pb2+) addition, different substances exhibited various affinities to different metal types. The locations of crosspeaks in asynchronous maps illustrated that protein-like substances were more affiliative with Cu2+, while humic-like substances were bound to Pb2+ earlier. Biodegradation had a conspicuous impact the metal binding ability of DOM in Dongping Lake. The effective quenching constants (LogK) of protein-like substances (protein-like component 2: LogKCu = 3.85 ± 0.23, LogKPb = 3.32 ± 0.23) were higher than those of humic-like substances (humic-like component 3: LogKCu = 3.15 ± 0.02, LogKPb = 2.93 ± 0.17) for both Cu2+ and Pb2+ before biodegradation. When biodegradation was finished, binding ability of humic-like substances was enhanced from 3.15 ± 0.02 to 3.41 ± 0.10 for DOM-Cu and 2.93 ± 0.17 to 3.79 ± 0.15 for DOM-Pb. On a spatial scale, metal binding ability of DOM in Dongping Lake also changed due to the influence of biodegradation. For both DOM-Cu and DOM-Pb, binding ability in south of Dongping Lake was stronger than that in other areas with the end of biodegradation.

A clean production process on oily sludge with a novel collaborative process via integrating multiple approaches

A clean production process is typically studied for oily sludge that a typical pollutant marked by a variety of pollution indicators, such as high concentrations of organic pollution and heavy metal pollution. However, it remains difficult to quickly and synchronously remove various pollutants from oily sludge up to now. In order to simultaneously reduce organic pollution and remove heavy metal pollutants on oily sludge, a clean production process needs to be developed. Here, chemical and biological processes: subcritical hydrothermal treatments (SHTs) and biodegradation processes (BPs) were organically integrated to develop a novel collaborative process (NCP). The different SHT and matched optimal conditions for the BPs were discussed, and the results showed that hydrolysis of catalyst under high temperature and high pressure (HHC) is the best set of conditions for obtaining new biodegradable substrate (NBS). These conditions can maximize the strength of the follow-up BPs and optimize the degradation effect of oily sludge based on a pure oxygen aeration-activated sludge process (POAAS) and air aeration-activated sludge process (AAAS). The results showed that the newly NCP process not only synergically enhances the advantages of SHT and BP in reducing organic pollution, with the degradation rate of oil content reaching 96.73% and COD reaching 95.79% within 10 days, but also significantly improves removal rate of typical heavy metals content, including Cd2+ up to 79.16%, Cr6+ up to 88.03%, As3+ up to 89.59%, Pb2+ up to 89.2% and Ni+ up to 70.1%. This study provides important research value for the clean production process on oily sludge with multiple pollution indicators.

Evaluating heavy metal pollution and potential risk of soil around a coal mining region of Tai’an City, China

Monitoring the spatial distribution characteristics of heavy metal pollution and evaluating its potential risks in the soil is essential for promoting regional socioeconomic development and maintaining the safety of the ecological environment. In this study, a representative coal mining region in Tai’an City, Chinas was selected as the study area, eight typical heavy metal elements (HMEs), i.g. Cu, Pb, Zn, Cd, Cr, As, Hg, Ni in the topsoil (0–20 cm) of 59 randomly generated sample sites were measured and monitored through sampling, testing and statistical analysis, and their spatial distribution patterns were analyzed accordingly. The single factor pollution index（SFPI) method, comprehensive pollution index (CPI) method and potential ecological hazard index (PEHI) method were employed to systematically computed and analyzed the single factor, comprehensive pollution and potential ecological risks of the selected HMEs in the soil. Results found that: (1) the average measured content of these elements all exceeded the referenced background value. The Cr element pollution was the lowest (3.39%), while the pollution of Ni, Cd and Hg elements were the highest (86.44%, 83.05 % and 81.36%, respectively). (2) The comprehensive pollution level was above mild pollution at all sample sites, and the comprehensive pollution was mainly ranged in the mild pollution level (59.32%); The moderate pollution level of comprehensive potential ecological risk accounted for 64.41%, and the spatial distribution was annular from northwest to southeast. (3) The values of potential ecological risk index indicated that Hg and Cd were the main pollution elements in this coal mining region, and Cd had the highest pollution rate. The findings of this study can be used to evaluate the pollution in other coal regions, and provide reference for the decision-making of soil heavy metal pollution control.

Spatial Distribution Trends and Influencing Factors of Typical Heavy Metals in Subtropical Alpine Forest Soils: A Case Study from Ailao Mountain in Yunnan Province

In this study, we hypothesized that the distribution patterns of trace metal elements in montane regions would be controlled by the local climate, human activities, vegetation distribution and soil development. Hence, we selected nine forest sites among the elevation of 850 m to 2650 m on the windward (western slope) and leeward (eastern slope) slopes of Ailao Mountain in Yunnan Province of China to determine the typical heavy metal concentrations in forest surface soils, and their differences for distribution trends along with the increasing elevations, and the corresponding environmental factors. The results showed that surface soil Cd, Sb, As, Cr, and Pb had relatively higher concentrations and distinct enrichment factors both on eastern and western slopes. Specifically, the concentrations of Cd and Sb in surface soils of the eastern and western slopes and Pb on the western slope all had obvious altitude distribution trends, which showed their concentrations increased with the increasing elevation. In addition, we found the concentrations of Cd, Sb, As, and Cr in surface soils of the western slope were significantly higher than those of the eastern slope at the same altitude. The correlation analysis and principal component analysis further depicted that the elevation trends of Cd and Sb were mainly controlled by the strong combining effects from long-range atmospheric input and soil organic matter strong absorption, and there was an obvious "cold trapping" effect in high altitude areas. The distribution variations of As and Cr were mainly derived from the weathering difference of soil parent material, while the variations for Pb were controlled by the weathering of bedrock minerals. This study highlights the important role of combining effects from long-range atmospheric input, and from precipitation and vegetation (such as "cold trapping" effect, promoting canopy filtration, litterfall deposition and bedrock weathering) on the distribution trends of trace metals in remote alpine soils.

The relationship between typical heavy metal content and physiological indexes of shrubs in bioretention facilities

Abstract Bioretention facilities have been widely constructed, but it is unknown whether rainfall runoff containing pollutants will hurt the plants in bioretention facilities. Experiments were carried out to explore the relationship between the heavy metal (Cd and Pb) contents of four shrubs and three physiological indexes. The results show the following: (1) The heavy metal absorption of shrubs may be directly proportional to the heavy metal content in stormwater runoff. (2) For the experimental devices, sand/soil-low concentration (SS-L) and sand/soil-high concentration (SS-H), except that the contents of Cd and Pb of L. vicaryi in SS-H showed a trend of increasing first and then decreasing, the contents of heavy metals in other shrubs showed a gradual increase. (3) For SS-L, the net photosynthetic rate (NPR) and transpiration rate (TR) of R. xanthina were in direct proportion to the contents of Cd and Pb in vivo. The NPRs and TRs of the other three shrubs and the chlorophyll content (CC) of L. vicaryi presented an inversely proportional relationship. For SS-H, the NPR of L. vicaryi was in direct proportion to its Cd and Pb contents. Almost all other conditions showed an inverse relationship.