Cadmium-contaminated Soil Research Articles

A Critical Review of the Effectiveness of Biochar Coupled with Arbuscular Mycorrhizal Fungi in Soil Cadmium Immobilization.

Cadmium-contaminated soil significantly threatens global food security and human health. This scenario gives rise to significant worries regarding widespread environmental pollution. Biochar and arbuscular mycorrhizal fungi (AMF) can effectively immobilize cadmium in the soil in an environmentally friendly way. Existing studies have separately focused on the feasibility of each in remediating polluted soil. However, their association during the remediation of cadmium-polluted soils remains unclear. This review paper aims to elucidate the potential of biochar, in conjunction with AMF, as a strategy to remediate soil contaminated with cadmium. This paper comprehensively analyzes the current understanding of the processes in cadmium immobilization in the soil environment by examining the synergistic interactions between biochar and AMF. Key factors influencing the efficacy of this approach, such as biochar properties, AMF species, and soil conditions, are discussed. The influences of biochar-AMF interactions on plant growth, nutrient uptake, and overall ecosystem health in cadmium-contaminated environments are highlighted. This review indicates that combining biochar and AMF can improve cadmium immobilization. The presence of AMF in the soil can create numerous binding sites on biochar for cadmium ions, effectively immobilizing them in the soil. Insights from this review contribute to a deeper understanding of sustainable and eco-friendly approaches to remediate cadmium-contaminated soils, offering potential applications in agriculture and environmental management.

Remediation of cadmium-contaminated soil by biochar-loaded nano-zero-valent iron and its microbial community responses

At present, cadmium (Cd)-contaminated soil has been increasingly serious, which is adverse to soil health. In this study, biochar (BC) and biochar-loaded nanoscale zero-valent iron (nZVI@BC) were synthesized for remediation of Cd-contaminated soil. The effects of various factors including reaction time, dosage, nZVI loading on Cd fractionation, soil available iron, pH, CEC, and soil enzyme activity were comprehensively discussed. It can be concluded that nZVI@BC exhibited more excellent immobilization effect of Cd, and was positively correlated with dosage and reaction time, but negatively related to nZVI loading. As a result, 5% nZVI@BC(1:3) performed the best. Soil available iron, pH, and CEC were significantly enhanced with increasing nZVI loading. The immobilization mechanism was analyzed, including ion exchange, physical adsorption, surface complexation, electrostatic attraction as well as co-precipitation. Besides, nZVI@BC remarkably promoted soil catalase activity, but inhibited urease and FDA hydrolase activities. Furthermore, the effects and differences on the diversity, abundance, and species composition of soil microbial communities were deeply explored. The order of bacterial community richness in each group was CK > Cd > BC > nZVI@BC, and the bacterial community diversity was CK > nZVI@BC > Cd > BC. The greatest difference of species abundance composition was observed between nZVI@BC treatment group and the control. Additionally, forty-three biomarkers were screened, which primarily belonged to Proteobacteria, Gemmatimonadetes, Firmicutes, and Actinobacteria. This study will provide the profound theoretical basis for nZVI@BC remediation of Cd-contaminated soil and its microbial community responses.

Changes in microRNAs expression of flax (Linum usitatissimum L.) planted in a cadmium-contaminated soil following the inoculation with root symbiotic fungi

Cadmium is one of the most harmful heavy metals that harm agricultural products. Evaluating microRNAs expression is a new and accurate method to study plant response in various environmental conditions. So this study aimed to evaluate the contribution of two symbiotic fungi in improving flax tolerance in a Cd-polluted soil using microRNAs and their target gene expression. A factorial pot experiment in a completely randomized design was conducted with different levels of Cd (0, 20, and 40 mg kg−1) on non-inoculated and inoculated flax with Claroideoglomus etunicatum and Serendipita indica. The results presented that increasing Cd levels caused a constant decline of alkaline phosphatase of soil (from 243 to 210 and 153 μg PNP g−1 h−1), respectively, from control (Cd0) to 20 and 40 mg Cd kg−1. However, the inoculation of flax with fungi significantly enhanced these properties. A negative correlation was observed between the expression level of microRNA 167 and microRNA 398 with their corresponding target genes, auxin response factor 8 and superoxide dismutase zinc/copper 1, respectively. The expression level of both microRNAs and their targets indicated that the inoculation with symbiont fungi could diminish Cd stress and enhance the growth of flax.

A study on the classification of geological background source cadmium migration phases in Zhejiang Province, China

The release of cadmium during the natural weathering process of cadmium-containing strata is a significant source of cadmium pollution in both water and soil. The Hetang formations, wildly located in Jiangxi Province Zhejiang Province and Anhui Province in China, is a typical example of a cadmium-rich black shale stratum and is one of the primary sources of soil cadmium contamination. The bottom coal seam of this formation has been found to contain high levels of cadmium, with concentrations up to 11.26 mg/kg. As a result of water flow eroding the riverbed, parent rocks containing cadmium undergo continuous weathering, releasing cadmium elements. This process contributes to cadmium pollution in downstream soil, originating from the geological background. By utilizing techniques such as FE-SEM, EDS, and optical microscopy, this study investigates the distribution of iron in rock fragments with varying degrees of weathering in the riverbed. The research aims to examine the influence of iron distribution on the migration of cadmium originating from geological background sources. Based on the co-occurrence and co-migration characteristics of iron and cadmium in the study area, this research aims to reveal the migration features of geological background source cadmium by exploring the distribution patterns of iron sediment within rock fragments. By comparing sediment samples from both upstream and downstream river channels, we were able to identify three distinct stages that indicate the presence of cadmium originating from geological sources under weathering conditions: the unweathered stage; the intra-detritus migration stage, and the completely weathered stage; intra-detritus migration stage; and completely weathered stage. Furthermore, after leaving the Hetang formations shale outcrop area, there was a sharp decrease in content for Hetang formations detritus. At this point geological background source cadmium had largely escaped from constraints imposed by rock microstructure and had come into full contact with water. The findings from this research deepen our understanding regarding migration patterns for geological background source cadmium. They also reveal formation processes for geological background source cadmium pollution and provide a theoretical basis for identification and treatment for geological background source cadmium pollution.

Combined application of biochar and metal-tolerant bacteria alleviates cadmium toxicity by modulating the antioxidant defense mechanism and physicochemical attributes in rice (Oryza sativa L.) grown in cadmium-contaminated soil

Agricultural soil contamination by heavy metal (cadmium) is a widespread issue and causes deleterious effects on crops. One of the most effective and ecofriendly methods for cadmium detoxification is microbe-assisted phytoremediation and soil amendment with biochar. The current study investigated the combined effect of biochar (Parthenium hysterophorus L.) and microbes (Bacillus cereus strain B2) in alleviating cadmium toxicity in rice grown in cadmium-contaminated soil (0, 10, 15, and 20 mg/kg). Results revealed that cadmium caused damage to plant health. Maximum reduction in plant biomass, gas exchange parameters, and chlorophyll content was observed on cadmium 20 mg/kg. As compared with the sole application of biochar (2 %) and microbes, the greatest plant height (33.68%), photosynthetic rate (23.52 %), stomatal conductance (48.93 %), water use efficiency (21.41 %), transpiration rate (58.87 %), chlorophyll a (74.81 %), chlorophyll b (31.28 %), total chlorophyll (60.53 %), and carotenoids (26.97 %) were recorded with combined application of biochar and microbes. Similarly, superoxidase (SOD), catalase (CAT), peroxidase (POD), and absorbate peroxidase (APX) activity was significantly boosted by combined application of microbes and biochar (2 %), which were 33.90 %, 24.18 %, 51.70 %, and 19.06 %, respectively, while significant reduction was found in the ROS (16.60 %), (20.06 %) and MDA (26.08 %) content in rice plants. However, cadmium concentrations in different parts of plant were decreased at higher concentrations of biochar (2 %) with microbes. These findings indicate that combined application of Bacillus cereus strain B2 and biochar could be a promising strategy for reducing rice crop cadmium toxicity and boosting its growth, physiology, and defense system efficiently as compared with sole application.

Inoculation of cadmium-tolerant bacteria to regulate microbial activity and key bacterial population in cadmium-contaminated soils during bioremediation

The perennial ryegrass Lolium perenne can be used in conjunction with cadmium (Cd)-tolerant bacteria such as Cdq4–2 (Enterococcus spp.) for bioremediation of Cd-contaminated soil. In this study, a theoretical basis was provided to increase the efficiency of L. perenne remediation of Cd-contaminated soil using microorganisms to maintain the stability of the soil microbiome. The experimental design involved three treatment groups: CK (soil without Cd addition) as the control, 20 mg·kg–1 Cd-contaminated soil, and 20 mg·kg–1 Cd-contaminated soil + Cdq4–2, all planted with L. perenne. The soil was collected on day 60 to determine the soil microbial activity and bacterial community structure and to analyze the correlation between soil variables, the bacterial community, available Cd content in the soil, Cd accumulation, and L. perenne growth. The soil microbial activity and bacterial community diversity decreased under Cd stress, and the soil microbial community composition was changed; while inoculation with Cdq4–2 significantly increased soil basal respiration and the activities of urease, invertase, and fluorescein diacetate (FDA) hydrolase by 83.65%, 79.72%, 19.88%, and 96.15% respectively; and the stability of the community structure was also enhanced. The Actinobacteriota biomass, the amount of available Cd, and the above- and belowground Cd content of L. perenne were significantly negatively correlated with the total phosphorus, total potassium, and pH. The activity of urease, invertase, and FDA hydrolase were significantly positively correlated with the biomasses of Acidobacteriota and L. perenne and significantly negatively correlated with the Chloroflexi biomass. Further, the available soil Cd content and the above- and belowground Cd levels of L. perenne were significantly positively correlated with the Actinobacteriota biomass and significantly negatively correlated with the Gemmatimonadetes biomass. Overall, inoculating Cd-tolerant bacteria improved the microbial activity, diversity, and abundance, and changed the microbial community composition, facilitating the remediation of Cd-contaminated soil by L. perenne.

Biochar and organic fertilizer drive the bacterial community to improve the productivity and quality of Sophora tonkinensis in cadmium-contaminated soil.

Excessive Cd accumulation in soil reduces the production of numerous plants, such as Sophora tonkinensis Gagnep., which is an important and widely cultivated medicinal plant whose roots and rhizomes are used in traditional Chinese medicine. Applying a mixture of biochar and organic fertilizers improved the overall health of the Cd-contaminated soil and increased the yield and quality of Sophora. However, the underlying mechanism between this mixed fertilization and the improvement of the yield and quality of Sophora remains uncovered. This study investigated the effect of biochar and organic fertilizer application (BO, biochar to organic fertilizer ratio of 1:2) on the growth of Sophora cultivated in Cd-contaminated soil. BO significantly reduced the total Cd content (TCd) in the Sophora rhizosphere soil and increased the soil water content, overall soil nutrient levels, and enzyme activities in the soil. Additionally, the α diversity of the soil bacterial community had been significantly improved after BO treatment. Soil pH, total Cd content, total carbon content, and dissolved organic carbon were the main reasons for the fluctuation of the bacterial dominant species. Further investigation demonstrated that the abundance of variable microorganisms, including Acidobacteria, Proteobacteria, Bacteroidetes, Firmicutes, Chloroflexi, Gemmatimonadetes, Patescibacteria, Armatimonadetes, Subgroups_ 6, Bacillus and Bacillus_ Acidiceler, was also significantly changed in Cd-contaminated soil. All these alterations could contribute to the reduction of the Cd content and, thus, the increase of the biomass and the content of the main secondary metabolites (matrine and oxymatrine) in Sophora. Our research demonstrated that the co-application of biochar and organic fertilizer has the potential to enhance soil health and increase the productivity and quality of plants by regulating the microorganisms in Cd-contaminated soil.

Effects of Nano-zero-valent Iron and Earthworms on Soil Physicochemical Properties and Microecology in Cadmium-Contaminated Soils

The capacity of nano-zero-valent iron (nZVI) and soil animals to remediate heavy metal–contaminated soil has been widely studied. However, the synergistic effect of soil animals and nZVI has not been thoroughly investigated. Here, we studied the combined effect of earthworms and nZVI on soil physicochemical properties and microecology during remediation of cadmium (Cd)–contaminated soil. The results showed that although amendment with nZVI reduced earthworm survival and biomass, the combination of nZVI and earthworms was effective at reducing the available Cd (ACd) content of soil and improving its quality. ACd most effectively reduced by 75.3% in the presence of earthworms under the 0.25% nZVI combination. Meanwhile, the combined action of earthworms and nZVI significantly improved soil properties and increased the diversity of soil microorganisms. In the earthworm-free system, nZVI reduced ACd by increasing soil pH and the abundance of Stenotrophobacter in Cd-contaminated soil, in addition to the co-precipitation and adsorption reported in previous studies. Correlation analysis revealed that the combination of nZVI and earthworms synergistically decreased ACd by decreasing soil OM and increasing the relative abundance of Opitutus and Gemmatta. Overall, our study indicates that the combination of nano-zero-valent iron and earthworms is a potential system for in situ remediation of Cd-contaminated soils and provides a deep understanding of the mechanisms involved in remediation.

Co-application of biochar and plant growth regulators improves maize growth and decreases Cd accumulation in cadmium-contaminated soil

To ensure the sustainable cultivation of agronomic crops in agricultural soils polluted with cadmium (Cd), the integrated application of Cd-remediation strategies at edaphic and foliar levels has been examined. However, the integrated application of biochar (BC) and plant growth regulators (PGRs) for mitigating Cd stress, especially in maize, remains unexplored. Additionally, the expression patterns of PGRs and heavy metal transporters during Cd stress are unknown. To address these gaps, a pot experiment (having four replications) was performed to explore the potential effects of the integrated application of BC (B0 = no BC added; B1 = low BC at 2.5% w/w; and B2 = high BC at 5% w/w) and PGRs (H0 = control; WS = water spray; GA = gibberellin, and IAA = auxin) on maize growth, Cd remediation, and productivity. The study was conducted following a factorial completely randomized design. The pots were artificially spiked with Cd (30 ppm) by using Cd(NO3)2 as a source. The synergistic application of IAA/GA and BC, improved the morphological characteristics, photosynthetic activity, stomatal conductance, and catalase activity of maize under Cd stress while simultaneously decreasing electrolyte leakage and oxidant activity. The leaf area, shoot fresh biomass (SFB), and root fresh biomass (RFB), were increased by (13.4, 11.7%), (52.8, 39.3%), and (89.2, 74.3%) in the synergistic application of PGRs (i.e., IAA and GA) + BC (5% w/w) treatments, respectively, than control. Furthermore, a drastic reduction in Cd uptake was observed in maize leaves by (201.53, 179.24%) under the dual application of PGRs + BC (5% w/w) treatments, compared to control, which altered Cd bioconcentration in plant parts and modified Cd species in the soil. Decreased expression of heavy metal transporter PMPCB gene and YCF1 indicated reduced Cd uptake in 5% w/w BC based on RT-PCR quantification. The synergistic application of BC with PGRs can serve as an environmentally friendly remediation to mitigate the hazardous effects of Cd stress on cultivated maize. This was achieved by reducing the bio-concentration and metal transport coefficients of Cd in plants through BC's absorption properties. Overall, applying BC and foliar application of PGRs could be suggested as a sustainable approach for cultivating crops on Cd-contaminated soils while ensuring safety.

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.

Study on the solidification/stabilization of cadmium-contaminated soil by red mud-assisted blast furnace slag under excitation conditions

In the context of contaminated soils and industrial solid waste utilizations, a low-carbon curing agent (RAS) was synthesized in this study using red mud (RM), blast furnace slag (GGBS), calcium carbide residue (CCR), and phosphogypsum (PG) for solidification/stabilization (S/S) of cadmium (Cd)-contaminated soils. The effects of Cd contents, RAS dosages, and curing times on the strength and leaching properties of the solidified/stabilized soil were investigated in this study. In addition, the main mechanisms governing the RAS-based S/S of the Cd-contaminated soil were revealed using an improved four-step extraction method (BCR), mercury intrusion porosimetry (MIP), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results showed that the RAS binder significantly enhanced the compressive strength and Cd chemical stability of the Cd-contaminated soil, thereby reducing Cd2+ leaching amounts and soil porosity. The soil strength and Cd2+ leaching amounts from the solidified/stabilized soil met their corresponding standards after 14 days of curing. The main products of the solidified/stabilized soil consisted of Cd precipitates, ettringite (AFt), and calcium silicate hydrate (C–S–H). Their contents were related to the initial soil Cd content, RAS dosage, and curing time. The Cd precipitate, C–S–H, and AFt products can not only fill inter-particle voids of the soil but also exhibit physical encapsulation, surface complexation, co-precipitation, electrostatic adsorption, and ion exchange effects on Cd. The results of this study can provide a novel approach for treating and utilizing solid wastes and an environmentally friendly, economical, and efficient curing agent for the remediation of Cd-contaminated soils.

Transcriptome analysis reveals how cadmium promotes root development and accumulates in Apocynum venetum, a promising plant for greening cadmium-contaminated soil

Cadmium (Cd) contamination poses a substantial threat the environment, necessitating effective remediation strategies. Phytoremediation emerges as a cost-efficient and eco-friendly approach for reducing Cd levels in the soil. In this study, the suitability of A. venetum for ameliorating Cd-contaminated soils was evaluated. Mild Cd stress promoted seedling and root growth, with the root being identified as the primary tissue for Cd accumulation. The Cd content of roots ranged from 0.35 to 0.55 mg/g under treatment with 10–50 µM CdCl2·2.5 H2O, and the bioaccumulation factor ranged from 28.78 to 84.43. Transcriptome sequencing revealed 20,292 unigenes, and 7507 nonredundant differentially expressed genes (DEGs) were identified across five comparison groups. DEGs belonging to the “MAPK signaling pathway-plant,” “monoterpenoid biosynthesis,” and “flavonoid biosynthesis pathway” exhibited higher expression levels in roots compared to stems and leaves. In addition, cytokinin-related DEGs, ROS scavenger genes, such as P450, glutathione-S-transferase (GST), and superoxide dismutase (SOD), and the cell wall biosynthesis-related genes, CSLG and D-GRL, were also upregulated in the root tissue, suggesting that Cd promotes root development. Conversely, certain ABC transporter genes, (e.g, NRAMP5), and some vacuolar iron transporters, predominantly expressed in the roots, displayed a strong correlation with Cd content, revealing the mechanism underlying the compartmentalized storage of Cd in the roots. KEGG enrichment analysis of DEGs showed that the pathways associated with the biosynthesis of flavonoids, lignin, and some terpenoids were significantly enriched in the roots under Cd stress, underscoring the pivotal role of these pathways in Cd detoxification. Our study suggests A. venetum as a potential Cd-contaminated phytoremediation plant and provides insights into the molecular-level mechanisms of root development promotion and accumulation mechanism in response to Cd stress.

Effective mitigation of Cadmium contamination in soil through Sawdust Biochar application

Cadmium (Cd) contamination in soil is a serious environmental concern, and this study examines the effectiveness of sawdust biochar in reducing Cd contamination over three months. The study explores different sawdust biochar application rates and their effects on the amount of extractable Cd in the soil. According to the study, sawdust biochar has a high potential for addressing Cd pollution. Importantly, over the duration of the investigation, extractable Cd concentrations gradually decreased as a result of the use of biochar. In particular, compared to lesser application rates of 2.5% and 1.25%, the highest biochar application rate (5%) resulted in a significant reduction in cumulative leachable Cd content. Additionally, compared to the control group, all biochar-amended soils showed considerably decreased cumulative leachable Cd levels. The leachate study demonstrated the time-dependent efficiency of biochar in lowering Cd concentrations, with Cd concentration declining from 14 mg/L in August 2023 to a meager 0.004 mg/L in October 2023. Diffusion within the porous structure of biochar was determined to be the main process underlying heavy metal adsorption. However, the observed decrease in the effectiveness of heavy metal removal with biochar may be explained by surface oxidation, which creates a greater number of accessible adsorption sites. Furthermore, the soil's capacity to absorb Cd2+ was greatly improved by the raised pH brought on by biochar application, further enhancing Cd removal. The study also showed the importance of pyrolysis temperature on biochar characteristics, with higher temperatures greatly improving Cd adsorption capability. This study's findings highlighted the significant potential of sawdust biochar as a powerful technique for reducing soil Cd pollution. These results highlighted the potential of biochar for Cd remediation and crucial role that pyrolysis temperature plays in determining biochar's characteristics and adsorption capacity.

Eco-friendly management of Meloidogyne incognita in cadmium-contaminated soil by using nematophagous fungus Purpureocillium lavendulum YMF1.683: Efficacy and mechanism

Root-knot nematodes (RKNs) are distributed globally, including in agricultural fields contaminated by heavy metals (HM), and can cause serious crop damages. Having a method that could control RKNs in HM-contaminated soil while limit HM accumulation in crops could provide significant benefits to both farmers and consumers. In this study, we showed that the nematophagous fungus Purpureocillium lavendulum YMF1.683 exhibited a high nematocidal activity against the RKN Meloidogyne incognita and a high tolerance to CdCl2. Comparing to the P. lavendulum YMF1.838 which showed low tolerance to Cd2+, strain YMF1.683 effectively suppressed M. incognita infection and significantly reduced the Cd2+ uptake in tomato root and fruit in soils contaminated by 100 mg/kg Cd2+. Transcriptome analyses and validation of gene expression by RT-PCR revealed that the mechanisms contributed to high Cd-resistance in YMF1.683 mainly included activating autophagy pathway, increasing exosome secretion of Cd2+, and activating antioxidation systems. The exosomal secretory inhibitor GW4869 reduced the tolerance of YMF1.683 to Cd2+, which firstly demonstrated that fungal exosome was involved in HM tolerance. The up-regulation of glutathione synthesis pathway, increasing enzyme activities of both catalase and superoxide dismutase also played important roles in Cd2+ tolerance of YMF1.683. In Cd2+-contaminated soil, YMF1.683 limited Cd2+-uptake in tomato by up-regulating the genes of ABCC family in favor of HM sequestration in plant, and down-regulating the genes of ZIP, HMA, NRAMP, YSL families associated with HM absorption, transport, and uptake in plant. Our results demonstrated that YMF1.683 could be a promising bio-agent in eco-friendly management of M. incognita in Cd2+ contaminated soils.

The effects of titanium dioxide nanoparticles on cadmium bioaccumulation in ramie and its application in remediation of cadmium-contaminated soil

Cadmium (Cd) is a toxic heavy metal contaminant in agricultural soils. Phytoremediation using hyperaccumulator plants is a promising remediation strategy. This study investigated the effects of TiO2 NPs on Cd uptake and accumulation in the hyperaccumulator ramie (Boehmeria nivea L.) grown in Cd-spiked soil. The aim was to evaluate the potential application of TiO2 NPs to enhance the phytoextraction efficiency of ramie for removing Cd from contaminated soils. Ramie was cultivated in soil spiked with 5 mg/kg Cd, with or without 500 mg/kg TiO2 NPs. The results showed TiO2 NPs significantly increased Cd concentrations in roots, stems, and leaves of ramie by 35%, 75%, and 278% respectively, compared to control plants. Cd levels reached 146 mg/kg in roots and 102 mg/kg in leaves with TiO2 NPs. The bioconcentration factor rose from 21.6 to 29.2 and translocation factor from 0.3 to 0.7 with nanoparticles. This indicates TiO2 NPs increased Cd bioavailability in soil and translocation to shoots. The higher Cd accumulation, especially in leaves, demonstrates the potential of TiO2 NPs to improve ramie's phytoextraction capacity. With TiO2 NP treatment, soil Cd levels decreased by an estimated 20–30% after 8 weeks of ramie cultivation, indicating enhanced phytoextraction. This study provides evidence that the application of TiO2 NPs can enhance the efficiency of phytoremediation using hyperaccumulator plants like ramie for remediation of Cd-contaminated soils.

Remediation characteristics and effects of electrokinetic-citric acid system on karst soil contaminated by arsenic and cadmium

The features and method of citric acid's remediation on arsenic and cadmium-contaminated soil under electrification were investigated by modeling arsenic and cadmium-contaminated soil in karst areas. According to the experimental findings, arsenic and cadmium in soil dissolve more effectively at higher citric acid concentrations. After being electrified, it can encourage the citric acid system, which breaks down cadmium and arsenic in soil. In soil, oxidizable and acid extractable arsenic are removed at rates of 89.19 % and 48.97 %, respectively, and oxidizable and acid extractable cadmium are removed at rates of 60.88 % and 87.87 %. Alkaline circumstances are also favorable for the desorption and migration of arsenic in karst environments; high calcium conditions, however, will inhibit the dissolution of arsenic while favoring the dissolution of cadmium. The morphological alterations of heavy metals during the electro-enhanced remediation process were examined using Visual MINTEQ software. The findings demonstrated that throughout the process, cadmium predominately existed in the forms of Cd2+ and Cd-Citrate-, whereas arsenic predominately existed in the forms of H2AsO4- and H3AsO4 in acidic environment and HAsO42- and H2AsO4- in alkaline conditions. In summary, electric citric acid plays a crucial role in removing cadmium and arsenic pollution in karst soil, which is of great significance for the remediation of soil contaminated by cadmium and arsenic compounds in karst environments.

Unraveling the influence of TiO2 nanoparticles on growth, physiological and phytochemical characteristics of Mentha piperita L. in cadmium-contaminated soil

Among the metals contaminants, cadmium (Cd) is one of the most toxic elements in cultivated soils, causing loss of yield and productivity in plants. Recently, nanomaterials have been shown to mitigate the negative consequences of environmental stresses in different plants. However, little is known about foliar application of titanium dioxide nanoparticles (TiO2 NPs) to alleviate Cd stress in medicinal plants, and their dual interactions on essential oil production. The objective of this study was to investigate the effects of foliar-applied TiO2 NPs on growth, Cd uptake, chlorophyll fluorescence, photosynthetic pigments, malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents, total phenols, anthocyanins, flavonoids, antioxidant enzymes (SOD, CAT and POD) activity and essential oil content of Mentha piperita L. (peppermint) under Cd stress. For this purpose, plants were grown in Cd-contaminated (0, 20, 40, and 60 mg L−1) soil, and different concentrations of TiO2 NPs (0, 75, and 150 mg L−1) were foliar sprayed at three times after full establishment until the beginning of flowering. Exposure to TiO2 NPs significantly (P < 0.01) increased shoot dry weight (37.8%) and the number of lateral branches (59.4%) and decreased Cd uptake in plant tissues as compared to the control. Application of TiO2 NPs increased the content of plastid pigments, and the ratio Fv/Fm (13.4%) as compared to the control. Additionally, TiO2 NPs reduced the stress markers, MDA and H2O2 contents and enhanced the activity of the phenylalanine ammonia-lyase (PAL) enzyme (60.5%), total phenols (56.1%), anthocyanins (42.6%), flavonoids (25.5%), and essential oil content (52.3%) in Cd-stressed peppermint compared to the control. The results also demonstrated that foliar spray of TiO2 NPs effectively improved the growth and chlorophyll fluorescence parameters and reduced Cd accumulation in peppermint, which was mainly attributed to the reduction of oxidative burst and enhancement of the enzymatic (SOD, CAT, and POD) antioxidant defense system due to the uptake of NPs. The findings provide insights into the regulatory mechanism of TiO2 NPs on peppermint plants growth, physiology and secondary metabolites production in Cd-contaminated soil.

Exploring the remediation potential of Hydrangea macrophylla (Thunb.) Ser. in cadmium-contaminated soil by comparing cultivars and seedling age

The current situation regarding soil cadmium pollution in China is far from optimistic, necessitating the exploration of more viable Cd pollution-remediating plants. Several studies have shown that ornamental plants have excellent potential for application in soil pollution remediation. However, research on the Cd tolerance capacity of Hydrangea remains scarce, and the effects of plant age on heavy metal tolerance has not been thoroughly investigated. In this study, greenhouse pot experiments were conducted with artificially prepared Cd-polluted soil at various concentrations (0–240 mg·kg−1). Two cultivars of H.macrophylla, “Endless Summer” (H.'ES') and “Classic Rood” (H.'CR'), were cultivated in different Cd-contaminated soil levels for 60 d, after which the growth response, physiological changes, mineral element absorption, and Cd concentration of different plant parts were measured. The effect of plant age on the heavy metal absorption capacity of H. macrophylla was also explored. The results showed that under Cd stress, the antioxidant activity and penetration-regulating substance content of H. macrophylla increased, and the absorption of Mg, Mn, and Zn changed. Under all Cd treatments, Cd concentrations in the roots were higher than those in the shoots of the cultivars, with a bioconcentration factor of > 1 and a translocation factor of < 1. The tolerance to Cd of the H.'CR' was stronger than that of the H.'ES'. The Cd tolerance of H. macrophylla increased with seedling age. This study indicated that H. macrophylla is a suitable candidate for Cd phytostabilization and the remediation of Cd-polluted soils to limit harm caused by Cd flow in the ecosystem.

Contrasting response of rice rhizosphere microbiomes to in situ cadmium-contaminated soil remediation

Contrasting response of rice rhizosphere microbiomes to in situ cadmium-contaminated soil remediation

Effect of the Substrate and Inoculation of Phosphate-Dissolving Bacterial and Fungal with Humic Acids in the Activity of the Alkaline Phosphatase Enzyme in Cadmium-Contaminated Soil

A laboratory experiment was carried out in the laboratories of the Department of Soil Sciences and Water Resources, College of Agriculture, University of Basrah, to identify the role of the bacteria Bacillus subtilis and the fungus Aspergillus niger, with humic acids extracted from fermented cow dung, the effectiveness of the alkaline phosphatase enzyme in soil contaminated with cadmium and compare it with uncontaminated soil. The soil was treated with a cadmium sulfate solution up to the critical limit (3 mg Cd L-1) and humic and fulvic acid were added at a level of 50 L ha-1 separately, leaving the treatment without addition for control. Then the soil was inoculated with bacterial B. subtilis and fungal A. niger isolates individually and with a mixture of isolates, leaving a treatment without inoculation for control, the treatments were incubated at a temperature of 28±2 °C. Different levels of substrate concentration were used (0.010, 0.025, 0.050, 0.075, and 0.100 M). The results showed that cadmium contamination decreased alkaline phosphatase enzyme activity by 12.28%. There was also an increase in the activity of the alkaline phosphatase enzyme at all inoculation treatments compared to the control treatment, with the bio-mixture treatment being superior to the rest of the treatments, reaching 436.944 µg P. nitrophenol gm-1 soil 1 hour-1 in uncontaminated soil and 402.558 µg P. nitrophenol gm-1 soil 1 hour-1 in cadmium contaminated soil. The humic acid treatment showed a similar increase in the activity of the alkaline phosphatase enzyme compared to the control treatment the highest increase was in the fulvic acid treatment. As for the effect of the substrate, the concentration of 0.075 M recorded the highest increase in alkaline phosphatase enzyme activity in unpolluted and cadmium-polluted soil for all treatments.