Remediation Of Heavy Metal Polluted Soils Research Articles

Research progress on the impact and mechanisms of different passivators on soil organic carbon transformation.

Passivators can reduce the bioavailability and mobility of heavy metals by forming stable complexes or precipitates, and achieve the remediation of heavy metal-polluted soil. Organic carbon is an important parameter reflecting soil quality and health. Organic carbon transformation process plays a decisive role in atmospheric chemistry and global carbon cycling, and is affected by land use ways, agronomic measures, and restoration activities. On the one hand, the application of passivators will change soil physical and chemical properties, such as soil structure, aggregate composition, pH, CEC, which in turn will affect the structure and diversity of soil microbial communities, the activities of organic carbon conversion enzymes, and the transformation of soil organic carbon. The above effects are regulated by various factors such as the type, application amount, and application time of passivators. We discussed the composition of soil organic carbon and its changes under different passivator application conditions, and explored the mechanism underlying the effect of passivators on soil organic carbon transformation. In the future, new types of passivator with both carbon sequestration and heavy metal passivation functions should be developed. The temporal and spatial distribution patterns of soil organic carbon turnover and stable organic carbon after the application of passivators should be examined.

Risk assessment of antimony-arsenic contaminated soil remediated using zero-valent iron at different pH values combined with freeze-thaw cycles.

Soil in mining wastelands is seriously polluted with heavy metals. Zero-valent iron (ZVI) is widely used for remediation of heavy metal-polluted soil because of its excellent adsorption properties; however, the remediation process is affected by complex environmental conditions, such as acid rain and freeze-thaw cycles. In this study, the effects of different pH values and freeze-thaw cycles on remediation of antimony (Sb)- and arsenic (As)-contaminated soil by ZVI were investigated in laboratory simulation experiments. The stability and potential human health risks associated with the remediated soil were evaluated. The results showed that ZVI has a significant stabilizing effect on Sb and As in both acidic and alkaline soils contaminated with dual levels of Sb and As, and the freeze-thaw process in different pH value solution systems further enhances the ability of ZVI to stabilize Sb and As, especially in acidic soils. However, it should be noted that apart from the pH=1.0 solution environment, ZVI's ability to stabilize As is attenuated under other circumstances, potentially leading to leaching of its unstable form and thereby increasing contamination risks. This indicates that the F1 (2% ZVI+pH=1 solution+freeze-thaw cycle) processing exhibits superior effectiveness. After F1 treatment, the bioavailability of Sb and As in both soils also significantly decreased during the gastric and intestinal stages (about 60.00%), the non-carcinogenic and carcinogenic risks of Sb and As in alkaline soils are eliminated for children and adults, with a decrease ranging from 60.00% to 70.00%, while in acidic soil, the non-carcinogenic and carcinogenic risks of As to adults and children is acceptable, but Sb still poses non-carcinogenic risks to children, despite reductions of about 65.00%. These findings demonstrate that soil pH is a crucial factor influencing the efficacy of ZVI in stabilizing Sb and As contaminants during freeze-thaw cycles. This provides a solid theoretical foundation for utilizing ZVI in the remediation of Sb- and As-contaminated soils, emphasizing the significance of considering both pH levels and freeze-thaw conditions to ensure effective and safe treatment.

Influence of biochar on the remediation of cadmium-contaminated soil in an Eisenia fetida–Solanum nigrum system

Biochar, plants, and earthworms have good remediation effects on cadmium (Cd)-contaminated soils. However, few studies have combined all three technologies to explore the treatment of Cd-contaminated soils. This study investigated the effect of corn straw biochar addition (1% and 5% mass ratios) on soil Cd treatment in an Eisenia fetida–Solanum nigrum system. The addition of corn straw biochar increased soil pH, total nitrogen (TN), total phosphorus (TP), and soil organic carbon (SOC); adding 5% (w/w) biochar under Cd stress resulted in significant increases (P < 0.05) of soil pH, TN, TP, and SOC. Adding 5% (w/w) biochar under Cd stress increased Cd enrichment by E. fetida and S. nigrum and significantly reduced the soil total and available Cd contents (P < 0.05). The addition of biochar increased the metallothionein content of E. fetida, which functions to resist Cd stress in high-Cd environments (P < 0.05); with the addition of 5% (w/w) biochar, the metallothionein content was 1.55 times higher than in the 1% (w/w) biochar treatment, at 23.78 ng L−1. Adding 5% (w/w) biochar significantly increased the Cd enrichment coefficient and transfer coefficient values of S. nigrum under high-Cd stress (P < 0.05), reaching 7.37 and 1.89, respectively. Adding 5% (w/w) biochar significantly reduced the exchangeable and acid-soluble fraction of Cd, increased the oxidizable fraction, reduced Cd bioavailability, and mitigated physiological damage (P < 0.05). The present study demonstrated that adding biochar to the E. fetida–S. nigrum system could effectively reduce the soil Cd pollution level, providing a new method and scientific guidance for the remediation of heavy metal-polluted soil.

Biochar Decreases Cr Toxicity and Accumulation in Sunflower Grown in Cr(VI)-Polluted Soil.

Biochar is preferentially recommended for the remediation of heavy metal-polluted soils. Sunflower is an important high-biomass oil crop with a promising potential for phytoremediation of Cr(VI)-polluted soil. However, how biochar affects sunflower growth and Cr accumulation in Cr(VI)-polluted soil needs to be elucidated. Here, a pot culture experiment was conducted to study whether soil amendment with biochar (0, 0.1%, 1%, and 5%, w/w) can mitigate Cr toxicity and accumulation in sunflower seedlings grown in soils artificially polluted with different levels of Cr(VI) (0, 50, and 250 mg Cr(VI)/kg soil). The addition of Cr(VI) exhibited significant phytotoxicity, as evidenced by inhibited plant growth and even the death of seedlings at 250 mg/kg Cr(VI). Overall, biochar amendment showed positive effects on plant growth and Cr immobilization, dependent on both the biochar dose and Cr addition level. When 50 mg/kg Cr(VI) was added, 1% biochar showed positive effects similar to 5% biochar on improving plant growth and mineral nutrition (particularly K), reducing Cr content in shoots and roots, and decreasing Cr availability and Cr(VI) content in the soil. In comparison with non-amendment, 1% and 5% biochar caused 85% and 100% increase in shoot dry weights, and 75% and 86% reduction in shoot Cr concentrations, respectively. When 250 mg/kg Cr(VI) was added, a 5% dose produced much better benefits than 1%, while a 0.1% dose did not help plants to survive. Overall, an appropriate dose of biochar enhanced Cr(VI) immobilization and subsequently decreased its toxicity and accumulation in sunflower seedlings. Our findings confirm that biochar can be used as an efficient amendment for the remediation of Cr(VI)-polluted soils and cleaner production of sunflower oil and biomass.

English

Immobilization is an efficient method in the remediation of heavy metal-polluted soils. A greenhouse experiment was conducted to investigate the influence of fish scale powder, chitin, and chitosan on the growth and chemical composition of rice grown on a soil contaminated with Zn, Pb, Cd, and Ni. Results showed that the application of fish scale powder, chitin, and chitosan significantly increased root and shoot dry matter yield of rice, but decreased Pb phytoextraction efficiency. Further, the translocation factor of Ni decreased following the application of fish scale powder and chitosan. Application of fish scale powder decreased Ni, Cd, Zn, and Pb bioavailability in soil. The addition of chitosan caused 56% decrease in shoots Ni concentration as compared to control. Among different amendments, only the application of chitosan had a significant effect on the reduction of Zn content in rice root by 70% as compared to control. Considering that the translocation factors were less than one in all treatments, it can be concluded that biostabilization of the studied metals has occurred. Based on the obtained results, fish scale derivatives including fish scale powder and chitosan play an important role in the removal of heavy metals due to having suitable functional groups. Therefore, it can be deduced that due to the economic feasibility, environmentally friendly, and high metal removal capability of chitosan and fish scale powder, these two amendments are highly recommendable to be applied in multi-metal polluted soils for increasing metals removal and hence decreasing their phytotoxicity.

Improving radish phosphorus utilization efficiency and inhibiting Cd and Pb uptake by using heavy metal-immobilizing and phosphate-solubilizing bacteria

Phosphate-solubilizing bacteria play a key role in increasing plant growth as potential suppliers of soluble phosphorus and have great potential for the remediation of heavy metal-polluted soils. However, the soil and microbiological mechanisms by which phosphate-solubilizing bacteria prevent heavy metal absorption in radish have not been adequately studied. Here, the mechanisms of phosphorus solubilization, Cd and Pb immobilization, and the inhibition of heavy metal absorption by phosphate-solubilizing bacteria were studied in radish through solution adsorption and pot experiments. Two phosphate-solubilizing bacteria with high Cd and Pb removal rates (46.9–97.12 %), Klebsiella sp. M2 and Kluyvera sp. M8, were isolated. The soluble phosphorus content released by strains M2 and M8 was 265–277 mg L−1, achieved by secreting oxalic acid, ascorbic acid, citric acid, and succinic acid in an inorganic phosphorus medium containing 3 mg L−1 Cd and 5 mg L−1 Pb. Furthermore, these two functional strains induced the formation of Pb2(PO4)2, Cd(PO3)2, Fe2Pb3(PO4)2, CdS, and PbS precipitates that immobilized Cd and Pb in the solution. In general, strains M2 and M8 inhibited the absorption of Cd and Pb by radish by the following mechanisms: i) bacterial cell wall adsorption, ii) induction of Pb2(PO4)2, Cd(PO3)2, Fe2Pb3(PO4)2, CdS, and PbS precipitation in the solution/soil, iii) increases in the Ca2P and FeP contents in the radish rhizosphere, and iv) the promotion of bacterial community enrichment toward phosphorus-solubilizing and plant growth-promoting properties (Ramlibacter, Enterobacter, Bacillus, Gemmatimonas, and Lysinibacillusin) in the radish rhizosphere. These results provide bacterial resources and technical approaches to heavy metal pollution amelioration and efficient phosphorus fertilizer use in farmland.

Pollution assessment and source apportionment of heavy metals in soil from lead – Zinc mining areas of south China

For the regulation and remediation of heavy metal-polluted soils in mining areas, it is important to study the spatial distribution of soil heavy metal accumulation, quantitatively describe the sources of soil heavy metals, and identify the main characteristic contaminants. Therefore, in this study, multivariate statistical and geostatistical analyses were combined with principal component analysis and positive matrix factorization to assess the spatial distribution of soil-contaminating heavy metals, to quantitatively describe the sources of soil heavy metal contamination in mining areas, and to identify the main contaminants in 15 Pb–Zn mining areas in six provinces of South China.The average concentrations of heavy metals were higher than the local soil background values. Mining soils were contaminated by multiple heavy metals, mainly Cd, Pb, and Zn. All the heavy metals have a strong spatial autocorrelation except for Sb. Cd and Zn mainly originated from smelting sources (24.0%), Pb mainly originated from transportation and mining sources (16.4%), As and Cu mainly arose from flux sources (25.0%), Cr, Ni, and Sb mainly originated from natural sources (34.6%). Overall, this study provides a solid research basis for the remediation and treatment of heavy metal-contaminated soils in Pb-Zn mining areas.

Distinct Responses of Rare and Abundant Microbial Taxa to In Situ Chemical Stabilization of Cadmium-Contaminated Soil.

ABSTRACTSoil microorganisms, which intricately link to ecosystem functions, are pivotal for the ecological restoration of heavy metal-contaminated soil. Despite the importance of rare and abundant microbial taxa in maintaining soil ecological function, the taxonomic and functional changes in rare and abundant communities during in situ chemical stabilization of cadmium (Cd)-contaminated soil and their contributions to the restoration of ecosystem functions remain elusive. Here, a 3-year field experiment was conducted to assess the effects of five soil amendments (CaCO3 as well as biochar and rice straw, individually or in combination with CaCO3) on rare and abundant microbial communities. The rare bacterial community exhibited a narrower niche breadth to soil pH and Cd speciation than the abundant community and was more sensitive to environmental changes altered by different soil amendments. However, soil amendments had comparable impacts on rare and abundant fungal communities. The assemblies of rare and abundant bacterial communities were dominated by variable selection and stochastic processes (dispersal limitation and undominated processes), respectively, while assemblies of both rare and abundant fungal communities were governed by dispersal limitation. Changes in soil pH, Cd speciation, and soil organic matter (SOM) by soil amendments may play essential roles in community assembly of rare bacterial taxa. Furthermore, the restored ecosystem multifunctionality by different amendments was closely related to the recovery of specific keystone species, especially rare bacterial taxa (Gemmatimonadaceae and Haliangiaceae) and rare fungal taxa (Ascomycota). Together, our results highlight the distinct responses of rare and abundant microbial taxa to soil amendments and their linkage with ecosystem multifunctionality.IMPORTANCE Understanding the ecological roles of rare and abundant species in the restoration of soil ecosystem functions is crucial to remediation of heavy metal-polluted soil. Our study assessed the efficiencies of five commonly used soil amendments on recovery of ecosystem multifunctionality and emphasized the relative contributions of rare and abundant microbial communities to ecosystem multifunctionality. We found great discrepancies in community composition, assembly, niche breadth, and environmental responses between rare and abundant communities during in situ chemical stabilization of Cd-contaminated soil. Application of different soil amendments triggered recovery of specific key microbial species, which were highly related to ecosystem multifunctionality. Together, our results highlighted the importance of rare bacterial as well as rare and abundant fungal communities underpinning restoration of soil ecosystem multifunctionality during the Cd stabilization process.

Hyperthermophilic Composting Technology for Organic Solid Waste Treatment: Recent Research Advances and Trends

Organic solid waste is considered a renewable resource that can be converted by various technologies into valuable products. Conventional thermophilic composting (TC), a well-studied and mature technology, can be applied to organic solid waste treatment to achieve waste reduction, mineralization, and humification simultaneously. However, poor efficiency, a long processing period, as well as low compost quality have always limited its wide application. In order to overcome these shortages, hyperthermophilic composting (HTC) has been recently put forward. This paper reviews the basic principle, process flow, operation parameters, research advances, and application status of HTC. Compared with the TC process, the shorter composting period and higher temperature and treatment efficiency, as well as more desirable compost quality, can be achieved during HTC by inoculating the waste with hyperthermophilic microbes. Additionally, HTC can reduce greenhouse gas emission, increase the removal rate of microplastics and antibiotic residues, and achieve in-situ remediation of heavy metal-polluted soils, which greatly improve its application potential for organic solid waste treatment. This paper also proposes the limitations and future prospects of HTC technology for a wider application. As a result, this review advances our understanding of the HTC process, which promotes its further investigation and application.

Biomass allocation strategies and Pb-enrichment characteristics of six dwarf bamboos under soil Pb stress

Dwarf bamboos are clonal plants with potential applications in the remediation of heavy metal-polluted soils, although their pollution adaptation strategies are unknown. This study examined the biomass allocation strategies and lead (Pb) enrichment characteristics of various dwarf bamboo tissues by the end of the growing season and explored their potential for phytoremediation of Pb stress in the soils. Six dwarf bamboo genotypes were treated with three levels (0, 300, and 1500 mg kg–1) of soil Pb stress. The majority of the bamboos adopted two biomass allocation strategies to adapt to Pb stress, namely, “reducing biomass allocation into new bamboo growth” and “increasing/stabilizing biomass allocation into rhizomes”. Pb accumulation was highest in the roots, rhizomes, and old stems and showed the following trend: rhizomes/old stems> new roots/old roots> old leaves> new leaves> new stems among various tissues. Moreover, the six bamboos used three different Pb-enrichment strategies, as follows: (i) “rhizome domination and old stem synergy” (Sasaella glabra (Nakai) f. albo-striata Muroi, Sasa auricoma (Mitford) E.G. Camus, Sasa fortunei (Van Houtte) Fiori, and Shibataea lanceifolia C.H. Hu); (ii) “old stem domination and rhizome synergy” (Indocalamus decorus Q.H. Dai); and (iii) “old stem domination and new root synergy” (Sasa argenteostriata (Regel) E.G. Camus). In Pb-contaminated soils, genotypes with TFs greater than 1 were Sasa fortunei (Van Houtte) Fiori, Sasa argenteostriata (Regel) E.G. Camus, and Indocalamus decorus Q.H. Dai; in addition, only S. argenteostriata had BCF values greater than 1. Furthermore, this study provides the first evidence that S. argenteostriata can extract 0.22 and 0.58 mgplant−1 of Pb ions in soil polluted with 300 and 1500 mg kg−1 Pb, respectively. S. argenteostriata showed the greatest potential for phytoremediation among the bamboo genotypes in both Pb-contaminated urban and mining sites.

Burkholderia sp. Y4 inhibits cadmium accumulation in rice by increasing essential nutrient uptake and preferentially absorbing cadmium

Microbial remediation of heavy metal-polluted soil is a commonly used method. Burkholderia sp. Y4, isolated from cadmium (Cd)-contaminated rice rhizosphere soil, was investigated for its direct and indirect effects on Cd accumulation in rice by SEM-EDS, FITR and sequencing analysis of the soil bacterial community. Burkholderia sp. Y4 inoculation reduced Cd accumulation in rice roots, rachises, and grains of the two rice varieties T705 and X24 and increased levels of essential elements, especially Fe and Mn, which competitively inhibited Cd transport through cationic channels. Living Burkholderia sp. Y4 cells, rather than non-living ones, could colonize the surface of rice roots and accumulated more Cd through direct biosorption associated with –CO and –NH/−CO bonds of amino acids and proteins. The results of soil microbial community showed that the colonization of externally added Burkholderia sp. Y4 could be maintained over some time to impact the total rhizospheric environment. Burkholderia sp. Y4 inoculation decreased the abundance of microbes involved in the iron cycle (Acidobacteria) as well as of those mediating the transformation of ammonium nitrogen to nitrate nitrogen (Nitrosomonadaceae and Nitrospira). So Burkholderia sp. Y4 inoculation may indirectly change the availability of micronutrients and Cd in rice rhizosphere soil through iron-nitrogen coupled cycles to increase essential nutrient uptake and inhibit Cd accumulation in rice by preferential Cd-biosorption. Therefore, Burkholderia sp. Y4 is potentially suitable for the bioremediation of Cd-contaminated paddy soil.

Prospect of phytoremediation combined with other approaches for remediation of heavy metal-polluted soils.

Accumulation of heavy metals in agricultural soils due to human production activities-mining, fossil fuel combustion, and application of chemical fertilizers/pesticides-results in severe environmental pollution. As the transmission of heavy metals through the food chain and their accumulation pose a serious risk to human health and safety, there has been increasing attention in the investigation of heavy metal pollution and search for effective soil remediation technologies. Here, we summarized and discussed the basic principles, strengths and weaknesses, and limitations of common standalone approaches such as those based on physics, chemistry, and biology, emphasizing their incompatibility with large-scale applications. Moreover, we explained the effects, advantages, and disadvantages of the combinations of common single repair approaches. We highlighted the latest research advances and prospects in phytoremediation-chemical, phytoremediation-microbe, and phytoremediation-genetic engineering combined with remediation approaches by changing metal availability, improving plant tolerance, promoting plant growth, improving phytoextraction and phytostabilization, etc. We then explained the improved safety and applicability of phytoremediation combined with other repair approaches compared to common standalone approaches. Finally, we established a prospective research direction of phytoremediation combined with multi-technology repair strategy.

Spectroscopic response of soil organic matter in mining area to Pb/Cd heavy metal interaction: A mirror of coherent structural variation

Understanding the interaction between heavy metals and soil organic matter (SOM) in mining area is important for the clarification of the environmental behaviors of heavy metals. In this work, the coherence of structural changes of SOM during interaction with Pb2+ and Cd2+ ions were examined by using UV–vis/fluorescence spectroscopy coupled with correlation analyses. The result showed that phenolic- and carboxylic-like groups of SOM were engaged in the complexation of heavy metals (Pb2+ and Cd2+) with SOM, resulting in the formation of highly conjugated macromolecules/aggregates and an increase in molecular weight/size. Fluorescent humic-like, fulvic-like, and protein-like species were involved in the binding with Pb2+/Cd2+ ions, which were closely correlated with phenolic-like and carboxylic-like constitutes. SOM was more favorable to bind with Pb2+ ions than Cd2+ ions, with a less susceptive of SOM structure to Pb2+/Cd2+ ions in the mining area compared to those off the mining area under heavy metal stress. These results may provide a new insight for the treatment and remediation of heavy metal-polluted soil in mining area.

Biosorption and Bioaccumulation Abilities of Actinomycetes/Streptomycetes Isolated from Metal Contaminated Sites

Heavy metal pollution is of great concern. Due to expansion of industrial activities, a large amount of metal is released into the environment, disturbing its fragile balance. Conventional methods of remediation of heavy metal-polluted soil and water are expensive and inefficient. Therefore, new techniques are needed to provide environmentally friendly and highly selective remediation. Streptomycetes, with their unique growth characteristics, ability to form spores and mycelia, and relatively rapid colonization of substrates, act as suitable agents for bioremediation of metals and organic compounds in polluted soil and water. A variety of mechanisms could be involved in reduction of metals in the environment, e.g., sorption to exopolymers, precipitation, biosorption and bioaccumulation. Studies performed on biosorption and bioaccumulation potential of streptomycetes could be used as a basis for further development in this field. Streptomycetes are of interest because of their ability to survive in environments contaminated by metals through the production of a wide range of metal ion chelators, such as siderophores, which provide protection from the negative effects of heavy metals or specific uptake for specialized metabolic processes. Many strains also have the equally important characteristic of resistance to high concentrations of heavy metals.

Rhizosphere effects of Loliumperenne L. and Beta vulgaris var. cicla L. on the immobilization of Cd by modified nanoscale black carbon in contaminated soil

Purpose The choice and stability of the immobilization agents in in situ remediation of heavy metal-polluted soil is particularly important. This study aimed at investigating the rhizosphere effects of different plants on the immobilization stability of Cd by modified nanoscale carbon black (MBC) in contaminated soil.

Potential use of cotton for remediating heavy metal-polluted soils in southern China

Southern China is an important agricultural production base, as well as an important mineral resource area. There is a big challenge of heavy metal pollution in the soils of this area. Base on the characterizations of cotton and our present results, we discussed the potentiality to remediate the heavy metal-polluted soils through planting cotton in southern China. This paper summarises recent research to provide a better understanding of the status and the causes of heavy metal pollution in southern China, compare the applicability of different remediation methods in this area, evaluate tolerance and accumulation of cotton to heavy metals, and discuss the socioeconomic benefits of cotton planting for remediation of heavy metal-polluted soils. Human activity could be causing heavy metal pollution in southern China, as lead pollution is the most prevalent and cadmium pollution is the most severe in this area. Physical and chemical methods are used to remediate the heavy metal-polluted soils in southern China, by which treated polluted soils could not satisfactorily address the problems of economic feasibility, “secondary damage” and “secondary pollution”. The use of plants can green the environment to a certain extent, so the phytoremediation method is widely accepted. Cotton does not reach the standard of hyperaccumulation plants but has a relatively large biomass and shows more excellent tolerance ability and enrichment ability to heavy metals. Especially, the Cd concentration is lower in cotton fibre than in other cotton organs. Cotton may be a potential crop to ameliorate the heavy metal pollution of farmland in southern China. In addition, cotton remediation combining with multiple repair measures of heavy metal pollution would obtain better repair effect and ecological benefits, and agronomic management practices could also effectively enhance cotton-remedied heavy metal-polluted soils.

Remediation of Heavy Metal-Polluted Agricultural Soils Using Clay Minerals: A Review

Heavy metal contamination of agricultural soils poses risks and hazards to humans. The remediation of heavy metal-polluted soils has become a hot topic in environmental science and engineering. In this review, the application of clay minerals for the remediation of heavy metal-polluted agricultural soils is summarized, in terms of their remediation effects and mechanisms, influencing factors, and future focus. Typical clay minerals, natural sepiolite, palygorskite, and bentonite, have been widely utilized for the in-situ immobilization of heavy metals in soils, especially Cd-polluted paddy soils and wastewater-irrigated farmland soils. Clay minerals are able to increase soil pH, decrease the chemical-extractable fractions and bioavailability of heavy metals in soils, and reduce the heavy metal contents in edible parts of plants. The immobilization effects have been confirmed in field-scale demonstrations and pot trials. Clay minerals can improve the environmental quality of soils and alleviate the hazards of heavy metals to plants. As main factors affecting the immobilization effects, the pH and water condition of soils have drawn academic attention. The remediation mechanisms mainly include liming, precipitation, and sorption effects. However, the molecular mechanisms of microscopic immobilization are unclear. Future studies should focus on the long-term stability and improvement of clay minerals in order to obtain a better remediation effect.

Removal of heavy metals from polluted soil using the citric acid fermentation broth: a promising washing agent

The citric acid fermentation broth was prepared and it was employed to washing remediation of heavy metal-polluted soil. A well-defined washing effect was obtained, the removal percentages using citric acid fermentation broth are that 48.2% for Pb, 30.6% for Cu, 43.7% for Cr, and 58.4% for Cd and higher than that using citric acid solution. The kinetics of heavy metals desorption can be described by the double constant equation and Elovich equation and is a heterogeneous diffusion process. The speciation analysis shows that the citric acid fermentation broth can effectively reduce bioavailability and environmental risk of heavy metals. Spectroscopy characteristics analysis suggests that the washing method has only a small effect on the mineral composition and does not destroy the framework of soil system. Therefore, the citric acid fermentation broth is a promising washing agent and possesses a potential practical application value in the field of remediation of soils with a good washing performance.

Mechanisms of Cd and Cr removal and tolerance by macrofungus Pleurotus ostreatus HAU-2

Fungi bioaccumulation is a novel and highly promising approach to remediate polluted soil. The present study revealed a high ability to tolerate Cd and Cr in the fungus Pleurotus ostreatus HAU-2. However, high concentrations of Cd and Cr can suppress fungal growth and result in a variation of hypha micromorphology. Batch experiments were performed to investigate Cd and Cr stress effects on the amount of active oxygen in fungi, activity of antioxidant enzyme, as well as the removal efficiency of Cd and Cr. The results revealed that Cd and Cr caused increasing active oxygen and malonaldehyde (MDA) concentrations. Antioxidant enzymes play a central role in removing active oxygen, while glutathione (GSH) aids the Cd detoxification within cells. In fluid culture, fungal removal rates of Cd and Cr ranged from 44.85% to 80.36% and 14.49% to 45.55%, respectively. Intracellular accumulation and extracellular adsorption were the major removal approaches. Bag cultivation testing indicated that the fungus absorbed Cd and Cr contained within soil. In particular, the accumulation ability of Cd (15.6mgkg−1) was higher compared to that of Cr (8.9mgkg−1). These results successfully establish P. ostreatus HAU-2 as promising candidate for the remediation of heavy-metal polluted soils.

Significance of diazotrophic plant growth-promoting Herbaspirillum sp. GW103 on phytoextraction of Pband Zn by Zea mays L.

Microbe-assisted phytoremediation has been considered a promising measure for the remediation of heavy metal-polluted soil. The aim of this study was to assess the effect of diazotrophic plant growth-promoting Herbaspirillum sp. GW103 on growth and lead (Pb) and zinc (Zn) accumulation in Zea mays L. The strain GW103 exhibited plant growth-promoting traits such as indole-3-acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylic deaminase. Treatment of Z. mays L. plants with GW103 significantly increased 19, 31, and 52% of plant biomass and 10, 50, and 126% of chlorophyll a contents in Pb, Zn, and Pb + Zn-amended soils, respectively. Similarly, the strain GW103 significantly increased Pb and Zn accumulation in shoots and roots of Z. mays L., which were 77 and 25% in Pb-amended soil, 42 and 73% in Zn-amended soil, and 27 and 84% in Pb + Zn-amended soil. Furthermore, addition of GW103 increased 8, 12, and 7% of total protein content, catalase, and superoxide dismutase levels, respectively, in Z. mays L. plants. The results pointed out that isolate GW103 could potentially reduce the phytotoxicity of metals and increase Pb and Zn accumulation in Z. mays L. plant.