Cadmium-contaminated Soil Research Articles

Remediation of cadmium-contaminated soil: GLDA-assisted extraction and sequential FeCl3–CaO-based post-stabilization

Cadmium (Cd) contamination of farmland soils is a growing concern because of its highly toxic impact on ecosystems and human health. Chelator-assisted washing and chemical immobilization are effective remediation strategies for Cd-contaminated soils. Ethylenediaminetetraacetic acid (EDTA) has traditionally been used for soil washing, but its persistence in the environment and subsequent toxicity have raised significant ecological concerns. Consequently, biodegradable chelators have gained increasing attention as eco-friendly alternatives to the persistent chelator, EDTA. Therefore, this study evaluated the performance and efficacy of three biodegradable chelators: L-glutamate-N,N′-diacetic acid (GLDA), methylglycine-diacetic acid (MGDA), and 3-hydroxy-2,2′-iminodisuccinic acid (HIDS) in comparison to EDTA for remediating a real Cd-contaminated agricultural soil. The influence of treatment parameters, including chelator variants, washing time, chelator concentration, solution pH, and liquid-to-soil ratio (L/S) on Cd extraction was studied and optimized to attain the maximum removal rate. Following chelator-assisted washing, the efficacy of a stabilization preference combining FeCl3 and CaO in reducing the leaching potential of residual Cd in chelator-washed soil residues was also investigated. GLDA demonstrated comparable Cd extraction efficiency to EDTA, and the Cd extraction efficiency was found to be positively correlated with the soil washing parameters. However, under the optimized conditions (chelator concentration: 10 mmol L−1; washing time: 3 h; solution pH: 3; L/S ratio: 10:1), GLDA exhibited a higher Cd extraction rate than EDTA or the other chelators. Furthermore, a post-treatment process incorporating FeCl3 and CaO substantially diminished the water-leachable Cd content in the resultant soil residues. The proposed remediation strategy, which combines chemically assisted washing and stabilization, could be a practical option for extracting bulk Cd from soil and reducing the leaching potential of residual Cd.

Effects of fungal carbon dots application on growth characteristics and cadmium uptake in maize

The advancement of nanotechnology has led to the increased use of nanomaterials for the purpose of restoring contaminated soils. However, so far no research has been reported on the interactions of carbon dots with heavy metals (loid)s in phytoremediation. The purpose of this study was to investigate the effect of a new carbon dots derived from fungal exopolysaccharide (EPSs) on the growth and cadmium uptake in maize plants. This research was carried out using a completely randomized design with three replications in a greenhouse condition. Treatments included control, carbon dots (150 mg kg−1), cadmium (50 mg kg−1) and cadmium + carbon dots (50 mg kg−1+150 mg kg−1). The carbon dots synthesized by hydrothermal method from EPSs. The results showed that shoot dry weight and chlorophyll content of maize increased 9.7% and 23.2% in the presence of carbon dots, respectively. Carbon dots improved the chlorophyll content of maize by 24.3% in the cadmium treatment. Cadmium concentration increased (106%) in maize shoot but it decreased in root maize (68%). Carbon dots caused an increase of 5.7 and 6.7 times in the transfer factor and phytoremediation rate of cadmium, respectively. The presence of carbon dots triggered an increase of 77.9% and 39.9% of dissolved organic carbon in non-contaminated and cadmium-contaminated soils, respectively. Soil microbial biomass carbon increased 54.9% and 24.1% carbon dots and cadmium + carbon dots treatments, respectively. The study demonstrates the potential of fungal carbon dots for phytoremediation of heavy metal (loid)s contaminated soils. It also highlights the potential of nanotechnology in environmental remediation efforts.

Drought-resistant and water-retaining tobermorite/starch composite hydrogel for the remediation of cadmium-contaminated soil

The objective of this work is utilizing fly ash to synthesize tobermorite (TOB) with a higher specific surface area and layered structure, and incorporating it into the starch/acrylic acid network to boost the drought resistance, water retention and heavy metal adsorption properties. The water absorption and water retention performance and cadmium adsorption characteristics of tobermorite/leftover rice-based composite hydrogel (TOB@LR-CH) were evaluated by water absorption swelling test, soil evaporation test and batch adsorption experiment. By adjusting the addition of TOB and other synthesized conditions, the swelling property (from 114.80 g/g to 322.64 g/g), water retention (71.80 %, 144 h) and Cd2+ adsorption characteristics (up to 591.36 mg/g) were significantly enhanced. Adding a moderate amount of TOB (2 wt%) provided the most uniform tobermorite dispersion during synthesis, and TOB2@LR-CH exhibited the most stable three-dimensional network and highest proportion of effective TOB. The adsorption behavior of cadmium on TOB2@LR-CH was more consistent with the pseudo-second-order kinetics and Langmuir isotherm models. Additionally, the regeneration test results displayed that the adsorption removal rate of cadmium by TOB2@LR-CH adsorbent remained stable after 5 cycles. This study demonstrates that TOB@LR-CH has good water absorption and water retention potential in arid and semi-arid soils, and also has potential application prospects in remediating Cd(II)-contaminated soil.

Effects of Exogenous Plant Hormone Spraying on the Phytoremediation by Bidens pilosa L. in Cadmium-contaminated Soil

To explore the effect of exogenous plant hormone spraying on the absorption of heavy metals by hyperaccumulated plants, Bidens pilosa L. was selected as the tested plant owing to the large biomass, short growth cycle, and high accumulation efficiency. Here, the effect of foliar spraying 6-benzylaminopurine (6-BA), salicylic acid (SA), and 24-epi-brassinosteroid (24-EBR) on the remediation of cadmium (Cd)-contaminated soil by B. pilosa L. was examined. The results showed:① the efficiency of the remediation in Cd-contaminated soil by B. pilosa L. was effectively enhanced after the spraying of all three kinds of exogenous plant hormones with appropriate concentrations. The spraying of the three exogenous plant hormones could promote the cadmium concentration in the leaves of B. pilosa L. to increase by 4.21%, 31.79%, and 14.89%; promote the translocation factor (TF) to increase by 9.67%, 18.83%, and 17.85%; promote the phytoextraction rates (PR) to increase by 15.36%, 32.33%, and 64.38%, respectively. ② The growth of B. pilosa L. was significantly promoted after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The spraying of the three exogenous plant hormones could promote plant growth under cadmium stress, and the dry weight of the plant root, stem, and leaf was increased by 37.53%, 74.50%, and 104.02%, respectively. ③ The photosynthesis of B. pilosa L. was significantly enhanced after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The chlorophyll concentration of the plant was significantly increased after foliar spraying with plant hormones, and the concentration of chlorophyll a was increased by 79.31%, 92.27%, and 51.12%; the photochemical quenching coefficient (qP) was increased by 11.32%, 89.16%, and 78.43%; and the non-photochemical quenching coefficient (NPQ) was increased by 51.71%, 241.12%, and 27.85%, respectively, after foliar spraying with appropriate concentrations of 6-BA, SA, and 24-EBR. ④ The antioxidant capacity of B. pilosa L. was significantly strengthened after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The malondialdehyde (MDA) concentration of the plant was reduced by 62.41%, 68.67%, and 46.76% after the application of 6-BA, SA, and 24-EBR, respectively. Meanwhile, superoxide dismutase (SOD) was increased by 68.33%, 10.28%, and 6.17%, and catalase (CAT) was increased by 31.43%, 37.87%, and 37.31%, respectively. Generally, the spraying of exogenous 6-BA, SA, and 24-EBR with the appropriate concentration under Cd stress could significantly increase the biomass of B. pilosa L. and promote the accumulation of heavy metals in the plant, improve the photosynthetic ability of the plant, reduce the oxidative damage of the plant under heavy metal stress, enhance the antioxidant capacity, and improve the absorption and tolerance of plants to Cd. It also could promote the transfer of Cd from roots to shoots, improve the phytoextraction rates of Cd from the plant, and effectively strengthen the phytoremediation efficiency. Among them, 30 mg·L-1 SA foliar spraying had the best effect.

Intercropping with Brassica juncea L. enhances maize yield and promotes phytoremediation of cadmium-contaminated soil by changing rhizosphere properties

Intercropping heavy metal hyperaccumulators and low-accumulating cultivars is a promising strategy for remediating contaminated soils without impeding agricultural production. A field plot experiment was conducted to explore the effects of intercropping maize with Brassica juncea L. on the rhizosphere microecological properties, plant growth and cadmium (Cd) accumulation. The results showed that the Cd bioaccumulation amount per unit area (BCAarea) of the intercropping system was 12.9% lower than that of the Brassica juncea L. monoculture but 87.5% higher than that of the maize monoculture. The grain yield of maize was increased by 10.5% through intercropping, and the land equivalent ratio (LER) was greater than 1. Soil available Cd in intercropped maize was 13.4% lower than that in monoculture maize but was 12.7% higher in intercropped Brassica juncea L. than in monoculture Brassica juncea L. Intercropping significantly increased the contents of malic acid and citric acid in the rhizospheres of maize and Brassica juncea L. The dominant microorganisms were similar in all studied soils but were different in relative abundance between the intercropping and monoculture treatments. These findings suggest that intercropping maize with Brassica juncea L. could be a promising approach for phytoremediation without reducing crop yield in Cd-contaminated soil.

In Situ Toxicity Reduction and Food Safety Assessment of Pak Choi (Brassica campestris L.) in Cadmium-Contaminated Soil by Jointly Using Alkaline Passivators and Organic Fertilizer.

An economical and effective method is still lacking for cadmium (Cd) toxicity reduction and food product safety improvement in soil-vegetable systems. Therefore, this study aimed to reduce the Cd toxicity to pak choi (Brassica campestris L.) by jointly using passivators and organic fertilizer, highlighting food products' safety based on pot experiments. The results showed that compared with the control, organic fertilizer decreased the Cd content in edible parts and the soil's available Cd by 48.4% and 20.9% on average, respectively, due to the 0.15-unit increases in soil pH. Once jointly applied with passivators, the decrements increased by 52.3-72.6% and 32.5-52.6% for the Cd content in edible parts and for the soil's available Cd, respectively, while the pH increment increased by 0.15-0.46 units. Compared with the control, the transport factor of Cd was reduced by 61.9% and 50.9-55.0% when applying organic fertilizer alone and together with the passivators, respectively. The combination treatment of biochar and organic fertilizer performed the best in decreasing the Cd content in the edible parts and the soil's available Cd. The combination treatment of fish bone meal and organic fertilizer induced the greatest increases in soil pH. The grey relational analysis results showed that the combination treatment of biochar and organic fertilizer performed the best in reducing the potential Cd pollution risk, thereby highlighting the vegetable food safety. This study provides a potential economical and effective technology for toxicity reduction and food safety in Cd-polluted soil.

Complex resistivity spectrum of pollutant soils with low-concentration heavy metals

Soil contamination by heavy metals occurs globally, with varying degrees of severity, especially in agricultural fields. Investigating the frequency response characteristics of different types of heavy metal pollutants through induced polarization can provide valuable evidence for surveys based on this method. Soil specimens with varying low concentrations of copper (Cu), chromium (Cr), cadmium (Cd), and lead (Pb) heavy metals were prepared for this study, and parameters including complex resistivity, amplitude-frequency, and resistivity phase were measured. Our findings reveal the following trends: Complex resistivity decreases as heavy metal concentrations increase, demonstrating significant shifts within lower concentration ranges but presenting limitations for assessing pollution in high-concentration areas. Conversely, amplitude-frequency increases with higher heavy metal concentrations, displaying excellent performance in high-concentration scenarios. The differences in complex resistivity and amplitude-frequency among different types of heavy metal pollutants are distinct. In contrast, the absolute phase decreases with rising heavy metal concentrations. The resistivity phase spectra for various heavy metal pollutants exhibit unique patterns. For example, copper-contaminated soil exhibits phase peaks in the frequency range of 8–32 Hz, whereas chromium-contaminated soil shows phase peaks at 16–64 Hz. Cadmium-contaminated soil displays phase peaks ranging from 0.25 Hz to 2 Hz, while lead-contaminated soil exhibits phase peaks within the 0.5 Hz–4 Hz range. Leveraging the frequency range corresponding to phase peaks as an identification method for heavy metal pollution types proves effective. The frequency response characteristics of induced polarization vary significantly among different types and concentrations of heavy metal pollutants, providing important foundations for the application of induced polarization method in the field of heavy metal pollution detection.

Responses of microbial communities in rhizocompartments of king grass to phytoremediation of cadmium-contaminated soil

King grass has been recognized as a potential phytoremediation plant species due to its high biomass and resistance to heavy metals (HMs). However, the possible impacts of cadmium (Cd) contamination on rhizocompartments' microbial activities in association with king grass have not been extensively explored. The utilization of 16S rRNA gene and ITS sequencing was carried out to examine alterations in the bacterial and fungal communities in the rhizosphere and rhizoplane of king grass in response to low and high Cd stress. Results demonstrated that both bacterial and fungal communities' diversity and richness were negatively impacted by Cd stress, regardless of its concentration. However, evenness did not exhibit any significant response to either of the concentrations. Additionally, nonmetric multidimensional scaling (NMDS) ordination demonstrated a significant difference (p < 0.001) in microbial communities under different treatments. The abundance of bacterial taxa such as Steroibacter, Nitrospira, Pseudoxanthomonas, Cellvirio, Phenylobacterium, Mycobacterium, Pirellula and Aquicella was adversely affected under Cd stress while Flavobacterium, Gemmata, Thiobacillus and Gemmatimonas showed no prominent response, indicating their resistance to Cd stress. Like that, certain fungal taxa for instance, Cladosporium, Cercophora, Acremonium, Mortierella, Aspergillus, Penicillium, Glomus and Sebacina were also highly reduced by low and high Cd stress. In contrast, Fusarium, Thanatephorus, Botrytis and Curvularia did not show any response to Cd stress. The identified taxa may have a crucial role in the growth of king grass under heavy metal contamination, making them promising candidates for developing bioinoculants to encourage plant performance and phytoremediation capability in HM-contaminated soils.

New-style electrokinetic-adsorption remediation of cadmium-contaminated soil using double-group electrodes coupled with chitosan-activated carbon composite membranes

Global soil cadmium (Cd(II)) contamination threatens the soil environment, food safety, and human health. Conventional electrokinetic remediation (EKR) and enhancement methods usually operate in strong electric fields, leading to strong side reactions and uneven removal. In this work, to remove Cd(II) from soil effectively in a low-voltage electric field, a new-style electrokinetic-adsorption remediation using double-group electrodes coupled with chitosan-activated carbon composite membranes (DE-EKR-CAC) was developed. Chitosan-activated carbon (CAC) composite membranes were synthesized for easy recovery and reuse of adsorbents. The effects of pH, contact time, initial concentration, and foreign ions on the removal of Cd(II) by the CAC composite membranes were determined. The CAC composite membranes performed well except in a strongly acidic environment (pH = 2.0). The soil pH varied between 3.4 and 5.0 in DE-EKR-CAC, where the CAC composite membranes were applicable. High concentrations of Ca2+ interfered with the adsorption of Cd(II), which means that the selectivity of CAC composite membranes for Cd(II) is not high enough. The Langmuir (R2 = 0.999) and pseudo-second-order kinetic (R2 = 1.0) models revealed the monolayer coverage and chemisorption mechanism, and the maximum adsorption capacity was 40.81 mg/g. Furthermore, SEM, FTIR, and XPS analyses suggest that physical adsorption, complexation of oxygen-containing functional groups, chelation of amino groups, and ion exchange are potential mechanisms for the adsorption of Cd(II) on CAC. DE-EKR-CAC performed better than the group remediated with one set of electrodes, with higher removal efficiencies and more uniform removal. The lowest energy consumption was 3.33 kWh/m3, which is lower than other enhancement methods. Separation of CAC composite membranes from soil is easy, and reuse performance is good. DE-EKR-CAC provides a potential option for Cd(II) removal from soil because of its better performance using low-voltage direct current, low energy consumption, and ease of recycling the adsorbent.

Recent Advances in Microbial-Assisted Remediation of Cadmium-Contaminated Soil.

Soil contamination with cadmium (Cd) is a severe concern for the developing world due to its non-biodegradability and significant potential to damage the ecosystem and associated services. Industries such as mining, manufacturing, building, etc., rapidly produce a substantial amount of Cd, posing environmental risks. Cd toxicity in crop plants decreases nutrient and water uptake and translocation, increases oxidative damage, interferes with plant metabolism and inhibits plant morphology and physiology. However, various conventional physicochemical approaches are available to remove Cd from the soil, including chemical reduction, immobilization, stabilization and electro-remediation. Nevertheless, these processes are costly and unfriendly to the environment because they require much energy, skilled labor and hazardous chemicals. In contrasting, contaminated soils can be restored by using bioremediation techniques, which use plants alone and in association with different beneficial microbes as cutting-edge approaches. This review covers the bioremediation of soils contaminated with Cd in various new ways. The bioremediation capability of bacteria and fungi alone and in combination with plants are studied and analyzed. Microbes, including bacteria, fungi and algae, are reported to have a high tolerance for metals, having a 98% bioremediation capability. The internal structure of microorganisms, their cell surface characteristics and the surrounding environmental circumstances are all discussed concerning how microbes detoxify metals. Moreover, issues affecting the effectiveness of bioremediation are explored, along with potential difficulties, solutions and prospects.

Crop effect and mechanism of amino acid-modified biomass ash in remediation of cadmium-contaminated soil.

Lignocellulosic biomass ash (BA) has certain adsorption and passivation effects on heavy metals, but its function is generally weak. Amino acid salt can facilitate the leaching of heavy metals in soil. Therefore, modification of BA with amino acid salt may realize a higher leaching rate and better passivation of heavy metals in soil. In this study, BA was modified by amino acid hydrolysate obtained from the hydrolysis of chicken feathers by sulfuric acid. The physicochemical properties of BA and modified BA (MBA), their effects on Chinese cabbage (CC) yield and nutritional quality, and passivation effects on soil cadmium (Cd) were compared, and the related mechanisms were investigated. SEM-EDS, XRD, and FTIR demonstrated that BA was a CaCO3-type soil amendment, while MBA was a CaSO4-type soil amendment with the loading of amino acid. Compared with BA, MBA significantly increased the fresh weight, soluble sugar, vitamin C (Vc), and protein contents of CC in both non-Cd contaminated soil and Cd contaminated soil, and obviously decreased the nitrate content and Cd uptake of CC in Cd-contaminated soil. After the application of MBA, cadmium species in potted soil were transformed from higher plant availability, representing by exchangeable and carbonate-bound, into lower plant availability, representing by iron-manganese oxide bound, which was identified as the key reason for the significant reduction of Cd content in CC under MBA application.

Biosorption of cadmium by Enterobacter ludwigii isolated from soil contaminated with cadmium near a coal-fired power plant in Korea

ABSTRACT This study aimed to isolate and characterize indigenous bacteria from cadmium-contaminated soil around a coal-fired power plant in Korea for their potential use in biosorption. The 16S ribosomal RNA analysis identified Enterobacter ludwigii G17–1 in the soil, exhibiting a remarkably high minimum inhibitory concentration (2,500 mg/L) for cadmium. The efficiency of cadmium biosorption was investigated under different pH levels (6–9), temperatures (15–40°C), and initial cadmium concentrations (25–100 mg/L), using both live and dead G17–1. The live G17–1 strain exhibited a maximum biosorption efficiency of 50% for 25 mg/L cadmium at 24 hours, while the highest efficiency achieved with dead G17–1 was 48% at 1 hour. The biosorption capacity decreased as the initial cadmium concentration increased. These findings suggest that the isolated bacterium, E. ludwigii G17–1, holds potential for the bioremediation of cadmium-contaminated water and wastewater.

Morphological responses of six sorghum varieties on cadmium-contaminated soil

Abstract. Hasanah NAU, Purwanto E, Harsono P, Samanhudi, Sakya AT. 2023. Morphological responses of six sorghum varieties on cadmium-contaminated soil. Biodiversitas 24: 3903-3915. Six sorghum varieties were planted on cadmium-contaminated soil and characterized from April to July 2020 at a rice field in Balecatur Gamping, Yogyakarta. The objectives of this experiment were to characterize themorphological responses of six sorghum varieties and select a variety with a high biomass and Cd uptake fora potential phytoremediator. This experiment used six sorghum varieties, namely Super-1, Samurai-1, Suri-3, Numbu, Kawali, and Hitam, following completely randomized design procedures with four replications. The observation of morphological and agronomical characteristics focused on ten plants as the sample of each plot. The result showed that there were differences in the morphological and agronomical characteristics among six sorghum varieties. Varieties were assessed in terms of distinctness and grouped based on the time of panicle emergence, plant height, panicle shape, and caryopsis color. There were threeclasses as follows: Class 1, i.e., time of panicle emergence: very early (Super-1, Suri-3, Numbu, and Hitam); plant height: long (Super-1), medium (Suri-3), short (Numbu and Hitam); panicle shape: panicle broader in the upper part (Numbu), symmetrical (Super-1 and Suri-3), pyramidal (Hitam); caryopsis color: white (Super-1), grayish orange (Suri-3 and Hitam), yellowish orange (Numbu). Class 2, time of panicle emergence: early (Samurai-1); plant height: medium (Samurai-1); panicle shape: panicle broader in the lower part (Samurai-1); caryopsis color: yellowish orange (Samurai-1). Class 3, time of panicle emergence: medium (Kawali); plant height: medium (Kawali); panicle shape: panicle broader in the lower part (Kawali); caryopsis color: yellowish white (Kawali). Assessment of agronomical characteristics revealed that fresh plant weight had a significant positive correlation with plant height R1, plant height R5, stem diameter, leaf bladewidth, thousand-grain weight, and stem sugar content. Several varieties, namely Super-1, Samurai-1 and Kawali, were found to have excellent agronomical characteristics to provide a solid varietal basis for selecting varieties as phytoremediators.

An Application of Rock Phosphate Increased Soil Cadmium Contamination and Hampered the Morphophysiological Growth of Brassica campestris L

An Application of Rock Phosphate Increased Soil Cadmium Contamination and Hampered the Morphophysiological Growth of Brassica campestris L

Cerium oxide nanoparticles alleviates stress in wheat grown on Cd contaminated alkaline soil

The cadmium contamination of soil is an alarming issue worldwide and among various mitigation strategies, nanotechnology mediated management of Cd contamination has become a well-accepted approach. The Cerium Oxide Nanoparticles (CeO2-NPs) are widely being explored for their novel works in Agro-Industry and Environment, including stress mitigation in crops. Very little work is reported regarding role of CeO2-NPs in management of Cd contamination in cereal crops like wheat. Present work was planned to check efficacy of CeO2-NPs in Cd stress mitigation of wheat under alkaline calcareous soil conditions. In this experiment, 4 sets of Cd contamination (Uncontaminated control-UCC, 10, 20, and 30 mg Cd per kg soil) and 5 sets of CeO2-NPs NPs (0, 200, 400, 600, and 1000 mg NP per kg soil) were applied in pots following completely randomized design (CRD) and wheat crop was grown. The growth, physiology, yield and Cd and Ce accumulation by wheat root, shoot and grain was monitored. The maximum Cd spiking level (30 mg kg−1) was found to be most toxic for plant growth. The results showed that the nanoparticles were overall beneficial for wheat growth and maximum level (1000 mg kg−1) being the most significant one under all Cd spiking sets. In Cd-30 sets, 1000 mg kg−1 NPs application resulted in decreased soil bioavailable Cd concentration (49.63% decrease compared to 30 mg kg−1 Cd spiked sets termed as Cd-30 Control), decreased Cd accumulation in all three tissues: root (58.36% decrease), shoot (52.30% decrease) and grain (55.56% decrease) while increased root dry weight (62.14%), shoot dry weight (89.32%), total grain yield (80.08%) and improved plant physiology with respect to Cd-30 control. Nanoparticles application substantially increased wheat root, shoot and grain Ce concentrations as well. The further prospects of these nanoparticles in relation to various biotic and abiotic stresses are advised to be explored.

Biochar may alter plant communities when remediating the cadmium-contaminated soil in the saline-alkaline wetland

It is thought remediating cadmium pollution with biochar can affect plant traits. However, the potential impact of this practice on plant communities is poorly understood. Here, we established natural-germinated plant communities using soil seed bank from a saline-alkaline wetland and applied a biochar treatment in Cd-polluted wetland soil. The outcomes illustrated that Juglans regia biochar (JBC), Spartina alterniflora biochar (SBC), and Flaveria bidentis biochar (FBC) promoted exchangeable Cd transform into FeMn oxide bound Cd. Additionally, most biochar addition reduced species abundance, root-shoot ratio, biomass, diversity, and community stability, yet enhanced community height. Among all treatments, the 5 % SBC demonstrated the most significant reduction in species abundance, biomass, species richness and functional richness. Specifically, it resulted in a reduction of 92.80 % in species abundance, 73.80 % in biomass, 66.67 % in species richness, and 95.14 % in functional richness compared to the CK. We also observed changes in root morphological traits and community structure after biochar addition. Soil pH, salinity, and nutrients played a dominant role in shaping plant community. These findings have implications for biodiversity conservation, and the use of biochar for the remediation of heavy metals like cadmium should be approached with caution due to its potential negative impacts on plant communities.

Microorganisms and Biochar Improve the Remediation Efficiency of Paspalum vaginatum and Pennisetum alopecuroides on Cadmium-Contaminated Soil.

Phytoremediation can help remediate potential toxic elements (PTE) in soil. Microorganisms and soil amendments are effective means to improve the efficiency of phytoremediation. This study selected three microorganisms that may promote phytoremediation, including bacteria (Ceratobasidium), fungi (Pseudomonas mendocina), and arbuscular-mycorrhizal fungi (AMF, Funneliformis caledonium). The effects of single or mixed inoculation of three microorganisms on the phytoremediation efficiency of Paspalum vaginatum and Pennisetum alopecuroides were tested under three different degrees of cadmium-contaminated soil (low 10 mg/kg, medium 50 mg/kg, and high 100 mg/kg). The results showed that single inoculation of AMF or Pseudomonas mendocina could significantly increase the biomass of two plants under three different degrees of cadmium-contaminated soil, and the growth-promoting effect of AMF was better than Pseudomonas mendocina. However, simultaneous inoculation of these two microorganisms did not show a better effect than the inoculation of one. Inoculation of Ceratobasidium reduced the biomass of the two plants under high concentrations of cadmium-contaminated soil. Among all treatments, the remediation ability of the two plants was the strongest when inoculated with AMF alone. On this basis, this study explored the effect of AMF combined with corn-straw-biochar on the phytoremediation efficiency of Paspalum vaginatum and Pennisetum alopecuroides. The results showed that biochar could affect plant biomass and Cd concentration in plants by reducing Cd concentration in soil. The combined use of biochar and AMF increased the biomass of Paspalum vaginatum by 8.9-48.6% and the biomass of Pennisetum alopecuroides by 8.04-32.92%. Compared with the single use of AMF or biochar, the combination of the two is better, which greatly improves the efficiency of phytoremediation.

Transport and retention of n-hexadecane in cadmium-/naphthalene-contaminated calcareous soil sampled in a karst area.

Studying the transport of petroleum hydrocarbons in cadmium-/naphthalene-contaminated calcareous soils is crucial to comprehensive assessment of environmental risks and developing appropriate strategies to remediate petroleum hydrocarbons pollution in karst areas. In this study, n-hexadecane was selected as a model petroleum hydrocarbon. Batch experiments were conducted to explore the adsorption behavior of n-hexadecane on cadmium-/naphthalene-contaminated calcareous soils at various pH, and column experiments were performed to investigate the transport and retention of n-hexadecane under various flow velocity. The results showed that Freundlich model better described the adsorption behavior of n-hexadecane in all cases (R2 > 0.9). Under the condition of pH = 5, it was advantageous for soil samples to adsorb more n-hexadecane, and the maximum adsorption content followed the order of: cadmium/naphthalene-contaminated > uncontaminated soils. The transport of n-hexadecane in cadmium/naphthalene-contaminated soils at various flow velocity was well described by two kinetic sites model of Hydrus-1D with R2 > 0.9. Due to the increased electrostatic repulsion between n-hexadecane and soil particles, n-hexadecane was more easily able to breakthrough cadmium/naphthalene-contaminated soils. Compared to low flow velocity (1mL/min), a higher concentration of n-hexadecane was determined at high flow velocity, with 67, 63, and 45% n-hexadecane in effluent from cadmium-contaminated soils, naphthalene-contaminated soils, and uncontaminated soils, respectively. These findings have important implications for the government of groundwater in calcareous soils from karst areas.

Response of rare and abundant rhizosphere microbial communities to inoculated rhizobium in cadmium-contaminated soil phytoremediation

Soil microorganisms play an important role in maintaining ecosystem balance and exerting ecological functions. The taxonomic and functional changes in rare and abundant communities during in bioremediation of cadmium-contaminated soils and their contributions to the remediation of ecosystem functions remain elusive despite the significance of rare and abundant microbial taxa in maintaining soil ecological function. Mesorhizobiumloti HZ76-inoculated seedlings of the Robinia pseudoacacia were used to create a symbiotic system. The effects of rhizobium inoculation on rare and abundant rhizosphere microbial populations were investigated in pot experiments. Despite having minimal effects on the α-diversity of rare and abundant microbial communities, inoculation altered microbial community composition and functional gene abundance. For example, abundant phyla such as Proteobacteria were enriched following inoculation, whereas rare phyla such as Ascomycota were depleted. After inoculation, the abundance of nifH gene increased, while the abundance of amoA, amoB, nirS, nirK and nosZ gene decreased. Rare bacterial populations were more susceptible to the inoculated rhizobium's environmental alterations. In rare communities compared to abundance communities, the α-diversity was higher. Stochastic processes predominated in the communities of uncommon and abundant microorganisms. Furthermore, keystone taxa, particularly rare bacterial taxa (Gemmatimonadaceae and Saprospiraceae) and rare fungal taxa (Ascomycota), more mediates nitrogen cycle processes and is directly associated to the abundance of nitrogen functional genes. Together, our findings demonstrate the different ways that rare and abundant microbial species react to rhizobia inoculation and their connections to the nitrogen cycle.

Treatment of cadmium-contaminated soil using ladle slag with and without CO2

Cement and lime are widely used to stabilize/solidify (S/S) contaminated soils, however, the production of ordinary Portland cement (OPC) and lime causes CO2 emission and consumption of energy and non-renewable resource. In this context, this study proposes a sustainable S/S approach by utilizing an industrial by-product, ladle slag (LS), and carbon dioxide (CO2), to substitute cement and lime for treating cadmium (Cd)-contaminated soil. In laboratory investigation, contaminated soils spiked by Cd with concentrations of 0–32,000 mg/kg were treated by LS with a binder content of 10 % and subjected to conventional curing and carbonation curing for different periods varying from 3 hours to 112 days. The results showed that LS with conventional curing could reduce the leaching of Cd, however, it was still less effective than OPC in S/S of Cd-contaminated soils under the same curing period of 28 days. When CO2 was introduced, LS with CO2 rapidly decreased the leaching of Cd in soils by five orders of magnitude, using only 104 hours to achieve better S/S efficacy than OPC with conventional curing for 28 days. The LS with carbonation curing also sequestered CO2 up to 16 % of LS mass and yielded higher strength than that without CO2.