Cr In Soil Research Articles

Long-distance mobilization of chromium(III) in soil associated with submicron Cr2O3

Trivalent chromium is generally assumed to form insoluble species, resulting in low mobility of Cr(III) in soils. Here, we report continuous distributions (0–19 m) of a high concentration of Cr(III) in the alkaline soils of a historically industrial site for producing Na2Cr2O7, CrO3, and Cr2O3, which challenges this abovementioned conventional wisdom. The thermodynamic equilibrium model showed the low possibility of Cr(III) originating from Cr(VI) reduction under the redox conditions of this study. The AF4-MALLS-ICP-MS and μ-XRF-XANES were used to identify the particle size distribution of Cr(III)-containing colloids and Cr(III) species in mobile colloids. In any soil layer, Cr(III) accounts for 71.1–94.3% of the total Cr in submicron soil colloids and is composed of submicron intrinsic Cr2O3 (55.2%−63.8%), Cr(OH)3 (0–33.0%), and Cr(III) adsorbed by ferrihydrite (0–19.0%) and clay montmorillonite (11.1%−21.1%) colloid. On the contrary, Cr(VI) was mainly distributed in bulk soil (> 2 µm) except for the topsoil, accounting for 62.6–90.0% of total Cr(VI). Organic matter content and soil texture are the most critical factors driving the mobilization of submicron colloids in soils by principal component analysis. Humic acid (HA) formed HA-corona on Cr2O3 surface and enhanced colloidal dispersion, thereby accelerating the long-distance mobilization of submicron Cr2O3 colloids in alkaline soil layers, whereas the heteroaggregation of clay colloid with Cr2O3 was only favorable for short-distance mobilization. Our findings help to re-recognize the potential migration risks of insoluble heavy metals in soils.

Preparing of layered double hydroxide- alginate microspheres for Cr(VI)-contaminated soil remediation

The powdered layered double hydroxide(LDH) synthesized by hydrothermal coprecipitation was compounded with sodium alginate to form microspheres(LDH-AL). The characterizations of the LDH-AL show that the microspheres were successfully prepared. Then the immobilization experiments of hexavalent chromium(Cr(VI)) were investigated. The results have proved the effectiveness of microspheres in the immobilization of Cr(VI) in soil. Other limiting factors including LDH percentage, the effects of pH, LDH-AL dosage, interlayer ions, and initial heavy metal concentration were also explored. The LDH-AL showed advantages and its maximum adsorption capacity is 17.0 mg/g. LDH contained in the materials plays a main role in the removal process. In addition, the toxicity characteristic leaching procedure (TCLP) experiment, plant potting tests, and simulation of natural aging processes were used to verify the stability of microspheres. While a series of characterization investigated the adsorption mechanism, the interlayer ion exchange and surface adsorption are the main reasons for Cr(VI) immobilization in contaminated soil. There are also isomer substitution and complexation adsorption phenomena. This study demonstrated the potential application of LDH-AL microspheres in the immobilization of Cr(VI) from contaminated soil.

Chromium Poisoning in Buffaloes in the Vicinity of Contaminated Pastureland, Punjab, Pakistan

This article focuses on the toxic element chromium (Cr) in wastewater, its incorporation into soil plant systems, and its relevant toxicity in the food chain as assessed by a health risk assessment from dietary intake. The Nili Ravi buffalo is an important cattle inhabiting Sargodha, Punjab, Pakistan, and forage crops grown on soils contaminated with Cr might cause toxicity in the food chain by local inhabitants eating meat. The soil, forage and animal blood samples were collected from five different locations in Tehsil Sahiwal (Chak Dhool, Bagabalocha, Chandia, Dhool Bala and Kakrani) twice at six-month intervals. A total of 30 samples from each ecological zone were collected from the soil and forage crops (Zea mays, Sorghum bicolor, Trifolium alexandrinum). The samples from zone-V and zone-IV showed the maximum concentration of Cr because these areas receive highly contaminated water for irrigation. The Cr was greater than the permissible limits. Environmental indices for all samples ranged below 1. The bioaccumulation and pollution load of Cr in soil and forage crops due to wastewater irrigation can contaminate the whole food chain via the soil, forages and animals. The health risk index (HRI) and a high value of enrichment factor were found for Cr in some sites. The Cr concentration was higher during the summer season than winter. Fodder crops with different concentrations and an elevated level of Cr were observed in maize. Attention should be paid when wastewater is used for fodder crop irrigation and its potential risks to human health following dairy product (milk, meat) entry into the food chain.

Effects of Different Carbon Types on the Growth and Chromium Accumulation of Peach Trees under Chromium Stress

Heavy metal pollution in agricultural soil is a serious problem, which threatens the environment and human safety. In this study, the effects of biochar (BC), activated carbon (AC), and nanocarbon (NC) on the growth of peach trees under chromium (Cr) stress were investigated through pot experiments. The experimental results showed that under Cr stress, BC, AC, and NC could increase the soil nutrient content and enhance the soil enzyme activity. Moreover, all carbon forms promoted the conversion of Cr speciation; decreased the content of exchangeable (EXE), carbonate-bound (CARB), and iron–manganese-oxide-bound (FeMnO) Cr in the soil; increased the organic-bound (Org) and precipitated (Pre) Cr content; and reduced Cr availability. After BC, AC, and NC treatment, the content of Org-Cr in the soil increased by 86.05%, 72.97%, and 65.02%; the content of EXE-Cr decreased by 75.30%, 75.33%, and 73.10% compared with the control under severe Cr treatment, respectively. Moreover, the accumulation of Cr in plants decreased by 29.70%, 22.07%, and 20.52%, respectively. At the same time, these three carbons reduced the accumulation of Cr in various parts of the peach tree, alleviated the oxidative damage caused by Cr stress, effectively protected the photosystem of the leaves, improved the photosynthetic capacity, and promoted the growth of the peach tree. Compared with the control, the dry matter accumulation increased by 20.81%, 9.54%, and 6.95% with BC, AC, and NC treatment under severe Cr treatment. Therefore, BC, AC, and NC can all effectively alleviate soil Cr toxicity, and BC has the best effect, which can be popularized in production.

Distribution and bioaccumulation of trace metals in urban semi-arid mangrove ecosystems

Mangrove ecosystems are known to act as filters for contaminants between land and sea. In New Caledonia, urbanization has increased along the coastline during the last decades. However, the impact of urbanization on contaminant cycling in mangrove forests has remained unexplored. In this study, we investigated trace metals (TM) dynamics in an urban mangrove soil and their transfer to mangrove tissues for the two dominant mangrove species in New Caledonia: Avicennia marina and Rhizophora stylosa. The results suggest that decades of urban rainwater runoff from an upper neighborhood induced large variations of mangrove soil physico-chemical properties compared to a control mangrove site sharing the same geological watershed. The urban mangrove site had a neutral pH and low salinity in the upper soil, while the control mangrove site presented acidic pH and a salinity ranging from 24 to 62 g L−1. Most TM were significantly less concentrated in the urban mangrove soil varying from 1.3 ± 0.3 μg g−1 at the urban site and 1.9 ± 0.5 μg g−1 at the control site for Cd, to 30 ± 8 mg g−1 and 49 ± 11 mg g−1 for Fe at the urban and control site, respectively. However, higher root bioconcentration factors were measured for As, Cd, Co, Cr, Fe, Mn, Ni, and Pb in the urban mangrove soil (1.7 ± 0.9, 0.14 ± 0.06, 0.23 ± 0.13, 0.042 ± 0.026, 0.088 ± 0.057, 0.47 ± 0.39, 0.21 ± 0.12, and 0.25 ± 0.09, respectively) compared to the control mangrove soil (0.11 ± 0.03, 0.041 ± 0.016, 0.045 ± 0.021, 0.010 ± 0.004, 0.013 ± 0.007, 0.094 ± 0.030, 0.022 ± 0.011, and 0.12 ± 0.03, respectively). The bioavailability of TM in the urban mangrove soil may be favored by suboxic conditions associated to less Cl-TM complexes and pyrite-TM complexes in the soil. Only Cu, Pb, Ti, and Zn, usually associated with urbanization, were more concentrated in the urban mangrove soil with mean concentrations of 27 ± 4, 17 ± 2, 4,571 ± 492, and 62 ± 12 μg g−1 at the urban site, respectively, and 21 ± 4, 10 ± 3, 2,834 ± 541, and 57 ± 12 μg g−1 at the control site, respectively. No significant difference in translocation factors was measured between the two sites, evidencing a regulation of TM translocation to the upper tissues by mangrove trees.

Characteristics of Heavy Metal Pollution in Farmland Soil of the Yangtze River Economic Belt Based on Bibliometric Analysis

The Yangtze River Economic Belt is one of the major strategic development regions in China. It is of great significance to clarify the characteristics and sources of heavy metal pollution in farmland soil of the Yangtze River Economic Belt for the prevention and control of heavy metal pollution and to ensure safe agricultural production. After collecting extensive literature data, we analyzed the pollution characteristics, environmental risk, and potential sources of heavy metals (Cd, Cr, Hg, As, Pb, Cu, Zn, and Ni) in farmland soil of the Yangtze River Economic Belt through the integrated use of spatial and geo-accumulation index analyses. The results showed that:① the proportion of soil samples exceeding the risk screening values for soil contamination of agricultural land of Cd, Cu, Pb, Hg, Zn, and As were 39.8%, 18.5%, 8.3%, 6.9%, 6.9%, and 6.4%, respectively. Compared with the risk standard, soil Cd had the highest rate of exceeding the standard. ② The contents of Cr, Cu, Zn, and Ni in the upper reaches were higher than those in the middle and lower reaches, and the contents of Cd, As, and Pb in the middle reaches were higher than those in the upper and lower reaches. ③ The results of the geo-accumulation index analysis showed that the contamination degree of the eight heavy metals decreased in the order of Cd(0.42)>Hg(-0.28)>Pb(-0.32)>Zn(-0.39)>Cu(-0.42)>Cr(-0.7)>As(-0.81)>Ni(-0.73), where the accumulation risk of soil Cd and Hg was relatively higher. ④ Higher environmental background and mining activities were the main factors affecting the accumulation of heavy metals in soils in the upper and middle reaches. By contrast, rapid urbanization, industrial production, and intensive agricultural activities were the main factors affecting the heavy metal accumulation in soils in the middle and lower reaches. In view of the current status and control needs of heavy metal pollution in the Yangtze River Economic Belt, it is recommended to strengthen source prevention and control and to also carry out hierarchical control and regional classification management of heavy metal pollution in farmland soils according to the degree of heavy metal pollution, geological background, and quality of agricultural products. The ultimate objective of this research was to archive the farmland soil environmental quality safety and agricultural green sustainable production in the Yangtze River Economic Belt.

Source identification and spatial distribution of heavy metals in soil of central urban area of Chongqing, China

ABSTRACT To understand the characteristics of heavy metal pollution in soil and identify the source of heavy metals, 342 surface soil samples were collected in Chongqing, China. The contents of 11 heavy metals (i.e., arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), copper (Cu), zinc (Zn), nickel (Ni), mercury (Hg), antimony (Sb), manganese (Mn), and molybdenum (Mo)) were determined. The Principal Component analysis/absolute Principal component fraction (PCA/APCS) receptor model, the classified regression (CATREG) model, and the hot spot model were employed to analyze the data. The contents of As, Cd, Cr, Pb, Cu, Zn, Ni, Hg, Sb, Mn, and Mo in soil were 5.80, 0.13, 76.56, 25.55, 23.99, 75.58, 30.50, 0.05, 0.64, 573.32, and 0.56 mg·kg−1, respectively. The results of principal component analysis showed that the main heavy metal elements under the first principal component load were Cu, Ni, Zn, Mn, Cr, Pb, and Cd. The second principal component is mainly loaded with Mo, As, Hg, and Sb. The results of classified regression analysis showed that population density mainly affected Cu (0.54), soil mainly affected Ni (0.41), Sb (0.49), Zn (0.47), and Mn (0.21), and water quality mainly affected As (0.45) and Mo (0.37). Air quality mainly affected Cd (0.33) and Cr (0.37), traffic activity mainly affected Hg (0.31), and slope mainly affected Pb (0.31). The research results can be used to trace the environmental sources of soil heavy metals, fundamentally prevent and repair soil heavy metal pollution, and protect urban soil environmental quality.

Morupule fly ash as amendments in agricultural soil in Central Botswana

The potential of Morupule fly ash as a soil amendment was evaluated using spinach and rape vegetables planted successively in Palapye soils added with 0 fly ash (FA), 5% FA, 10% FA, and 15% FA (w/w) in combination with four nutrient sources as no fertilizer (-NF), compost (+COMP) at 20 tones ha −1 , inorganic NPK (+NPK) and a combination of 1 2 NPK and 1 2 compost (+NPK+COMP). Spinach was grown first for 40 days followed by rape as a second crop planted on the same pots and treatments after harvesting spinach. The application of FA increased the pH, EC, and the total concentration of As, Cu, and Pb of soil while compost increased the total Zn. The available concentration of Cr, Cu, Mn, Ni, and Pb were significantly reduced by FA. FA increased the yield of spinach and rape, especially in 10FA+NPK+COMP. The heavy metal concentration in the shoots of spinach and rape were below the maximum acceptable limits (MAL) for vegetables in 10FA+NPK and 10FA+NPK+COMP treatments. Overall, an application rate of 10% FA combined with compost and fertilization gave the highest yield and safe level of As, Cr, Cu, Mn, Ni, Pb, and Zn in the edible shoots. • First report on using Morupule fly ash as an amendment in agricultural soils in Botswana. • A combined with compost and inorganic fertilizer improved the growth and yield of spinach and rape grown successively. • Fly ash amendments reduced the available concentration of Cr, Cu, Mn, Ni, and Pb in soil. • Fly ash at 10% application combined with compost and inorganic fertilizer produced spinach and rape safe for human consumption.

Potential of plant growth promoting rhizobacteria to mitigate chromium contamination

The main threats to human health and agriculture from heavy metals are associated with exposure to chromium, lead, cadmium, mercury, and arsenic. Among the metals, Chromium is one of the most lethal heavy metals because of its toxicity and hazardous nature. It affects biological activities in soil and metabolism of animals, plants, and human health. Among various forms of chromium, trivalent Cr (III) and hexavalent Cr (VI) are more stable in nature. The higher concentration of Cr (VI) in soil may affect many biochemical and physiological processes and consequently inhibits plant growth. Plant growth promoting rhizobacteria (PGPR) are involved in regulation of seed germination, growth promotion, metabolic rate, and other physiological activities of plants. PGPR may reduce toxic effects of Cr (VI) on plant growth through reducing Cr (VI) to Cr (III). Many recent reports describe the application of heavy metal resistant-PGPRs to enhance agricultural yields without accumulation of metal in plant tissues. This review provides information about the mechanisms possessed by heavy metal resistant-PGPRs that ameliorate metal stress to plants and decrease the accumulation of these metals in plant, and finally gives some perspectives for research on these bacteria in agriculture in the future. • Cr(VI) of industrial effluents impact negatively on human health and environment. • The removal of Cr(VI) from wastewater and soil requires serious and immediate attention. • Biological removal of Cr(VI) is a sustainable and environmentally friendly technology. • Cr(VI)-bioremediation strategies are applied in different systems and scales. • Research is essential to solve the problems associated to the large-scale remediation.

SPECIATION, MOBILITY AND POTENTIAL TOXICITY OF METALS (CR, CO, CU AND MN) IN SOIL SAMPLES FROM DUMPSITES IN KANO METROPOLIS

Soil pollution by heavy metals is a global environmental problem. The need to keep the environment clean is increasingly becoming a global concern. Heavy metals are one group of pollutants that are widespread in our environment. They tend to persist indefinitely once they enter the soil. Their mobility and toxicity depend on their forms and oxidation states in the soil. This research presents the speciation, mobility and potential toxicity of Cr, Co, Cu and Mn in soils from some dumpsites in Kano, using a six-step sequential extraction method and AAS analysis. The results revealed the pH of the soils to range from 6.20-7.80. Percentage composition of clay and organic matter ranged from 6.00-16.58 % and 0.48- 4.30 % respectively. The results showed that the metals are bioavailable at different forms evident from their distribution pattern in the different fractions and therefore the soils should not be used for cultivation to avoid the metals getting into the food chain. The mobility factor values ranging between 14.38 % and 61.48 % for dry season; 15.63 % and 74.74 % for rainy season showed the metals to be very mobile especially Co, Cu, and Mn. This could lead to potential pollution of the agricultural produce and ground water in this area and hence have toxic effects on human lives. This result can serve as a guide to researchers on the appropriate method to reclaim the soils in this area based on the pattern of distribution of the metals in different geochemical phases.

Fate and transport of chromium in industrial sites: Dynamic simulation on soil profile

Direct discharge of chromium-containing waste water and improper disposal of waste residues in industrial sites may lead to the vertical migration of metals into aquifers, posing serious threat to soil-groundwater system. The heterogeneity in soil profile further aggravates the complexity and unpredictability of this transport process. However, topsoil was the main focus of most studies. Herein, the vertical transport and transformation of Cr in soils at different depths in three industrial sites (i.e., Shijiazhuang, Zhuzhou, and Guangzhou) were investigated to delineate Cr transport and retention characteristics under complex conditions. Regional and vertical differences in soil properties led to the specificity in Cr migration behaviors among these three sites. Correlation analysis showed that soil pH (r = −0.909, p < 0.05) and Fe content (r = 0.949, p < 0.01) were the major controlling factors of Cr(VI) migration and transformation in aquifers. Furthermore, the soil of Zhuzhou site showed the maximum adsorption capacity for Cr(VI) (0.225 mol/kg), and the strongest reduction ability of Cr(VI) was observed in the Guangzhou soil. Results of model-based long-term forecast indicated that the Cr(III) concentration in the liquid phase of Guangzhou subsoil could reach 0.08 mol/m3 within 20 years. Heavier rainfall condition exacerbated the contamination due to an increased pollutant flux and enhanced convection. Specially, Cr was fixed in the topsoil of Zhuzhou site with the formation of PbCrO4 and presented least vertical migration risk. The conclusions above can provide scientific theoretical guidance for heavy metal pollution prevention and control in industrial contaminated regions.

Health Risk Assessment of Children Exposed to the Soil Containing Potentially Toxic Elements: A Case Study from Coal Mining Areas

Coal mine activities lead to the release of potentially toxic elements (PTEs) to the surrounding areas. The present study concerns the health risk caused due to the exposure of PTEs (Hg, As, Cd, Cr, and Pb) in the children residing in the areas around coal mines. The PTEs content and bioaccumulation coefficient (BAC) in the plant, viz., Albizia lebbeck and Madhuca longifolia growing on the nearby soils of the coal mine affected areas were also estimated. The results demonstrated that the hazard quotient (HQ) for Cr (0.211) in the roadside soil (RSS) was higher than other PTEs. The hazard index (HI) was also at the maximum in the RSS (0.553) followed by the core zone soil (0.541). In RSS, Cr contributed the maximum for the HI value (38%) which elucidated that Cr might cause health problem in the long term. The Cr concentration (5.49 mg kg−1) was also higher than other PTEs in the plant leaves of M. longifolia and was two-fold higher than A. lebbeck. Except Cd, the accumulation of other PTEs in the leaves of both the species were low, which could be due to their low availability in soils. The BAC for Cr in M longifolia was comparatively higher than A. lebbeck and was found at the maximum for Cd (0.29) in M longifolia. The outcomes of the study elucidated that although there is no severe health risk in children, the data indicated that the prolonged exposure to PTEs might lead to serious health issues.

Heavy metal contamination assessment and probabilistic health risks in soil and maize near coal mines.

ObjectiveCoal mining activities have continuously introduced heavy metals into the soil–crop system, causing increasing damage to crops. This study integrated the analysis of the heavy metal contamination status and human health risk in soil and maize near coal mines to help formulate control strategies for soil quality, maize production, and safe consumption.MethodThis study was carried out on maize agricultural land near a coal mining plant. Heavy metal contamination was assessed by the geo-accumulation index (Igeo), enrichment factor (EF), and bioaccumulation factor (BCF). The Monte Carlo simulation was used to estimate the probabilistic health risk of heavy metals exposure in soil and maize. The relationship between the concentration of heavy metal in the soil and that in maize was further visualized by correlation analysis and random forest analysis.ResultsThe results revealed that the mean concentrations of soil Ni, Cu, As, Cd, Sn, Zn, Pb, and Hg were all above the local background level. Ni was the most severely polluted heavy metal in maize and had a concentration higher than the risk control standard for corn in China (NY 861-2004). The Igeo values of all heavy metals were low, and EF values showed enrichment in V, Cr, Ti, Ni, and As. The assessment of probabilistic health risk exposed by heavy metals in soil and maize indicated that 1.16 and 1.46% of residents exceeded the carcinogenic risk level due to heavy metal exposure from soil and maize, respectively. Children were the most sensitive to maize and soil heavy metal exposure in the contaminated area. Ingestion of heavy metals was associated with the highest health risk to residents, followed by dermal contact and inhalation. As and Cr in soil and Cr and Ni in maize had the greatest impact on human health risk. Furthermore, maize heavy metals were affected the most by soil Cr, Cd, and V.ConclusionThese results may provide useful information for human carcinogenic risk associated with soil and maize heavy metal exposure due to coal mining activities.

Health Risk Assessment during In Situ Remediation of Cr(VI)-Contaminated Groundwater by Permeable Reactive Barriers: A Field-Scale Study.

The presence of residual Cr(VI) in soils causes groundwater contamination in aquifers, affecting the health of exposed populations. Initially, permeable reactive barriers(PRB) effectively removed Cr(VI) from groundwater. However, as PRB clogging increased and Cr(VI) was released from upstream soils, the contamination plume continued to spread downstream. By 2020, the level of contamination in the downstream was nearly identical to that in the upstream. The study results show that during normal operation, the PRB can successfully remove Cr(VI) from contaminated groundwater and reduce the carcinogenic and non-carcinogenic risks to humans from the downstream side of groundwater. However, the remediated groundwater still poses an unacceptable risk to human health. The sensitivity analysis revealed that the concentration of the pollutant was the most sensitive parameter and interacted significantly with other factors. Ultimately, it was determined that the residual Cr(VI) in the soil of the study region continues to contaminate the groundwater and constitutes a serious health danger to residents in the vicinity. As remediated groundwater still poses a severe threat to human health, PRB may not be as effective as people believe.

Chemistry-driven Enchytraeidae assemblages acting as soil and ecosystem engineers in edaphic communities

Smaller body-sized invertebrate groups are known to be highly sensitive to environmental pollution. Like soil nematodes, enchytraeids have very permeable cuticles and come into direct contact with heavy metals; therefore they can be adversely affected by soil pollution. However, in contrast to nematodes, fewer data on enchytraeids are at our disposal to assess their functional responses to heavy metals. Such an assessment would be of greatest value, as in any edaphic community, enchytraeids are the only functional group bridging the detrital energy flux across the bacterial-driven and the fungal-driven pathways. For this purpose we investigated and evaluated the effect of heavy metals on the occurrence and biomass of enchytraeids in different soils in The Netherlands. Samplings of topsoils were carried out in 297 sites with Pleistocene sandy soils, river clay and sea clay under different environmental stress and all recovered enchytraeid species have been included in three existing phylogenetical clades (hereafter: A, B, and C). Our results show that the biomass of the enchytraeid species belonging to the Clade C is highly correlated with Cr, Cu and Zn in sandy soils (all 2-tails significance values share p < 0.005, n = 186) but is correlated with Cu and Hg in loamy soils (p < 0.05, n = 111), whilst the biomass of the enchytraeid species belonging to the Clade B is highly correlated with either Cd + Cu + Pb in sandy soils (p < 0.025, n = 186) or Hg + Pb in loamy soils (p < 0.05, n = 111). The entire enchytraeid community actively contributes to promote the rapid turnover of soil organic matter. Given that clay-rich soils retain a much higher amount of heavy metals in contrast to sandy soils, most enchytraeids share different values as bioindicators according to the soil type, even comparing river clay with sea clay. Hence, elemental availabilities have disproportionately strong effects on enchytraeids and on the entire edaphic community according to the soil types.

Remediation of Cr(VI)-Contaminated Soil by Biochar-Supported Nanoscale Zero-Valent Iron and the Consequences for Indigenous Microbial Communities.

Biochar/nano-zero-valent iron (BC-nZVI) composites are currently of great interest as an efficient remediation material for contaminated soil, but their potential to remediate Cr-contaminated soils and effect on soil microecology is unclear. The purpose of this study was to investigate the effect of BC-nZVI composites on the removal of Cr(VI) from soil, and indigenous microbial diversity and community composition. The results showed that after 15 days of remediation with 10 g/kg of BC-nZVI, 86.55% of Cr(VI) was removed from the soil. The remediation of the Cr-contaminated soil with BC-nZVI resulted in a significant increase in OTUs and α-diversity index, and even a significant increase in the abundance and diversity of indigenous bacteria and unique bacterial species in the community by reducing the toxic concentration of Cr, changing soil properties, and providing habitat for survival. These results confirm that BC-nZVI is effective in removing Cr(VI) and stabilizing Cr in soil with no significant adverse effects on soil quality or soil microorganisms.

Spatial Distribution and Sources of Heavy Metals in Soil of a Typical Lead-Zinc Mining Area, Yangshuo

Taking a typical lead-zinc mining area in Yangshuo county, Guangxi as the research object, the contents of 10 metal elements (Cr, Mn, Ni, Cu, Zn, As, Cd, Sb, Hg, and Pb) in the surface soil of Sidihe River basin in Yangshuo were analyzed and determined. Pearson correlation analysis, principal component analysis (PCA), positive definite matrix factorization (PMF), and other methods were comprehensively used to quantitatively analyze their contributions and identify pollution sources. In total, 168 surface soil samples were collected across the study area. The mean concentrations of Zn, Cd, Hg, and Pb in the soils were higher than the National Environmental Quality Standards for Soils in China. The mean contents of Sb, Cd, Cu, Pb, and Zn were higher than their corresponding local background values by approximately 1.01, 5.50, 3.29, 9.11, and 10.67 times, respectively, indicating that heavy metals have been enriched in topsoil. The Igeo showed that the major pollutant element in the soils was Hg, followed by Pb, Zn, and Mn. Correlation analysis and principal component analysis showed that the sources of metal pollution in surface soil in the study area were complex and mainly from human activities. Cu, Zn, Cd, Sb, As, and Pb were mainly derived from mining activities; Hg, Cr, and Ni were controlled by soil parent material sources; and Mn and Cd were mainly derived from mining activities and agricultural activities. PMF model analysis results showed that the metal pollution sources in the surface soil were jointly affected by these three sources. Mining activities, natural sources, and a mixed source of mining activities and agricultural activities were the main sources of heavy metal pollution in the soils, accounting for 58.0%, 13.5%, and 28.6% of the total heavy metal accumulation, respectively. Ni, Cu, Zn, As, Sb, Hg, and Pb were derived mainly from mining activities. Cr, Ni, and Hg were mainly attributed to natural sources, such as soil parent materials and rainfall erosion (44.6%, 23.2%, and 21.0%, respectively), and Mn and Cd were associated with a mixed source of mining activities and agricultural activities (75.4% and 70.4%).

Heavy Metal Emissions from Coal-fired Power Plants and Heavy Metal Pollution Characteristics and Health Risks in Surrounding Soils

The aim of this study was to reveal the influence of heavy metal emissions from the flue gas of coal-fired power plants on the surrounding soil environment. Seven heavy metals, including As, Cd, Cr, Cu, Pb, Hg, and Ni, were detected in the flue gas of six coal-fired power plants in Shijiazhuang, and the heavy metals in the soil surrounding the power plants were analyzed. The source analysis and health risk assessment of the heavy metals were carried out. The results showed that after a series of flue gas pollutant control measures, the emission concentrations of different heavy metals in the flue gas of the coal-fired power plants ranged from 0.11 to 6.32 mg·(MW·h)-1, and Cu, Cr, and Ni were the main pollutants. The total amount of the seven heavy metal elements discharged into the atmosphere by each power plant was 33.56-275.71 kg·a-1. The average contents of Cr, Cu, Pb, Hg, and Ni in the surface soil surrounding the coal-fired power plant were higher than the background values of Hebei soil, and the contents were 1.16-2.32 times higher than the background values. The heavy metal content in the soil around the power plants was proportional to the heavy metal emissions in the flue gas. The heavy metal content in the soil under different wind directions first increased and then decreased gradually with the increase in distance from the power plants. Source analysis showed that coal combustion emissions contributed the most to heavy metals in soil around the power plants (41.4%), followed by industrial emissions (23.6%) and transportation emissions (19.6%). Altogether, human activities played a leading role in soil heavy metal enrichment, accounting for 84.6%. The health risk assessment showed that the overall health risk of metal elements in the soil surrounding the power plant was within acceptable limits.

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.

Accumulation of Cd, Cr, and Pb and Sustainable Detoxification in Sewage-Irrigated Soils

Accumulation of Cd, Cr, and Pb and Sustainable Detoxification in Sewage-Irrigated Soils