Rice rhizospheric effects and mechanism on soil cadmium bioavailability during silicon application

Exogenous Si mitigates the mobility and bioavailability of Cd in the soil, thereby alleviating its phytotoxicity. This study focused on specific Si-induced immobilisation effects within the rhizosphere (S1), near-rhizosphere (S2), and far-rhizosphere (S3) zones. Based on the rhizobox experiment, we found that applying Si significantly elevated soil pH, and the variation amplitudes in the S3 soil exceeded those in the S1 and S2 soils. Si-induced changes in the rhizosphere also included enhanced dissolved organic carbon and diminished soil Eh, particularly in the Si400 treatment. Meanwhile, the introduction of Si greatly enhanced the Fe2+ and Mn2+ concentrations in the S1 soil, but reduced them in the S2 soil. The rhizosphere effect of Si which enriched Fe2+ and Mn2+ subsequently promoted the formation of Fe and Mn oxides/hydro-oxides near the rice roots. Consequently, the addition of Si significantly reduced the available Cd concentrations in S1, surpassing the reductions in S2 and S3. Moreover, Si-treated rice exhibited increased Fe plaque generation and fixation on soil Cd, resulting in decreased Cd concentrations in rice tissues, accompanied by reduced Cd translocation from roots to shoots and shoots to grains. Structural equation modelling further highlighted that Si is essential in Cd availability in S1 and Fe plaque development, ultimately mitigating Cd accumulation in rice. Si-treated rice also exhibited higher biomass and grain yield than those of control groups. These findings provide valuable insights into Si-based strategies for addressing the Cd contamination of agricultural soils.

Overexpression of Lias Gene Alleviates Cadmium-Induced Kidney Injury in Mice Involving Multiple Effects: Metabolism, Oxidative Stress, and Inflammation

Oxidative stress is an important mechanism underlying toxicity induced by cadmium (Cd) exposure. However, there are significant differences of the antioxidant baseline in different populations. This means that different human has different intensity of oxidative stress in vivo after exposure to toxicants. LiasH/H mouse is a specific model which is created by genetically modifying the Lias 3'-untranslated region (3'-UTR). LiasH/H mice express high levels of LA and have high endogenous antioxidant capacity which is approximately 150% higher than wild-type C57BL/6 J mice (WT, Lias+/+). But more importantly, they have dual roles of metal chelator and antioxidant. Here, we applied this mouse model to evaluate the effect of endogenous antioxidant levels in the body on alleviating Cd-induced renal injury including Cd metabolism, oxidative stress, and inflammation. In the experiment, mice drank water containing Cd (50 mg/L), for 12 weeks. Many biomarkers of Cd metabolism, oxidative stress, inflammation, and major pathological changes in the kidney were examined. The results showed overexpression of the Lias gene decreased Cd burden in the body of mice, mitigated oxidative stress, attenuated the inflammatory response, and subsequent alleviated cadmium-induced kidney injury in mice.

Nano‑selenium alleviates cadmium-induced blood-brain barrier destruction by restoring the Wnt7A/β-catenin pathway

Selenium (Se), a highly beneficial animal feed additive, exhibits remarkable antioxidant and anti-inflammatory properties. Nano‑selenium (Nano-Se) is an advanced formulation of Se featuring a specialized drug delivery vehicle, with good bioavailability, higher efficacy, and lower toxicity compared to the traditional form of Se. With the advancement of industry, cadmium (Cd) contamination occurs in different countries and regions and thereby contaminating different food crops, and the degree of pollution is degree increasing year by year. The present investigation entailed the oral administration of CdCl2 and/or Nano-Se to male chickens of the Hy-Line Variety White breed, which are one day old, subsequent to a 7-day adaptive feeding period, for a duration of 90 days. The study aimed to elucidate the potential protective impact of Nano-Se on Cd exposure. The study found that Nano-Se demonstrates potential in mitigating the blood-brain barrier (BBB) dysfunction characterized by impairment of adherens junctions (AJS) and tight junctions (TJS) by inhibiting reactive oxygen species (ROS) overproduction. In addition, the data uncovered that Nano-Se demonstrates a proficient ability in alleviating BBB impairment and inflammatory reactions caused by Cd through the modulation of the Wnt7A/β-catenin pathway, highlights its potential to maintain brain homeostasis. Hence, this research anticipates that the utilization of Nano-Se effectively mitigate the detrimental impacts associated with Cd exposure on the BBB.

Sources apportionments of heavy metal(loid)s in the farmland soils close to industrial parks: Integrated application of positive matrix factorization (PMF) and cadmium isotopic fractionation

Understanding the source identification and distribution of heavy metal(loid)s in soil is essential for risk management. The sources of heavy metal(loid)s in farmland soil, especially in areas with rapid economic development, were complicated and need to be explored urgently. This study combined geographic information system (GIS) mapping, positive matrix factorization (PMF) model and cadmium (Cd) isotope fingerprinting methods to identify heavy metal(loid) sources in a typical town in the economically developed Yangtze River Delta region of China. Cd, As, Cu, Zn, Pb, Ni and Co in different samples were detected. The results showed that Cd was the most severely contaminated element, with an exceedance rate of 78.0 %. GIS mapping results indicated that the hotspot area was located in the northeastern area with prolonged operational histories of electroplating and non-ferrous metal smelting industries. The PMF model analysis also identified emissions from smelting and electroplating enterprises as the main sources of Cd in the soil, counted for 49.28 %, followed by traffic (25.66 %) and agricultural (25.06 %) sources. Through further isotopic analysis, it was found that in soil samples near the industrial park, the contribution of electroplating and non-ferrous metal smelting enterprises to cadmium pollution was significantly higher than other regions. The integrated use of various methodologies allows for precise analysis of sources and input pathways, offering valuable insights for future pollution control and soil remediation endeavors.

Effects of sertraline hydrochloride with As(III) or Cd on rhizosphere micro-environment and root endophytes in rice

This study investigated the effects of the antidepressant sertraline hydrochloride (Ser-HCI) on rice physiology when combined with arsenic (III) and cadmium. Hydroponic experiments revealed that combined lower concentrations (0.2 and 0.6 mg L-1) of Ser-HCl and As (III) or Cd increased rice biomass and reduced pH and low molecular weight organic acids. The fluorescence intensity was enhanced with Ser-HCl and As-only treatments, with a significant difference (p < 0.05) in the dissolved organic matter index. There was a decrease in endophyte-specific operational taxonomic units, with proteobacteria dominating the rice root endophytes. The addition of Ser-HCl resulted in a 535% increase in the Verrucomicrobiota, which was positively correlated with malic acid and negatively correlated with pH. Functional annotation highlighted alterations in carbohydrate metabolism pathways. This study provides insights into the interactive effects of Ser-HCl on rice when combined with As (III) and Cd, addressing gaps in our understanding of the impact of antidepressants on plant systems.

Influences of coexisting aged polystyrene microplastics on the ecological and health risks of cadmium in soils: A leachability and oral bioaccessibility based study

Whether coexisting microplastics (MPs) affect the ecological and health risks of cadmium (Cd) in soils is a cutting-edge scientific issue. In this study, four typical Chinese soils were prepared as artificially Cd-contaminated soils with/without aged polystyrene (PS). TCLP and in vitro PBET model were used to determine the leachability (ecological risk) and oral bioaccessibility (human health risk) of soil Cd. The mechanisms by which MPs influence soil Cd were discussed from direct and indirect perspectives. Results showed that there was no significant difference in the leachability of soil Cd with/without aged PS. Additionally, aged PS led to a significant decrease in the bioaccessibility of soil Cd in gastric phase, but not in small intestinal phase. The increase in surface roughness and the new characteristic peaks (e.g., Si-O-Si) of aged PS directly accounted for the change in Cd bioaccessibility. The change in organic matter content indirectly accounted for the exceptional increase in Cd bioaccessibility of black soil with aged PS in small intestinal phase. Furthermore, the changes in cation exchange capacity and Cd mobility factor caused by aged PS explained the change in Cd leachability. These results contribute to a deeper understanding about environmental and public health in complicated emerging scenarios.

Tourmaline-enhanced bioremediation of Cd/BDE-153 co-contaminated soil: Migration, soil microorganism structure and enzyme activities

The efficient remediation of the soil co-contaminated with heavy metals and polybrominated diphenyl ethers (PBDEs) from electronic disassembly zones is a new challenge. Here, we screened a fungus of F. solani (F.s) can immobilize Cd and remove PBDEs. wIt combined with tourmaline enhances the remediation of co- pollutants in the soil. Furthermore, the environment risks of the enhanced technology were assessed through the amount of Cd/BDE-153 in Amaranthus tricolor L. (amaranth) migrated from soil, as well as the changes of soil microorganism communities and enzyme activities. The results showed the combined treatment of tourmaline and F.s made the removal percentage of BDE-153 in rhizosphere soil co-contaminated with BDE-153 and Cd reached 46.5%. And the weak acid extractable Cd in rhizosphere soil decreased by 33.7% compared to control group. In addition, the combined remediation technology resulted in a 32.5% (22.8%), 45.5% (37.2%), and 50.7% (38.1%) decrease in BDE-153 (Cd) content in the roots, stems, and leaves of amaranth, respectively. Tourmaline combined with F.s can significantly increase soil microorganism diversity, soil dehydrogenase and urease activities, further improving the remediation rate of Cd and BDE-153co-pollutants in soil and the biomass of amaranth. This study provides the remediation technology of soil co-contaminated with heavy metal and PBDEs and ensure the maintenance of food security.

Rutin Nanoparticles Alleviate Cadmium-Induced Oxidative and Immune Damage in Broilers' Bursa of Fabricius via Modulating Hsp70/TLR4/NF-κB Signaling Pathway

Cadmium (Cd) is a serious environmental pollutant affecting various tissues/organs in broilers and compromising their immunological function and productivity. Therefore, the current study aimed to investigate Cd-induced immunotoxicity and potential immunoprotective effect of rutin nanoparticles (RNPs) in the bursal tissue of broilers. A total number of 150 chicks from the Hubbard breed were randomly divided into 5 groups. Group I was fed on standard basal diet (SD) with normal drinking water (DW), Group II received SD containing RNPs (50 mg/kg feed) with DW, Group III fed on SD and DW containing Cd (150 mg/L), Group IV co-treated with rutin-enforced SD (50 mg/kg diet) and DW containing Cd (150 mg/L), and finally, Group V co-supplemented with RNP-enhanced SD (50 mg/kg diet) DW containing Cd (150 mg/L). Productive performance, economic efficiency, oxidative biomarkers, histopathological changes, and the expression level of TLR-4, HSP-70, caspase 3, NF-κB, Bcl-2, and Bax were assessed in the BF tissue. Cd led to severe production and economic losses in exposed birds with a marked surge of oxidative biomarkers, pro-inflammatory cytokines, and histopathological changes in the bursal tissue which could be explained through upregulation of the Hsp70/TLR4/NF-κB molecular pathway in the BF tissue. Meanwhile, RNPs could alleviate most of these changes and prevail optimistic immunomodulatory properties which subsequently could enhance broilers' productivity when incorporated in their diets.

Rice straw returning enhances cadmium activation by accelerating iron cycling thus hydroxyl radical production in paddy soils during drainage

Straw returning is widely found elevating the bioavailability of cadmium (Cd) in paddy soils with unclear biogeochemical mechanisms. Here, a series of microcosm incubation experiments were conducted and spectroscopic and microscopic analyses were employed. The results showed that returning rice straw (RS) efficiently increased amorphous Fe and low crystalline Fe (II) to promote the production of hydroxyl radicals (OH) thus Cd availability in paddy soils during drainage. On the whole, RS increased OH and extractable Cd by 0.2-1.4 and 0.1-3.3 times, respectively. While the addition of RS effectively improved the oxidation rate of structural Fe (II) mineral (i.e., FeS) to enhance soil Cd activation (up to 38.5 %) induced by the increased OH (up to 69.2 %). Additionally, the existence of CO32- significantly increased the efficiency level on OH production and Cd activation, which was attributed to the improved reactivity of Fe (II) by CO32- in paddy soils. Conclusively, this study emphasizes risks of activating soil Cd induced by RS returning-derived OH, providing a new insight into evaluating the safety of straw recycling.

Potential Protective Effect of SeleniumEnriched Lactobacillus plantarum on Cadmium-Induced Liver Injury in Mice

Cadmium (Cd) is a prevalent environmental contaminant that poses a potential hazard to the health of both humans and animals. In this study, biosynthesized selenium-enriched Lactobacillus plantarum and selenium nanoparticles (SeNPs) were developed and evaluated for their protective effects against Cd-induced hepatic injury in mice through oral administration for 4 weeks. Cadmium exposure resulted in severe impairment of liver function, as evidenced by increased levels of serum markers of liver injury and, oxidative stress and significant damage to liver tissue, and a notable decrease in the diversity of the intestinal microbiota. Oral administration of Se-enriched L. plantarum (LS) reduced cadmium accumulation in the liver by 49.5% and, restored other cadmium-induced damage markers to normal levels. A comparison of the effects with those of L. plantarum (L) and SeNPs isolated from LS revealed that LS could more effectively alleviate hepatic oxidative stress and reduce the intrahepatic inflammatory responses of the liver, further protecting against cadmiuminduced liver injury. These findings suggest that the development of LS may be effective at protecting the liver and intestinal tract from cadmium-induced damage.

Enhancing soil redox dynamics: Comparative effects of Fe-modified biochar (N-Fe and S-Fe) on Fe oxide transformation and Cd immobilization

Biochar and modified biochar have gained wide attention for Cd-contaminated soil remediation. This study investigates the effects of rape straw biochar (RSB), sulfur-iron modified biochar (S-FeBC), and nitrogen-iron modified biochar (N-FeBC) on soil Fe oxide transformation and Cd immobilization. The mediated electrochemical analysis results showed that Fe modification effectively enhanced the electron exchange capacity (EEC) of biochar. After 40 days of anaerobic incubation, compared to the treatment without biochar (CK), the concentrations of CaCl2-extractable Cd in N-FeBC, S-FeBC, and RSB treatments decreased by 79%, 53%, and 23%, respectively. Compared with S-FeBC, N-FeBC significantly decreased the soil Eh and increased soil pH within the first 15 days, which could be attributed to its higher EEC and alkalinity. There is a negative correlation between the concentration of CaCl2-extractable Cd and soil pH (p < 0.01). The sequential extraction results showed that both N-FeBC and S-FeBC promoted Cd transfer from acid-soluble to Fe/Mn oxides bound fraction (Fe/Mn-Cd). N-FeBC significantly increased the concentration of amorphous Fe oxides (amFeox) from 4.0 g kg-1 in day 1 to 4.6 g kg-1 in day 15 by promoting the NO3--reducing Fe(II) oxidation process, while S-FeBC significantly increased amFeox from 4.0 g kg-1 in day 15 to 4.8 g kg-1 in day 40 by promoting the Fe(II) recrystallization. There is a positive correlation between the concentration of amFeox and Fe/Mn-Cd (p < 0.01). The scanning electron microscopy analysis showed that Cd was bound to the amFeox coating on the surface of Fe-modified biochar. By acting as an electron shuttle, the active surface of Fe-modified biochar may serve as a hotspot for Fe transformation, which promotes amFeox formation and Cd immobilization. This study highlights the potential of Fe-modified biochar for the remediation of Cd-contaminated soils and provides valuable insights into the development of effective remediation approaches for Cd-contaminated soils.

Comparison of water-soluble organic matter (WSOM)-containing and WSOM-free biochars for simultaneous sorption of lead and cadmium

The effects of individual biochar constituents and natural environmental media on the immobilization behaviors and chemical activities of toxic heavy metals are still poorly understood. In this work, the physicochemical properties of raw corn straw (CS) and CS-derived biochar materials as well as their sorption abilities and retention mechanisms for lead (Pb) and cadmium (Cd) were evaluated by combining batch experiments and spectral approaches. According to the spectral analysis results and single variable principle, the setting of biochars after soaking in solution as the control group was suggested when evaluating their retention mechanisms for Pb and Cd. The rising of ionic strength did not apparently affect the immobilization of Pb by biochar prepared at 500 °C (i.e., CB500) and Pb/Cd by water-soluble organic matter (WSOM)-free CB500 (i.e., DCB500), while slightly inhibited the sorption of Cd by CB500. Pb and Cd exhibited a mutual inhibition effect on their sorption trends with a higher sorption preference of Pb. The dominant fixation mechanism of Pb by CB500 and DCB500 was identified to be mineral precipitation. In contrast, the main sorption mechanism of Cd changed from mineral precipitation in the single-metal system to surface complexation in the binary-metal system. The sorption ratios of Pb and Cd on CB500 were comparable to those on DCB500 with the coexistence of mixed natural organic matters (NOM) and ferrihydrite. The current experimental findings suggested that DCB500 was a suitable remediation agent for regulating the migration behaviors of toxic Pb and Cd in acidic and NOM-rich soil and water systems.

Cadmium toxicity to and accumulation in a soil collembolan (Folsomia candida): major factors and prediction using a back-propagation neural network model

Accurate prediction of cadmium (Cd) ecotoxicity to and accumulation in soil biota is important in soil health. However, very limited information on Cd ecotoxicity on naturally contaminated soils. Herein, we investigated soil Cd ecotoxicity using Folsomia candida, a standard single-species test animal, in 28 naturally Cd-contaminated soils, and the back-propagation neural network (BPNN) model was used to predict Cd ecotoxicity to and accumulation in F. candida. Soil total Cd and pH were the primary soil properties affecting Cd toxicity. However, soil pH was the main factor when the total Cd concentration was < 3 mg kg-1. Interestingly, correlation analysis and the K-spiked test confirmed nutrient potassium (K) was essential for Cd accumulation, highlighting the significance of studying K in Cd accumulation. The BPNN model showed greater prediction accuracy of collembolan survival rate (R2 = 0.797), reproduction inhibitory rate (R2 = 0.827), body Cd concentration (R2 = 0.961), and Cd bioaccumulation factor (R2 = 0.964) than multiple linear regression models. Then the developed BPNN model was used to predict Cd ecological risks in 57 soils in southern China. Compared to multiple linear regression models, the BPNN models can better identify high-risk regions. This study highlights the potential of BPNN as a novel and rapid tool for the evaluation and monitoring of Cd ecotoxicity in naturally contaminated soils.

Bioremediation of paddy soil with amphitropic mixture markedly attenuates rice cadmium: Effect of soil cadmium removal and Fe/S-cycling bacteria in rhizosphere

Cadmium (Cd) pollution in paddy soil can easily lead to excessive Cd in rice, thereby considerably threatening human health. Microbial leaching is an effective pathway for the mobilization and removal of Cd from soil. In this study, an amphitropic mixture (AM) composed of autotrophic and heterotrophic microbial strains was used to leach Cd-contaminated paddy fields. Chemical analysis showed that the AM effectively removed 52 % of the total Cd, 39 % of the available Cd, and 60 % of the exchangeable and carbonate-bound Cd from the paddy soil. After bioleaching, the Cd in the discarded AM solution was adsorbed using a metal adsorbent. Effects of remediation on the soil nutrients or secondary pollution were not significant. Microbial analysis showed that >96 % and 67 % of the indigenous bacteria and fungi, respectively, remained in the AM-remediated soil. Double-cropped rice was cultivated to evaluate the Cd removal efficiency of grains using AM remediation. The Cd in early and late brown rice decreased by 86 % and 56 %, respectively, which was higher than that found for a series of biochemical remediation materials reported in other studies. Furthermore, the AM remediation promoted the growth of iron (Fe)- and sulfur (S)-cycling bacteria in the rice rhizosphere, such as Sulfuricurvum, Desulfurivibrio and Geobacter etc., which reduced the Cd availability in the soil and rice uptake. This study shows that AM has potential applications in the remediation of Cd-contaminated paddy fields and provides a new pathway for safe rice production.

[Effect of EDDS Application on Soil Cu/Cd Availability and Uptake/transport by Castor]

To investigate the effect of chelating agents on plant uptake of heavy metals, castor (Ricinus communis L.) was used as the test plant. Soil culture and pot experiments were conducted to study the effects of different concentrations of ethylenediamine disuccinic acid (EDDS) on the forms of Cu and Cd in soil and their absorption and transport by castor. The results showed that the application of EDDS significantly increased the content of available Cu and Cd. After 15 days of cultivation, the available Cu and Cd concentrations in the soil increased by 43.01%-103.55% and 51.78%-69.43%, respectively. EDDS promoted the conversion of reducible Cu to weak acid extractable and increased the mobility of Cu. Meanwhile, the application of EDDS promoted the absorption, transport, and enrichment of Cu in castor. Under the application of 2.5 mmol·kg-1 EDDS and 5.0 mmol·kg-1 EDDS, the Cu concentrations in the shoots were 4.88 times and 16.65 times higher than that of the control (P< 0.05), and the Cu concentrations in the roots were 2.89 times and 3.60 times higher than that of the control (P< 0.05), respectively. The Cu transport coefficient significantly increased by 72.73% and 381.82% when treated with EDDS 2.5 and EDDS 5.0. Simultaneously, the phytoextraction of Cu in shoots, roots, and their sum were 14.08, 2.16, and 4.70 times higher than that of the control (P<0.05), respectively, when treated with EDDS 5.0. Furthermore, EDDS significantly increased the Cd concentrations in castor. When treated with EDDS 2.5 the shoots and roots increased by 15.15% and 57.42%, respectively, and the phytoextraction of total Cd significantly increased by 13.44%. Generally, the EDDS treatment could increase the available Cu and Cd in soil, promote the uptake of Cu and Cd, and improve the phytoremediation efficiency of castor. Among them, the addition of 5.0 mmol·kg-1 EDDS had the best effect for Cu, whereas the addition of 2.5 mmol kg-1 EDDS had a higher increase in the phytoextraction of Cd.

Susceptibility of Cd availability in microplastics contaminated paddy soil: Influence of ferric minerals and sulfate reduction

The combined contamination of cadmium (Cd) and microplastics (MPs) in paddy soil always occurred, while its influence on Cd availability remained unclear. This study investigated the Cd availability in Cd-MPs co-contaminated paddy soil in consideration of both ferric minerals and sulfate reduction under flooding conditions. The presence of MPs resulted in a higher Cd releasing risk, as represented by the increase in the available Cd and decrease in Fe-Mn oxide-bound Cd contents, especially on the 7th and 14th days based on the sequential extraction results. MPs facilitated the formation of Fe-organic ligands, which accelerated the reductive dissolution of iron minerals but decreased the amounts of amorphous iron minerals due to the release of dissolved organic substances into pore water. Furthermore, MPs promoted the relative abundance of sulfate-reducing bacteria (such as Streptomyces and Desulfovibrio genera), thus increasing the contents of reductive S species, which was advantageous to the co-precipitation of Fe, S, and Cd on the surface of MPs based on our experimental and statistical results. Taken together, both iron and sulfate reduction under anaerobic conditions played a critical role in Cd mobilization in Cd-MPs co-contaminated paddy fields.

Adsorption mechanism of Cd2+ on microbial inoculant and its potential for remediation Cd-polluted farmland soils

The adsorption characteristics and mechanism of Cd2+ on microbial inoculant (MI) mainly composed of Bacillus subtilis, Bacillus thuringiensis and Bacillus amyloliquefaciens, and its potential for remediation Cd polluted soils through batch adsorption and soil incubation experiments. It was found that the Freundlich isotherm model and the pseudo-second-order kinetics were more in line with the adsorption processes of Cd2+. The maximum adsorption capacity predicted by Langmuir isotherm model suggested that of MI was 57.38 mg g-1. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) images exhibited the surface structure of MI was damaged to varying degrees after adsorption, and Cd element was distributed on the surface of MI through ion exchange. X-ray diffraction (XRD) results showed that CdCO3 was formed on the surface of MI. Moreover, the functional groups (-OH, C-H, and -NH) involved in the adsorption of Cd2+ through fourier transform infrared spectroscopy (FTIR). After applying MI to Cd-contaminated soil, it was found that soil pH, conductivity (EC) and soil organic matter (SOM) increased by 0.84 %-2.43 %, 31.6 %-241.48 %, and 8.11 %-24.1 %, respectively, when compared with the control treatments. The content of DTPA-Cd in the soils was significantly (P < 0.05) reduced by 15.48 %-29.68 % in contrast with CK, and the Cd speciation was transformed into a more stable residual fraction. The activities of urease, phosphatase and sucrose were increased by 3.5 %-45.18 %, 57.00 %-134.18 % and 52.51 %-70.52 %, respectively, compared with CK. Therefore, MI could be used as an ecofriendly and sustainable material for bioremediation of Cd-contaminated soils.

The dissolution characteristics of cadmium containing birnessite produced from paddy crusts

The cadmium (Cd) accumulates in birnessite as it forms on the surface of paddy crusts (PC). The stability of Cd-containing birnessite is influenced by environmental factors, and destabilized birnessite releases dissolved Cd. We report the effects of pH, oxalic acid, and light on the dissolution of Cd-containing birnessite. We found that at pH 4.0, with light and 0.20 mol/L oxalic acid, the ratio of dissolved Cd and manganese (Mn) peaked after 24 h at 2978.0 μg/g and 326.8 mg/g, respectively. The three environmental factors affected the dissolution of Cd-containing birnessite in the following order: pH > oxalic acid > light. During dissolution process, Cd and Mn did not dissolve simultaneously, and the dissolved Cd/Mn ratio in the solution was significantly lower than that of the pristine mineral (33.5 × 10-3). Compared with Mn, Cd dissolution was inhibited by strong acidity (pH 4.0-5.0), and the dissolved Cd/Mn ratio was 5-10 × 10-3. Mild acidity (pH 6.0) was weakly inhibitory, with a Cd/Mn ratio of 6-15 × 10-3. In an alkaline (pH 8.0) oxalate environment, light illumination inhibited Cd dissolution, and the Cd/Mn ratio decreased over time due to the stability of the products formed by oxalate and carbonate, with Cd being more stable than those formed by Mn. Our findings would provide insights into the migration and transformation of PC-associated Cd in paddy fields.

Effects of different aging methods on the ability of biochar to adsorb heavy metal cadmium and its physical and chemical properties

The aging process can affect the physical and chemical properties as well as adsorption capacity of biochar. This study focuses on the heavy metal cadmium (Cd) as the research object, and artificially ages biochar prepared from rice straw and corn straw through accelerated freeze-thaw cycles, alternating dry wet cycles, and ultraviolet light treatment, in order to evaluate the effects of different aging conditions on the physical and chemical properties of the two different types of biochar and on their adsorption capacities for Cd. After aging, the pH of rice and corn biochar decreased to varying degrees, respectively. The surface structure was ruptured, the average pore diameter was decreased, and the specific surface area was increased by 27.3%, 21.9%, and 9.8% (rice) and 95.4%, 27.7%, and 13.4% (corn). Ultraviolet light aging has the most significant impact on the elemental content of biochar, and the C content was decreased by 12.4% (rice) and 9.3% (corn). The O content was increased by 11.2% (rice) and 44.1% (corn), and the numbers of O/C, H/C, (O + N)/C, and oxygen-containing functional groups were increased. These results demonstrate that the aging process reduces the degree of aromatization of biochar, while enhancing its polarity and Cd adsorption capacity. Rice straw biochar (RSB) has a greater ability to adsorb Cd than corn straw biochar (CSB). In addition, ultraviolet light aging is particularly effective in increasing heavy metal adsorption.

Nano zero-valent iron and melatonin synergistically alters uptake and translocation of Cd and As in soil-rice system and mechanism in soil chemistry and microbiology

Nanoscale zero-valent iron (Fe) is a promising nanomaterial for remediating heavy metal-contaminated soils. Melatonin (MT) is essential to alleviate environmental stress in plants. However, the conjunction effects of Fe and MT (FeMT) on rice Cd, As accumulation and the mechanism of soil chemical and microbial factors interaction are unclear. Here, a pot experiment was conducted to evaluated the effects of the FeMT for rice Cd, As accumulation and underlying mechanisms. The findings showed that FeMT significantly reduced grains Cd by 92%-87% and As by over 90%, whereas improving grains Fe by over 213%. Soil available-Cd and iron plaques-Cd (extracted by dithionite-citrate-bicarbonate solution, DCB-Cd) significantly regulated roots Cd, thus affected Cd transport to grains. Soil pH significantly affected soil As and DCB-As, which further influenced roots As uptake and the transport to shoots and grains. The interactions between the soil bacterial community and soil Fe, available Fe, and DCB-Fe together affected root Fe absorption and transportation in rice. FeMT significantly influenced rhizosphere soil bacterial α- and β-diversity. Firmicutes as the dominant phylum exhibited a significant positive response to FeMT measure, and acted a key role in reducing soil Cd and As availability mainly by improving iron-manganese plaques. The increase of soil pH caused by FeMT was beneficial only for Actinobacteriota growth, which reduced Cd, As availability probably through complexation and adsorption. FeMT also showed greater potential in reducing human health and ecological risks by rice consumption and straw returning. These results showed the important role of both soil chemical and microbial factors in FeMT-mediated rice Cd, As reduction efficiency. This study opens a novel strategy for safe rice production and improvement of rice iron nutrition level in heavy-metals polluted soil, but also provides new insights into the intricate regulatory relationships among soil biochemistry, toxic elements, microorganism, and plants.

Toxic effects of combined exposure to cadmium and diclofenac on freshwater crayfish (Procambarus clarkii): Insights from antioxidant enzyme activity, histopathology, and gut microbiome

In recent years, excessive discharge of pollutants has led to increasing concentrations of cadmium (Cd) and diclofenac (DCF) in water; however, the toxicity mechanism of combined exposure of the two pollutants to aquatic animals has not been fully studied. Procambarus clarkii is an economically important aquatic species that is easily affected by Cd and DCF. This study examined the effects of combined exposure to Cd and DCF on the tissue accumulation, physiology, biochemistry, and gut microflora of P. clarkii. The results showed that Cd and DCF accumulated in tissues in the order of hepatopancreas > gill > intestine > muscle. The hepatopancreas and intestines were subjected to severe oxidative stress, with significantly increased antioxidant enzyme activity. Pathological examination revealed lumen expansion and epithelial vacuolisation in the hepatopancreas and damage to the villous capillaries and wall in the intestine. The co-exposure to Cadmium (Cd) and Diclofenac (DCF) disrupts the Firmicutes/Bacteroidetes (F/B) ratio, impairing the regular functioning of intestinal microbiota in carbon (C) and nitrogen (N) cycling. This disturbance consequently hinders the absorption and utilization of energy and nutrients in Procambarus clarkii. This study offers critical insights into the toxicological mechanisms underlying the combined effects of Cd and DCF, and suggests potential approaches to alleviate their adverse impacts on aquatic ecosystems.

Competition of Cd(II) and Pb(II) on the bacterial cells: a new insight from bioaccumulation based on NanoSIMS imaging

Polymetallic exposure causes complex toxicity to microorganisms. In this study, we investigated the responses of Escherichia coli under co-existence of cadmium (Cd) and lead (Pb), primarily based on biochemical analysis and RNA sequencing. Cd completely inhibited bacterial growth at a concentration of 2.41 mmol/L, with its removal rate as low as <10%. In contrast, the Pb removal rate was >95% under equimolar sole Pb stress. In addition, the Raman analysis confirmed the loss of proteins for the bacterial cells. Under the co-existence of Cd and Pb, the Cd toxicity to E. coli was alleviated. Meanwhile, the biosorption of Pb cations was more intense during the competitive sorption with Cd. Transmission electron microscopy images showed that a few cells were elongated during incubation, i.e., the average cellular length increased from 1.535 ± 0.407 to 1.845 ± 0.620 µm. Moreover, NanoSIMS imaging showed that the intracellular distribution of Cd and Pb was coupled with sulfur. Genes regulating sulfate transporter were also upregulated to promote sulfate assimilation. Then, the subsequent production of biogenic sulfide and sulfur-containing amino acids was enhanced. Although this strategy based on S enrichment could resist the polymetallic stress, not all related genes were induced to upregulate under sole Cd stress. Therefore, the S metabolism might remodel the microbial resistance to variable occurrence of heavy metals. Furthermore, the competitive sorption (in contrast to sole Cd stress) could prevent microbial cells from strong Cd toxicity.IMPORTANCEMicrobial tolerance and resistance to heavy metals have been widely studied under stress of single metals. However, the polymetallic exposure seems to prevail in the environment. Though microbial resistance can alleviate the effects of exogenous stress, the taxonomic or functional response to polymetallic exposure is still not fully understood. We determined the strong cytotoxicity of cadmium (Cd) on growth, and cell elongation would be driven by Cd stress. The addition of appropriate lead (Pb) showed a stimulating effect on microbial bioactivity. Meanwhile, the biosorption of Pb was more intense during co-existence of Pb and Cd. Our work also revealed the spatial coupling of intracellular S and Cd/Pb. In particular, the S assimilation was promoted by Pb stress. This work elucidated the microbial responses to polymetallic exposure and may provide new insights into the antagonistic function during metal stresses.

Chlorella pyrenoidosa as a potential bioremediator: Its tolerance and molecular responses to cadmium and lead

Heavy metal contamination negatively affects plants and animals in water as well as soils. Some microalgae can remove heavy metal contaminants from wastewater. The aim of this study was to screen green microalgae (GM) to identify those that tolerate high concentrations of toxic heavy metals in water as possible candidates for phytoremediation. Analyses of the tolerance, physiological parameters, ultrastructure, and transcriptomes of GM under Cd/Pb treatments were conducted. Compared with the other GM, Chlorella pyrenoidosa showed stronger tolerance to high concentrations of Cd/Pb. The reduced glutathione content and peroxidase activity were higher in C. pyrenoidosa than those in the other GM. Ultrastructural observations showed that, compared with other GM, C. pyrenoidosa had less damage to the cell surface and interior under Cd/Pb toxicity. Transcriptome analyses indicated that the "peroxisome" and "sulfur metabolism" pathways were enriched with differentially expressed genes under Cd/Pb treatments, and that CpSAT, CpSBP, CpKAT2, Cp2HPCL, CpACOX, CpACOX2, and CpACOX4, all of which encode antioxidant enzymes, were up-regulated under Cd/Pb treatments. These results show that C. pyrenoidosa has potential applications in the remediation of polluted water, and indicate that antioxidant enzymes contribute to Cd/Pb detoxification. These findings will be useful for producing algal strains for the purpose of bioremediation in water contamination.

Low-frequency noise aggravates the toxicity of cadmium in sea slug Onchdium reevesii

Industrial development not only triggers heavy metal pollution but also introduces a less easily discernible disturbance: low-frequency noise pollution. Low-frequency noise can disrupt wildlife behavior, potentially exerting complex effects through interacting with heavy metals. Nevertheless, the cumulative impacts of low-frequency noise and cadmium (Cd) pollution on marine organisms remain largely unexplored. This study aimed to evaluate the immune defense response of sea slugs (Onchdium reevesii) exposed to Cd (1.32 mg/L) and low-frequency noise (500 Hz, 1000 Hz). Our results show that Cd exposure results in Cd2+ accumulation in the sea slug's hepatopancreas, leading to a decrease in total antioxidant capacity (TAC) and a significant increase in enzyme activities, including glutathione (GSH), lipid peroxidation (LPO), and aspartate transferase (AST). Additionally, there is a substantial upregulation in the expression of genes related to tumor protein p53 (p53), Cytochrome C (CytC), Caspase 3, and Caspase 9, as well as metallothionein (MT) and heat shock protein 70 (Hsp70) genes. Concurrently, an excessive production of reactive oxygen species (ROS) occurs in the hemocytes, resulting in apoptosis and subsequent diminished cell viability, with these effects positively correlating with the exposure duration. Furthermore, when sea slugs were exposed to both Cd and low-frequency noise, there was a decrease in the hepatopancreas's antioxidant capacity and an enhancement in hemocytes immune responses, which positively correlated with low-frequency noise frequency. The comprehensive assessment of biomarker responses highlights that low-frequency noise has the potential to amplify the deleterious effects of Cd on sea slug physiology, with this negative impact positively linked to noise frequency. Consequently, our study underscores that the combined influence of low-frequency noise and Cd pollution magnifies the effects on sea slug health. This could potentially disrupt the population stability of this species within its natural habitat, providing fresh insights into the evaluation of cumulative environmental pollution risks.

Stable Isotope Analyses Reveal Impact of Fe and Zn on Cd Uptake and Translocation by Theobroma cacao

High concentrations of toxic cadmium (Cd) in soils are problematic as the element accumulates in food crops such as rice and cacao. A mitigation strategy to minimise Cd accumulation is to enhance the competitive uptake of plant-essential metals. Theobroma cacao seedlings were grown hydroponically with added Cd. Eight different treatments were used, which included/excluded hydroponic or foliar zinc (Zn) and/or iron (Fe) for the final growth period. Analyses of Cd concentrations and natural stable isotope compositions by multiple collector ICP-MS were conducted. Cadmium uptake and translocation decreased when Fe was removed from the hydroponic solutions, while the application of foliar Zn-EDTA may enhance Cd translocation. No significant differences in isotope fractionation during uptake were found between treatments. Data from all treatments fit a single Cd isotope fractionation model associated with sequestration (seq) of isotopically light Cd in roots and unidirectional mobilisation (mob) of isotopically heavier Cd to the leaves (ε114Cdseq-mob = -0.13‱). This result is in excellent agreement with data from an investigation of 19 genetically diverse cacao clones. The different Cd dynamics exhibited by the clones and seen in response to different Fe availability may be linked to similar physiological processes, such as the regulation of specific transporter proteins.

Si-enriched biochars improved soil properties, reduced Cd bioavailability while enhanced Cd translocation to grains of rice

Biochar and silicon (Si) have been widely considered to play an important role in mitigating cadmium (Cd) toxicity. In this study, wild-type rice (WT, high-Si) and Si-deficient mutant rice (lsi1, low-Si) were used as raw materials to prepare biochar at 500℃; the Si concentrations of high- and low-Si biochar were 15.9% and 5.3%, respectively. The impacts of different application rates (0%, 2%, 4%) of high- and low-Si biochars on soil chemical properties, Si and Cd fractions and availability, Cd absorption, and translocation were investigated. The results showed that both types of biochars increased soil pH, soil available nitrogen, and available phosphorus and potassium; and promoted Si uptake and plant growth of rice. Soil available Si, CaCl2-Si, acetic-Si, H2O2-Si, oxalate-Si, and Na2CO3-Si were also increased by biochar supply, especially for high-Si biochar treatments. In addition, both types of biochars had no effects on soil total Cd, but reduced soil available Cd by 2-17% in early season 2022, and reduced oxidizable Cd and residual Cd. Biochar application did not influence Cd concentrations in roots, stems, and leaves, but significantly increased Cd uptake and transport from stems and leaves to grains. The results suggested that Si-rich biochar could improve soil nutrients, change soil Si/Cd fractions and availability, promote rice growth but increase the risk of Cd toxicity in grains, indicating the complex of straw biochar in remediating Cd-contaminated paddy soil.

Co-utilization of sepiolite and ferromanganese ore reduces rice Cd and As concentrations via soil immobilization and root Fe-Mn plaque resistance

Cadmium (Cd) and arsenic (As), common toxic elements in farmland soil, are easily absorbed by rice and accumulate in grains. Combined amendment is likely to ameliorate Cd-As-contaminated soil; however, studies on this aspect are limited. Therefore, we explored the effects of co-utilizing sepiolite and ferromanganese ore (SF) on Cd-As accumulation in rice by conducting pot experiments on Cd-As-contaminated paddy soil. The results showed that 4 g kg-1 SF (4SF) reduced Cd (55.9 %/48.5 %) and As (82.9 %/64.7 %) concentrations in grain in early and late rice. The Fe concentration in Fe-Mn plaque (IMP) (FeIMP) first decreased and then increased, and the Mn concentration in IMP (MnIMP) increased with an increase in the SF addition amount. This resulted in the 4SF treatment maximizing the Cd adsorption capacity of IMP, whereas the 2 g kg-1 SF treatment (2SF) minimized the As adsorption capacity of IMP. More importantly, when the total Cd and As were 9.7 mg kg-1 and 304.2 mg kg-1, respectively, in the soil, 4SF application reduced CaCl2-extractable Cd (80.5 %/87.9 %), and 2SF reduced available As (24.0 %/20.9 %) in early and late rice. Additionally, SF decreased the Cd and As ion contents in soil pore water. Overall, SF has good immobilization and sustained effect on Cd-As and can be used as an effective material for remediation of Cd-As-contaminated soil.

The intrinsic and extrinsic mechanisms regulated by functional carbon nanodots for the phytoremediation of multi-metal pollution in soils

Functional carbon nanodots (FCNs) were currently demonstrated to regulate plant behavior in the agricultural and environmental areas. However, their regulation mechanisms on the interactions of plant-soil system during phytoremediation remain unrevealed. Here, Solanum nigrum L. was employed to explore the intrinsic and extrinsic mechanisms regulated by FCNs in the phytoremediation of Cd-Pb co-contaminated soils. The mediation of FCNs on metal removal and plant growth showed a hormesis manner, wherein the maximum induction effect was contributed by 15 mg kg-1 FCNs. Cd/Pb removal were enhanced by 8.5% and 31.6%, respectively. Moreover, FCNs reallocate metal distribution in plant by immobilized metals in roots and suppressed metal translocation to leaves. Improving plant growth (by 82.8% for root), stimulating plant hormesis, and activating plant detoxification pathways are the intrinsic mechanism for the phytoremediation smartly regulated by FCNs. Notably, FCNs induced soil enzyme activities that associated with soil nutrients recycling, up-regulated the microbial diversity and the soil immune system, and regulated S. nigrum L. to recruit beneficial microbials in the rhizosphere. The above-mentioned comprehensive improvement of soil micro-environment is the extrinsic mechanism regulated by FCNs. This study provides new insights to evaluate the interactions of nanomaterials with plant-soil system under soil contamination.

Comparative study of efficiencies of purification of cadmium contaminated irrigation water by different purification systems

Cadmium (Cd) contamination in rice threats food safety and human health. Control of Cd pollution has become an urgent need. Most existing studies on heavy metal pollution control have focused on industrial wastewater and few on irrigation water. Some researchers have found ecological ditches, plant ponds and constructed wetlands have the potential of treating heavy metal contaminated irrigation water, but they examined only one of the methods and the validity needs to be verified by field studies. Our study has filled the gap by combining the methods and using field experiments. We examined efficiencies of removal of Cadmium from irrigation water by 14 different combinations of ecological ditches, plant ponds, and constructed wetlands using field experiments. The effects of the purification on Cd concentration in paddy soil and rice grains were also examined. Results showed that there were significant differences among efficiencies of purification of Cd contaminated irrigation water using different systems and that pH, chemical form of Cd in irrigation water, vegetation coverage and biomass of aquatic plants significantly affect the efficiency. Of the 14 purification systems, seven resulted in the concentration of Cd in the effluent water meeting the National Standard for Irrigation Water Quality (GB5084-2021) for all days of the experiment period. The highest amount and rate of Cd removal were achieved by the combination of two-stage ecological ditch, two-stage plant pond, and one-stage constructed wetland, while the highest removal amount and rate per 100 m2 was achieved by the combination of one-stage plant pond and one-stage constructed wetland. Considering purification efficiency, area of coverage, and cost of construction and maintenance, we suggest that combination of plant pond and constructed wetland be a priority choice for purification of Cd pollution in irrigation water. Compared to the control data collected from rice grain and paddy soil irrigated by unpurified water, Cd concentration in rice grain and paddy soil irrigated by purified water declined by 5.08-19.42 % and 30.93-77.15 % respectively. All results showed that removal of Cd contamination from irrigation water effectively controlled cadmium pollution in rice grain and paddy soil. Our study not only contributes to pollution control practice, but also warrants further investigation of the mechanisms of how the treatment systems work. The most efficient method we identified could be applied locally, regionally and in areas of similar topography, climate, soil, vegetation, agriculture, and heavy metal pollution.

Red light alleviates Cd toxicity in Egeria densa by modifying carbon-nitrogen metabolism and boosting energy metabolism

Among the various pollutants detected in aquatic ecosystems, cadmium (Cd) is considered as one of the most hazardous. Freshwater macrophytes have been recognized as possible candidates for eliminating Cd from environment. Nevertheless, the impact of light quality on their ability to tolerate Cd toxicity remains unclear, and the underlying mechanisms have yet to be fully elucidated. In this study, we utilized physiological testing and metabolomics to explore the potential mechanisms by which light quality influences the ability of Egeria densa, a significant Cd hyperaccumulator, to withstand Cd toxicity. The study demonstrated that following Cd treatment, E. densa grown under red light exhibited superior photosynthetic efficiency compared to those grown under blue light, as evidenced by significantly increased photosynthetic rate, higher starch content, and greater activity of photosynthetic enzymes. Moreover, metabolomic analyses revealed that under Cd stress, E. densa grown under red light exhibited an enhanced glycolysis for increased energy production. Sucrose metabolism was also improved to generate sufficient sugar including glucose, fructose and mannose for osmotic adjustment. Moreover, under red light, the heightened production of α-ketoglutarate via tricarboxylic acid (TCA) cycle redirected nitrogen flow towards the synthesis of resilient substances such as γ-Aminobutyric Acid (GABA) and methionine. The production of these substances was ∼2.0 and 1.3 times greater than that of treatment with Cd under blue light, thereby improving E. densa's capacity to withstand Cd stress. This study represents the initial investigation into the possible mechanisms by which light quality influences the ability of E. densa to withstand Cd toxicity through regulating CN metabolism. Furthermore, these findings have the potential to improve phytoremediation strategies aimed at reducing Cd pollution.

2,2',4,4'-Tetrabromodiphenyl ether and cadmium co-exposure activates aryl hydrocarbon receptor pathway to induce ROS and GSDME-dependent pyroptosis in renal tubular epithelial cells

We have previously found that a mixture exposure of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and cadmium (Cd) causes kidney damage; however, the mechanism was not fully understood. The aryl hydrocarbon receptor (AhR) is a ligand-receptor transcription factor that plays an important role in the adaptive response or metabolic detoxification of environmental toxins. Thus, this study aimed to examine the role of AhR in kidney toxicity. BDE-47 (50 μM) or Cd (5 μM) exposure reduced cell viability in renal tubular epithelial cells (HKC), with a larger effect observed in co-treatment. The cell morphology presented pyroptotic changes, including swollen cells, large bubbles, and plasma membrane pore formation. The gene expressions of AhR, heat shock protein 90 (Hsp90), AhR nuclear translocator (ARNT), and cytochrome P450 1B1 (CYP1B1) were increased, while CYP1A1 was decreased. Reactive oxygen species (ROS) were generated, which was reduced by the AhR antagonist CH223191. The apoptosis, necrosis, and intracellular lactated hydrogenase (LDH) release was elevated, and this was attenuated by N-acetylcysteine (NAC). Furthermore, the pyroptosis pathway was activated with increased protein levels of cleaved-caspase-3 and gasdermin E N-terminal (GSDME-NT), while caspase-8, caspase-3, and GSDME were decreased. These effects were alleviated by NAC and CH223191. Our data demonstrate a combined effect of BDE-47 and Cd on nephrotoxicity by activating AhR to induce ROS contributing to GSDME-dependent pyroptosis, and retardation of the AhR pathway could reduce this toxicity.

Roles of Cyt-c/Caspase-9/Caspase-3/Bax/Bcl-2 pathway in Cd-induced testicular injury in rats and the protective effect of quercetin

Cadmium (Cd) exposure causes oxidative damage to mitochondria, which would adversely affect rat testicular tissue. Quercetin (Que) is a natural antioxidant with anti-inflammatory, antioxidant and anti-apoptotic effects. However, the mechanism by which Que inhibits Cd-induced apoptosis of testicular cells remains unclear. The purpose of this study was to investigate the role of mitochondrial apoptosis pathway (Cyt-c/Caspase-9/Caspase-3/Bax/Bcl-2 pathway) in inhibiting Cd-induced apoptosis of testicular cells by Que. We used SD rats to simulate Cd chloride exposure by treating all sides of the rats with CdCl2 and/or Que. The levels of GSH and MDA in rat testis were detected using reagent kits. The effects of CdCl2 and/or Que on tissue damage, apoptosis, and gene and protein expression of the Cyt-c/Caspase-9/Caspase-3/Bax/Bcl-2 pathway in rat testis were examined by HE, TUNEL, RNA extraction and reverse-transcriptase polymerase chain reaction (RT-PCR), and Western blot (Wb). The results show that Cd significantly increased the contents of GSH and MDA in rat testis (P < 0.01); conversely, Que significantly reduced the contents of GSH and MDA (P < 0.01). Cd inflicted damage to testicular tissue, and Que addition significantly reduced the damage. Cd increased the number of apoptosis of testicle cells, and Que inhibited testicle-cell apoptosis. In addition, the results of reverse transcription PCR and Wb assays confirmed that, as expected, Cd increased the expression levels of Cyt-c, Caspase-9, Caspase-3, and Bax mRNAs as well as proteins. And at the same time decreased the expression of the anti-apoptotic factor Bcl-2 in the cells. Surprisingly, these effects were reversed when Que was added. Therefore, Que can play an antioxidant and anti-apoptotic role in reducing the testicular tissue damage caused by Cd exposure. This provides a conceptual basis for the later development and utilization of Que as well as the prevention and treatment of tissue damage caused by Cd exposure.

Biochar Derived from Urban Green Waste Can Enhance the Removal of Cd from Water and Reduce Soil Cd Bioavailability

The beneficial utilization of potentially increasing urban green waste (UGW) is critical for sustainable urban development in China. In this study, UGW was pyrolyzed at different temperatures, and the resulting biochar was used to amend Cd-contaminated soils to grow cabbage. Our results showed that the Cd adsorption capacity of UGW-biochar was positively correlated with the surface area, O/C, and (O+N)/C value of biochar. Furthermore, UGW-biochar was incorporated into three Cd-contaminated soils, including one acidic soil and two neutral soils, to assess its impact on the availability of Cd. The most substantial reduction in the concentration of available Cd was observed in the acidic soil, of the three tested soils. In the neutral soils, a more substantial reduction was found in the heavily Cd-contaminated soil compared to the lightly Cd-contaminated soil. UGW-biochar amendments to the three Cd-contaminated soils resulted in an increase in the cabbage biomass in acidic soil, whereas in neutral soils, it increased in lightly contaminated soils but decreased in heavily contaminated soils. Additionally, the Cd bioaccumulation factor (BCF), translocation factor (TF), and removal efficiency (RE), as impacted by the biochar application, were calculated in the lightly Cd-contaminated soil-cabbage system. The BCF decreased from 5.84 to 3.80 as the dosage of the UGW-biochar increased from 0% to 3%, indicating that the UGW-biochar immobilized Cd and reduced its bioaccumulation in cabbage roots. Based on our investigations, UGW-biochar effectively immobilizes Cd by reducing its mobility and bioavailability in a lightly contaminated environment matrix.

Mitigation effects of foliar supply of different sulfur forms on uptake, translocation and grain accumulation of Cd and As by paddy rice on basis of liming

Co-contamination of Cd and As in strongly acidic paddy soil has posed great challenges for remediation practice due to their distinct properties. Liming is a necessary but inadequate measure for normal growth of paddy rice and for Cd and As remediation in strongly acidic paddy soils rich in iron minerals. A greenhouse rice pot cultivation experiment was conducted to explore the efficiency and mechanisms of how foliar supply of different sulfur forms (K2S, K2SO4) could further mediate the uptake, translocation and grain accumulation of Cd and As by paddy rice on basis of liming. Results showed that compared to liming alone (CK), co-application of liming and foliar supply of K2S (L + FK2S) significantly reduced contents of Cd and As in brown rice by 44.4 % and 24.7 %, respectively. Contrastingly, co-application of liming and foliar supply of K2SO4 (L + FK2SO4) decreased Cd content of brown rice by 55.5 %, but had no effect on As content. Foliar supply of K2S and K2SO4 dramatically facilitated Cd upward transfer from roots to shoots by enhancing root Cd transfer from cell wall into trophoplast. On the other hand, both sulfur forms remarkably elevated sulfur contents in leaves and significantly inhibited Cd translocation from leaves to grain by enhancing vacuolar sequestration of Cd in leaves. Compared to CK and L + FK2SO4 treatment, it was by enhancing glutathione synthesis, cell wall deposition in roots and vacuolar sequestration of As in leaves that L + FK2S showed greater inhibiting effects on transfer of As from roots, stems and leaves to grain. Foliar supply of either sulfate or sulfide could efficiently decrease grain Cd of paddy rice, but only foliar supply of sulfide is effective in reducing grain As.

Dietary Exposure to Toxic Metals (Cd, Pb and Hg) from Cereals Marketed in Madeira and the Azores

Cereals and cereal-based foods continue to be basic foods in all diets. Despite being known for their high nutritional value; they can also contain contaminants (hazards) such as toxic metals. This study assesses the Cd, Pb and Hg dietary exposure from cereals and derivatives marketed in Madeira and the Azores and characterizes the risks by evaluating the Cd and Hg intake contributions to the tolerable intakes and by estimating the Margin of Exposure (MOE) in the case of Pb. In Madeira, metals follow the descending order of Cd > Pb > Hg. Cd stands out as having the highest levels (0.307 mg Cd/kg in oats; 0.237 mg/kg in rye). High levels of Pb (0.347 mg/kg) were also detected in rye. Regarding total mercury, rice stands out (0.0013 mg/kg) followed by wheat (0.001 mg/kg). While all cereals and derivatives except maize consumed in Madeira exceed the maximum value of Cd allowed by the EU, 50.0% of the rye and 25.0% of the corn flour samples exceeded the European Pb limit. The daily consumption of 100 g of oats, rye flour and rye represent high contributions to the TWI of Cd (93.2 - 120%). The MOE values of Pb from the consumption of rye (100 g/day) are 1,294 (nephrotoxic effects) and 3,082 (cardiotoxic effects). In the Azores, corn flour (0.72 mg Pb/kg) stands out with 85.7% of the samples exceeding the maximum Pb EU limit and MOE values of 626 (nephrotoxic effects) and 1,490 (cardiotoxic effects). Regular daily consumption of corn flour makes a low (< 10%) contribution to the Cd TDI. In conclusion, the Pb exposure from the consumption of cereals and derivatives could have toxic effects such as nephrotoxicity or cardiotoxicity in adults. The results highlight the need to set up monitoring and surveillance programs for the safety of cereals and their derivatives in Madeira and the Azores in terms of lead and cadmium.

Elevated carbon dioxide concentrations increase the risk of Cd exposure in rice

Since the Industrial Revolution, crops have been exposed to various changes in the environment, including elevated atmospheric carbon dioxide (CO2) concentration and cadmium (Cd) pollution in soil. However, information about how combined changes affect crop is limited. Here, we have investigated the changes of japonica and indica rice subspecies seedlings under elevated CO2 level (1200 ppm) and Cd exposure (5 μM Cd) conditions compared with ambient CO2 level (400 ppm) and without Cd exposure in CO2 growth chambers with hydroponic experiment. The results showed that elevated CO2 levels significantly promoted seedling growth and rescued the growth inhibition under Cd stress. However, the elevated CO2 levels led to a significant increase in the shoot Cd accumulation of the two rice subspecies. Especially, the increase of shoot Cd accumulation in indica rice was more than 50% compared with control. Further investigation revealed that the decreases in the photosynthetic pigments and photosynthetic rates caused by Cd were attenuated by the elevated CO2 levels. In addition, elevated CO2 levels increased the non-enzymatic antioxidants and significantly enhanced the ascorbate peroxidase (APX) and glutathione reductase (GR) activities, alleviating the lipid peroxidation and reactive oxygen species (ROS) accumulation induced by Cd. Overall, the research revealed how rice responded to the elevated CO2 levels and Cd exposure, which can help modify agricultural practices to ensure food security and food safety in a future high-CO2 world.

Induced mechanism of phosphatase hormesis by Cd ions and rhizosphere metabolites of Trifolium repens L

Rhizosphere phosphatases can exhibit hormetic effects in response to cadmium (Cd) ion stimulation. However, understanding the mechanisms underlying hormesis effects on soil ecosystems is challenging as studies on hormesis are usually specific to an organism, cell, or organ. To comprehensively investigate the mechanism of phosphatase hormesis, this study utilized in situ zymography and metabolomics to analyze the rhizosphere of Trifolium repens L. (white clover). Zymograms showed that rhizosphere phosphatase displayed a hormetic effect in 10 mg kg-1 Cd contaminated soil, with a hotspot area 1.8 times larger than non-Cd contaminated soil and a slight increase in enzyme activity. Nevertheless, the phosphatase activity was substantially suppressed upon elevating the Cd concentration in the soil to 50 mg kg-1. Differential metabolite identification and KEEG pathway enrichment analysis revealed that both rhizosphere organic acids and amino acid compounds positively affected phosphatase activity, and both were able to stabilize complexation with Cd ions via carboxyl groups. Besides, molecular docking models suggested that Cd ions act as cofactors to induce the formation of hydrogen bonds between amino acids/organic acids and phosphatase residues to form a triplet complex with a more stable structure, thereby improving phosphatase activity. The results indicated that amino acids and organic acids are heavily enriched in the rhizosphere of white clover and form a particular structure with soil Cd ions and phosphatase, which is essential for inducing the phosphatase hormesis as a detoxification mechanism in the rhizosphere micro-ecosystem.

Heavy metals contamination of seafood from the crude oil-impacted Niger Delta Region of Nigeria: A systematic review and meta-analysis

This study aims at computing the pooled mean estimate (PME) and health risks of heavy metals in seafood obtained from the Niger Delta Region of Nigeria (NDRN), using data from existing literatures. Pubmed, Scopus and Google Scholar were searched to retrieve articles that investigated the heavy metal contents of edible seafood from the NDRN. Search hits were screened against predetermined criteria following which relevant data were extracted from eligible articles. The PME for each metal was computed by performing a maximum likelihood random effect model meta-analysis using the R Studio Software. Outcome from the meta-analysis involving 58 studies and a total of 2983 seafood samples revealed the following PMEs (mg/kg dry wt seafood) for the investigated heavy metals: As (0.777), Cd (0.985), Co (4.039), Cr (2.26), Cu (11.45), Fe (143.39), Hg (0.0058), Mn (13.56), Ni (5.26), Pb (4.35), and Zn (29.32). The health risk assessment suggests that seafood from this region poses considerable carcinogenic and non-carcinogenic risks to human consumers. Our finding calls for urgent actions aimed at identifying and eliminating point sources of heavy metals pollution of the NDRN marine environment. Inhabitants of NDRN are encouraged to reduce seafood consumption while diversifying their protein sources to include non-seafood options.

Coupling of different antioxidative systems in rice under the simultaneous influence of selenium and cadmium

Selenium (Se) elevates the antioxidant ability of rice against cadmium (Cd) stress, but previous studies only focused on the variation in antioxidant enzymes or nonenzymatic substances induced by Se under Cd stress and ignored the relationships between different antioxidant parameters during the interaction. Here, hydroponic experiments with rice were performed by adding both Cd and Se at doses in the range of 0-50 μM to explore the physiological responses of rice and their relationships in the presence of different levels of Se and Cd. Exogenous Cd markedly promoted the activity of antioxidant enzymes with the exception of catalase (CAT) and the concentration of nonenzymatic substances in aerial parts. Se enhanced the antioxidant capacity by improving the activities of all the enzymes tested in this study and increasing the concentrations of nonenzymatic compounds. The couplings among different antioxidant substances within paddy rice were then determined based on cluster and linear fitting results and their metabolic process and physiological functions. The findings specifically highlight that couplings among the ascorbic acid (AsA)-glutathione (GSH) cycle, glutathione synthase (GS)-phytochelatin synthetase (PCS) coupling system and glutathione peroxidase (GPX)-superoxide dismutase (SOD) coupling system in aerial parts helps protect plants from Cd stress. These coupling systems form likely due to the fact that one enzyme generated a product that could be the substrate for another enzyme. Noticeably, such coupling systems do not emerge in roots because the stronger damage to roots than other organs activates the ascorbate peroxidase (APX)-GPX-CAT and PCS-GS-SOD systems with distinct functions and structures. This study provides new insights into the detoxification mechanisms of rice caused by the combined effect of Se and Cd.

Populus euphratica plant cadmium tolerance PePCR3 improves cadmium tolerance

Contamination of soils with toxic heavy metals is a major environmental problem. Growing crop plants that can promote the efflux of heavy metals is an effective strategy in contaminated soils. The plant cadmium resistance (PCR) protein is involved in the translocation of heavy metals, specifically zinc and cadmium (Cd). In this study, yeast expressing Populus euphratica PCR3 (PePCR3) showed enhanced Cd tolerance and decreased Cd accumulation under Cd treatment. Real-time quantitative PCR analyses revealed up-regulation of PePCR3 in poplar seedlings under Cd stress. Localization analysis revealed that PePCR3 localizes at the plasma membrane. The plant growth and biomass were greater in PePCR3-overexpressing (OE) transgenic hybrid poplar lines than in wild type (WT). Physiological parameters analyses indicated that, compared with WT, PePCR3-OE transgenic lines were more tolerant to Cd. In addition, more Cd was excreted in the roots of the PePCR3-OE transgenic lines than in those of WT, but the remaining Cd in transgenic lines was more translocated into the stems and leaves. Eight genes encoding transporters showed increased transcript levels in PePCR3-OE transgenic lines under Cd treatment, implying that PePCR3 interacts with other transporters to translocate Cd. Thus, PePCR3 may be an important genetic resource for generating new lines that can enhance Cd translocation to phytoremediation in contaminated soils.

Straw removal or non-removal affects cadmium (Cd) accumulation in soil-rice (Oryza sativa L.) system at different ambient air Cd levels

Despite the potential importance of the removal of contaminated straw for heavy metal output from agricultural soils, previous studies have primarily focused on the variation in the metal concentration without considering the impact input of heavy metals from atmospheric deposition. Here, rice was grown under field conditions, and, as a reference, in a deposition-free environment, and exposed to different ambient air Cd levels. Two consecutive years of pot experiments were conducted in two study areas (ZZ and LY) to examine the changes in soil physicochemical properties as well as Cd accumulation in the soil-rice (Oryza sativa L.) system in response to straw return or removal. The results showed that rice straw return enhanced the soil pH and organic matter (OM) content, but reduced the soil redox potential (Eh); and the variation in amplitude increased with number of cultivation years. After two years of cultivation, the concentrations of soil total Cd and extractable Cd in the straw-removal treatments reduced by 9.89-29.49% and 4.88-37.74%, respectively, whereas those in the straw-return treatments exhibited a slight decrease, or even an increase. This indicated that straw removal could effectively reduce the concentration and bioavailability of Cd in contaminated farmland, which was further confirmed by the results for accumulation of Cd in rice tissues. In addition, the contribution from atmospheric deposition was confirmed by the greater variation in Cd concentration in soils and rice tissues under deposition-free conditions. A major implication of our findings is that the adoption of reasonable straw-treatment measures and proper control over ambient air heavy metals can promote the remediation efficiency of Cd-contaminated fields.

Effects of Agricultural Intensification on Mediterranean Diets: A Narrative Review

INTRODUCTION

Mediterranean diets (MedDiets) are linked to substantial health benefits. However, there is also growing evidence that the intensification of food production over the last 60 years has resulted in nutritionally relevant changes in the composition of foods that may augment the health benefits of MedDiets.

OBJECTIVE

To synthesize, summarize, and critically evaluate the currently available evidence for changes in food composition resulting from agricultural intensification practices and their potential impact on the health benefits of MedDiets.

METHODS

We summarized/synthesized information from (i) systematic literature reviews/meta-analyses and more recently published articles on composition differences between conventional and organic foods, (ii) desk studies which compared food composition data from before and after agricultural intensification, (iii) recent retail and farm surveys and/or factorial field experiments that identified specific agronomic practices responsible for nutritionally relevant changes in food composition, and (iv) a recent systematic literature review and a small number of subsequently published observational and dietary intervention studies that investigated the potential health impacts of changes in food composition resulting from agricultural intensification.

RESULTS AND DISCUSSION

There has been growing evidence that the intensification of food production has resulted in (i) lower concentrations of nutritionally desirable compounds (e.g., phenolics, certain vitamins, mineral micronutrients including Se, Zn, and omega-3 fatty acids, α-tocopherol) and/or (ii) higher concentrations of nutritionally undesirable or toxic compounds (pesticide residues, cadmium, omega-6 fatty acids) in many of the foods (including wholegrain cereals, fruit and vegetables, olive oil, dairy products and meat from small ruminants, and fish) that are thought to contribute to the health benefits associated with MedDiets. The evidence for negative health impacts of consuming foods from intensified conventional production systems has also increased but is still limited and based primarily on evidence from observational studies. Limitations and gaps in the current evidence base are discussed. Conclusions: There is now substantial evidence that the intensification of agricultural food production has resulted in a decline in the nutritional quality of many of the foods that are recognized to contribute to the positive health impacts associated with adhering to traditional MedDiets. Further research is needed to quantify to what extent this decline augments the positive health impacts of adhering to a traditional MedDiet.

[Effects of Chlorine-based and Sulfur-based Fertilizers on Rice Bioavailability of Cd in Soils]

To explore the effects of single or combined application of chlorine-and sulfur-based fertilizers on rice bioavailability of Cd in soils, pot experiments with reddish clayey soil (developed from quaternary red clay parent materials) under three exogenous Cd levels (0, 0.5, and 2.0 mg·kg-1) were conducted. Meanwhile, chlorine-based fertilizers (KCl, NH4Cl) and sulfur-based fertilizers[K2SO4, (NH4)2SO4] were added in different proportions. The soil pH, Cd morphology, and Cd accumulation in rice at different growth stages were analyzed. The results revealed that both chlorine-and sulfur-based fertilizers could acidify the soil; however, the effect of chlorine-based fertilizers was more significant. During the filling stage of rice, the soil pH value of the treatment of applying single chlorine-based fertilizer decreased by 0.28 on average compared with that of applying single sulfur-based fertilizer. At the maturity stage of rice, chlorine-based fertilizer could activate the residual Cd, whereas sulfur-based fertilizer passivated the acid-extracted Cd to its residual state. Compared with the single application of the same fertilizer, the combined application of chlorine-and sulfur-based fertilizers was more likely to promote the accumulation of Cd in rice plants. The highest Cd accumulation of brown rice was 0.21 mg·kg-1 (2.0 mg·kg-1 exogenous Cd level) in the 1:1 (mole ratios of Cl:S) treatment of chlorine-and sulfur-based fertilizers, which was 16.4% higher than that of single chlorine-based fertilizer and 113.3% higher than that of single sulfur-based fertilizer. Therefore, the combined application of chlorine-fertilizers and sulfur-based fertilizers will increase the concentration of Cd in brown rice. To ensure food quality and safety, it is more advisable to apply single sulfur-based fertilizer for rice planting.

Assessing the Effects of Dietary Cadmium Exposure on the Gastrointestinal Tract of Beef Cattle via Microbiota and Transcriptome Profile

Cadmium (Cd) is an environmental pollutant, widely existing in soil, and can be absorbed and accumulated by plants. Hunan Province exhibits the worst cadmium contamination of farmland in China. Ruminants possess an abundant microbial population in the rumen, which enables them to tolerate various poisonous plants. To investigate whether the rumen microbiota could respond to Cd and mitigate the toxicity of Cd-accumulated maize to ruminants, 6-month-old cattle were fed with 85.82% (fresh basis) normal whole-plant maize silage diet (CON, n = 10) or Cd-accumulated whole-plant maize silage diet (CAM, n = 10) for 107 days. When compared to the CON cattle, CAM cattle showed significantly higher gain-to-feed ratio and an increased total bacterial population in the rumen, but a decreased total bacterial population in the colon. CAM cattle had higher relative abundance of Prevotella and Lachnospiraceae ND3007 group in the rumen, and Lachnospiraceae NK4A136 group and Clostridia vadinBB60 group in the colon. Notably, microbial correlations were enhanced in all segments of CAM cattle, especially Peptostreptococcaceae in the jejunum. Transcriptome analysis revealed down-regulation of several immune-related genes in the rumen of CAM cattle, and differentially expressed genes in the rumen were mostly involved in immune regulation. These findings indicated that feeding Cd-accumulated maize diet with a Cd concentration of 6.74 mg/kg dry matter (DM) could stimulate SCFA-related bacteria in the rumen, induce hormesis to promote weight gain, and improve energy utilization of cattle.

Inventory of cadmium-transporter genes in the root of mangrove plant Avicennia marina under cadmium stress

Mangrove Avicennia marina has the importantly potential for cadmium (Cd) pollution remediation in coastal wetlands. Unfortunately, the molecular mechanisms and transporter members for Cd uptake by the roots of A. marina are not well documented. In this study, photosynthetic and phenotypic analysis indicated that A. marina is particularly tolerant to Cd. The content and flux analysis indicated that Cd is mainly retained in the roots, with greater Cd influx in fine roots than that in coarse roots, and higher Cd influx in the root meristem zone as well. Using transcriptomic analysis, a total of 5238 differentially expressed genes were identified between the Cd treatment and control group. Moreover, we found that 54 genes were responsible for inorganic ion transport. Among these genes, AmHMA2, AmIRT1, and AmPCR2 were localized in the plasma membrane and AmZIP1 was localized in both plasma membrane and cytoplasm. All above gene encoding transporters showed significant Cd transport activities using function assay in yeast cells. In addition, the overexpression of AmZIP1 or AmPCR2 in Arabidopsis improved the Cd tolerance of transgenic plants. This is particularly significant as it provides insight into the molecular mechanism for Cd uptake by the roots of mangrove plants and a theoretical basis for coastal wetland phytoremediation.

Amino-carboxyl cellulose for adsorption of Cd2+ and Pb2

An amino-carboxyl cellulose was synthesized using the grafting of glycine on the aldehyde cellulose through a Schiff base reaction for the adsorption of heavy metals with Cd2+ and Pb2+ as the representative. Higher affinity of the amino-carboxyl cellulose was found at pH 4.5-5.0 for Cd2+ and 4.0-5.5 for Pb2+. The equilibrium was achieved within 30 min. The adsorption capacities of amino-carboxyl cellulose (Cd2+: 85.7 mg g-1, Pb2+: 115.1 mg g-1, Cu2+: 68.2 mg g-1, Co2+: 60.1 mg g-1, Ni2+ 48.5 mg g-1 and Zn2+: 52.8 mg g-1) at 30 °C were observed. A mild increase in the adsorption capacities of Cd2+ and Pb2+ from 15 to 45 °C was observed. Adsorption data correlated well with the Langmuir and pseudo-second order equations, illustrating chemisorption of Cd2+ and Pb2+ by the amino-carboxyl cellulose. The adsorption of the amino-carboxyl cellulose for Cd2+ and Pb2+ was a spontaneous and endothermic. The amino-carboxyl cellulose owned a high reusability after 4 cycles.

Rape straw biochar enhanced Cd immobilization in flooded paddy soil by promoting Fe and sulfur transformation

Cd is normally associated with sulfide and Fe oxides in flooded paddy soil. The mechanisms of biochar enhanced Cd immobilization by promoting Fe transformation and sulfide formation are unclear. Rape straw biochar (RSB) pyrolyzed at 450 °C (LB) and 800 °C (HB) was added to Cd-contaminated paddy soil at 1% (LB1, HB1) and 2% (LB2, HB2) doses. The results showed that Fe/Mn oxide-Cd (Fe/Mn-Cd) and free Fe oxide (Fed) concentrations decreased in the first 12 days and then rose, while Fe2+ in pore water (W-Fe2+) tended to rise first and then fall. The electron transfer rate of soil in the HB2 treatment was 4.9-fold higher than that in the treatment without biochar (CK). Fe oxide reduction was enhanced by RSB, with a maximum increase in W-Fe2+ by 62.1% in HB2 on Day 12. The negative correlation between W-Fe2+ and Fed showed that Fe2+ promoted the reformatted of seconded Fe minerals after Day 12, and the Fed in the HB2 treatments increased by 31.5% in this period. RSB addition also promoted the reformation of poorly crystallized Fe oxide (Feo) by increasing soil pH, which increased by 17.2% and 15.1% on average in the LB2 and HB2 treatments, respectively, compared to CK. Compared to Day 7, the increased rate of Fe/Mn-Cd on Day 30 in RSB was approximately twice that of CK. Compared to the molybdate group, the maximum decrease in CaCl2-Cd was 29.1% in LB2 on Day 12. LB2 increased SO42- and acid-volatile sulfide concentrations by 6.9- and 4.1-fold, respectively, compared to CK. These results suggested that RSB, particularly HB, promoted more Cd adsorption in Fe minerals by increasing Fe hydroxylation and recrystallization processes. LB increased the contribution of sulfide to Cd immobility.

Cadmium (Cd) and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) co-exposure induces acute kidney injury through oxidative stress and RIPK3-dependent necroptosis

Environmental pollution is complex, and co-exposure can accurately reflect the true environmental conditions that are important for assessment of human health. Cadmium (Cd) is a widespread toxicant that can cause acute kidney injury (AKI), while its combined effect with 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) is not fully understood. Thus, we used an in vivo model where C57BL/6J mice were treated with low dietary intake of Cd (5 mg/kg/day) and/or BDE-47 (1 mg/kg/day) for 28 days to examine AKI, and in vitro experiments to investigate the possible mechanism. Results showed that Cd or BDE-47 caused pathological kidney damage, accompanied by elevated urea nitrogen (BUN) and urinary creatinine, as well as increased interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), and reduced IL-10 in kidney tissues. In vitro Cd or BDE-47 exposure decreased cell viability and induced cell swelling and blebbing of human embryonic kidney 293 (HEK-293) and renal tubular epithelial cell lines (HKCs), and changes in co-exposure was larger than that in Cd and BDE-47 treatment. Oxidative stress indicators of the reactive oxygen species (ROS) and malondialdehyde (MDA) were elevated, while the antioxidant superoxide dismutase (SOD) was decreased. Necrosis occurred with increased lactate dehydrogenase (LDH) release and propidium iodide (PI) staining, which was attenuated by the ROS scavenger N-acetyl-L-cysteine (NAC). Furthermore, necroptotic genes of receptor-interacting protein kinase-3 (RIPK3), classical mixed lineage kinase domain-like protein-dependent (MLKL), IL-1β and TNF-α were up-regulated, whereas RIPK1 was down-regulated, which was attenuated by the RIPK3 inhibitor GSK872. These findings demonstrate that Cd or BDE-47 alone produces kidney toxicities, and co-exposure poses an additive effect, resulting in AKI via inducing oxidative stress and regulating RIPK3-dependent necroptosis, which offers a further mechanistic understanding for kidney damage, and the combined effect of environmental pollutants should be noticed.

Isolation of cadmium-resistant microbial strains and their immobilisation of cadmium in soil

Six cadmium (Cd)-resistant microbial strains were isolated and their ability to immobilise Cd2+ in soil investigated. Cd-1, Cd-2, Cd-5, and Cd-6 were identified as Stenotrophomonas sp., Cd-3 as Achromobacter sp., and Cd-7 as Staphylococcus sp. The six strains showed a wide adaptation range for salinity and a strong tolerance to Cd2+. The effects of the initial Cd2+ concentration (1-100 mg/L), duration (18-72 h), temperature (10-40 °C), and pH (5.0-9.0) on the efficiency of Cd2+ removal were analysed. The results revealed that the Cd2+ removal rate was higher at an initial Cd2+ concentration of 5-100 mg/L than at 1 mg/L. The maximum Cd2+ removal effect was at a culture duration of 36 h, temperature of 10-35 °C, and pH of 5.0-7.0. X-ray diffraction (XRD) analysis revealed that the Cd2+ was immobilised by Stenotrophomonas sp. Cd-2 and Staphylococcus sp. Cd-7 through bio-precipitation. X-ray photoelectron spectroscopy (XPS) revealed that the Cd2+ was adsorbed by Stenotrophomonas sp. Cd-2, Achromobacter sp. Cd-3, and Staphylococcus sp. Cd-7. Fourier transform infrared spectroscopy (FTIR) analysis revealed that the isolates reacted with the Cd2+ mainly through the O-H, protein N-H, C-N, lipid C-H, fatty acid COO, polysaccharide C-O, P-O, and other functional groups, as well as with lipid molecules on the cell wall surfaces. Scanning electron microscopy (SEM) analysis revealed that there was little difference in the cells after Cd2+ treatment. The results of the soil remediation experiments indicated that the toxicity of Cd in soil could be effectively reduced using certain strains of microbe.

Synergistic interplay between ABA-generating bacteria and biochar in the reduction of heavy metal accumulation in radish, pakchoi, and tomato

Heavy metal (HM) contamination is an environmental concern that threatens the agricultural product safety and human health. To address this concern, we developed a novel strategy involving the synergistic application of Azospirillum brasilense, a growth-promoting rhizobacterium which produces abscisic acid (ABA), and biochar to minimize HM accumulation in the edible parts of vegetable crops. Compared to A. brasilense or biochar alone, the concentrations of Cd, Ni, Pb, and Zn in radish (Raphanus sativus L.), pakchoi (Brassica chinensis L.), and tomato (Lycopersicon esculentum L.) decreased by 18-63% and 14-56%, respectively. Additionally, the synergistic treatment led to a 14-63% decrease in the bioconcentration factor. The biomass of the edible parts of the three crops increased by 65-278% after synergistic treatment, surpassing the effects of single treatments. Furthermore, the synergistic application enhanced the SPAD values by 1-45% compared to single treatments. The MDA concentrations in stressed plants decreased by 16-39% with the bacteria-biochar co-treatment compared to single treatments. Co-treatment also resulted in increased soluble protein and sugar concentrations by 8-174%, and improvements in flavonoids, total phenols, ascorbic acid, and DPPH levels by 2-50%. Pearson correlation analysis and structural equation modeling revealed that the synergistic effect was attributed to the enhanced growth of A. brasilense facilitated by biochar and the improved availability of HMs in soils. Notably, although ABA concentrations were not as high as those achieved with A. brasilense alone, they were maintained at relatively high levels. Overall, the synergistic application of A. brasilense-biochar might have remarkable potential for reducing the accumulation of HMs while promoting growth and improving nutritional and antioxidant qualities in tuberous, leafy, and fruit crops.