Fraction Of Cd Research Articles

Alternating Direct Current Field Assistant Promoting Chemical Stabilization of Combined Heavy Metals Contaminated Soil

To enhance the remediation efficiency and reduce the chemicals consumption, the combined heavy metals Lead (Pb), Copper (Cu) and Cadmium (Cd) contaminated soil were stabilized by chemical passivators with alternating direct current field (ADC) assistant. The results showed that ADC treatment activated initial heavy metal compounds in the soil. The leaching concentrations of Pb, Cu and Cd in soil under ADC condition increased by 19.61%, 38.77% and 49.10% in comparison with no electric field, respectively. The exchangeable fractions of Pb, Cu and Cd increased while the reducible, oxidizable and residual fractions decreased substantially. Thus, the chemical passivators addition companied with ADC treatment in the beginning increased stabilization efficiency of heavy metals in the soil and reduced over 30% amount of chemical agent consumption, comparing with only chemical passivator stabilization. The mechanism can be speculated that ADC assistant facilitated more heavy metal ions in the soil reacting with phosphorus- containing passivator to formed more complex and stable metal phosphates. It was confirmed by XRD measurement that silicon element in the crystal structure of metallic compound was replaced by phosphorus element.

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.

Mercapto–palygorskite decreases the Cd uptake of wheat by changing Fe and Mn fraction in Cd contaminated alkaline soil

Wheat is one of the major sources of dietary nutrition for human body, and excessive Cadmium (Cd) in wheat poses a serious risk to human health. Mercapto–palygorskite (MP) has been proven to efficiently reduce Cd stress in wheat, but the contribution of major soil oxides to the stability of soil Cd under MP treatment is unclear. Here, a wheat pot experiment was conducted to evaluate the effects of soil Fe and Mn oxides on the Cd fraction under MP treatment. The results showed that the application of MP decreased the diethylenetriaminepentaacetic acid (DTPA)–extractable Cd by 24.0–34.7 %, increased the Fe and Mn oxide-bound Cd (OX–Cd) by 5.0–12.0 % and significantly reduced the Cd content in wheat grains (17.9–69.5 %). It also decreased the soil’s free Fe and Mn oxides by 6.1–11.7 %and 6.9–12.4 %, respectively, and increased the amorphous Fe and Mn oxides by 19.3–32.5 % and 21.9–24.1 %, respectively. In addition, the application of MP increased the concentration of Fe and Cd in soil colloid by 19.3–33.3 % and 11.3–45.3 %, respectively. Correlation analysis indicated that the amorphous Fe, Mn oxides in soil had a significant positive correlation with the content of Fe and Mn bound Cd in soil (P < 0.01). Primary component analysis (PCA) analysis shows colloidal Fe and Mn on the soil available Cd had relatively high positively loadings. Meanwhile, soil colloidal Fe exhibited a significant positive correlation with colloidal Cd (P < 0.01) and amorphous Fe oxides (P < 0.01). These results indicated that MP remediated Cd-contaminated soil by promoting an increase in amorphous Fe, Mn oxides and their adsorption and precipitation of Cd on these oxides.

Prevalence of antibiotic and metal resistance genes in phytoremediated cadmium and zinc contaminated soil assisted by chitosan and Trichoderma harzianum

Heavy metal in soil have been shown to be toxic with high concentrations and acts as selective pressure on both bacterial metal and antibiotic resistance determinants, posing a serious risk to public health. In cadmium (Cd) and zinc (Zn) contaminated soil, chitosan (Chi) and Trichoderma harzianum (Tri) were applied alone and in combination to assist phytoremediation by Amaranthus hypochondriacus L. Prevalence of antibiotic and metal resistance genes (ARGs and MRGs) in the soil was also evaluated using metagenomic approach. Results indicated that the phytoremediation of Cd and Zn contaminated soil was promoted by Chi, and Tri further reinforced this effect, along with the increased availability of Cd and Zn in soil. Meanwhile, combination of Chi and Tri enhanced the prevalence of ARGs (e.g., multidrug and β-lactam resistance genes) and maintained a high level of MRGs (e.g., chromium, copper) in soil. Soil available Zn and Cd fractions were the main factors contributing to ARGs profile by co-selection, while boosted bacterial hosts (e.g., Mitsuaria, Solirubrobacter, Ramlibacter) contributed to prevalence of most MRGs (e.g., Cd). These findings indicate the potential risk of ARGs and MRGs propagation in phytoremediation of metal contaminated soils assisted by organic and biological agents.

Organic amendment application affects the release behaviour, bioavailability, and speciation of heavy metals in zinc smelting slag: Insight into dissolved organic matter

Organic amendments are commonly used in assisted phytostabilization of mine wastes by improving their physicochemical and biological properties. These amendments are susceptible to leaching and degradation, resulting in the generation of dissolved organic matter (DOM), which significantly influences the geochemical behaviour of heavy metals (HMs). However, the geochemical behaviour of HMs in metal smelting slag driven by organic amendment-derived DOM remains unclear. In this study, we investigated the impact of cow manure-derived DOM on the release behaviour, bioavailability, and speciation of HMs (Cu, Pb, Zn, and Cd) in zinc smelting slag using a multidisciplinary approach. The results showed that DOM enhanced the weathering of the slag, with a minimal impact on the slag’s mineral phases, except for causing gypsum dissolution. The DOM addition resulted in a slight increase in HM release from the slag during the initial inoculation period, followed by a reduction in HM release during the later period. Furthermore, the DOM addition increased the diversity and relative abundance of the bacterial community. This, in turn, led to a decrease in the dissolved organic carbon (DOC) content and enhanced the transformation of labile DOM compounds into recalcitrant compounds. The variation in HM release during various inoculation periods can be attributed to the bacterial decomposition and transformation of DOM, which further enhanced the transformation of HM fractions. Specifically, during the later period, DOM promoted the conversion of a portion of the reducible and oxidizable fractions of Cu, Pb, and Zn into the acid-soluble and residual fractions. Moreover, it partially transformed the reducible, oxidizable, and residual fractions of Cd into the acid-soluble fraction. Overall, this study provides new insights into the geochemical behaviour of HMs in slag governed by the coupling effect of DOM and the bacterial community. These findings have implications for the use of organic amendments in assisted phytostabilization of metal smelting slag. Environmental implicationMetal smelting slag is hazardous due to its high levels of HMs, and its improper disposal has serious consequences for the ecosystem. Organic amendments are employed in assisted phytostabilization of the slag site by improving its microecological properties. However, the impact of organic amendment-derived DOM on HM migration and transformation in slag remains unclear. This study indicated that the coupling effects of DOM and microbes governed the geochemical behaviour of HMs in slag. These findings provide new insights into how organic amendments impact the geochemical behaviour of HMs in slag, contributing to the development of phytostabilization technology.

Accumulation of livestock manure–derived heavy metals in the Hexi Corridor oasis agricultural alkaline soil and bioavailability to Chinese cabbage (Brassica pekinensis L.) after 4-year continuous application

Hexi Corridor is one of the most important base of vegetable producing areas in China. Livestock manure (LM) applied to agricultural field could lead to soil heavy metal (HM) pollution. Previous studies have focused on HM pollution following LM application in acidic polluted soils; however, fewer studies have been conducted in alkaline unpolluted soils. A 4–year field vegetable production experiment was conducted using pig manure (PM) and chicken manure (CM) at five application rates (0, 15, 30, 45, and 60 t ha−1) to elucidate potential risks of HMs in an alkaline unpolluted soil in the Hexi Corridor oasis agricultural area and HM uptake by Chinese cabbage. The results showed that LM application caused a significant build–up of Cu, Zn, Pb, Cd, and Ni content in topsoil by 30.6–99.7%, 11.4–51.7%, 1.4–31.3%, 5.6–44.9%, 14%–40.8%, respectively. The Cd, Cu, Zn could potentially exceed the soil threshold in next 8–65 years after 15–60 t ha−1 LM application. Under LM treatment, the soil DTPA–extractable Cu, Zn, Fe, the acid–extractable fraction of Cu, Zn, Fe, Cd, Ni, and the Oxidable fraction of Cu, Zn, Fe, Mn, Cd, Ni significantly increased, but the DTPA–extractable Pb, Cd, the acid–extractable fraction of Pb, and the reducible fraction of Cd significantly decreased. Cu and Zn could migrate to the deeper soil and relatively increase in DTPA–extracted Cu, Zn were found in 20–40 cm soil depth after LM application. The pH and SOM could influence the bioavailability of HMs in soil. The bioaccumulation factor and transfer factor (TF) values were <1 except Mn (TF > 1). HMs in leaf did not approach the threshold for HM toxicity due to the “dilution effect”. Recommend the type of manure was the PM and the annual PM application rate was 30 t ha−1 to ensure a 20–year period of clean production in alkaline unpolluted Fluvo–aqiuc vegetable soils.

Alkaline humic acid fertilizer alters the distribution, availability, and translocation of cadmium and zinc in the acidic soil–Sauropus androgynus system

Humic acids (HA) are a popular soil additive to reduce metal availability, but they have the drawbacks of reduced effectiveness over time and a significant reduction in soil pH. An alkaline humic acid fertilizer (AHAF) combining alkaline additives with HA was developed to overcome such drawbacks. A field experiment was conducted to investigate the effects of different AHAF application rates on the physicochemical properties, bioavailability, accumulation, and translocation of Cd and Zn heavy metals in Sauropus androgynus grown in acidic soil. Based on our results, the 100AF (100% AHAF) treatment significantly increased soil pH, cation exchange capacity (CEC), and organic matter content (OM) after one year of application. Compared with the control treatment (CK), the application of different rates of AHAF resulted in a 37.1–40.3% decrease in soil exchangeable Cd fractions (Exc-Cd) and an increase in the humic acid-bound Cd fractions (HA-Cd) Fe- and Mn-oxide-bound Cd fractions (OX-Cd), and organic matter-bound Cd fractions (OM-Cd) by 9.5–64.6%, 24.8–45.1%, and 158.8–191.2%, respectively (P < 0.05). The different AHAF treatments decreased the Res-Zn, Exc-Zn, and OM-Zn fractions by 69.6–73.0%, 7.4–23.9%, and 18.1–23.2%, respectively (P < 0.05), and increased the HA-Zn fraction by 8.4–28.1%. In the control treatment, the bioconcentration factors (BCFs) for Cd and Zn in different S. androgynus plant organs were in the following order: (Cd) Leaves > Stems > Branches > Roots > Edible branches; (Zn) Roots > Stems > Leaves > Branches > Edible branches. The transfer factors (TFs) of Cd and Zn in S. androgynus were classified as follows: TF2 > TF1 > TF3 > TF4. Thus, S. androgynus stems, and roots had a strong ability to transport Cd and Zn to the leaves. Compared with CK, the 100AF treatment significantly increased the BCFs for Zn in all plant parts (except BCFedible branches). In contrast, it significantly decreased all BCFs and TFs for Cd and the TF4 for Zn, effectively reducing Cd and Zn accumulation in the edible branches of S. androgynus. Soil pH, CEC, OM, and HA-M fraction were highly and significantly negatively correlated with Cd and Zn content in edible branches (P < 0.001). Stepwise multiple linear regression analysis revealed that the soil HA-M fraction was the key contributing factor for Zn accumulation and translocation in S. androgynus. Moreover, based on our findings, the absorption, uptake, and translocation of Cd and Zn were mainly determined by metal speciation and the pH in the soil. Moreover, the competitive antagonistic mechanisms between Zn and Cd absorption also affected their accumulation in S. androgynus. Thus, AHAF can be used as a soil amendment to sustainably improve acidic soils and effectively reduce Cd and Zn accumulation in edible branches of S. androgynus.

Carbothermal treatment of municipal solid waste incineration fly ash: Purification and valuable elements extraction

Thermal separation of heavy metals from municipal solid waste incineration fly ash (MSWI FA) is a promising approach for both fly ash purification and heavy metal recovery. However, its commercial viability is hindered by excessive energy consumption. In this study, we introduce carbothermal reduction for MSWI FA treatment as an innovative strategy to enhance heavy metal volatilization and reduce the required heating temperature. By incorporating carbon (FA/Carbon = 1:0.2), the volatilization fractions of Pb, Cd and Zn reached 96.5 %, 100 %, and 63.9 %, respectively, when subjected to 900 °C for 2 h. Remarkably, these volatilization amount surpassed the volatilization fractions attained when raw fly ash (RFA) was independently calcined at 1000 °C for 2 h: Pb (90.2 %), Cd (92.9 %) and Zn (30.2 %). Conversely, Cu volatilization was impeded by carbon inclusion. Comparable trends were shown in washing fly ash (WFA). Notably, concentrated carbothermal reduction led to substantial concentrations of Pb (2.5–7.1 %) and Zn (4.9–20.7 %), rendering them amenable for recycling through metallurgical routes. Intriguingly, higher carbon content (FA/Carbon = 1:0.3) hindered rather than enhanced heavy metal volatilization from RFA. We found that condensation of NaCl and KCl occurred in carbon pores, causing the formation of molten eutectic which trapped the heavy metals at high temperatures. Therefore, more carbon showed more enhancement of heavy metal volatilization from WFA which was free of NaCl and KCl. Ultimately, two comprehensive pathways for the resourceful utilization of fly ash based on carbon thermal reduction were proposed and compared. This study demonstrates carbothermal reduction as an effective approach for simultaneous purification and metal recovery of MSWI FA, exhibiting promising potential for industrial application.

Surface-loaded magnesium and phosphorus-modified lignite adsorbents: Efficient adsorption and immobilization for remediation of Cd-contaminated water and soil

Lignite is a resource-rich material with favorable adsorption properties and can be used as an environmentally friendly material for removing heavy metals. In this study, we loaded magnesium and phosphate ions onto the surface of lignite (LM) by using chemical modification to generate modified lignite materials, Mg-LM and P-LM, which were used for the adsorption and immobilization of Cd (II) in polluted water and soil. Characterization analysis showed the introduction of exchangeable Mg ions and enhancement of the pore structure in Mg-LM; the increase in the number of oxygenated functional groups and, exchangeable calcium ions and P content of P-LM may favor the adsorption and immobilization of Cd (II). Cd (II) adsorption on Mg-LM and P-LM was consistent with the pseudo-secondary kinetics and Langmuir isotherm models. The maximum adsorption capacity of Cd (II) on Mg-LM and P-LM was 1033 mg/g and 55 mg/g, respectively. The reduction in the soil DTPA-Cd content (32.9%) was greater under P-LM treatment than under Mg-LM (20.2%) and LM (11.1%) treatments. In addition, successive BCR extractions confirmed that Mg-LM and P-LM promoted the transformation of unstable Cd fractions to stable Cd fractions in the soil. The XRD, FTIR, and XPS results indicated that electrostatic interactions, ion exchange, surface complexation and precipitation might be the main mechanisms involved in the adsorption and immobilization of Cd (II) by Mg-LM and P-LM. Our results suggest that Mg-LM is more suitable than P-LM for the remediation of Cd-contaminated water, and less applicable than in Cd-contaminated soil.

Selenate reduced wheat grain cadmium accumulation by inhibiting cadmium absorption and increasing root cadmium retention

Selenium (Se) fertilizer has been recently used to reduce cadmium (Cd) accumulation in plant. A pot culture was performed to analyze Cd uptake, translocation, and distribution in wheat plants during the reproductive growth period in a Cd–contaminated soil after selenate was applied to the soil, and a hydroponic culture was carried out to investigate the effects of selenate application on Cd2+ influx, subcellular Cd distribution, and Cd accumulation in wheat seedlings. Results showed that selenate application had no significant effect on DTPA–Cd and Cd fraction in soil. The application of selenate greatly inhibited the whole–plant Cd absorption by 14%–23%. In addition, selenate prompted the retention of Cd in root by increasing the Cd distribution in the vacuole, which reduced the root–to–shoot Cd translocation by 18%–53%. The application of selenate increased the Cd concentration in nodes, inhibited Cd remobilization from nutritive organs to grain, and ultimately reduced Cd accumulation in wheat grain. Further, heading to grain filling was the key growth stage for exogenous selenate to regulate grain Cd accumulation. In summary, soil selenate application is an effective method to reduce grain Cd concentration in wheat, which provided scientific basis for remediation of Cd–contaminated soil.

Surface Co-application of Dolomitic Lime with Either Biochar or Compost Changes the Fractionation of Cd in the Soil and Its Uptake by Cacao Seedlings

The purpose of this study was to determine the effects of the application of compost or biochar on the mobility of soil-applied dolomite lime in the soil and its impact on Cd bioavailability, as well as its uptake by cacao seedlings. The experiment was conducted in a greenhouse for 120 days. Dolomite lime was applied superficially without incorporation, individually or in co-application with commercial compost or corn straw-derived biochar. Soil samples were collected at four depths (0–10, 10–20, 20–30, and 30–40 cm). Subsequently, pH, electrical conductivity, and dissolved organic carbon were measured. Bioavailable Cd and geochemical fractionation of Cd were measured at each soil depth. Root- and leaf-Cd concentrations in cacao seedlings were also determined. The results illustrate that the application of either compost or biochar has a pronounced impact on enhancing the mobility of dolomite lime within the soil (up to 40 cm). Notably, heightened alkalinity penetration was observed when dolomite lime and biochar were jointly applied. Concurrently applying biochar with dolomite lime led to a significant elevation in soil pH and a marked reduction in the concentration of bioavailable Cd. Furthermore, the concentration of leaf-Cd underwent a reduction exceeding 50% (± 2%) due to the application of dolomite lime and biochar. Potential mechanisms connected to Cd immobilization may encompass ion exchange and the formation of co-precipitates. Overall, the simultaneous use of dolomite lime and biochar was effective in decreasing Cd concentrations in cacao seedlings.

Spatial-temporal Variations and Pollution Assessment of Heavy Metals in Sediments of Qionghai Lake in Xichang City

Based on the analysis of the total concentrations of 10 metals in the sediment core and total concentrations and chemical fractions of seven metals in the surface sediments of Qionghai Lake in Xichang City, Sichuan Province, the spatial-temporal characteristics of metal accumulation and pollution over the past century and the potential ecological risk of metals in surface sediments were studied. Before the 1970s, metal concentrations in the sediment core were stable. The total concentrations of Al, Fe, K, and Cr in the sediment core exhibited visible peaks in the 1970s, which were related to the enhanced input of fine-grained topsoil caused by increasing precipitation, lake reclamation, and deforestation. Since the 1990s, the total concentrations of Al, Fe, K, and Cr decreased with the reduced topsoil erosion, whereas the total concentrations of As, Cd, Cu, Pb, and Zn gradually increased or remained stable. The enrichment factor results showed that Cd, Pb, and Zn were the main contaminants, with Cd as the typical contaminant in the sediment core. The Cd contamination started in the 1960s and has remained at a moderate level since the 1990s. In the surface sediments, the total concentrations of Cd were higher in the northwest lake area, and no visible spatial concentration trends of the other metals were displayed. The bioavailable fractions of Cd, Pb, and Zn accounted for 95%, 63%, and 48% of the total metal concentrations on average. Among the bioavailable fractions, Cd was mainly in the acid-soluble fraction, and Pb and Zn were mainly in the reducible and oxidized fractions. The bioavailable fractions of the other metals were less than 27%. The results of total concentrations and bioavailable fractions of metals revealed that Pb and Zn in the surface sediments were slightly or moderately contaminated, and Cd was moderately contaminated on average. Cd contamination was at a severe level in the northwest lake area. The concentrations of anthropogenic Cd, Pb, and Zn in the surface sediments estimated from the total and bioavailable concentrations were comparable (P>0.05), indicating that anthropogenic metals primarily existed in bioavailable fractions in the sediment. Integrating the assessment results from sediment quality guidelines, potential ecological risk index, and chemical forms of metals, Cd in surface sediments may pose a high ecological risk, whereas the other metals has a low ecological risk.

The influence of cysteine in transformation of Cd fractionation and microbial community structure and functional profile in contaminated paddy soil

Remediating cadmium (Cd) contaminated paddy soil is vital for agroecology, food safety, and human health. Soil washing is more feasible to reduce remediation method due to its high efficiency. However, green, low-cost and more efficient washing agents are still required. In this study, we investigated the ability of cysteine as a washing agent for soil washing to remove Cd from contaminated paddy soil. Through a batch experiment, we evaluated the removal efficiency of cysteine as a washing agent by comparing their removal rate with that of a microbial inoculant and sulphuric acid as other washing agents. The transformation of Cd fractionation and microbial community structure and functional profile in paddy soils after cysteine leaching was studied by using sequential extraction and high-throughput sequencing. Results showed that cysteine had better efficiency in the removal of Cd from paddy soil in comparison to sulphuric acid and the microbial inoculant, and could achieve a maximum removal rate of 97 % Cd in paddy soil. Cysteine decreased the proportion of Cd in the exchangeable fraction, carbonate bound fraction, iron and manganese bound fraction, and organic matter bound fraction and was best for the removal of the residual fraction, which contributed to its higher Cd removal ability. Considering the economic benefits of the reagents used, cysteine was shown to be economically feasible for use as a leaching agent. In addition, cysteine could significantly increase the relative abundance of Thermochromatium, Sideroxydans, Streptacidiphilus, and Frankia which promoted the nitrogen and sulfur metabolism in the paddy soil. In summary, this study revealed that cysteine was readily available, cheap, non-toxic, highly efficient, and even has fertilizing properties, making it eco-friendly and ideal for remediation of Cd-contaminated paddy soils. Besides, the health of paddy soils would also benefit from cysteine's promotion of microbial nitrogen and sulfur metabolism.

The responses of soil Cd fractions to disinfestation regimes associated with microbial communities

While reductive soil disinfestation (RSD)-related practices have been shown to mediate soil cadmium (Cd) fraction to a certain extent, the underlying mechanisms remain unclear. Here, a pot experiment was conducted to investigate the effects of various reductive soil disinfestation regimes on Cd fraction and its driving mechanisms underlying them. Five Cd fractions, soil physicochemical properties as well as microbial communities were simultaneously measured. Results revealed that, relative to the control treatment, all RSD-related regimes contributed to decrease exchangeable Cd fraction (EX-Cd) by transforming it to unexchangeable Cd fractions (RES-Cd CB/OX-Cd fractions) (P < 0.05). RSD with Hermetia illucens L. feces treatment (abbr.: HI treatment) had the greatest reduction rate (9.7 %), which higher than that of other treatment (3.5 % and 2.6 %), this largely attributed to more functional genera in association with Cd fixation and Fe (III) reduction enriched. In addition, soil disinfestation regimes altered soil microbial community composition and structure, which was a critical factor responsible for the changes of soil Cd fraction. Correlation analysis showed that the changes of Cd fraction were closely related to biotic and abiotic factors. Both pH and soil organic material were main abiotic factors, while microbial groups, including Bacteroidetes, Hydrogenedentes (Hydrogenispora), Ascomycota, Acidobacteria and Verrucucomicrobia were key biotic factors for Cd conversion and immobilization. The validation experiment in four vegetables further confirmed that RSD-related regimes were indeed favorable for decreasing soil availability and plant uptake of Cd by improving soil pH, and HI treatment showed optimal remediation and utilization potential to Cd-contaminated soils. Together, the results provide a theoretical basis and reference for the RSD-related disinfestation regimes in remediation of Cd-contaminated soils, and highlighted the significant potential of Hermetia illucens L. feces as a novel addition in RSD technology for reducing available Cd from soils.

Cotton-based bionic tree-shaped photothermal evaporator for extraction of heavy metals from river sediment

Pollution of river sediments with heavy metals poses significant threats to both ecological and human health. Thus, in-situ extraction of heavy metals from sediments has emerged as a challenging and important research issue. To address this issue, a cotton-based bionic tree-shaped photothermal evaporator was designed to enhance water evaporation and facilitate heavy metals extraction from sediment porewater. The evaporator demonstrated a remarkable evaporation flux of 3.25 kg m-2 h-1 under 1 sun illumination. Over a 28-day solar-driven evaporative remediation (SDER) process, the removal efficiencies of total Pb and Cd were 17.4% and 29.9%, respectively. Importantly, the bioavailable fractions of residual Pb and Cd were also reduced by 46.3% and 25.0%, respectively. Furthermore, cabbage cultivation experiments to assess the practical efficacy of SDER showed that accumulation of Pb and Cd in cabbage roots was decreased by 66.0% and 46.3%, respectively, and accumulation in shoots was decreased by 57.2% and 55.7%, respectively. Thus, SDER was demonstrated to effectively reduce biological toxicity in sediment. This study introduces a novel approach that efficiently utilizes sunlight for the rapid extraction of heavy metals from sediment, presenting a promising general strategy for the low energy remediation of heavy metals-contaminated sediments.

Elucidating the Potential of Biochar-Bentonite Composite and Kaolinite-Based Seed Balls for the Remediation of Coal Mining Impacted Heavy Metals Contaminated Soil

Globally, open-pit coal mining is associated with severe land use impact and the contamination of soil and water resources with heavy metals. Thus, in growing economies like India, where coal is a significant energy source, the heavy metals contamination of soil and water become ubiquitous. This study uses a unique remediation approach by developing biochar-bentonite-based seed balls encapsulating Shorgham grass seeds at their core for application in the contaminated soil. The seed ball was developed by using the bentonite biochar composite in varying weight fractions of 0.5–5% with respect to the kaolinite, whose fractions in the seed ball also varied at one, three, and five parts. The seed balls were applied to the pots containing 3 kg of heavy-metals-contaminated soil for a pot-culture study in a polyhouse for a period of four months. Initial soil analysis results indicated that the mine soil samples showed poor nutrient and organic matter content and were contaminated with heavy metals such as Ni, Zn, Cr, and Cd. Post-pot-culture soil analysis results indicated that the application of seed balls containing five fractions of biochar composite with its combination with three and five-weight fractions of kaolinite showed substantial improvement in the pH, available nutrients, organic matter content, soil enzymes, and overall soil fertility index compared to the controlled study and other cases. The same combination of seed balls also significantly reduced the plant-available fractions of Ni, Zn, Cr, and Cd in the soil, indicating the stabilization of heavy metals within the soil matrix. Also, the application of seed balls substantially improved the plant physiology and reduced the release of stress hormones within the plant cells, indicating improvement in the plant’s biotic and abiotic stress factors. Thus, the application of seed balls in heavy metals contaminated soils, particularly over a large stretch of land, could be a low-cost and viable remediation technique.

Cd isotope fractionation in a soil-rice system: Roles of pH and mineral transformation during Cd immobilization and migration processes

Cd speciation in soil and its transport to rice roots are influenced by the soil pH, oxidation-reduction potential, and mineral transformation; however, the immobilization and migration of Cd in soil-rice systems with different pH values under distinct water regimes remain unclear. This study used Cd isotope fractionation, soil physical analysis, and root gene quantification to elucidate the immobilization and transport of Cd in different soil-rice systems. In drainage soils, the high soil pH enhanced the transformation and magnitude of negative fractionation of Cd from MgCl2 extract to FeMn oxide-bound pool; however, it favored Cd uptake and root-to-grain transport. Compared with drainage regimes, the flooding regimes shifted fractionation toward heavy isotopes from MgCl2-extracted Cd to FeMn oxide-bound Cd in acidic soils (∆114/110CdMgCl2 extract – FeMn oxide-bound Cd = −0.09 ± 0.03 ‰) and to light isotopes from MgCl2-extracted Cd to carbonate-bound Cd in neutral and alkaline soils (∆114/110CdMgCl2 extract – carbonate-bound Cd = 0.29–0.40 ‰). The submerged soils facilitated the forming of carbonate and poorly crystalline minerals (such as ferrihydrite), which were transformed into highly crystalline forms (such as goethite). These results demonstrated that the dissolution-precipitation process of iron oxides was essential for controlling soil Cd availability under flooding regimes, and the relative contribution of carbonate minerals to Cd immobilization was promoted by a high soil pH. Flooding regimes induced lower expressions of OsNRAMP1 and OsNRAMP5 to limit the uptake of light Cd isotopes from MgCl2-extract pool, whereas a teeter-totter effect on gene expression patterns in roots (including those of OsHMA3 and OsHMA2) limited the transport of heavy Cd isotopes from root to grain. These findings demonstrate that flooding regimes could exert multiple effects on soil Cd immobilization and Cd transport to grain. Moreover, alkaline soil was conducive to forming carbonate minerals to sequester Cd.

Effects of four amendments on cadmium and arsenic immobilization and their exposure risks from pakchoi consumption

Exposure to heavy metal(loid)s (HM) through contaminated food chains poses significant health risks to humans. While soil amendments are known to reduce HM bioavailability, their effects on bioaccessibility and health risks in soil-pakchoi-human systems remain unclear. To address this knowledge gap, we conducted a greenhouse pot experiment coupling soil immobilization with bioaccessibility-based health risk assessment for Cd and As exposure from pakchoi consumption. Four amendments (attapulgite, shell powder, nanoscale zero-valent iron, and biochar) were applied to soil, resulting in changes to soil characteristics (pH and organic matter), plant dry weight, and exchangeable fractions of As and Cd. Among the tested amendments, biochar exhibited the highest effectiveness in reducing the risk of Cd and As exposure from pakchoi consumption. The bioaccessibility-based health risk assessment revealed that the application of 5% biochar resulted in the lowest hazard index, significantly decreasing it from 1.36 to 0.33 in contaminated soil. Furthermore, the structural equation model demonstrated that pH played a critical role in influencing remediation efficiency, impacting the exposure of the human body to Cd and As. In conclusion, our study offers a new perspective on mitigating exposure risks of soil HM and promoting safe crop production. The results underscore the importance of considering bioaccessibility in health risk assessment and highlight the potential of biochar as a promising amendment for reducing Cd and As exposure from pakchoi consumption.

Soil microbial community compositions and metabolite profiles of Achnatherum inebrians affect phytoremediation potential in Cd contaminated soil

Cadmium (Cd) contamination poses serious risks to soil ecosystems and human health. Herein, the effect of two drunken horse grasses (Achnatherum inebrians) including endophytes Epichloë gansuensis infected (E+ ) and uninfected (E-) on the phytoremediation of Cd-contaminated soils were analyzed by coupling high-throughput sequencing and soil metabolomics. The results showed that the high-risk soil Cd decreased and the medium- and low-risk Cd fraction increased to varying degrees after planting E+ and E- plants in the soil. Meanwhile, total Cd content decreased by 19.7 % and 35.1 % in E+ and E- A. inebrians-planted soils, respectively. Principal coordinate analysis revealed a significant impact of E+ and E- plants on the soil microbial community. Most stress-tolerant and gram-positive functional bacterial taxa were enriched to stabilize Cd(II) in E+ planted soil. Several beneficial fungal groups related to saprotroph and symbiotroph were enriched to absorb Cd(II) in E- soil. Soil metabolomic analysis showed that the introduction of A. inebrians could weaken the threat of CdCl2 to soil microbe metabolism and improve soil quality, which in turn promoted plant growth and improved phytoremediation efficiency in Cd-contaminated soil. In conclusion, A. inebrians plants alleviate soil Cd pollution by regulating soil microbial metabolism and microbial community structure. These results provide valuable information for an in-depth understanding of the phytoremediation mechanisms of A. inebrians.

Investigation of potential metal emissions from galvanic anodes in offshore wind farms into North Sea sediments

To evaluate potential metal emissions from offshore wind farms (OWFs), 215 surface sediment samples from different German North Sea OWFs taken between 2016 and 2022 were analyzed for their mass fractions of metals and their isotopic composition of Sr. For the first time, this study provides large-scale elemental data from OWFs of the previously proposed galvanic anode tracers Cd, Pb, Zn, Ga and In. Results show that mass fractions of the legacy pollutants Cd, Pb and Zn were mostly within the known variability of North Sea sediments. At the current stage the analyzed Ga and In mass fractions as well as Ga/In ratios do not point towards an accumulation in sediments caused by galvanic anodes used in OWFs. However, further investigations are advisable to evaluate long-term effects over the expected lifetime of OWFs, especially with regard to the current intensification of offshore wind energy development.