Cd-polluted Soil Research Articles

Synergistic promotion mechanism and structure-function relationship of nonmetallic atoms doped carbon nanodots driving Tagetes patula L. to remediate cadmium-contaminated soils

Phytoremediation is an economical and effective strategy to remove cadmium (Cd) from polluted environments. To improve its efficiency, nanotechnology has been proposed to collaborate with hyperaccumulators in the remediation of Cd-polluted soils. However, the intricate structure-function relationship and the underlying regulatory mechanisms by which nanomaterials regulate Cd migration and conversion within the soil-plant system remained unrevealed. In this study, functional carbon nanodots (FCNs) were modified by doping with nitrogen and (or) sulfur elements. The synthesized nonmetallic atoms-doped FCNs were utilized to investigate their structure-function relationship and the regulatory mechanisms underlying their role in the phytoremediation of Cd-polluted soils by Tagetes patula L. FCNs-based nanomaterials can regulate the migration and bioaccumulation of Cd in the soil-plant system, which exhibits an obvious structural dependency. Specifically, the synergistic application of sulfur doped FCNs and Tagetes patula L. had the highest Cd removal efficiency of 53.2%, which was 20.1% higher than Tagetes patula L. alone. The uptake and migration of Cd in the soil-plant system are regulated by FCNs-based nanomaterials through both direct and indirect mechanisms, involving interfacial reactions, plant physiology regulation and environmental influence. This study not only sheds light on the fate of FCNs-based nanomaterials and Cd in the soil-plant system, but also provides innovative nanotools for reinforcing phytoremediation efficiency in contaminated soils.

Differential effects of pH on cadmium accumulation in Artemisia argyi growing in low and moderately cadmium-contaminated paddy soils

BackgroundPhytoremediation is affected by physical and chemical properties of the soil such as soil pH, moisture, and nutrient content. Soil pH is a key element influencing Cd bioavailability and can be easily adjusted in agricultural practices. The soil pH level may relate to the effectiveness of phytoremediation; however, this has not been extensively investigated. In the current study, we evaluated the effect of Cd contamination level (0.56 and 0.92 mg/kg) and soil pH (5, 6, and 7) on Cd accumulation and allocation in Artemisia argyi, a fast-growing perennial crop.ResultsOur results indicated that higher soil Cd concentrations reduce A. argyi biomass, and the loss of the root mass was particularly significant. Higher soil pH decreased Cd content in stems and roots of A. argyi cultivated in moderately Cd-polluted soil, and increased Cd content in stems and roots of the plant grown in low Cd-polluted soil. Higher soil pH decreased the percentage of Cd distributed in the soluble fraction and cell walls and increased the percentage of Cd in the organelles of leaf cells for moderate soil Cd levels. The bioconcentration and translocation factor exceeded 4.0 and 1.0, respectively, across all tested treatments, indicating that A. argyi is a promising candidate for phytoremediation. Notably, the effects of soil pH on Cd accumulation and subcellular distribution in A. argyi differed between low and moderately Cd-contaminated soils.ConclusionAdjustments to soil pH based on the degree of Cd contamination can enhance Cd extraction by A. argyi, thereby reducing the overall remediation cycle of cadmium-polluted paddy fields of South China.Graphical

Ecotoxicological impacts of cadmium on soil microorganisms and earthworms Eisenia foetida: from gene regulation to physiological processes

Cadmium is a hazardous heavy metal that is commonly found in the soil and poses significant risks to soil organisms. The toxic effects of Cd on soil microorganisms and earthworms (Eisenia foetida) have been extensively studied, but most studies focused on high Cd pollution levels. Therefore, this study aims to investigate the different responses of soil organisms to moderate and low levels of Cd contamination. According to the study, the presence of 2.5 mg/kg of Cd had a significant impact on the microbial community’s composition and diversity. The relative abundance of most microbes decreased, while the abundance of Firmicutes and Actinobacteriota showed a considerable increase. The LEFSE analysis revealed that the Bacillus genus of the Firmicutes phylum can serve as a biomarker in soil contaminated with 2.5 mg/kg of Cd. At the same time, the functional analysis of PICRUSt 2 shows that microorganisms found in polluted soil have a noticeable decrease in their ability to metabolize lipids. On the other hand, our findings indicate that Cd has a detrimental effect on the biomass of earthworms and induces oxidative stress in these animals. The activation of superoxide dismutase (SOD) and catalase (CAT) enzymes in earthworms was carried out to mitigate oxidative stress. The study found a strong positive relationship between SOD and both time and Cd pollution. However, CAT exhibited inhibition throughout the later stages of the experiment, particularly when exposed to relatively higher levels of pollution. The analysis of RNA in earthworms revealed that soil Cd pollution at a concentration of 2.5 mg/kg primarily impacts the cellular structure and function of earthworms. This pollution disrupts the integrity of the cytoskeleton structure, hampers DNA replication, and compromises the precision of cell signaling. Simultaneously, when compared to the control group, several metabolic pathways exhibited abnormalities.

Regulating facility soil microbial community and reducing cadmium enrichment in lettuce by reductive soil disinfestation

The accumulation of cadmium (Cd) in facility soil is attracting increasing attention. Reductive soil disinfestation (RSD) is an effective soil disinfection method, while also having a certain passivating effect on Cd. The application of organic matter is crucial for the success of RSD, but the reduction efficiencies of different organic materials vary. Here, five treatments, namely untreated soil (CK), bean dregs (BD), peanut dregs (PD), sesame dregs (SD), and apple dregs (AD) were applied, and their performances in Cd immobilization in Cd-contaminated soil were assessed. Changes in soil properties and microbial communities were monitored. The results showed that the overall soil pH following RSD treatment decreased significantly, while organic matter, hydrolyzed nitrogen, available phosphorus, available potassium, exchangeable calcium, and exchangeable magnesium increased significantly. Compared to CK, the exchangeable (EX)-Cd contents after treatments SD and AD significantly decreased by 25.4% and 23.7%, respectively. RSD led to significant changes in the composition of soil microbial communities. SD treatment significantly increased the number of soil fungal operational taxonomic units (OTU), while BD, PD, and SD significantly increased the relative abundances of Bacteroidetes, Chloroflexi, Deinococus Thermus, and Basidiomycota in bacterial communities. The Gemmatimonadetes phylum showed a highly significant negative correlation with EX-Cd, indicating that it might have a positive effect on the fixation of Cd in polluted soil. SD significantly reduced the Cd content in the above-ground parts of lettuce by 74.76%, and had the least impact on lettuce biomass. It can be inferred that RSD is an ecologically effective method for the remediation of Cd pollution in facility soil by improving soil characteristics and altering microbial community composition to reduce Cd activity. However, further in-depth research is needed to optimize the types and amounts of organic materials applied.

The Combination of Biochar and Phosphorus-Containing Materials Can Effectively Enhance the Remediation Capacity of Amaranth on Cadmium-Contaminated Soil and Improve the Structure of Microbial Communities

Cadmium (Cd) pollution in soil has become a huge problem for agricultural production in China and even the world. Passivation and phytoremediation are two important remediation technologies for Cd pollution. In this study, the cadmium-contaminated and phosphorus-poor farmland soil around a mining area in Huainan was taken as the research object, and the remediation effect of biochar and phosphorus-containing materials on soil cadmium pollution was discussed. The results showed that the combined application of biochar and phosphorus-containing materials significantly reduced the pH of non-rhizosphere soil and rhizosphere soil, and increased the content of soil dissolved organic carbon (DOC). The combined application of biochar and phosphorus-containing materials significantly reduced soil pore water Cd and soil available Cd. In addition, both a single application of biochar and synergistic application of biochar and phosphorus-containing materials significantly increased the biomass of aboveground and underground parts of amaranth and soil urease and catalase activities. Phosphorus application reduced the bioavailability of Cd in soil. With the increase in phosphorus application, the content of available Cd in soil decreased significantly, and there was a certain negative correlation between Cd content and phosphorus content in plants. The abundance of beneficial microorganisms such as Ochrobactrum, Anaerolinea, Achromobacter, and Cellvibrio in soil was significantly increased after the synergistic application of biochar and phosphorus-containing materials.

Combining SiO2 NPs with biochar: a novel composite for enhanced cadmium removal from wastewater and alleviation of soil cadmium stress.

Cadmium (Cd) pollution in water and soil seriously threatens human health. Biochar and nanomaterials have high potential for solving the cadmium pollution problem due to their abundant pores and high specific surface area. Here, the preparation of the composite material SiO2NPs@BC (SBC) using SiO2 NPs (SN) and silkworm excrement biochar (BC) is described, along with its application in the remediation of cadmium-contaminated water and soil. Characterization experiments (SEM&EDS, BET, FTIR, XRD, and XPS) demonstrated that SiO2NPs@BC has a high specific surface area (46.5767m2/g), a well-developed pore structure (0.608375cm3/g), and abundant surface functional groups (Si-C, Si-O, Si-O-Si), providing active sites for the adsorption of Cd. Batch adsorption experiments in water showed that the adsorption capacity of SBC is higher than that of biochar (BC) and SN, with a maximum Langmuir adsorption capacity of 141.99mg/g. After five adsorption cycles, the removal rate of SBC was 73.04%, significantly higher than the 64.97% obtained for BC. The application of SBC not only improved the soil physicochemical properties by increasing the soil pH, the cation exchange capacity, and the soil organic matter content but also by reducing the amount of DTPA-Cd (24.6%) and the plant bioconcentration factor (28.28%) in the soil, converting Cd into more stable fractions (Red-Cd, Ox-Cd). Based on the results, SBC can effectively reduce Cd pollution.

Phosphate Fertilizers’ Dual Role in Cadmium-Polluted Acidic Agricultural Soils: Dosage Dependency and Passivation Potential

Cadmium (Cd) contamination in agricultural soils is a common issue, posing health risks as it enters the human body through the food chain. Commonly used phosphate fertilizers (PFs) not only provide essential phosphorus (P) nutrients to crops but also serve as P-containing materials for immobilizing heavy metals (HMs) like Cd in soils. Therefore, understanding the passivation effects of PFs on soil Cd and their potential influencing factors is crucial for mitigating soil Cd pollution. In this study, the impact of multi-crop applications (75 mg P kg−1, 150 mg P kg−1) of four kinds of PFs on reducing soil Cd toxicity and decreasing Cd accumulation in spinach was investigated. The results indicated that under the low application rate (75.0 mg P kg−1), all PFs could passivate Cd, and CMP demonstrated the most effective passivation of Cd. However, under the high application rate (150 mg P kg−1), the immobilization effect diminished or even activated Cd. Among the different types of PFs, CMP application alleviated soil acidification and significantly reduced soil-available Cd, showing the best performance in promoting spinach growth and Cd inhibition. These results suggest that PF application in Cd-contaminated soils affects spinach growth and Cd accumulation, with soil pH, available phosphorus (AP), and Cd dynamics being crucial; moreover, low-P, micronutrient-rich, alkaline PFs like CMP optimize spinach yields and minimize Cd uptake, and excessive application of soluble PFs decreases pH, increases Cd mobility, and poses health risks, suggesting a need for balanced fertilizer use.

Endogenous silicon-activated rice husk biochar prepared for the remediation of cadmium-contaminated soils: Performance and mechanism

Biochar is widely used for the remediation of heavy metal-contaminated soils. However, pristine biochar generally has limited active functional groups and adsorption sites, thereby exhibiting low immobilization performance for heavy metals. In addition to carbon (C), silicon (Si) is another common macro-element present in rice husk biochar, but it often exists in the form of amorphous oxide and therefore contributes little to the adsorption performance for heavy metals. The transformation of amorphous Si oxide to dissolved silicate through a precipitation effect can significantly improve its heavy metal immobilization capability. Herein, the amorphous Si oxide in rice husk biochar was activated by sodium hydroxide and then the dissolved silicate was immobilized by calcium salt. The as-synthetized Si-activated biochar was used to remediate cadmium (Cd)-contaminated soils. The results indicated that Si-activated rice husk biochar could reduce Cd migration and environmental risks by the transformation from exchangeable Cd into carbonate-bound and residual Cd. With increasing Ca: Si molar ratio, the content of CaCl2 and H2O-extractable Cd exhibited a decreasing trend. Moreover, a higher addition amount of Si-activated biochar improved the Cd immobilization efficiency. The application of 1.0% Ca/Si molar ratio of 2: 2 Si-activated rice husk biochar decreased the CaCl2-Cd and H2O-Cd concentration by a maximum of 83.7% and 90.5% compared with pristine rice husk biochar, respectively. The present work proposes an approach for highly efficient remediation of Cd-polluted soils by biochar.

Stable isotopic evidence of cadmium enrichment in soils of black shale distribution areas

Black shale-derived soils exhibit significant heavy metal enrichment, notably cadmium (Cd) enrichment. This study pioneered the reporting of δ114/110Cd isotopic values within a black shale-soil system, offering novel insights into the geochemical behaviors and enrichment mechanisms of Cd during soil formation processes influenced by weathering. Systematic rock‒soil sampling was conducted on the lower Cambrian Hetang Formation in western Zhejiang, China, which is characterized by Cd-rich black shale. Employing analytical methods, including principal component analysis and multiple linear regression, we investigated the factors influencing heavy metal content in soil, such as element dissolution during weathering, soil pH, and the presence of iron-manganese oxides, sulfides, organic matter, and clay minerals. Our findings revealed a compositional range of δ114/110Cd in black shale (1.93‰–3.31‰) contrasting with that in adjacent soils (0.31‰–1.82‰), illustrating significant Cd isotopic fractionation during weathering, where heavier Cd isotopes are preferentially leached, and lighter isotopes are enriched in the soil in association with iron-manganese oxides. This research not only deepens the understanding of Cd enrichment mechanisms within the rock‒soil system against a black shale geological background but also elucidates the formation processes of soil Cd pollution in areas with a high geochemical background.

Neglected pathways of heavy metal input into agricultural soil: Water–land migration of heavy metals due to flooding events

Flooding, carrying sediments, inundates farmlands across the world due to extreme adverse weather conditions. The casualties and property damage associated with flooding are important direct impacts. However, there is currently insufficient understanding of the remobilization and distribution of heavy metals (HMs) caused by flooding. Few studies have specifically considered flooding as a pathway for HMs contamination of soil. Herein, a novel methodological framework for revealing the input pathways of HMs in agricultural soils in mining-intensive areas is proposed and applied. Flooding is considered one of the pathways for HMs inputs during source apportionment. The results demonstrated a high degree of overlap between the distribution characteristics of major HMs in agricultural soils and sediments. The degree of soil Cd pollution was significantly positively correlated with the inundation depth in the flooded area. It took 8.4–11.5 times of flood inundation or 98.5–119.9 years of accumulation of atmospheric deposition to reach HMs contamination levels in the soil of the study area. Flooding brought in most of the soil Cd, while atmospheric deposition was the primary input pathway for soil Pb and Zn. Our results identified the role of flood inundation on the input of HMs in mining-intensive areas. These results demonstrated the value of our framework for studying the impact of flooding on HMs in agricultural soils from the perspective of input pathways, providing new insights not only into identifying the sources of soil HMs but also into enhancing understanding of the impact of flooding on soil environments. With the potential increase in the frequency and intensity of flooding inundating farmlands in the future, it is essential to consider flooding as a pathway for HMs inputs in order to comprehensively assess their environmental impact.

Zinc oxide nanoparticles reduce cadmium accumulation in hydroponic lettuce (Lactuca sativa L.) by increasing photosynthetic capacity and regulating phenylpropane metabolism

Due to the continuous production of industrial wastes and the excessive use of chemical fertilizers and pesticides, severe cadmium (Cd) pollution in soil has occurred globally. This study investigated the impacts of incorporating zinc oxide nanoparticles (ZnONPs) into hydroponically grown lettuce (Lactuca sativa) under cadmium stress conditions, to seek effective methods to minimize Cd buildup in green leafy vegetables. The results showed that 1 mg/L of Cd significantly inhibited lettuce growth, decreasing in leaves (29 %) and roots (33 %) biomass. However, when lettuce was exposed to 2.5 mg/L ZnONPs under cadmium stress, the growth, chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), actual photochemical efficiency of PSII (φPSII), and activity of key enzymes in photosynthesis were all significantly enhanced. Furthermore, ZnONPs significantly decreased the accumulation of Cd in lettuce leaves (36 %) and roots (13 %). They altered the subcellular distribution and chemical morphology of Cd in lettuce by modifying the composition of cell walls (such as pectin content) and the levels of phenolic compounds, resulting in a reduction of 27 % in Cd translocation from roots to leaves. RNA sequencing yielded 45.9 × 107 and 53.4 × 107 clean reads from plant leaves and roots in control (T0), Cd (T1), Cd+ZnONPs (T2), and ZnONPs (T3) treatment groups respectively, and 3614 and 1873 differentially expressed genes (DEGs) were identified. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis identified photosynthesis, carbon fixation, and phenylpropanoid metabolism as the main causes of ZnONPs-mediated alleviation of Cd stress in lettuce. Specifically, the DEGs identified included 12 associated with photosystem I, 13 with photosystem II and 23 DEGs with the carbon fixation pathway of photosynthesis. Additionally, DEGs related to phenylalanine ammonia-lyase, caffeoyl CoA 3-O-methyltransferase, peroxidase, 4-coumarate-CoA ligase, hydroxycinnamoyl transferase, and cytochrome P450 proteins were also identified. Therefore, further research is recommended to elucidate the molecular mechanisms by which ZnONPs reduce Cd absorption in lettuce through phenolic acid components in the phenylpropanoid metabolism pathway. Overall, treatments with ZnONPs are recommended to effectively reduce Cd accumulation in the edible portion of lettuce.

Aged polylactic acid microplastics with ultraviolet irradiation alleviated the toxic effect of Cd on pakchoi (Brassica chinensis L.) in hydroponics

Biodegradable microplastics (BMPs) and cadmium (Cd) present substantial risks to agricultural systems, primarily affecting plants. Most current studies have focused on the ecological effects of virgin BMPs. However, the effects of ultraviolet (UV)-aged BMPs and their interactions with cadmium (Cd) on pakchoi remain largely unknown. Therefore, this study addressed this gap by aging polylactic acid (PLA) microplastics (MPs) through UV irradiation and conducting an indoor hydroponic experiment. The research systematically examined the individual and combined impacts of Cd, virgin, and UV-aged BMPs on pakchoi (Brassica chinensis L.), focusing on plant growth, photosynthesis, antioxidant systems, and Cd accumulation. The results showed that after 21 days of UV irradiation (UPLA MPs), UPLA MPs with a fractured surface had a more significant impact on pakchoi than untreated PLA MPs. Cd alone inhibited pakchoi growth, development, and photosynthesis, while PLA/UPLA MPs alone promoted these processes. Under the combination of Cd and PLA/UPLA MPs, UPLA MPs could effectively alleviate the toxic effect of Cd on pakchoi. Besides, Cd coexisted with PLA/UPLA MPs, and with the increase of Cd concentration, UPLA MPs(41.22 %, 66.80 %, 45.57 %) decreased the Cd content of pakchoi more significantly than PLA MPs(37.87 %, 55.91 %, 26.35 %). Meanwhile, the results of Partial least squares structural equation models (PLS-SEM) further showed that UPLA MPs could effectively reduce the accumulation of Cd in plants. Therefore, the results of this study can provide a new perspective and reference for the ecological risk evaluation of Cd and BMPs pollution in agricultural soils.

Transcriptome analysis of potassium-mediated cadmium accumulation in sweet sorghum

Cadmium (Cd) pollution in the soil is a serious environmental issue worldwide. Phytoextraction of Cd-polluted soil is a cost-effective, sustainable and environmentally-friendly strategy. Agricultural fertilizer management is beneficial for promoting the Cd phytoremediation efficiency. Potassium (K) is the nutrient required in the largest amount cation by plants. Sweet sorghum exhibits a substantial phytoremediation potential of Cd-polluted soil. Clarifying the mechanism of K-mediated Cd accumulation in sweet sorghum is imperative. Sweet sorghum plants were grown hydroponically with an extra K supply in the presence or absence of Cd treatment. An extra K application significantly increased plant growth under non-Cd addition, while K lost the profitable effect under Cd stress. K supplementation remarkably enhanced Cd concentrations and Cd accumulation in shoots and roots of sweet sorghum. Transcriptome analysis demonstrated that zinc ion transport, cysteine and methionine metabolism, flavonoid biosynthesis and phenylpropanoid biosynthesis pathways might contribute to the increased Cd accumulation as affected by an extra K supply. Furthermore, SbZIP9, SbSTP8, SbYS1, SbMAG and SbFOMT-like were targeted as they closely correlated with both plant growth and Cd stress in sweet sorghum. SbFOMT-like showed an independent pathway, while SbZIP9, SbSTP8, SbYS1 and SbMAG displayed positive correlations mutually. Notably, SbZIP9 and SbFOMT-like were highly expressed when compared with other target genes. Taken together, SbZIP9 and SbFOMT-like were upregulated and downregulated by an extra K supply under Cd stress, suggesting that SbZIP9 and SbFOMT-like enhances and declines Cd accumulation as regulated by K addition in sweet sorghum respectively.

Exploring phytoremediation potential of willow NJU513 for cadmium-contaminated soil with and without epibrassinolide treatment

There has been a growing concern over soil cadmium (Cd) pollution, underscoring the importance of finding effective remediation strategies. Willow trees have emerged as promising candidates for phytoremediation of Cd-contaminated soils. Nevertheless, the specific potential of a novel willow genotype, NJU513, in remediating Cd-polluted soil remains unexplored. Hence, the primary objectives of this study were twofold: firstly, to ascertain the suitability of the willow genotype NJU513 for remediating Cd-contaminated soil; and secondly, to elevate its remediation efficciency with the application of epibrassinolide (Brs). In the pot-culture experiment without Brs, its leaf and stem Cd concentrations were 203 mg kg−1 and 65.1 mg kg−1, with a bioaccumulation factor (BCF) of 20.8 and 6.68, respectively. In the pot-culture experiment with Brs, the corresponding Cd concentrations were 226 mg kg−1 and 59.2 mg kg−1, with a BCF of 23.1 and 6.06, respectively. In addition, the extracted Cd contents were higher in the Brs treatments (1.11–1.37 mg plant−1) than in the no-Brs treatments (0.78–0.96 mg plant−1) because Brs increased the plant biomass and leaf BCF. The mechanism underlying the Cd accumulation of NJU513 leaves with and without Brs was revealed by a transcriptome analysis. The expression levels of genes related to metal ion binding, channel activity, and transporters in leaves were up-regulated, which contributed to the high Cd accumulation and stress tolerance. Analyses of soil metabolites and bacteria in the presence and absence of Brs spraying on willow leaves indicated that soil organic compounds with carboxyl and amino groups may induce Cd activation and passivation, respectively. This study provides valuable insights for developing woody plant varieties that can be used for remediating Cd-contaminated soil.

Vermicompost application enhances soil health and plant physiological and antioxidant defense to conferring heavy metals tolerance in fragrant rice

Cadmium (Cd) contamination in agricultural soils and its accumulation in plant organs have become a global issue due to its harmful effects on human health. The in-situ stabilizing technique, which involves using organic amendments, is commonly employed for removing Cd from agricultural soils. Thus, the current study investigated the effect of vermicompost (VC) on soil properties and plant physio-biochemical attributes, leaf ultrastructure analysis, antioxidant defense mechanisms, and grain yields of two different fragrant rice cultivars, Xiangyaxiangzhan (XGZ) and Meixiangzhan-2 (MXZ-2), under Cd-stress conditions. The results showed that Cd toxicity deteriorates soil quality, the plant’s photosynthetic apparatus, and the plant’s antioxidant defense mechanism. Moreover, under Cd stress, both cultivars produced significantly lower (p < 0.05) rice grain yields compared to non-Cd stress conditions. However, the VC application alleviated the Cd toxicity and improved soil qualitative traits, such as soil organic carbon, available nitrogen, total nitrogen, phosphorus, and potassium. Similarly, VC amendments improved leaf physiological activity, photosynthetic apparatus function, antioxidant enzyme activities and its related gene expression under Cd stress These enhancements led to increased grain yields of both fragrant under Cd toxicity. The addition of VC mitigated the adverse effects of Cd on the leaf chloroplast structure by reducing Cd uptake and accumulation in tissues. This helped prevent Cd-induced peroxidation damage to leaf membrane lipids by increasing the activities of antioxidant enzymes such as ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). On average across the growth stages, the Pos-Cd + VC3 treatment increased SOD, APX, CAT, and POD activities by122.2 and 112.5%, 118.6, and 120.6%, 44.6 and 40.6%, and 38.6 and 33.2% in MXZ-2 and XGZ, respectively, compared to the plants treated with Pos-Cd treated alone. Enhancements in leaf physiological activity and plant antioxidant enzyme activity strengthen the plant’s antioxidant defense mechanism against Cd toxicity. In addition, correlation analysis showed a strong relationship between the leaf net photosynthetic rate and soil chemical attributes, suggesting that improved soil fertility enhances leaf physiological activity and boosts rice grain yields. Of the treatments, Pos-Cd + VC3 proved to be the most effective treatment in terms of enhancing soil health and achieving high fragrant rice yields. Thus, the outcomes of this study show that the addition of VC in Cd-contaminated soils could be useful for sustainable rice production and safe utilization of Cd-polluted soil.

Influence of Foliar Zinc Application on Cadmium and Zinc Bioaccessibility in Brassica chinensis L.: In Vitro Digestion and Chemical Sequential Extraction.

Foliar zinc (Zn) application can affect the accumulation and bioaccessibility of cadmium (Cd) and Zn in crops. However, the mechanisms by which foliar Zn application influences Cd and Zn bioaccessibility remain elusive. This study examined the effects of spraying ZnSO4 and ZnNa2EDTA on bioaccessibility and chemical forms of Cd and Zn in pakchoi (Brassica chinensis L.) shoots and evaluated human health risks via pakchoi consumption. Spraying ZnSO4 reduced the concentrations of ethanol-extractable (Fethanol) and deionized water-extractable (Fd-H2O) Cd, as well as the corresponding bioaccessible Cd concentrations (20.3-66.4%) and attendant health risks of Cd, whereas spraying high-dose ZnNa2EDTA significantly increased the concentrations of both Cd forms and bioaccessible Cd. Spraying ZnSO4 and high-dose ZnNa2EDTA significantly increased the concentrations of Zn in Fethanol and Fd-H2O and the corresponding bioaccessible Zn concentrations (0.8-8.3-fold). Fethanol and Fd-H2O were the primary sources of bioaccessible Cd and Zn, contributing more than 59% of the bioaccessible Cd and Zn. These results indicate that foliar Zn application can affect Cd and Zn bioaccessibility in pakchoi mainly by modulating Cd and Zn in Fethanol and Fd-H2O. These findings provide scientific support for the development of more efficient measures to produce safe and high-quality leafy vegetables from Cd-polluted soils.

Exogenously applied nano-zinc oxide mitigates cadmium stress in Zea mays L. through modulation of physiochemical activities and nutrients homeostasis

The increasing levels of cadmium (Cd) pollution in agricultural soil reduces plant growth and yield. This study aims to determine the impact of green synthesized zinc oxide nanoparticles (ZnO-NPs) on the physiochemical activities, nutrition, growth, and yield of Zea mays L. under Cd stress conditions. For this purpose, ZnO-NPs (450 ppm and 600 ppm) synthesized from Syzygium aromaticum were applied through foliar spray to Z. mays and also used as seed priming agents. A significant decline in plant height (35.24%), biomass production (43.86%), mineral content, gas exchange attributes, and yield (37.62%) was observed in Cd-spiked plants compared to the control. While, 450 ppm ZnO-NPs primed seed increased plant height (18.46%), total chlorophyll (80.07%), improved ascorbic acid (25.10%), DPPH activity (26.66%), and soil mineral uptake (Mg+2 (38.86%), K+ (27.83%), and Zn+2 (43.68%) as compared to plants only spiked with Cd. On the contrary, the foliar-applied 450 ppm ZnO-NPs increased plant height (8.22%), total chlorophyll content (73.59%), ascorbic acid (21.39%), and DPPH activity (17.61%) and yield parameters; cob diameter (19.45%), and kernels numbers 6.35% enhanced compared to plants that were spiked only with Cd. The findings of the current study pave the way for safer and more cost-effective crop production in Cd-stressed soils by using green synthesized NPs and provide deep insights into the underlying mechanisms of NPs treatment at the molecular level to provide compelling evidence for the use of NPs in improving plant growth and yield.

The spatial distribution and source of heavy metals in soil-plant-atmosphere system in a large coal mining area

Due to the lack coupling analysis of heavy metals in soil-plant-atmosphere system, the migration and transformation of heavy metals remains unclear. In this study, 240 surface (0–20 cm) soil samples, 365 plant samples and 168 atmospheric dust samples were collected in a large coal mining area, in which selected heavy metals arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), plumbum (Pb), zinc (Zn) were analyzed, to elucidate the spatial distribution and source of heavy metals and their bioavailability. According to the results of ArcGIS mapping analysis, the distribution patterns of Cd, Cu, Pb, and Zn in the three media are similar, while the distribution characteristics of Cr and Ni are highly consistent. The factors contributing to these spatial distribution characteristics of heavy metals could be associated with human activities and the characteristics of the elements. Compared with the background value, Zn, Cr, Pb in soil, Zn, Cr, Cu in plants and Zn, Pb, Cu in atmospheric dust apparently accumulated. The geological accumulation pollution index (Igeo) shows that there exist mild to moderate levels of Cr and Cd pollution in soil, and mild to moderate levels of Cd, Cr, Pb, and Zn pollution in the air. The evaluation of potential risks of heavy metals showed moderate ecological hazards in soil and strong ecological hazards in atmospheric dust. The sources of heavy metals were assessed using principal component analysis (PCA), land use type, and spatial analysis. Anthropogenic factors are the main sources of heavy metal content. Coal-related industrial processes related to coal, sewage irrigation, the use of agricultural chemicals, and vehicle emissions may be anthropogenic sources of heavy metals.

Machine learning-based prediction of cadmium pollution in topsoil and identification of critical driving factors in a mining area.

Mining activities have resulted in a substantial accumulation of cadmium (Cd) in agricultural soils, particularly in southern China. Long-term Cd exposure can cause plant growth inhibition and various diseases. Rapid identification of the extent of soil Cd pollution and its driving factors are essential for soil management and risk assessment. However, traditional geostatistical methods are difficult to simulate the complex nonlinear relationships between soil Cd and potential features. In this study, sequential extraction and hotspot analyses indicated that Cd accumulation increased significantly near mining sites and exhibited high mobility. The concentration of Cd was estimated using three machine learning models based on 3169 topsoil samples, seven quantitative variables (soil pH, Fe, Ca, Mn, TOC, Al/Si and ba value) and three quantitative variables (soil parent rock, terrain and soil type). The random forest model achieved marginally better performance than the other models, with an R2 of 0.78. Importance analysis revealed that soil pH and Ca and Mn contents were the most significant factors affecting Cd accumulation and migration. Conversely, due to the essence of controlling Cd migration being soil property, soil type, terrain, and soil parent materials had little impact on the spatial distribution of soil Cd under the influence of mining activities. Our results provide a better understanding of the geochemical behavior of soil Cd in mining areas, which could be helpful for environmental management departments in controlling the diffusion of Cd pollution and capturing key targets for soil remediation.

Defense of cabbages against herbivore cutworm Spodoptera litura under Cd stress and insect herbivory stress simultaneously

Biotic (e.g., heavy metal) and abiotic stress (e.g., insect attack) can affect plant chemical defense, but little is known about the changes in plant defense when they occur concurrently. Herein, the impacts of heavy metal cadmium (Cd) stress and insect herbivory stress on the direct and indirect defense of two cultivar cabbages of Brassica campestris, the low-Cd cultivar Lvbao701 and the high-Cd cultivar Chicaixin No.4, against the herbivore cutworm Spodoptera litura were investigated. Although 10 mg kg−1 Cd stress alone inhibited leaf secondary metabolites (total phenolics, flavonoids), it reduced the feeding rate and odor selection of S. litura towards both cultivar cabbages, especially for Lvbao701, by increasing leaf Cd content and repellent volatile organic compounds (VOCs) (6-methyl-5-hepten-2-one, 7,9-di-tert-butyl-1-oxaspiro (4,5)deca-6,9-diene-2,8-dione), and reducing soluble sugar and attractive VOCs (3-methyl-3-pentanol, 2,5-hexanedione, tetradecanal). Under 2.5 mg kg−1 Cd and herbivory stress, although leaf total phenolics and flavonoids increased significantly, the feeding rate and odor selection of S. litura towards both cultivar cabbages increased, especially for Chicaixin No.4, indicating that the chemical defense of cabbages was depressed. Therefore, Cd stress alone improved the insect resistance of cabbages, whereas herbivory stress weakened the enhanced cabbages defence by Cd stress. The low-Cd cultivar Lvbao701 presented stronger insect resistance than Chicaixin No.4, suggesting that Lvbao701 application in Cd-polluted soil can not only decrease Cd transmission to higher levels in the food chain but also reduce pest occurrence.