Selenium nanomaterials alleviate Brassica chinensis L cadmium stress: Reducing accumulation, regulating microorganisms and activating glutathione metabolism

Stabilization effects and mechanisms of lignin-based hydrogel-coated sulfide nano-zero-valent iron on lead and cadmium contamination in soil

Nano zero-valent iron (nZVI) is extensively employed in soil remediation due to its superior capacity for removing heavy metals, however, issues related to its agglomeration and oxidation hinder its practical application. Therefore, in this study, lignin-based hydrogel-coated nano ferric sulfide (BLS-nZVI@LH) was synthesized and evaluated for its stabilizing effect, underlying mechanism, and influence on the soil microenvironment and health risks. The results indicate that BLS-nZVI@LH significantly mitigated nZVI agglomeration and oxidation, thereby enhancing its reactivity. The formation of FeS on the particle surface provided additional active sites for stabilizing Pb and Cd in the soil. In soil incubation experiments, BLS-nZVI@LH significantly improved the stability of Pb and Cd after 90 days. Compared to sulfide nano-zero-valent iron (S-nZVI) and ball-milled lignin sulfide nano-zero-valent iron (BLS-nZVI), BLS-nZVI@LH increased the soil's residual Cd content by 23.0 % and 31.0 %, respectively, and the oxidizable Pb content by 10.9 % and 20.8 %. Characterization analysis revealed that precipitation, redox reactions, and surface complexation primarily govern Cd stabilization by BLS-nZVI@LH, whereas complexation and reduction predominantly contribute to Pb immobilization. Furthermore, BLS-nZVI@LH improved soil pH and organic carbon content, boosting β-glucosidase and peroxidase activities. It also promoted the richness and diversity of soil microbial communities, particularly enhancing the growth of Sphingomonas, Gemmatimonas, and RB41, thereby improving the soil microenvironment and boosting remediation capacity. In continuous cropping experiments, the addition of 0.5 % and 1 % BLS-nZVI@LH significantly reduced Pb and Cd absorption and accumulation in Chinese broccoli. Notably, 1 % supplementation lowered Pb and Cd levels in edible parts below the national food safety standard (Pb ＜ 0.3, Cd ＜ 0.2 mg·kg-1), thereby effectively mitigating dietary health risks across different populations. This study offers technical insights into the development of highly active modified materials and provides scientific evidence for the application of BLS-nZVI@LH in stabilizing Pb and Cd contamination in soils, improving soil health, and reducing heavy metal accumulation in crops.

Nano-selenium modified green eggshell biochar reduces cadmium accumulation in shallots (Allium schoenoprasum L.)

Green eggshell biochar, a renewable biomass material, demonstrates promising potential for environmental remediation. This study systematically prepared biochar under varying pyrolysis conditions and identified nano-selenium-modified biochar (produced at 600 °C for 3 h, termed 6-3 S) as the optimal formulation for cadmium (Cd) immobilization. Compared to untreated soil, the 6-3 S biochar reduced bioavailable Cd content by 38.65 % in contaminated soil. Correspondingly, Cd accumulation in shallot tissues decreased by 56.64 % (white parts) and 82.69 % (green parts). Furthermore, the 6-3 S treatment enhanced plant selenium levels by 21.3-29.8 % and preserved leaf microstructure integrity, reducing stomatal deformation by 44.2 % compared to controls. Additionally, Nitro Blue Tetrazolium (NBT) staining area decreased from 39.03 % to 24.00 %, indicating reduced oxidative stress. These dual effects-Cd suppression and selenium enrichment-significantly improved shallot quality and safety. The findings establish a scientific foundation for deploying nano-selenium-modified biochar in heavy metal-contaminated agricultural systems.

Synergistic toxicity of DBDPE and Cd in a microcosm agrosystem: Insights into physiological, biochemical, nutrient elements and amino acid metabolic responses

Agricultural soil contamination by flame retardants and heavy metals has become an environmental concern, with decabromodiphenyl ethane (DBDPE) and cadmium (Cd) being frequently detected in e-waste dismantling areas. While previous studies mostly focused on single-organism system or individual toxicity, the combined effects of DBDPE and Cd on agricultural ecosystems remain largely unknown. This study aimed to reveal the joint toxicity mechanisms of DBDPE and Cd by examining physiological responses, amino acid metabolism, nutrient element distribution, and DBDPE degradation pathways in this integrated system. Results demonstrated that co-exposure to DBDPE and Cd intensified toxicity compared to single exposure. In lettuce, DBDPE amplified the inhibitory effects of Cd on plant growth (height and fresh weight of the aerial part decreased by 3.8 % and 5.8 %). Co-exposure inhibited chlorophyll synthesis (particularly carotenoid production, decreased by 53.33 %), disrupted amino acid metabolism, and impaired nutrient elements uptake, ultimately leading to reduced plant growth. In earthworms, co-exposure altered amino acid profiles, disrupted nutrient elements absorption and transport, thereby reducing their antioxidant defense capacity. Both organisms showed limited ability to detoxify DBDPE through similar debromination pathways. This study reveals the synergistic toxicological impacts of DBDPE and Cd in agricultural systems, highlighting the elevated ecological risks of their co-occurrence and emphasizing the need for comprehensive pollution control strategies in contaminated agricultural soils.

Poly-γ-glutamic acid chelates chromium (III) and copper (II), alleviating their toxicity in cucumber and affecting rhizosphere bacterial community assembly

The accumulation of chromium (Cr) and copper (Cu) in soil during industrialization and modernization poses an extreme threat to crops. Poly-γ-glutamic acid (γ-PGA) has the potential to stabilize heavy metals in soil through chelation because of the numerous carboxyl groups in its side chain. The rhizosphere microbiome contributes to plant detoxification by participating in heavy metal passivation. However, it is still unclear whether γ-PGA can alleviate the toxicity of Cr and Cu to plants and whether this effect is associated with changes in the rhizosphere microbiome assembly. Here, we found that γ-PGA application significantly reduced the content of Cr or Cu in cucumber plants by 67.45%-86.77% and 94.67%-98.21, respectively, and alleviated the oxidative stress of Cr or Cu to plants. Moreover, γ-PGA significantly increased the biomass of cucumber fruits in the plot experiment by 13.5% and 25.3% under Cr and Cu stress, respectively. The content of Cr or Cu in the cucumber fruit was below limits of detection, in contrast to the 31.23 mg/kg Cr or 9.86 mg/kg Cu detected in the no-γ-PGA treatment. γ-PGA effectively chelated Cr and Cu in vitro, and less than 30% of their chelates were degraded in 20 weeks, suggesting the strong stability of these chelates. γ-PGA significantly altered the rhizosphere bacterial community composition of cucumber by enriching phyla Gemmatimonadota, Acidobacteriota and Firmicutes, and genera Gemmatimonas and Stenotrophomonas, which potentially involved in reducing the mobility of Cr and Cu in soils. Furthermore, γ-PGA significantly enriched taxa assigned to plant growth-promoting bacteria (PGPB). Together, our results suggest that γ-PGA can reduce the Cr and Cu contents in cucumber, and this process is strongly associated with the chelation capacity of γ-PGA and its effects on rhizosphere microbiome composition. These results highlight the exciting potential to use γ-PGA for the remediation of heavy metal-contaminated soils.

Nanopriming with phytofabricated selenium nanoparticles alleviates arsenite-induced oxidative stress in Spinacia oleracea L

Arsenic (As) contamination of agricultural soil has become a major concern due to its adverse effects on plant growth and human health. Selenium nanoparticles (SeNPs), a novel selenium (Se) source, are characterised by their exceptional biocompatibility, degradability, and bioactivities. In the present study, SeNPs were biogenically synthesised and further characterised using UV-visible spectroscopy, XRD, FTIR, and TEM analysis. Different concentrations of the synthesised SeNPs were used to treat Spinacia oleracea L. (spinach) seeds to determine their impact on growth profile, gas exchange, photosynthetic pigments, oxidative stress, and antioxidant enzyme status upon arsenite (AsIII) treatment. The findings revealed that SeNP supplementation at a concentration of 100 µM (SeNPs100) led to a significant reduction in As accumulation by twofold in roots and 1.5-fold in leaves when compared to plants exposed to AsIII100 (µM) alone. Interestingly, the photosynthetic efficiency was also remarkably enhanced upon SeNPs100 treatment, associated with increased activities of the defence enzymes (ascorbate peroxidase, catalase, and glutathione peroxidase) in the AsIII + SeNP-exposed spinach plants as compared to AsIII treatment alone. Overall, the present study highlights the potential of biogenic SeNP supplementation in promoting plant growth and mitigating As toxicity in spinach under AsIII stress. This study could have significant implications for the use of SeNPs as a nanofertiliser in regions grappling with As-contaminated soils for sustainable agriculture and human health.

The role and transcriptomic mechanism of cell wall in the mutual antagonized effects between selenium nanoparticles and cadmium in wheat

Selenium nanoparticles (SeNPs) has been reported as a beneficial role in alleviating cadmium (Cd) toxicity in plant. However, underlying molecular mechanisms about SeNPs reducing Cd accumulation and alleviating Cd toxicity in wheat are not well understood. A hydroponic culture was performed to evaluate Cd and Se accumulation, cell wall components, oxidative stress and antioxidative system, and transcriptomic response of wheat seedlings after SeNPs addition under Cd stress. Results showed that SeNPs application notably reduced Cd concentration in root and in shoot by 56.9% and 37.3%, respectively. Additionally, SeNPs prompted Cd distribution in root cell wall by 54.7%, and increased lignin, pectin and hemicellulose contents by regulating cell wall biosynthesis and metabolism-related genes. Further, SeNPs alleviated oxidative stress caused by Cd in wheat through signal transduction pathways. We also observed that Cd addition reduced Se accumulation by downregulating the expression level of aquaporin 7. These results indicated that SeNPs alleviated Cd toxicity and reduced Cd accumulation in wheat, which were associated with the synergetic regulation of cell wall biosynthesis pathway, uptake transporters, and antioxidative system via signaling pathways.

Biosynthesized Selenium Nanoparticles as an Effective Tool to Combat Soil Metal Stresses in Rice (Oryza sativa L.)

Nanotechnology has demonstrated significant potential to improve agricultural production and increase crop tolerance to abiotic stress including exposure to heavy metals. The present study investigated the mechanisms by which aloe vera extract gel-biosynthesized (AVGE) selenium nanoparticles (Se NPs) alleviated cadmium (Cd)-induced toxicity to rice (Oryza sativa L.). AVGE Se NPs, chemically synthesized bare Se NPs, and NaSeO3 as an ionic control were applied to Cd-stressed rice seedlings via root exposure in both hydroponic and soil systems. Upon exposure to AVGE Se NPs at 15 mg Se/L, the fresh root biomass was significantly increased by 100.7% and 19.5% as compared to Cd control and conventional bare Se NPs. Transcriptional analyses highlighted that AVGE Se NPs activated stress signaling and defense related pathways, including glutathione metabolism, phenylpropanoid biosynthesis and plant hormone signal transduction. Specifically, exposure to AVGE Se NPs upregulated the expression of genes associated with the gibberellic acid (GA) biosynthesis by and 4.79- and 3.29-fold as compared to the Cd-alone treatment and the untreated control, respectively. Importantly, AVGE Se NPs restored the composition of the endophyte community and recruit of beneficial species under Cd exposure; the relative abundance of Azospirillum was significantly increased in roots, shoots, and the rhizosphere soil by 0.73-, 4.58- and 0.37-fold, respectively, relative to the Cd-alone treatment. Collectively, these findings highlight the significant potential of AVGE Se NPs to enhance plant growth and to minimize the Cd-induced toxicity in rice and provide a promising nanoenabled strategy to enhance food safety upon crop cultivation in contaminated agricultural soils.

Inhibitory effects of Pseudomonas sp. W112 on cadmium accumulation in wheat grains: Reduced the bioavailability in soil and enhanced the interception by plant organs

Microorganisms play an important role in heavy metal bioremediation and soil fertility. The effects of soil inoculation with Pseudomonas sp. W112 on Cd accumulation in wheat were investigated by analyzing the transport, subcellular distribution and speciation of Cd in the soil and plants. Pseudomonas sp. W112 application significantly decreased Cd content in the roots, internode and grains by 10.2%, 29.5% and 33.0%, respectively, and decreased Cd transfer from the basal nodes to internodes by 63.5%. Treatment with strain W112 decreased the inorganic and water-soluble Cd content in the roots and increased the proportion of residual Cd in both the roots and basal nodes. At the subcellular level, the Cd content in the root cell wall and basal node cytosol increased by 19.6% and 61.8%, respectively, indicating that strain W112 improved the ability of the root cell wall and basal node cytosol to fix Cd. In the rhizosphere soil, strain W112 effectively colonized and significantly decreased the exchangeable Cd, carbonate-bound Cd and iron-manganese oxide-bound Cd content by 43.5%, 27.3% and 17.6%, respectively, while it increased the proportion of residual Cd by up to 65.2%. Moreover, a 3.1% and 23.5% increase in the pH and inorganic nitrogen content in the rhizosphere soil, respectively, was recorded. Similarly, soil bacterial community sequencing revealed that inoculating with strain W112 increased the abundance of Pseudomonas, Thauera and Azoarcus, which are associated with inorganic nitrogen metabolism, and decreased that of Acidobacteria, which is indicative of soil alkalinization. Hence, root application of Pseudomonas sp. W112 improved soil nitrogen availability and inhibited Cd accumulation in the wheat grains in a two-stage process: by reducing the Cd availability in the rhizosphere soil and by improving Cd interception and fixation in the wheat roots and basal nodes. Pseudomonas sp. W112 may be a suitable bioremediation agent for restoring Cd-contaminated wheat fields.