Identification of the Microbial Transformation Products of Secoisolariciresinol Using an Untargeted Metabolomics Approach and Evaluation of the Osteogenic Activities of the Metabolites.

Secoisolariciresinol (SECO) is one of the major lignans occurring in various grains, seeds, fruits, and vegetables. The gut microbiota plays an important role in the biotransformation of dietary lignans into enterolignans, which might exhibit more potent bioactivities than the precursor lignans. This study aimed to identify, synthesize, and evaluate the microbial metabolites of SECO and to develop efficient lead compounds from the metabolites for the treatment of osteoporosis. SECO was fermented with human gut microbiota in anaerobic or micro-aerobic environments at different time points. Samples derived from microbial transformation were analyzed using an untargeted metabolomics approach for metabolite identification. Nine metabolites were identified and synthesized. Their effects on cell viability, osteoblastic differentiation, and gene expression were examined. The results showed that five of the microbial metabolites exerted potential osteogenic effects similar to those of SECO or better. The results suggested that the enterolignans might account for the osteoporotic effects of SECO in vivo. Thus, the presence of the gut microbiota could offer a good way to form diverse enterolignans with bone-protective effects. The current study improves our understanding of the microbial transformation products of SECO and provides new approaches for new candidate identification in the treatment of osteoporosis.

Knockdown of EDA2R alleviates hyperoxia-induced lung epithelial cell injury by inhibiting NF-κB pathway.

BACKGROUND: Long-term hyperoxia impairs growth of the lungs and contributes to development of bronchopulmonary dysplasia. Ectodysplasin A (EDA) binds to ectodysplasin A2 receptor (EDA2R) and is essential for normal prenatal development. The functioning of EDA2R in bronchopulmonary dysplasia is investigated in this study. METHODS: Murine lung epithelial cells (MLE-12) were exposed to hyperoxia to induce cell injury. Cell viability and apoptosis were detected, respectively, by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) assay and flow cytometry. Inflammation and oxidative stress were evaluated by enzyme-linked immunosorbent serologic assay. RESULTS: Hyperoxia decreased cell viability and promoted cell apoptosis of MLE-12. EDA2R was elevated in hyperoxia-induced MLE-12. Silencing of EDA2R enhanced cell viability and reduced cell apoptosis of hyperoxia-induced MLE-12. Hyperoxia-induced up-regulation of tumor necrosis factor alpha (TNF-α), Interleukin (IL)-1ß, and IL-18 as well as MLE-12 was suppressed by knockdown of EDA2R. Inhibition of EDA2R down-regulated the level of malondialdehyde (MDA), up-regulated superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) in hyperoxia-induced MLE-12. Interference of EDA2R attenuated hyperoxia-induced increase in p-p65 in MLE-12. CONCLUSION: Knockdown of EDA2R exerted anti-inflammatory and antioxidant effects against hyperoxia-induced injury in lung epithelial cells through inhibition of nuclear factor kappa B (NF-κB) pathway.

Impacts of Chemical and Organic Fertilizers on the Bacterial Communities, Sulfonamides and Sulfonamide Resistance Genes in Paddy Soil Under Rice-Wheat Rotation.

The responses of sulfonamides, sulfonamide-resistance genes (sul) and soil bacterial communities to different fertilization regimes were investigated by performing a field experiment using paddy soil with no fertilizer applied, chemical fertilizer applied, organic fertilizer applied, and combination of chemical and organic fertilizer applied. Applying organic fertilizer increased the bacterial community diversity and affected the bacterial community composition. Eutrophic bacteria (Bacteroidetes, Gemmatimonadetes, and Proteobacteria) were significantly enriched by applying organic fertilizer. It was also found organic fertilizer application increased sulfamethazine content and the relative abundances of sul1 and sul2 in the soil. In contrast, applying chemical fertilizer significantly increased the abundance of Nitrospirae, Parcubacteria, and Verrucomicrobia and caused no obvious changes on sul. Correlation analysis indicated that sul enrichment was associated with the increases in sulfamethazine content and potential hosts (e.g., Novosphingobium and Rhodoplanes) population. The potential ecological risks of antibiotics in paddy soil with organic fertilizer applied cannot be ignored.

In-situ immobilization of cadmium-polluted upland soil: A ten-year field study.

In-situ immobilization is an effective and economically viable strategy for remediation of soil extensively polluted with heavy metals. The long-term sustainability is critical for the remediation practice. In the present study, a ten-year experiment was performed in a Cd-polluted agricultural field to evaluate the long-term stability of lime, silicon fertilizer (SF), fused calcium magnesium phosphate fertilizer (FCMP), bone charcoal, steel slag, and blast furnace slag with one-off application. All amendments had no significant effect on biomass but significantly reduced Cd uptake by Artemisia selengensis at higher dose. Among them, SF and FCMP applied at 1% could reduce Cd uptake by more than 40% to meet the Chinese maximum permissible limit for Cd content in food products (50 µg kg-1). These amendments stimulated high Cd immobilization by increasing the soil pH and decreasing the soil acid-extractable Cd content, which were closely associated with Cd uptake. In addition, the two amendments altered the soil microbial structure and stimulated metabolism pathways, including amino acid, carbohydrate, and lipid metabolism, which are beneficial for soil function and quality. The results proved that SF and FCMP at 1% are stable and ecologically safe amendments, suitable for long-term Cd immobilization, and provide a strategy to mitigate the risk of food product contamination in heavy-metal-polluted soil.

Integrated Assessment of Cd-contaminated Paddy Soil with Application of Combined Ameliorants: A Three-Year Field Study.

Cadmium accumulation in rice is a major source of Cd exposure in humans worldwide. A three-year field experiment was conducted to investigate the ecological safety and long-term stability of biochar combined with lime or silicon fertilizer for Cd immobilization in a polluted rice paddy. The results showed that the application of combined ameliorants could reduce the Cd content in brown rice to meet the Chinese maximum permissible limit for Cd content in food products (0.2 mg/kg). In addition, such amendments stimulated metabolic pathways in soil bacteria, including carbon metabolism, citrate cycle, pyruvate metabolism, biosynthesis of amino acids, and glycolysis/gluconeogenesis, revealing improvements in soil biological activity and soil health. Therefore, the results provide a practical strategy for the safe utilization of farmland with mild levels of heavy metal pollution.

Effects of CeO2 Nanoparticles on Microcystis aeruginosa Growth and Microcystin Production.

The interaction between metal oxide nanoparticles and toxin-producing cyanobacteria is relatively unknown. The present work exposed Microcystis sp.7806 to different concentrations of cerium oxide nanoparticles (CeO2 NPs) (1 mg/L, 10 mg/L and 50 mg/L), and evaluated the growth, photosynthetic activity, reactive oxygen species level, and the extra-(intra-) cellular microcystin-LR (MC-LR) contents. The particle size, zeta potential and cerium ions released into the medium were analyzed. Results showed 10 mg/L NP treatment promoted algae growth but slightly inhibited the photosynthetic yield of algae, and the 50 mg/L treatment reduced algae biomass. The algal cells remarkably responded to oxidative stress at higher concentrations (10 mg/L and 50 mg/L). CeO2 NPs largely increased the intracellular MC-LR content at 50 mg/L, and significantly reduced the extracellular MC-LR content at any concentration. This demonstrates CeO2 NPs may pose an ecological risk potential during harmful algal blooms by stimulating toxin production.

Metabolomics Reveals the "Invisible" Responses of Spinach Plants Exposed to CeO2 Nanoparticles.

Engineered nanoparticles (NPs) with activities that mimic antioxidant enzymes have good prospects in agriculture because they can increase photosynthesis and improve stress tolerance. Here, the interaction between cerium oxide NPs with spinach plants ( Spinacia oleracea) was investigated by integrating phenotypic and metabolomic analyses. Soil-grown, four-week-old spinach plants were foliar exposed for 3 weeks to CeO2 NPs at 0, 0.3, and 3 mg per plant. Phenotypic parameters (chlorophyll fluorescence, photosynthetic pigment contents, plant biomass, lipid peroxidation, and membrane permeability) were not affected. However, metabolomics analysis revealed that both doses of CeO2 NPs induced metabolic reprogramming in leaves and roots in a non-dose-dependent manner. The low dose of CeO2 NPs (0.3 mg per plant) induced stronger metabolic reprogramming in spinach leaves than high dose of CeO2 NPs. However, the high dose of CeO2 NPs triggered more metabolic changes in roots, compared to the low dose. Foliar spray of CeO2 NPs at 3 mg/plant induced marked down-regulation of a number of amino acids (threonine, tryptophan, l-cysteine, methionine, cycloleucine, aspartic acid, asparagine, tyrosine, and glutamic acid). In addition, Zn decreased by 44% and 54% in leaves and Ca decreased by 38% and 32% in roots under exposure to CeO2 NPs at 0.3 and 3 mg/plant, respectively. These results provide better understanding of the intrinsic phenotypic and metabolic changes imposed by CeO2 NPs in spinach plants.

Transcriptome Reveals the Rice Response to Elevated Free Air CO2 Concentration and TiO2 Nanoparticles.

Increasing CO2 levels are speculated to change the effects of engineered nanomaterials in soil and on plant growth. How plants will respond to a combination of elevated CO2 and nanomaterials stress has rarely been investigated, and the underlying mechanism remains largely unknown. Here, we conducted a field experiment to investigate the rice (Oryza sativa L. cv. IIyou) response to TiO2 nanoparticles (nano-TiO2, 0 and 200 mg kg-1) using a free-air CO2 enrichment system with different CO2 levels (ambient ∼370 µmol mol-1 and elevated ∼570 µmol mol-1). The results showed that elevated CO2 or nano-TiO2 alone did not significantly affect rice chlorophyll content and antioxidant enzyme activities. However, in the presence of nano-TiO2, elevated CO2 significantly enhanced the rice height, shoot biomass, and panicle biomass (by 9.4%, 12.8%, and 15.8%, respectively). Furthermore, the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that genes involved in photosynthesis were up-regulated while most genes associated with secondary metabolite biosynthesis were down-regulated in combination-treated rice. This indicated that elevated CO2 and nano-TiO2 might stimulate rice growth by adjusting resource allocation between photosynthesis and metabolism. This study provides novel insights into rice responses to increasing contamination under climate change.

Metabolomics Reveals How Cucumber ( Cucumis sativus) Reprograms Metabolites To Cope with Silver Ions and Silver Nanoparticle-Induced Oxidative Stress.

Due to their well-known antifungal activity, the intentional use of silver nanoparticles (AgNPs) as sustainable nanofungicides is expected to increase in agriculture. However, the impacts of AgNPs on plants must be critically evaluated to guarantee their safe use in food production. In this study, 4-week-old cucumber ( Cucumis sativus) plants received a foliar application of AgNPs (4 or 40 mg/plant) or Ag+ (0.04 or 0.4 mg/plant) for 7 days. Gas chromatography-mass spectrometry (GC-MS)=based nontarget metabolomics enabled the identification and quantification of 268 metabolites in cucumber leaves. Multivariate analysis revealed that all the treatments significantly altered the metabolite profile. Exposure to AgNPs resulted in metabolic reprogramming, including activation of antioxidant defense systems (upregulation of phenolic compounds) and downregulation of photosynthesis (upregulation of phytol). Additionally, AgNPs enhanced respiration (upregulation of tricarboxylic acid cycle intermediates), inhibited photorespiration (downregulation of glycine/serine ratio), altered membrane properties (upregulation of pentadecanoic and arachidonic acids, downregulation of linoleic and linolenic acids), and reduced inorganic nitrogen fixation (downregulation of glutamine and asparagine). Although Ag ions induced some of the same metabolic changes, alterations in the levels of carbazole, lactulose, raffinose, citraconic acid, lactamide, acetanilide, and p-benzoquinone were AgNP-specific. The results of this study offer new insight into the molecular mechanisms by which cucumber responds to AgNP exposure and provide important information to support the sustainable use of AgNPs in agriculture.

Physiological and Biochemical Changes Imposed by CeO2 Nanoparticles on Wheat: A Life Cycle Field Study.

Interactions of nCeO2 with plants have been mostly evaluated at seedling stage and under controlled conditions. In this study, the effects of nCeO2 at 0 (control), 100 (low), and 400 (high) mg/kg were monitored for the entire life cycle (about 7 months) of wheat plants grown in a field lysimeter. Results showed that at high concentration nCeO2 decreased the chlorophyll content and increased catalase and superoxide dismutase activities, compared with control. Both concentrations changed root and leaf cell microstructures by agglomerating chromatin in nuclei, delaying flowering by 1 week, and reduced the size of starch grains in endosperm. Exposed to low concentration produced embryos with larger vacuoles, while exposure to high concentration reduced number of vacuoles, compared with control. There were no effects on the final biomass and yield, Ce concentration in shoots, as well as sugar and starch contents in grains, but grain protein increased by 24.8% and 32.6% at 100 and 400 mg/kg, respectively. Results suggest that more field life cycle studies are needed in order to better understand the effects of nCeO2 in crop plants.

Effect of ultraviolet aged polytetrafluoroethylene microplastics on copper bioavailability and Microcystis aeruginosa growth.

Microplastics (MPs) are ubiquitous in aquatic environments, which can act as carriers to affect the bioavailability of heavy metals. The aging process in the environment changes the physicochemical properties of MPs, thereby affecting their environmental behavior and co-toxicity with other pollutants. However, relevant research is limited. In this study, we compared the properties and Cu2+ adsorption capacity of pristine and aged polytetrafluoroethylene (PTFE) MPs and further explored the influence on copper bioavailability and bio-effects on Microcystis aeruginosa. Aging process induced surface oxidation and cracks of PTFE MPs, and decreased the stability of MPs in water by increasing zeta potential. PTFE MPs had a strong adsorption capacity for Cu2+ and increased the bioavailability of copper to microalgae, which was not affected by the aging process. Pristine and aged PTFE MPs adhered to cyanobacterium surfaces and caused shrinkage and deformation of cells. Inhibition of cyanobacterium growth, photosynthesis and reduction of total antioxidant capacity were observed in the treatment of PTFE MPs. Combined exposure of pristine MPs and Cu2+ had stronger toxic effects to cyanobacterium, and increased Microcystin-LR release, which could cause harm to aquatic environment. Aging reduced the toxic effects of PTFE MPs on microalgae. Furthermore, soluble exopolysaccharide (EPS) content was significantly higher in co-exposure of aged MPs and Cu2+, which could reduce the toxicity to cyanobacterium cells. These results indicate that aging process alleviates the toxicity to microalgae and environmental risks caused by PTFE MPs. This study improves understanding of the combined toxicity of aged MPs and metals in freshwater ecosystems.

Structure-aware diffusion for low-dose CT imaging.

Reducing the radiation dose leads to the x-ray computed tomography (CT) images suffering from heavy noise and artifacts, which inevitably interferes with the subsequent clinic diagnostic and analysis. Leading works have explored diffusion models for low-dose CT imaging to avoid the structure degeneration and blurring effects of previous deep denoising models. However, most of them always begin their generative processes with Gaussian noise, which has little or no structure priors of the clean data distribution, thereby leading to long-time inference and unpleasant reconstruction quality. To alleviate these problems, this paper presents a Structure-Aware Diffusion model (SAD), an end-to-end self-guided learning framework for high-fidelity CT image reconstruction. First, SAD builds a nonlinear diffusion bridge between clean and degraded data distributions, which could directly learn the implicit physical degradation prior from observed measurements. Second, SAD integrates the prompt learning mechanism and implicit neural representation into the diffusion process, where rich and diverse structure representations extracted by degraded inputs are exploited as prompts, which provides global and local structure priors, to guide CT image reconstruction. Finally, we devise an efficient self-guided diffusion architecture using an iterative updated strategy, which further refines structural prompts during each generative step to drive finer image reconstruction. Extensive experiments on AAPM-Mayo and LoDoPaB-CT datasets demonstrate that our SAD could achieve superior performance in terms of noise removal, structure preservation, and blind-dose generalization, with few generative steps, even one step only.

A field study of a novel permeable-reactive-biobarrier to remediate chlorinated hydrocarbons contaminated groundwater.

Chlorinated hydrocarbons (CHs) pose significant health risks due to their suspected carcinogenicity, necessitating urgent remediation efforts. While the combination of zero-valent iron (Fe0) and microbial action shows promise in mitigating CH contamination, field studies on this approach are scarce. We devised a novel three-layer permeable reactive barrier (PRB) material incorporating Fe0 and coconut shell biochar, effectively implemented at a typical CH-contaminated site. Field monitoring data revealed conducive conditions for reductive dechlorination of CHs, characterized by low oxygen levels and a relatively neutral pH in the groundwater. The engineered PRB material consistently released organic carbon and iron, fostering the proliferation of CH-dechlorinating bacteria. Over a 250-day operational period, the pilot-scale PRB demonstrated remarkable efficacy in CH removal, achieving removal efficiencies ranging from 21.9% to 99.6% for various CH compounds. Initially, CHs were predominantly eliminated through adsorption and iron-mediated reductive dechlorination. However, microbial reductive dechlorination emerged as the predominant mechanism for sustained and long-term CHs removal. These findings underscore the economic viability and effectiveness of our approach in treating CH-contaminated groundwater, offering promising prospects for broader application in environmental remediation efforts.

Elevated CO2 exacerbates the risk of methylmercury exposure in consuming aquatic products: Evidence from a complex paddy wetland ecosystem.

Elevated CO2 levels and methylmercury (MeHg) pollution are important environmental issues faced across the globe. However, the impact of elevated CO2 on MeHg production and its biological utilization remains to be fully understood, particularly in realistic complex systems with biotic interactions. Here, a complete paddy wetland microcosm, namely, the rice-fish-snail co-culture system, was constructed to investigate the impacts of elevated CO2 (600 ppm) on MeHg formation, bioaccumulation, and possible health risks, in multiple environmental and biological media. The results revealed that elevated CO2 significantly increased MeHg concentrations in the overlying water, periphyton, snails and fish, by 135.5%, 66.9%, 45.5%, and 52.1%, respectively. A high MeHg concentration in periphyton, the main diet of snails and fish, was the key factor influencing the enhanced MeHg in aquatic products. Furthermore, elevated CO2 alleviated the carbon limitation in the overlying water and proliferated green algae, with subsequent changes in physico-chemical properties and nutrient concentrations in the overlying water. More algal-derived organic matter promoted an enriched abundance of Archaea-hgcA and Deltaproteobacteria-hgcA genes. This consequently increased the MeHg in the overlying water and food chain. However, MeHg concentrations in rice and soil did not increase under elevated CO2, nor did hgcA gene abundance in soil. The results reveal that elevated CO2 exacerbated the risk of MeHg intake from aquatic products in paddy wetland, indicating an intensified MeHg threat under future elevated CO2 levels.

Fate and ecological effects of decabromodiphenyl ether in a field lysimeter.

Flame-retardant polybrominated diphenyl ethers (PBDEs) are environmental contaminants. Deca-BDE is increasingly used commercially, but little is known about the long-term fate and impact of its major component, decabromodiphenyl ether (BDE-209), on the soil environment. In this study, we investigated the fate and ecological effect of BDE-209 over 4 years in outdoor lysimeters in a field planted with a rice-wheat rotation. BDE-209 and six lower-brominated PBDEs (BDE-28, -47, -99, -153, -154, and -183) were detected in soil layers of the test lysimeter. We calculated an average BDE-209 migration rate of 1.54 mg·m(-2)·yr(-1). In samples collected in May 2008, November 2008, November 2009, November 2010, and November 2011, 95.5%, 94.3%, 108.1%, 33.8%, and 35.5% of the spiked BDE-209 were recovered, respectively. We predicted the major pathway for debromination of BDE-209 in soil to be: BDE-209→BDE-183→BDE-153/BDE-154→BDE-99→BDE-47→BDE-28. In plants, BDE-209 and seven lower-brominated PBDEs (BDE-28, -47, -99, -100, -153, -154, and -183) were detected. BDE-100 was mainly derived from the debromination of BDE-154 in plants, but sources of other lower-brominated PBDEs were still difficult to determine. In soils containing BDE-209 for 4 years, soil urease activity increased, and soil protease activity slightly decreased. Our results provide important insights for understanding the behavior of BDE-209 in agricultural soils.

Climatic CO2 level-driven changes in the bioavailability, accumulation, and health risks of Cd and Pb in paddy soil-rice systems.

Rising atmospheric carbon dioxide (CO2) and soil heavy metal pollution, which affects safe rice production and soil ecosystem stability, have caused widespread concern. In this study, we evaluated the effects of elevated CO2 on Cd and Pb accumulation in rice plants (Oryza sativa L.), Cd and Pb bioavailability, and soil bacterial communities in Cd-Pb co-contaminated paddy soils via rice pot experiments. We showed that elevated CO2 accelerates the accumulation of Cd and Pb in rice grains by 48.4-75.4% and 20.5-39.1%, respectively. Elevated CO2 levels decreased soil pH value by 0.2 units, which increased Cd and Pb bioavailability in soil but inhibited iron plaque formation on rice roots, ultimately promoting Cd and Pb uptake. 16S rRNA sequencing analysis revealed that elevated CO2 increased the relative abundance of certain soil bacteria (e.g., Acidobacteria, Alphaproteobacteria, Holophagae, and Burkholderiaceae). A health risk assessment showed that elevated CO2 markedly increased the total carcinogenic risk values for children, adult males, and adult females by 75.3% (P < 0.05), 65.6% (P < 0.05), and 71.1% (P < 0.05), respectively. These results demonstrate the serious performance of elevated CO2 levels in accelerating the bioavailability and accumulation of Cd and Pb in paddy soil-rice ecosystems, with particular risks for future safe rice production.

Efflux pumps activation caused by mercury contamination prompts antibiotic resistance and pathogen's virulence under ambient and elevated CO2 concentration.

The occurrence and development of antibiotic resistance genes (ARGs) in pathogens poses serious threatens to global health. Agricultural soils provide reservoirs for pathogens and ARGs, closely related to public health and food safety. Especially, metals stress provides more long-standing selection pressure for ARGs, and climate change is a "threat multiplier" for the spread of ARGs. However, little is known about the impact of metals contamination on pathogens and ARGs in agricultural soils and their sensitivity to ongoing climate changes. To fill this gap, a pot experiment was conducted in open-top chambers (OTCs) to investigate the influence of mercury (Hg) contamination on the distribution of soil pathogens and ARGs under ambient and elevated CO2 concentration. Results showed that the relative abundance of common plant and human pathogens increased significantly in Hg-contaminated soil under two CO2 concentrations. Hg contamination was a positive effector of the activation of efflux pumps and offensive virulence factors (adhere and secretion system) under two CO2 levels. Activation of efflux pumps caused by Hg contamination might contribute to changes of virulence or fitness of certain pathogens. Overall, our study emphasizes the critical role of efflux pumps as an intersection of antibiotic resistance and pathogen's virulence under Hg stress.

A 24-epibrassinolide treatment and intercropping willow with alfalfa increase the efficiency of the phytoremediation of cadmium-contaminated soil.

Cadmium contamination in agricultural soils threatens food security and human health, and that has caused widespread concern worldwide. Willow and alfalfa are widely used for the phytoremediation of cadmium (Cd)-contaminated soil, and willow NJU513 is the promising plant for remediating Cd-contaminated soil. In order to discuss the effect of intercropping willow NJU513 with alfalfa on the phytoremediation of Cd-contaminated soil, a pot-culture experiment was conducted in the greenhouse. The result showed that the phytoremediation of Cd-contaminated soil was enhanced by this intercropping because of the 25.90 % increase in the available Cd content. In order to increase the phytoremediation efficiency of Cd in the intercropping treatment, a 24-epibrassinolide (Brs) treatment was designed in the current study. The results showed that the phytoremediation of Cd-contaminated soil by willow and alfalfa improved following a Brs treatment because of the 16.32-74.15 % and 16.91-44.48 % increases in the plant biomass and available Cd content, respectively. Additionally, the extracted Cd by plants in the intercropping treatments with and without Brs was 0.56 and 0.31 mg pot-1, respectively. Transcriptome analyses of willow leaves revealed that Brs up-regulated the expression of genes related to calcium channel activity, calcium and zinc transmembrane transport, photosynthesis, catalase/antioxidant activity, glutathione metabolic processes and detoxification, phagosomes, and vacuoles, and that these upregulated genes promoted plant remediation efficiency and resistance to Cd stress. Brs promoted the phosphate ion transporter activity in willow leaves, which may have enhanced the solubilization of insoluble phosphate minerals by bacterial species (e.g., Vicinamibacterales, Bacillus, and Gaiella) to release Cd, ultimately leading to increased phytoremediation efficiency. In addition, plants with and without Brs treatments induced the bacteria-mediated transformation of available Cd to stable Cd. The study findings may be useful for improving the phytoremediation of Cd-contaminated paddy soil.

Potential microbial mechanisms underlying the effects of rising atmospheric CO2 levels on the reduction and methylation processes of arsenic in the paddy soil.

Many studies have demonstrated that climate change affects the biogeochemical cycle of pollutants, but the mechanisms of arsenic (As) biogeochemical processes under high CO2 levels are unknown. Here, rice pot experiments were carried out to explore the underlying mechanisms of the impacts of elevated CO2 on the reduction and methylation processes of As in paddy soils. The results revealed that elevated CO2 might increase As bioavailability and promote As(V)-to-As(III) transformation in the soil as well as higher As(III) and dimethyl arsenate (DMA) accumulation in rice grains, thus increasing health risk. In As-contaminated paddy soil, two key genes involved in the biotransformation of As (arsC and arsM) and associated host microbes were identified as being significantly promoted by increasing CO2 levels. Elevated CO2 enriched the soil microbes harboring arsC (Bradyrhizobiaceae and Gallionellaceae), which aided in the reduction of As(V) to As(III). Simultaneously, elevated CO2 enriched soil microbes harboring arsM (Methylobacteriaceae and Geobacteraceae), allowing As(V) to be reduced to As(III) and then methylated to DMA. The findings of the Incremental Lifetime Cancer Risk (ILTR) assessment suggested that elevated CO2 exacerbated the individual adult ILTR from rice food As(III) consumption by 9.0 % (p < 0.05). These findings show that elevated CO2 aggravates the exposure risk of As(III) and DMA in rice grains by changing microbial populations involved in As biotransformation in paddy soils.

Joint effects of CuO nanoparticles and perfluorooctanoic acid on cabbage (Brassica pekinensis L.).

Coexisting nanoparticles (NPs) may change plant accumulation and toxicity of perfluorooctanoic acid (PFOA) in soil, but research is very scarce. In this study, cabbage (Brassica pekinensis L.) was exposed to single or combined treatments of PFOA (2 mg/kg and 4 mg/kg) and copper oxide NPs (nCuO, 200 mg/kg and 400 mg/kg) for 40 days. At harvest, biomass, photosynthesis index, and nutrient composition of cabbage, as well as plant accumulation of PFOA and Cu, were measured. Results showed that nCuO and PFOA were adverse to cabbage growth by decreasing chlorophyll contents, inhibiting photosynthesis and transpiration, and interfering with the utilization of nutrient components. Besides, they also affected each other's plant utilization and transmission. Especially, nCuO at a high dose (400 mg/kg) significantly increased the transport of coexisting PFOA (4 mg/kg) content (by 124.9% and 118.2%) to cabbage shoots. The interaction mechanism between nCuO and PFOA is unknown, and more research is needed to evaluate their composite phytotoxicity.