Sb In Soils Research Articles

Fast and efficient remediation of antimony-contaminated surface water and field soil using alumina supported Fe–Mn binary oxide

Antimony (Sb) pollution in surface water and soil has earned extensive attention. Our previous study synthesized a new class of alumina supported Fe–Mn binary oxide (Fe–Mn@Al2O3) and found that MnO2 in the composite oxidized Sb(III) to Sb(V) and FeOOH and Al2O3 played an indispensable role in adsorption of Sb(III) and Sb(V). This study further explored the removal of Sb in surface water and in situ sequestration of Sb in Sb-contaminated field soil via Fe–Mn@Al2O3. Sb removal from water was pH independent and the removal efficiencies of Sb(III) and total Sb kept constant at 95.4% and 60.5%, respectively, over a pH range of 5.0–10.0. Increasing dissolved organic matter (DOM) from 0 to 22.8 mg/L had negligible effect on Sb(III) removal whereas inhibited the total Sb removal from 60.5% to 51.2%. Dissolved oxygen cannot oxidize aqueous Sb(III), yet, enhanced the Sb(III) removal whereas decreased the total Sb removal. The composite performed well in natural surface water with high DOM and inorganic ligands. In addition, the composite effectively immobilized Sb in field soil. 5% of the composite significantly inhibited the H2SO4 and HNO3 leachable Sb by 93.6% after 30 d. The amendment transformed the Sb speciation from more easily available fractions (i.e., exchangeable, carbonate-bound, and Fe–Mn oxides-bound species) into more stable fractions (i.e., organic material bound and residual species), leading to declined Sb bioaccessibility and reduced environmental risk. The composite facilitated a long-term stability of Sb in soil. The study demonstrated an easy, fast, and effective strategy for efficient immobilization of Sb in water and soil.

Factors driving antimony accumulation in soil-pakchoi and wheat agroecosystems: Insights and predictive models

The accumulation of antimony (Sb) in plants and its potential effects on human health are of increasing concern. Nevertheless, only a few countries or regions have established soil Sb thresholds for agricultural purposes, and soil properties have not been taken into account. This study investigated the accumulation of Sb in the edible parts of pakchoi and wheat grain by adding exogenous Sb to 21 soils with varying properties. The results revealed a positive correlation between bioavailable Sb (Sbava, extracted by 0.1 M K2HPO4) in soil and Sb in the edible parts of pakchoi (R2 = 0.77, p < 0.05) and wheat grain (R2 = 0.54, p < 0.05). Both machine learning and traditional multiple regression analysis indicated Sbava was the most critical feature and the main soil properties that contributed to Sb uptake by pakchoi and wheat were CaCO3 and clay, respectively. The advisory food limits for Sb in pakchoi and wheat were estimated based on health risk assessment, and used to derive soil thresholds for safe pakchoi and wheat production based on Sbtot and Sbava, respectively. These findings hold potential for predicting Sb uptake by crops with different soil properties and informing safe production management strategies.

A novel magnetic graphene-loaded biochar gel for the remediation of arsenic- and antimony-contaminated mining soil

Metalloid co-contamination such as arsenic (As) and antimony (Sb) in soils has posed a significant threat to ecological balance and human well-being. In this study, a novel magnetic graphene-loaded biochar gel (FeBG) was developed, and its remediation potential for the reclamation of AsSb spoiled soil was assessed through a six-month soil incubation experiment. Results showed that the incorporation of iron substances and graphene imparted FeBG with enhanced surface characteristics, such as the formation of a new FeO bond and an enlarged surface area compared to the pristine biochar (BC) (80.5 m2 g−1 vs 57.4 m2 g−1). Application of FeBG significantly decreased Na2HPO4-extractable concentration of As in soils by 9.9 %, whilst BC addition had a non-significant influence on As availability, compared to the control. Additionally, both BC (8.2 %) and FeBG (16.4 %) treatments decreased the Na2HPO4-extractable concentration of Sb in soils. The enhanced immobilization efficiency of FeBG for As/Sb could be attributed to FeBG-induced electrostatic attraction, complexation (Fe–O(H)–As/Sb), and π-π electron donor-acceptor coordination mechanisms. Additionally, the FeBG application boosted the activities of sucrase (9.6 %) and leucine aminopeptidase (7.7 %), compared to the control. PLS-PM analysis revealed a significant negative impact of soil physicochemical properties on the availability of As (β = −0.611, P < 0.01) and Sb (β = −0.848, P < 0.001) in soils, in which Sb availability subsequently led to a suppression in soil enzyme activities (β = −0.514, P < 0.01). Overall, the novel FeBG could be a potential amendment for the simultaneous stabilization of As/Sb and the improvement of soil quality in contaminated soils.

Effect of freeze-thaw frequency plus rainfall on As and Sb metal(loid)s leaching from the solidified/stabilized soil remediated with Fe-based composite agent

The composite agent of ferrous sulfate, fly ash, and calcium lignosulfonate (FFC) can remediate the soil contaminated by As and Sb under cyclic freeze-thaw (F-T) via stabilization/solidification (S/S). However, the impact of high-frequency F-T cycles on the leaching behavior and migration of As and Sb in FFC-treated soils remains unclear. Here the leaching concentrations, heavy metal speciation (Wenzel's method), and Hydrus-1d simulations were investigated. The results showed that FFC effectively maintained the long-term S/S efficiency of arsenic remediation subject to an extended rainfall and freeze-thaw cycles, and stabilized the easily mobile form of As. The short-term S/S effect on Sb in the remediated soils suffering from F-T cycles was demonstrated in the presence of FFC. In a 20-year span, the mobility of Sb was affected by the number of F-T cycles (FT60 > FT20 > FT40 > FT0) in soil with a depth of 100 cm. As leaching progressed, FFC slowed the upward proportion of adsorbed As fractions but converted parts of the residual Sb to the form of crystalline Fe/Al (hydro) oxide. Moreover, the adsorption rate and capacity of As also preceded that of Sb. Long-term curative effects of FFC could be observed for As, but further development of agents capable of remedying Sb under cyclic F-T and long-term rainfall was needed. The predictive results on the migration and leaching behavior of heavy metals in S/S remediated soils may provide new insight into the long-term assessment of S/S under natural conditions.

Re-Interpretation of Metal(Loid) Concentrations in Urban Soils of Two Different Land Uses by Positive Matrix Factorisation

Positive matrix factorisation (PMF) is a receptor model, which is frequently used in environmental geochemistry for metal(loid)s’ source apportionment in various matrices. In this study, concentration data for As, Cu, Co, Cr, Fe, Mn, Ni, Pb, Sb, V and Zn in urban soils of two land uses (playground and roadside soils) from the city of Bratislava (Slovak Republic) were reinterpreted using the PMF model to quantify the contributions of individual sources of metal(loid)s in soils. Brake and tyre abrasion (27.0%), mixed traffic/industrial sources (14.3%), and natural origin (58.7%) were identified for roadside soils, while mixed traffic sources (28.4%), Cu-specific source (24.6%), and natural origin (47.0%) contributed to the metal(loid) concentrations in playground soils. Factor contributions revealed prevailing non-exhaust sources dominated by Cu, Sb and Zn over mixed traffic/industrial sources in roadside soils, following the world trend. Strong negative correlations of the 206Pb/207Pb isotopic ratio with Factor 1 in both groups of soils, representing traffic and industrial sources, are an evidence of the correct assignment of the obtained factor profiles to the actual sources of metal(loid)s in soils. There were significant differences in the proportion of mixed traffic sources in playground soils among the five urban districts, while the largest proportion of this source was identified in the city centre with the longest urbanisation and industrial history. Error estimation methods (displacement, bootstrap, displacement with bootstrap) proved that the data fit the model well and there was a minimal rotational ambiguity and random errors in the base model run.

Source-based health risk assessment of heavy metal contamination in soil: a case study from a polymetallic mining region in Southeastern Hubei, Central China.

To conduct a precise health risk assessment of heavy metals (HMs) in soil, it is imperative to ascertain the primary sources of potential health risks. In this study, we conducted comprehensive measurements of HMs, specifically focusing on the accumulation of Cu, Cd, Sb, Zn, and Pb in local soil, which may pose threats to environmental quality. To achieve our objective, we employed a method that combines positive matrix factorization with a health risk assessment model to quantify the health risks associated with specific sources. The results obtained from the geo-accumulation index indicate that the majority of HMs found in the local soil are influenced by anthropogenic activities. Among these sources, local industrial-related activities contributed the largest proportion of HMs to the soil at 34.7%, followed by natural sources at 28.7%, mining and metallurgy-related activities at 28.2%, and traffic-related activities at 8.40%. Although the non-carcinogenic and carcinogenic risks associated with individual HMs were found to be below safety thresholds, the cumulative health risks stemming from total HMs exceeded safety limits for children. Moreover, the unacceptable health risks for children originating from industrial-related activities, natural sources, and mining and metallurgy-related activities were primarily concentrated in proximity to mining sites and industrial areas within the local region. This investigation furnishes valuable insights that can aid governmental authorities in formulating precise control policies to mitigate health threats posed by soils in polymetallic mining areas.

Phytoremediation of Iron and Antimony Polluted Waste Dump Sites in Anyigba Kogi State, Nigeria: A Multivariate Statistical Technique

Soil degradation by anthropogenic means is increasing day after day all over the globe, particularly in Nigeria. This research became necessary to show how plants grown surrounding waste dumps are able to mitigate soil pollution by Fe and Sb. Both media (plants and soils) were collected, and leached, and analyses were performed to assess the quantum of Iron and Antimony found within sampled media. The EDX3600B X-ray fluorescence spectrometer was used to analyze for soil and plants sampled. The bioconcentration factor (BCF), translocation factor (TF), bioaccumulation coefficient (BAC), and metal uptake efficacy (%) ME for both media were calculated. The evaluated data revealed that Colocasia esculent and Amaranthus viridis showed the maximum capacity as Fe hyperaccumulators. Also, Colocasia asculenta, Physalis angulate, and Zea mays were suitable plants as hyperaccumulators of Sb. Only Loportea aestuans suffices as phytoextractor for Antimony. Amaranthus hybridus, Colocasia asculenta, and Corchorus aestuans have capacities to stabilize Sb in soils. Species collected showed the required ability as phytominers of Sb. The quantities of Iron and Antimony in acquired media were higher than allowable benchmarks in leaves (vegetables). From this investigation, the acquired plants showed evidence of good specimens with abilities to remove Iron and Antimony from the soil. The collected species also showed attributes and characteristics of good reservoirs of Iron and Antimony.

Effects of vegetation restoration on the concentrations of multiple metal elements in post-mining soils

Vegetation restoration is vital for soil ecological restoration in post-mining areas, but a global-scale quantitative assessment of its effects on soil metal elements is lacking. Here, we conducted a meta-analysis with 2308 paired observations collected from 137 publications to evaluate vegetation restoration effects on the concentrations of 17 metal elements, namely K, AK (available K), Ca, Na, Mg, Fe, Mn, Zn, Cu, Al, Cr, Co, Ni, Cd, Sb, Hg, and Pb in post-mining soils. We found that (1) vegetation restoration significantly increased the concentrations of K, AK, Ca, Mg and Co by 43.2, 42.5, 53.4, 53.7, and 137.2%, respectively, but did not affect the concentrations of Na, Fe, Mn, Zn, Cu, Al, Cr, Ni, Cd, Sb, Hg, and Pb; (2) the effects of vegetation restoration on soil metal concentration were seldom impacted by vegetation type, while soil depth only affected the responses of AK, Cd, and Pb concentrations to vegetation restoration, and leaf type only impacted the responses of Ca and Ni concentrations to vegetation restoration; (3) latitude, elevation, restoration year, climate, and initial soil properties were also important moderator variables of vegetation restoration effects, but their impacts varied among different metals. Overall, our results clearly showed that vegetation restoration in posting-mining areas generally have a positive effect on the concentrations of nutrient elements but did not influence that of toxic elements, which provides useful information for the restoration and reconstruction of soil ecosystem in post-mining areas.

Unraveling the aging dynamics in the simultaneous immobilization of soil metal(loid)s using oxides

Immobilization represents the most extensively utilized technique for the remediation of soils contaminated by heavy metals and metalloids. However, it is crucial to acknowledge that contaminants are not removed during this process, thereby leaving room for potential mobilization over time. Currently, our comprehension of the temporal variations in immobilization efficacy, specifically in relation to amendments suitable for industrial sites, remains very limited. To address this knowledge gap, our research delved into the aging characteristics of diverse oxides, hydroxides, and hydroxy-oxides (collectively referred to as oxides) for the simultaneous immobilization of arsenic (As), cadmium (Cd), and antimony (Sb) in soils procured from 16 contaminated industrial sites. Our findings unveiled that Ca-oxides initially showed excellent immobilization performance for As and Sb within 7 days but experienced substantial mobilization by up to 71 and 13 times within 1 year, respectively. In contrast, the efficacy of Cd immobilization by Ca-oxides was enhanced with the passage of time. Fe- and Mg-oxides, which primarily operate through encapsulation or surface complexation, exhibited steady immobilization performances over time. This reliable and commendable immobilization effect was observed across distinct soils characterized by varying physicochemical properties, including pH, texture, CEC, TOC, and EC, underscoring the suitability of such amendments for immobilizing metal(loid)s in diverse soil types. MgO, in particular, displayed even superior immobilization performance over time, owing primarily to gradual hydration and physical entrapment effects. Remarkably, Mg-Al LDHs emerged as the most effective candidate for the simultaneous immobilization of As, Cd, and Sb. The results obtained from this study furnish valuable data for future investigations on the immobilization of metals and metalloids in industrial soils. They enable the projection of immobilization performance and offer practical guidance in selecting suitable amendments for the immobilization of metal(loid)s.

Can antimony contamination in soil undermine the ecological contributions of earthworms?

As antimony (Sb) has been increasingly used in manufacturing industries (e.g., alloy, polymer and electronics industries), Sb contamination in the soil environment becomes widely reported and has drawn growing attention due to the toxicity of Sb to living organisms. Whether soil-dwelling organisms can tolerate Sb toxicity and maintain their ecological functions remains poorly understood. Using a cosmopolitan, ecologically important earthworm species (Eisenia fetida) as an ideal model organism, we examine the effects of Sb on the physiological, molecular and behavioural responses of earthworms to different levels of Sb contamination in soil (0, 10, 50, 100, 250 and 500 mg/kg). We found that earthworms could tolerate heavy Sb contamination (100 mg/kg) by boosting their antioxidant defence (POD and GST) and immune systems (ACP) so that their body weight and survival rate were sustained (c.f. control). However, these systems were compromised under extreme Sb contamination (500 mg/kg), leading to mortality. As such, earthworms exhibited avoidance behaviour to escape from the Sb-contaminated soil, implying the loss of their ecological contributions to the environment (e.g., increase in soil aeration and maintenance of soil structure). By measuring various types of biomarkers along a concentration gradient, this study provides a mechanistic understanding of how earthworms resist or succumb to Sb toxicity. Since extreme Sb contamination in soil (>100 mg/kg) is rarely found in nature, we are optimistic that the health and performance of earthworms are not influenced by Sb in most circumstances, but regular monitoring of Sb in soil is recommended to ensure the integrity and functioning of soil environment. Further studies are recommended to evaluate the long-term impact of Sb in the soil ecosystem through bioaccumulation and trophic transfer among soil-dwelling organisms.

Airborne soil and dust are potential sources of antimony to residents across Delhi: Exposure likely to occur via dermal route

BackgroundThere is an urgent need to assess sources of toxic metals in highly urbanized environments, to identify high risk areas for testing to enable planning to minimize exposure to residents. Notable toxic metals identified in this study were Antimony (Sb) and mercury (Hg), listed as priority pollutants by USEPA that can cause a variety of diseases in humans, and cobalt (Co), compounds of which have been shown to be carcinogenic in animal studies. ObjectivesObjectives of this study were to measure the level and spatial distribution of toxic metals in roadside soil and road dust across a large area of Delhi. Toxic metals with notably high levels were identified and assessed for potential environmental exposure, non-carcinogenic and carcinogenic risks to the population in the study area. Research methodsA sampling scheme was designed to collect soil from a wide range of roadside environments across the urban region of Delhi. The soil and dust fractions were separated and selected toxic metals extracted and analyzed on Inductively Coupled Plasma – Mass Spectroscopy (ICP–MS) adopting USEPA methodology. ResultsMean concentrations of Sb (2.62 and 3.59 in μgg−1) were 13 and 18 times higher than background level (0.2 μgg−1) in fine fractions of roadside soil and road dust, respectively in all areas sampled. The Hg and Co were moderately and minimally enriched in a fine fraction of soil and dust, respectively. The fine fraction of soil and dust showed a significant decrease in the Cu/Sb ratio compared to the coarse fraction suggesting an anthropogenic addition of Sb from vehicular brake pads. This study is the first of its type to calculate the cancer risk assessment of Sb from inhalation exposure. ConclusionMeasurements of Sb, Hg and Co in roadside soil and dust are mapped to highlight regions where testing of the population would be advisable. In addition, toxic levels of Sb may enter the human body via a dermal route and cause various diseases including diabetes mellitus and gestational diabetes mellitus. Finally, our results suggest an immediate change to antimony free brake pads for all vehicles is recommended.

Kinetics of coupled sorption and abiotic oxidation of antimony(III) in soils

A quantitative evaluation of the dynamics of antimony (Sb) species transformation when Sb(III) enters the soil matrix would facilitate the understanding of the speciation and environmental fate of Sb in natural environments. Towards this end, the coupled sorption and abiotic oxidation kinetics of Sb(III) were examined across 12 soils with a 24 h timeframe. The soil-solution distribution coefficients (Kd) of Sb ranged between 214 and 5965 L kg−1. Both apparent and mechanistic kinetic models were used to described the process. The apparent kinetic model indicated a two-rate oxidation and associated stabilization behavior of Sb in soils. The fast oxidation rate constants ranged from 0.147 to 0.763 h−1, which were one to two orders of magnitudes higher than the slow rate constants (0.002–0.039 h−1). Iron and Mn oxides were identified as the key soil components associated with adsorptive-oxidative sites (SOH) and oxidative sites (Mn-OH) of soils for Sb species, and these were subsequently integrated into the mechanistic kinetic model. This model included the adsorption–desorption of Sb(III) as well as the oxidation product, Sb(V) on the SOH, the oxidation of Sb(III) by SOH and Mn-OH, and the stabilization of both Sb(III) and Sb(V). The model produced a global fit for dissolved and adsorbed Sb species across the 12 soils. This study provides new information for predicting the dynamics of Sb in soils when multiple adsorption–desorption, oxidation and stabilization reactions are coupled in natural environments.

Geographic distribution, source analysis, and ecological risk assessment of PTEs in the topsoil of different land uses around the antimony tailings tank: A case study of Longwangchi tailings pond, Hunan, China

Few studies have addressed the contamination of surface soils around antimony tailings ponds, and studying the contamination levels and sources of potentially toxic elements (PTEs) in soils around antimony tailings ponds and assessing the associated environmental risks are key steps in conducting environmental protection. Therefore, this study is the first to investigate the current status, spatial distribution, potential sources and ecological risks of Pb, Sb, Cr, Zn, Cd, As and Cu contamination in surface soils in woodlands, grasslands, farmlands and construction areas around the Longwangchi antimony tailings pond in Hunan, China. According to the analytic results of soil samples, the order of PTEs in terms of average concentration is: Sb > Zn > Cu > Pb > As > Cr > Cd. The cumulative index of land was applied to define Sb and Cd as extremely heavy pollution, and PLI divides the overall pollution level of soil into serious pollution levels. The ecological risk index was used to evaluate the risk characteristics of PTEs. The results showed that the ecological risk of Sb was particularly prominent, and 95% of the study area had reached a very high risk level. A quantitative comparison of ecological risk levels between different land uses revealed that there was a clear dividing line between regions, with built-up areas contributing the most to higher ecological risk at 8.89%, followed by 1.72% for grassland, 1.15% for agricultural land, and 0.57% for woodland. The visualization results of spatial distribution of PTEs exhibited that severe pollution occurred in the middle, north and southeast of the study area, and these distribution characteristics are mainly dictated by the polluted runoffs from tailings ponds and human activities. Principal component analysis (PCA) and positive matrix decomposition (PMF) were employed to identify the exact pollution sources, and the closer the determination coefficient (R2) of PMF was to 1, the finer the pollution sources analyzed. A total of six potential sources of PTEs were analyzed by PMF: 36% of tailings pond contamination and mining operations, 8% atmospheric deposition, 19% traffic emissions, 9% combustion emissions, 11% natural sources, and 17% inputs related to agricultural production. This study is a complement to the study of environmental pollution around antimony tailing ponds, providing evaluation criteria for the pollution identification indicators of antimony tailing ponds.

Risk Assessment and Spatial Distribution of Heavy Metals with an Emphasis on Antimony (Sb) in Urban Soil in Bojnourd, Iran

Recently, one of the major environmental issues is the pollution of soil with Antimony (Sb), which is ecologically detrimental and potentially carcinogenic to humans. In developing countries such as Iran, Sb concentrations in soils have not yet been accurately determined. Therefore, the purpose of this study was to examine the levels of Sb and the other HMs (Pb, Cd, As, Ni, Hg and Cr) in the surface soils of Bojnourd, Iran, as well as their distribution and potential risks to the environment and human health. A total of 37 soil samples (0–20 cm) were taken from different sampling stations: 900 × 900 m regular grid for traffic areas (TA), residential areas (RA) and suburb areas (SA). The contamination factor (CF) and geo-accumulation index (Igeo) are two indices that were used to reflect the potential ecological risk from HMs. Geographic information system (GIS), Spearman correlation matrix and health risk indexes were utilized to investigate the source and potential hazard of HMs. The results showed that the average concentration of HMs in TA was highly enriched compared to other areas. Most soil samples were identified to have low levels of Sb and Ni pollution, while having moderate to high levels of Pb, Cr, As, Hg and Cd pollution, as determined by the pollution indices (Igeo and CF). Geostatistical analysis and GIS mapping of the spatial distribution of HM concentrations showed that there have been similar patterns of spatial distribution for Cd, Cr, Ni and Sb and their hot spots were in the southeast, west and center of the city. Neither the hazard quotient (HQ) nor the hazard index (HI) of the examined HMs indicated any non-carcinogenic risk to adults or children. However, carcinogenic risk assessment revealed that cancer risk was raised from Cr and Cd contents for children, while these elements showed an acceptable risk for adults. Furthermore, children’s carcinogenic and non-carcinogenic values were greater than adults’, indicating more potential health hazards associated with these HMs. Therefore, assessing the risk posed by HM pollution in urban surface soil is vital and urgent for children. A more detailed investigation is also required to identify the spatial distribution of soil pollution in areas recognized as enriched in Sb. A proper assessment of the environmental risk and the corresponding risk to humans from HM in a study area can be critical to developing an appropriate remediation method.

Attenuation of Pb and Sb in shooting range soils by Fe amendments

Lead (Pb) and antimony (Sb) contamination pose a major environmental risk at firing ranges and threaten land sustainability. Methods for the stabilization of metal (loid) contaminants are necessary to prevent off-site migration of metals in surface and ground water or from soil erosion. In the present study, two remediation treatments (ferric chloride/calcium carbonate and nanoscale zero-valent iron (nZVI)) were applied to flow-through soil columns containing four types of soils (sand, sandy loam, loamy sand, and silty loam) to study Pb and Sb behavior. Water runoff was continuously monitored for three months prior to amendment addition and for the following ten months. Soils were characterized before and after reaction. We found Sb was more mobile than Pb in all soil systems and was primarily present in the dissolved fraction whereas Pb was associated with both soil organic matter (SOM) and Fe colloids. Dominant Pb solid phase species were comprised of Pb0, PbO, PbCO3, and Pb sorbed to Fe(III) oxides while Sb was present as fully oxidized Sb(V) in soil and soil solution. The nZVI addition had minimal impact on Pb and Sb immobilization compared to control soil. The FeCl2 and CaCO3 amendment decreased pore water Sb concentrations by >80% for all soil types and >96% reduction in the fine- and coarse-grained soil types (silt loam and sand). Lead was initially mobilized coinciding with a decrease in pH from the hydrolysis of Fe(II) in solution. Additional soil treatments have the potential to be effective for system-wide immobilization with adequate additions of CaCO3 buffer. Though this study focused on bullet fragment weathering as a source of Pb and Sb the results have application to environmental monitoring and remediation efforts at mining or industrial runoff sites.

Pollution and health-risk assessments of Cr-contaminated soils from a tannery waste lagoon, Hebei, north China: With emphasis on Cr speciation

In this paper, heavy metals (i.e., V, Cr, Co, Cu, Zn, Cd, Pb, and Sb) in soils from a tannery waste lagoon, Hebei, north China were investigated. Element concentrates were determined by a portable X-ray fluorescence in situ and an inductively coupled plasma mass spectrometry in the lab. Two sets of indexes, including geological accumulation index, contamination factor, and pollution load index, and hazard quotient and total carcinogenic risk were adopted to evaluate the pollution and health-risk of heavy metals. A scanning electron microscopy in conjunction with an energy dispersive X-ray spectroscopy and an X-ray photoelectron spectroscopy was used to observe chromium occurrence and speciation. With an average of 6493.11 mg/kg, chromium contents in the lagoon soils reached up to 12971.19 mg/kg, 211-times higher than the threshold of Chinese soils (61.00 mg/kg). Elevated Cr contents resulted in significantly high pollution and noncarcinogenic and carcinogenic risks in the studied area. Chromium in most soils occurred predominately as Cr3+ (60–74%), and to a lesser extent, Cr6+. The mechanism responsible for decreasing Cr6+ percentages in soils with increasing depth was summarized: Cr6+ favors aqueous environment; soil moisture decreased with increasing depth; in soils especially in the lower portion, Cr6+ was reduced by Fe0 and Fe2, transforming into Cr3+ and Fe3+. In addition, the alkaline condition promoted Cr3+ to precipitate, resulting more Cr3+ absorbing in soils. The intimate association of Cr and Fe in soils (i.e., Cr mainly occurred in Fe oxides and dolomite) further confirmed our assumptions. A combined application of microorganism (e.g., Aeromonas hydrophila) and biochar (prepared from maize stalk or peanut shells) were recommended to alleviate Cr pollution in the soils.

BEHAVIOR OF HEAVY METALS IN SOIL-CONDENSATE-PLANTS SYSTEM IN THE ULAN-UDE LANDFILLS

The impact of waste dumps on environmental components, i.e., soil, evaporating soil water (condensate) and plants is studied. It has been revealed that industrial and municipal waste dumps continue to affect significantly the environment after their closure. The behavior of heavy metals (Pb, Cu, Zn, Ni, Cd, Co, Sb, Sn, Bi, Hg, and Cr) in soils, plants, and condensate in landfill areas and beyond them (the background) has been studied in detail. It has been found out that soils, plants and condensate at landfills are enriched in heavy metals as compared to the background sites. The degree of soil contamination at waste dumps depends on the reclamation stage of the latter. The landfill soils exceed the norms of maximum permissible concentrations for heavy metals by 1.1–90 times. Concentrations of heavy metals in plants exceed the background values from 1.1 to 104 times at all dumps. The maximum level of heavy metals in plants is exceeded for Zn, Cd, Cr. In the condensate sampled at the dumps, MPC is exceeded for Cu, Zn, and Hg. Based on the analysis results, the geochemical rows of heavy metal distribution in different landfill environments were compiled: in plants – Zn Cu Cr Ni Pb Cd Co Hg Sn Bi; in condensate – Zn Cu Ni Cr Pb Sn Co Hg Sb Cd Bi; in the soil – Zn Cr Cu Ni Pb Co Sb = Sn Cd. The distribution of heavy metals in the condensate and plants is similar. In these environments, contribution of Zn and Cu is more than 80%, contribution of Cr, Ni, Pb varies from 1 to 10%; contribution of Cd, Co, Sb, Sn, Bi, Hg is less than 1%. Heavy metals are distributed in soil according to a different pattern: the main contributors are Zn and Cr (their input is more than 50%), then go Ni, Cu, Co, and Pb (their content in soil varies from 1 to 50%), followed by Sb, Sn, and Cd (their content is less than 1%). Total pollution indices (Zc) of the soil, condensate and plants have been calculated for each landfill. Based on Zc, the landfills were grouped in a ranking series, which can form the basis for assigning the sequence of landfill reclamation measures.

A molecular level understanding of antimony immobilization mechanism on goethite by the combination of X-ray absorption spectroscopy and density functional theory calculations

A molecular level understanding of antimony (Sb) immobilization mechanism on Fe oxides is required to clarify the fate of Sb in the soil. In this study, macroscopic sorption experiments, combined with extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT), were utilized to explore the interaction between Sb and goethite. The ion strength has no effect on Sb sorption on goethite, indicating the inner-sphere complex Sb formed on goethite. Goethite has the higher sorption potential to Sb(III) than Sb(V), consistent with the higher thermodynamic stability of the geometry for Sb(III) formed on goethite than Sb(V) revealed by DFT calculations. By comparing the Sb-Fe distances obtained by EXAFS spectroscopy and DFT, eight kinds of Sb(III) surface complexes and nine kinds of Sb(V) surface complexes were considered to be the possible geometries Sb formed on different crystal planes of goethite, including monodentate mononuclear, bidentate mononuclear, bidentate binuclear, tridentate mononuclear, tridentate binuclear, tridentate four-nuclear complexes. The structural and energetic details of these filtered geometries provide comprehensive information on Sb immobilization mechanism on goethite, helpful in clarifying the fate of Sb in soils.

Stabilization of arsenic, antimony, and lead in contaminated soil with montmorillonite modified by ferrihydrite: Efficiency and mechanism

Co-contamination of As, Sb, and Pb in soil has aroused public concern due to their wide application in industries. However, the efficient stabilization materials with simultaneous cations and anions stabilization capacities are still lacking and remain a challenge. Herein, a new type of montmorillonite modified by amorphous ferrihydrite (amFe@Mont) was synthesized and the immobilization performance of amFe@Mont for As, Sb, and Pb in soil was investigated comprehensively, mainly by TCLP, SBET, and DTPA extraction. The stabilization efficiency assessed by TCLP reached 86.28 % for Sb and 94.60 % for Pb after 56 days, and the As could not be detected in the leachate after 10 days. For As, Sb and Pb, the SBET method achieved a reduction of 87.34 %, 54.59 % and 17.59 % respectively. The DTPA extractable content of the metal(loid)s also declined significantly, especially for As. By applying amFe@Mont, the soil properties as well as the bacterial richness and diversity in the soil were obviously improved. The amFe@Mont adsorption data are well fitted to the Langmuir model and the pseudo-second-order model. The principal stabilization mechanisms were ascribed to inner-sphere complexation, surface precipitation and co-precipitation, and structural incorporation into amFe@Mont. This is the first study to exhibit the feasibility of amFe@Mont as an effective and environmentally friendly stabilizer for remediation of As/Sb/Pb co-contaminated soils.

Enrichment, contamination, ecological and health risks of toxic metals in agricultural soils of an industrial city, northwestern China

BackgroundThe impacts of rapid urbanization and industrialization often cause toxic metal contamination in agricultural soils, which has been a global environmental issue. MethodsAgricultural soil samples were obtained from Lanzhou city, a typical industrial city in northwestern China. The levels of six toxic metals (i.e., Cd, Cr, Cu, Pb, Sb, and Zn) were determined in soil samples using Inductively Coupled Plasma Optical Emission Spectrometer. Afterwards, enrichment, contamination, ecological and health risks of them were comprehensively evaluated. ResultsThe average concentrations of toxic metals were 0.30, 79.7, 21.6, 26.7, 0.97, and 69.0 mg kg−1 for Cd, Cr, Cu, Pb, Sb, and Zn, respectively in soils. Cd was moderately enrichment while other metals were minimally enriched in soils of Lanzhou. The agricultural soils were characterized by moderate to considerable contamination of Cd and low contamination of other metals. Moreover, Cd might cause noticeable ecological risks at most sites. In addition, the average target hazard quotient (THQ) for children was 0.727, almost ten times higher than that for adults. Cr, Pb, and Sb were the most sensitive factors affecting the health risk assessment and contributed over 99% to the THQ. ConclusionLithogenic source, industrial and mining activities, and phosphorus fertilizer usage were the three main factors affecting the concentrations of Cd, Cr, Cu, Pb, Sb, and Zn in agricultural soils of Lanzhou, which should be taken into consideration in future supervision and management. Health risks of these metals, especially Cd, Cr, and Sb, for children should receive considerable attention due to their health hazard.