Bioavailability Of Metals In Soils Research Articles

Remediation of Pb and Cd contaminated sediments by wheat straw biochar and microbial community analysis

Wheat straw biochar (BC) or modified wheat straw biochar (MBC) could affect the aggregate structure of soil, effectively adsorb heavy metal and reduce the bioavailability of heavy metals in soil. TGA, BET, FTIR and SEM were used to characterize the surface morphology and structure of BC and MBC. The adsorption properties of BC and MBC on Pb(‌II) and Cd(‌II) in solution systems were investigated by batch experiments, and the remediation performance of Pb and Cd contaminated sediment by BC or MBC were studied by pot experiments. The results showed that MBC had a larger specific surface area of 46.04 m2/g and total pore volume 0.0555 cm3/g; the adsorption isotherms of Pb(II) and Cd(II) for BC and MBC were more suitable for Langmuir model (R2 over 0.91), and the maximum adsorption capacities of Pb(II) and Cd(II) by MBC could reach 71.14 and 115.64 mg/g, respectively. BC or MBC promoted the transformation of Pb and Cd from the extractable acid fraction to the oxidizable and residual fraction, reduced the migration of heavy metals and enhanced the stability of aggregates. Therefore, the results provided a perspective for the dredged contaminated sediments used as planting soil. In addition, BC or MBC, as soil amendments, could improve the abundance of microbial community. At the phylum level, the main dominant bacteria were Proteobacteria and Bacteroidetes.

Effects of Ageing on Surface Properties of Biochar and Bioavailability of Heavy Metals in Soil

This study aims to explore the effects of biochar ageing on its surface properties and the bioavailability of heavy metals in soil. The biochar was subjected to chemical oxidation/dry–wet cycles (CDWs), chemical oxidation/freeze–thaw cycles (CFTs), and natural ageing (NT) to analyze changes in the elemental composition, pH, specific surface area, pore volume, and surface functional groups. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were applied to characterize the functional groups and microstructure, and the BCR sequential extraction method was employed to demonstrate the fractionation distribution of Cu, Cd, and Pb. The results showed that the CDWs and CFTs treatments significantly reduced the carbon content of the biochar (with a maximum reduction to 47.70%), increased the oxygen content (up to 49.17%), and notably increased the specific surface area and pore volume. The pH decreased significantly from 9.91 to 4.92 and 4.99 for the CDWs and the CFTs, respectively. The FTIR analysis indicated notable changes in hydroxyl and carboxyl functional groups, and the SEM revealed severe microstructural damage in biochar after the CDWs and CFTs treatments. The heavy metal fractionation analysis indicated that exchangeable Cu, Cd, and Pb significantly increased after the CDWs treatment, reaching 31.40%, 5.25%, and 6.79%, respectively. In conclusion, biochar ageing significantly affects its physicochemical properties and increases the bioavailability of heavy metals, raising concerns about its long-term remediation effectiveness.

Bioassessment of Cd and Pb at Multiple Growth Stages of Wheat Grown in Texturally Different Soils Using Diffusive Gradients in Thin Films and Traditional Extractants: A Comparative Study.

The bioavailability of heavy metals in soil is a crucial factor in determining their potential uptake by plants and their subsequent entry into the food chain. Various methods, including traditional chemical extractants and the diffusive gradients in thin films (DGT) technique, are employed to assess this bioavailability. The bioavailability of heavy metals, particularly cadmium (Cd) and lead (Pb), is also influenced by soil texture and their concentrations in the soil solution. The primary objectives of this experiment were to compare and correlate the assessment of the Cd and Pb bioavailability using the DGT technique and traditional extractants across two soil textural classes: sandy clay loam (SCL) and clay loam (CL) at two contamination levels: aged contaminated (NC) and artificially contaminated (AC). The specific objectives included assessing the bioavailability of Cd and Pb at different growth stages of the wheat plant and correlating the DGT-based bioassessments of Cd and Pb with their concentrations in various plant parts at different growth stages. This study also compared the effectiveness of the DGT method and traditional extraction techniques in assessing the bioavailable fractions of Cd and Pb in soil. The regression analysis demonstrated strong positive correlations between the DGT method and various extraction methods. The results showed that the wheat plants grown in the AC soils exhibited lower root, shoot, and grain weights compared to those grown in the NC soils, indicating that metal contamination negatively impacts plant performance. The concentrations of Cd and Pb in the wheat tissues varied across different growth stages, with the highest levels observed during the grain filling (S3) and maturity (S4) stages. It is concluded that the in situ assessment of Cd and Pb though DGT was strongly and positively correlated with the Cd and Pb concentration in wheat plant parts at the maturity stage. A correlation and regression analysis of the DGT assessment and traditional extractants showed that the DGT method provides a reliable tool for assessing the bioavailability of Cd and Pb in soils and helped in developing sustainable soil management strategies to ensure the safety of agricultural products for human consumption.

Assessing the Risk, Bioavailability, and Phytoremediation of Heavy Metals in Agricultural Soils: Implications for Crop Safety and Human Health

This review addresses heavy metal contamination in agricultural soils, focusing on bioavailability, toxicity, and phytoremediation techniques. We identify significant regional variations in cadmium and lead levels, posing health risks through crop consumption. Effective phytoremediation methods, such as phytoextraction and Phytostabilization, have shown marked improvements over recent years. Recommendations include best practices for soil management, stringent regulatory measures, and advanced research in biotechnological remediation methods. This study underscores the urgent need for integrated strategies to ensure food safety and sustainable agriculture in sector.

Impact of Green Manures in Mitigating Heavy Metal Toxicity: A Review

The contamination of soil with heavy metals poses a serious threat to both ecology and public health. Human activity, such as mining, excessive fertilizer application, and industrial processes, are among the various sources of heavy metal pollution. There are various green manure plant species used as potential for mitigating heavy metal toxicity, certain legume plants like Albizia leibbeck L., Bauhinia purpurea L., Dalbergia sissoo, Millettia peguensis Ali, and Pongamia pinnata are being looked for applications in phytoremediation. Various techniques such as bioremediation, phytoextraction, phytofiltration, phytovolatilization, rhizofiltration, phytodegradation, and phyto desalinization are employed to address environmental pollution. Phytoremediation, in particular, aims to collect pollutants from the environment and convert them into forms that can be easily extracted from plant tissues. Contamination by heavy metals is a severe environmental matter. However, there are various contemporary methods that offer potential solutions to address this issue. One such approach involves the use of biochar to decrease the bioavailability of heavy metals in soil. By binding to them reducing their availability for plant absorption and entry into the food chain. Genetic engineering permits researchers to insert genes into plants that improve their acceptance of heavy metals or increase their ability to accumulate them (phytoextraction). Consequently, the utilization of these conventional methods in phytoremediation has demonstrated the most favourable and sustainable outcomes, ensuring an eco-friendly approach for the ecosystem.

Inhibition of high sulfur on functional microorganisms and genes in slightly contaminated soil by cadmium and chromium

It is generally accepted that sulfur can passivate the bioavailability of heavy metals in soil, but it is not clear whether high sulfur in cadmium (Cd) and chromium (Cr) contaminated soil has negative effect on soil microbial community and ecological function. In this study, total sulfur (TS) inhibited the Chao 1, Shannon, Phylogenetic diversity (Pd) of bacterial and Pd of fungi in slightly contaminated soil by Cd and Cr around pyrite. TS, total potassium, pH, total chromium, total cadmium, total nitrogen, soil organic matter were the predominant factors for soil microbial community; the contribution of TS in shaping bacterial and fungal communities ranked at first and fifth, respectively. Compared with the low sulfur group, the abundance of sulfur sensitive microorganisms Gemmatimonas, Pseudolabrys, MND1, and Schizothecium were decreased by 68.79–97.22% (p < 0.01) at high sulfur one; the carbon fixation, nitrogen cycling, phosphorus cycling and resistance genes abundance were significantly lower (p < 0.01) at the latter. Such variations were strongly and closely correlated to the suppression of energy metabolism (M00009, M00011, M00086) and carbon fixation (M00173, M00376) functional module genes abundance in the high sulfur group. Collectively, high sulfur significantly suppressed the abundances of functional microorganisms and functional genes in slightly contaminated soil with Cd and Cr, possibly through inhibition of energy metabolism and carbon fixation of functional microorganisms. This study provided new insights into the environmental behavior of sulfur in slightly contaminated soil with Cd and Cr.

Impacts of atmospheric deposition on the heavy metal mobilization and bioavailability in soils amended by lime

Atmospheric deposition is an important source of heavy metal in agricultural soils, but there is limited research on the mobility of these metals in soil and their impact on soil amendment. Here, we performed a dust incubation experiment in soils in the laboratory and a factorial transplant experiment at three field sites with a gradient of atmospheric deposition to examine the impacts of atmospherically deposited heavy metals (Cu, Cd, and Pb) on the mobility and bioavailability in soils with and without lime applications. Results showed that the atmospherically deposited heavy metals showed high mobility and were primarily presented in the soluble ionic fractions in the wet part and acid-exchangeable and reducible fractions in the dry part of atmospheric deposition. Atmospheric dust addition caused the 2p3/2 and 2p1/2 electrons of Cu atoms in uncontaminated soils to transition the 3d vacant states, resulting in similar copper absorption peaks as atmospheric particles by the observation of X-ray absorption near-edge spectroscopy (XANES). In the field, atmospheric deposition can only increase the mobile fractions in the surface soils, but not in the deeper layers. However, the deposition can increase the soluble and diffusive gradients in thin films (DGT)-measured bioavailable fractions in profile along with the soil depth. Lime applications cannot significantly reduce the mobile fractions of heavy metals in the surface soils exposed to atmospheric deposition, but significantly reduce the heavy metal concentrations in soil solutions and the DGT-measured bioavailable concentrations, particularly in the deeper layer (6–10 cm). The major implication is that atmospherically deposited heavy metals can significantly increase their bioavailable concentrations in the plough horizon of soil and constrain the effects of soil amendments on heavy metal immobilization, thereby increasing the risks of crop uptake.

Agro-Waste Biochar to Reduce the Leaching of Heavy Metals from Coal Fly Ash Amended Soil

The soils added with coal fly ash may contain heavy metals potentially up to the levels of toxicity. Biochars have been successfully used in the past to reduce the bioavailability and leaching of heavy metals in contaminated soils. Therefore, the co-application of biochar together with coal fly ash could positively change the bioavailability and leaching characteristics of heavy metals in sandy soils through various fixing mechanisms. In the present study, the authors investigated the effect of agro-waste biochar in modifying the leaching loss of heavy metals from coal fly ash contaminated soils. Column leaching tests with simulated rainfall conditions were conducted for sandy Ultisol soils mixed with coal fly ash and avocado branch cut biomass biochar at 5 tons/ha rate. The results showed the presence of heavy metals in the leachate of fly ash added soil. Application of biochar significantly reduced the leachability of all the tested heavy metals in the study. The reduction rates were up to 55% compared to non-amended samples. Therefore, the agro-waste biochar can effective be used in stabilizing the heavy metals in coal fly ash contaminated soils, to minimize the risk of environmental contamination.

Effects of ferrous sulfate modification on the fate of phosphorous in sewage sludge biochar and its releasing mechanisms in heavy metal contaminated soils.

Modifications of sludge biochar with metal-based materials can enhance its fertilizing efficiency and improve safety. To elucidate the effects of ferrous sulfate modification on the fate of phosphorus in sludge biochar and its effect on phosphorus fractionation in soil, we investigated the changes in fractionation and bioavailability of phosphorus in modified sludge biochar and studied the changes in soil characteristics, microbial diversity and response, bioavailability, plant uptake of phosphorus, and heavy metals in contaminated soils after treatment with ferrous sulfate modified sludge biochar. The results demonstrated that ferrous sulfate modifications were conducive to the formation of moderately labile phosphorus in sludge biochar, and the concentrations increased by a factor of 2.7 compared to control. The application of ferrous sulfate-modified sludge biochar to alkaline heavy metal-contaminated soils enhanced the bioavailable, labile, and moderately labile phosphorus contents by a factor of 2.9, 3.0, and 1.6, respectively, whereas it obviously reduced the leachability and bioavailability of heavy metals in soils, exhibited great potentials in the fertilization and remediation of actual heavy metal-contaminated soils in mining areas. The biochar-induced reduction in soil pH, enhancement of organic matter, surface oxygen-containing functional groups, the abundance of Gammaproteobacteria, and its phosphonate degradation activity were primarily responsible for the solubilization of phosphorus from modified biochar in heavy metal-contaminated soils.

Bioavailability, Sources, and Transfer Behavior of Heavy Metals in Soil–Crop Systems from a High Geological Background Area Impacted by Artisanal Zn Smelting in Guizhou Province, Southwest China

The environmental risk posed by heavy metals in agricultural soil is primarily influenced by their sources, bioavailability, and geochemical transfer behavior. This study focused on Weining County, a region in Guizhou province, Southwest China, with a high geological background and long-term impact from artisanal Zn smelting. Vertical soil profiles, crop, and rhizospheric soil samples were collected and analyzed for heavy metal concentration (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, V, and Zn) including the total concentration and chemical fraction. The results revealed elevated concentrations of Cd (range: 0.7–6.9 mg·kg−1), Co (range: 19.3–120.0 mg·kg−1), Cu (range: 71.6–386.0 mg·kg−1), Ni (range: 51.0–121.0 mg·kg−1), and V (range: 310.0–721.0 mg·kg−1) in all soil samples compared to the background values of Guizhou Province. Chemical fractionation analysis indicated that Cr, Ni, As, Cu, and Zn were predominantly present in the residual fraction, while Hg and Pb were predominantly found in the potentially bioavailable fraction. Cd exhibited the highest bioavailability, accounting for 58.5% of its total concentration. Enrichment factor analysis suggested that artisanal Zn smelting activities were the main sources of Cd, Pb, and Zn contamination. Furthermore, Cd, Pb, and Zn were found to be highly accumulated in the surface soil layer (0–20 cm). Notably, 90.0% of potato and 9.4% of maize grain samples exceeded the food hygiene standards for Cd concentration, posing potential health risks to consumers. The bioconcentration factor (soil-to-root) and translocation factor (root-to-grain) analyses indicated that maize roots had a higher tendency to accumulate Cd from the soil, while Zn and Cu showed a significant transferability from roots to maize grains. These findings offer valuable insights for devising heavy metal remediation strategies in similar areas.

The effects of microplastics on heavy metals bioavailability in soils: a meta-analysis

The combined pollution of heavy metals and microplastics is common in natural soil environments. Here, we collected 790 data sets from 39 studies to investigate the effects of microplastics on heavy metal bioavailability. The results showed that microplastics could increase the bioavailability of Cu, Pb, Cd, Fe, and Mn. The heavy metal bioavailability was positively correlated with microplastic size, soil sand concentration, and exposure time, but negatively correlated with soil pH and organic matter. The bioavailability of heavy metals can be promoted by microplastics of all shapes. Hydrolysable microplastics, which contain N, might have less influence. Furthermore, the size of microplastics and soil organic matter were positively correlated with the acid-soluble and reducible fractions of heavy metals, while the microplastic concentration, soil pH, and exposure time were positively correlated with the oxidizable fractions of heavy metals. The interaction detector results indicated that there was an interaction between microplastic characteristics, especially polymer types, and soil physicochemical indexes on the bioavailability of heavy metals. These findings suggested that long-term combined pollution of microplastics and heavy metals might increase heavy metal bioavailability in soils, thereby extending their migratory and hazardous range and bringing further risks to the environment and public health safety.

Extended application of diffusive gradients in thin films (DGT) in assessing arsenic bioavailability and human health risks in brownfield soils

The environmental and human health risks of arsenic (As) mainly depend on its bioavailability in the soil. However, precise determination of bioavailable As in situ is still challenging due to the complexity of soil types and hydrogeological conditions in polluted sites. Diffusive gradients in thin films (DGT) is one of the reliable analysis technology in the in situ analysis of bioavailable chemicals in waters, sediments and farmland soils. However, few studies have investigated the application of DGT in evaluating the bioavailability of heavy metals in brownfield soils. In this study, DGT was extended applied to evaluate the availability of As in 16 contaminated soil samples from seven brownfield sites. The correlation between the bioavailable As measured by DGT and the bioaccessible As determined by the Unified BRAGE method (UBM) assay was also analyzed. In addition, the human health risks were evaluated, and the DGT-based prediction model for bioavailable As was also developed (R2=0.852, P< 0.001). The results indicated that considering bioavailability in risk assessments can improve the accuracy of calculations for site-specific health risks and provide guidance for effective remediation. The study will demonstrate the effectiveness of DGT in characterizing bioavailable heavy metals in contaminated site soils and provide decision-making support for the soil remediation.

Coupling effect of DOM and microbe on arsenic speciation and bioavailability in tailings soil after the addition of different biologically stabilized sludges

Dissolved organic matter (DOM) and microbes co-mediate the transformation of heavy metals in soil. However, few previous studies have investigated the effects of interaction between DOM and microbes on the transformation and bioavailability of heavy metals in tailings soil at the molecular level after the addition of organic wastes. This study used co-occurrence network analysis based on Fourier-transform ion cyclone resonance mass spectrometry and high-throughput sequencing to investigate the molecular mechanisms of different bio-stabilized sludge addition on arsenic fraction transformation and bioavailability in tailings soil. It was found that sludge amendments decreased the arsenic bioavailable fraction from 3.62% to 1.74% and 1.68% and promoted humification of DOM in soil. The extra inorganic salt ions introduced with sludge desorb the adsorbed As(V) into soil solution. Specifically, bio-stabilized sludge increased the contents of labile compounds that provided nutrients for microbial metabolism and shaped the microbial community composition into a more copiotrophic state, which increased the abundance of As(V)-reducing bacteria and then converted the As(V) into As(III) and precipitated as As2S3. This work innovatively explores the transformation mechanisms of As fractions through the perspectives of microbial community and DOM molecular characterization, providing an important basis for the remediation of As-contaminated soil using biosolids.

Effects of novel Cd mobilization bacteria and bone meal on the structure and function of soil bacterial communities and cadmium phytoremediation potential

Phytoremediation techniques for heavy metals in soils are inefficient due to phytotoxicity and low bioavailability of heavy metals in soils. Therefore, it is crucial to improve the bioavailability of cadmium (Cd) in soils and plant biomass. In this study, bacteria (L8) with high tolerance to heavy metals were isolated and screened from landfills. Bone meal (BM) was used as an organic amendment to form a synergistic enhancement system with L8 to improve the efficiency of phytoextraction of Cd from soil. A total of four treatments were set up: Control treatment (CK), L8 treatment (T1), 0.5% bone meal treatment (T2), and 0.5% bone meal + L8 treatment (T3). Compared with CK, ryegrass biomass and Cd accumulation in the T3 treatment group increased by 28.36% and 131.81%, respectively. Microbiome and metabolome analyses showed that the combination of bone meal and L8 significantly altered the inter-root microbial community and increased the levels of metabolites associated with the stress response. The combination of bone meal and L8 increased ryegrass biomass and plant detoxification. This was mainly attributed to an increase in the content of amino acids, esters, carbohydrates and sugars in the soil, as well as an increase in antioxidants and soil enzyme activity associated with stress tolerance.The results of this study provide novel insights into efficient remediation of heavy metals in soils, and present a simple and environmentally friendly method to facilitate the mobilization and phytoextraction of Cd from contaminated soils.

Immobilization of Cr3+, Cd2+, and Pb2+ added to calcareous soil amended with composted agro-industrial residues

The bioavailability of trace metals in soils poses a major threat to the environment, especially with massive mineral fertilizers added to increase plant yield. A plot experiment was conducted for the effectiveness evaluation of compost and vermicompost, recycled from agro-industrial wastes, in immobilizing chromium, cadmium, and lead added to calcareous soil (artificially contaminated). Moreover, immobilization efficiency was compared to the natural occurrence of these metals in the soil without metal addition (uncontaminated soil). In both soils, amendments and mineral fertilizers were applied at three different levels alone and combined to each other. The experimental design was arranged in factorial complete randomized blocks using contamination, organic and mineral fertilizer levels, and their combination as categorical factors. The distribution of metal fractions and their bioavailability in soils and bioaccumulation in wheat grains were evaluated. Soil alkalinity, the contents of soil organic carbon and nitrogen, available phosphorus, and soil micronutrients were significantly improved under vermicompost and compost compared to mineral fertilizer and control. Vermicompost was more effective than compost in reducing metals bioavailability in contaminated soils by increasing the immobilized organic fractions, but it regressed when combined with mineral fertilizers. The bioavailability of the naturally occurring metal levels in uncontaminated soil did not change significantly compared to contaminated soil. Likewise, wheat yield, plant biomass, and nutrient enrichment in wheat grains improved due to enhanced soil nutrient availability. These composted agro-industrial residues, by-products from food industries, can be classified as environmentally-friendly soil amendments for their great potential to enrich soil nutrients, reduce mineral fertilizer addition, enhance plant growth, and stabilize Cr, Cd, and Pb in contaminated calcareous soils under wheat plants.

Clean-Up of Heavy Metals from Contaminated Soil by Phytoremediation: A Multidisciplinary and Eco-Friendly Approach.

Pollution from heavy metals is one of the significant environmental concerns facing the world today. Human activities, such as mining, farming, and manufacturing plant operations, can allow them access to the environment. Heavy metals polluting soil can harm crops, change the food chain, and endanger human health. Thus, the overarching goal for humans and the environment should be the avoidance of soil contamination by heavy metals. Heavy metals persistently present in the soil can be absorbed by plant tissues, enter the biosphere, and accumulate in the trophic levels of the food chain. The removal of heavy metals from contaminated soil can be accomplished using various physical, synthetic, and natural remediation techniques (both in situ and ex situ). The most controllable (affordable and eco-friendly) method among these is phytoremediation. The removal of heavy metal defilements can be accomplished using phytoremediation techniques, including phytoextraction, phytovolatilization, phytostabilization, and phytofiltration. The bioavailability of heavy metals in soil and the biomass of plants are the two main factors affecting how effectively phytoremediation works. The focus in phytoremediation and phytomining is on new metal hyperaccumulators with high efficiency. Subsequently, this study comprehensively examines different frameworks and biotechnological techniques available for eliminating heavy metals according to environmental guidelines, underscoring the difficulties and limitations of phytoremediation and its potential application in the clean-up of other harmful pollutants. Additionally, we share in-depth experience of safe removing the plants used in phytoremediation-a factor frequently overlooked when choosing plants to remove heavy metals in contaminated conditions.

Mobility, bioaccumulation in plants, and risk assessment of metals in soils

Heavy metal contamination of soils is one of the main factors contributing to soil quality decline and loss of biodiversity, which is also associated with plant contamination, as metals accumulate in the surface layer of soils and then enter the trophic chain. The aims of the study were to assess the mobility and bioavailability of metals in soils to plants, and to estimate the ecological and health risks associated with heavy metal content in soils. 320 topsoil and 206 plant samples were collected. Fractional analysis showed that for most of the samples, there was no or low risk associated with the mobility of Cr, Pb, Cu, Ni, Zn, and low and medium for Cd. High and very high metal release risk was only shown for Cd (28 % of samples), and Zn and Pb (2 % of samples). The bioaccumulation factor found moderate levels of accumulation for Cd, Zn, Cu, Ni. High accumulation of Cd and Zn was found in 38 % and 15 % of plant samples. Alivibrio fischeri proved to be a more sensitive indicator of soil ecotoxicity compared to Sinapis alba. In the 81 % of the soil samples found a low probability of adverse effects on ecological receptors associated with exposure to soilborne metals. In the case of human health risk, no harmful health effects were observed due to accidental ingestion of metal-containing soils in the study area. In assessing metal risks, the choice of indicators is crucial. Moreover, the properties of soils have a significant impact on the mobility of metals and their bioaccumulation by plants. This means that the more varied the choice of indicators, the more comprehensive, reliable and close to reality the risk assessment of heavy metals in soils will be.

Pb contaminated soil from a lead-acid battery plant immobilized by municipal sludge and raw clay

ABSTRACT Soil heavy metal pollution poses a serious threat to the eco-environment. Municipal sludge-based passivators and clay minerals have been widely applied to immobilize heavy metal contamination in soils. However, little is known about the immobilization effect and mechanisms of raw municipal sludge and clay in reducing the mobility and bioavailability of heavy metals in soils. Here, municipal sludge, raw clay and mixtures of thereof were used to remediate Pb-contaminated soil from a Pb-acid battery factory. The remediation performance was evaluated through acid leaching, sequential extraction, and plant assay. Results showed that the leachable Pb content in the soil decreased from 5.0 mg kg−1 to 4.8, 4.8 and 4.4 mg kg−1 after 30 d of remediation with MS and RC added at equal weights to give total dosage of 20, 40 wt% and 60 wt %, respectively. The leachable Pb further decreased to 1.7, 2.0 and 1.7 mg kg−1 after 180 d of remediation. Speciation analysis of the soil Pb indicated that the exchangeable and Fe-Mn oxide-bound Pb were transformed into residual Pb in the early stage of remediation, and the carbonate-bound Pb and organic matter-bound Pb were transformed into residual Pb in the later stage of remediation. As a result, Pb accumulation in mung beans decreased by 78.5%, 81.1% and 83.4% after 180 days of remediation. These results indicate that the leaching toxicity and phytotoxicity of Pb in remediated soils were significantly reduced, presenting a better and low-cost method for soil remediation.

Amended compost alleviated the stress of heavy metals to pakchoi plants and affected the distribution of heavy metals in soil-plant system

With the development of the social economy, soil heavy metal pollution has become a common worldwide issue. Therefore, the remediation of soil heavy metal pollution is imminent. This study aimed to investigate the effect of amended compost on reducing heavy metal bioavailability in soil and relieving heavy metals stress on plants under Cu and Zn stress in a pot experiment. To model the restoration of heavy metal-polluted farming soil, conventional compost (CKw), activated carbon compost (ACw), modified biochar compost (BCw) and rhamnolipid compost (RLw) were utilized. The results showed that the application of amended compost could promote the growth and quality of pakchoi and enhance the stress ability of malondialdehyde and antioxidant enzymes to heavy metals. The distribution of Cu and Zn in different subcellular parts of pakchoi was also affected. The application of amended compost significantly reduced the heavy metals content in the shoot of pakchoi, among which the content of Cu and Zn in the shoot of pakchoi in RLw was significantly decreased by 57.29% and 60.07%, respectively. Our results can provide a new understanding for efficient remediation of contaminated farmland soil by multiple heavy metals.

Metal Fractionation and Leaching in Soils from a Gold Mining Area in the Equatorial Rainforest Zone

In this article, a modified BCR procedure and a column leaching test were used to examine the bioavailability and mobility of heavy metals in soils collected from a gold mining area in Ghana. The results for the fractionation of Cd, Cr, Fe, and Mn indicated that high percentages of metals were found in the residual fraction. This implies that the concentrations of metals in the soil are stable under normal environmental conditions. The bioavailability of metals in the soils declined in the following order: Mn (92.4%) &gt; Cd (64.6%) &gt; Cr (46.4%) &gt; Fe (39%). However, the concentrations of labile metals may pose no risk to the environment. In the column test, different rainwater conditions (i.e., natural rainwater and acidified rainwater) were used to imitate the leaching potential of the metals in the actual field. The pH of the soil primarily controlled metal migration into deeper layers. Cumulative metal concentrations in the leachates showed that Fe, Mn, and Cd were high in the tested soils but present at low concentrations, except for Cd. Cadmium showed a higher concentration than the WHO guideline for drinking water, and its seepage into deeper layers may affect the quality of groundwater.