51Cr Release Research Articles

Influences of Cr(VI) on SOD Activity, MDA, and MT Content in the Hepatopancreas and Gill of Portunus trituberculatus

The toxic effect and differences of Cr(VI) on superoxide dismutase (SOD) activity, MDA, and metallothionein (MT) content in the hepatopancreas and gill of Portunus trituberculatus were investigated during Cr(VI) enrichment (15 days) and release experiments (15 days). Results showed that the 1.50 and 0.30 mg/L test groups significantly exhibited higher SOD, MDA, and MT content in the hepatopancreas and gill compared with the control group after 15 days of enrichment (p < 0.05). After 15 days of Cr release, the SOD, MDA, and MT content in the hepatopancreas and gill of both test groups recovered to the normal level of the control group (p > 0.05). The gill of P. trituberculatus achieved the highest SOD activity, MDA, and MT content earlier than the hepatopancreas, but the highest values were lower. The gill showed a shorter recovery time than the hepatopancreas. We concluded that the gill of P. trituberculatus exhibited a more rapid response to, and recovery from, Cr(VI) exposure compared to the hepatopancreas, making it a more sensitive tissue for assessing Cr(VI) toxicity, though both tissues showed a capacity for recovery after the removal of the contaminant.

Sight of Aged Microplastics Adsorbing Heavy Metal Exacerbated Intestinal Injury: A Mechanistic Study of Autophagy-Mediated Toxicity Response.

Contaminant-bearing polystyrene microplastics (PSMPs) may exert significantly different toxicity profiles from their contaminant-free counterparts, with the role of PSMPs in promoting contaminant uptake being recognized. However, studies investigating the environmentally relevant exposure and toxic mechanisms of aged PSMPs binding to Cr are limited. Here, we show that loading of chromium (Cr) markedly alters the physicochemical properties and toxicological profiles of aged PSMPs. Specifically, Cr-bearing aged PSMPs induced severe body weight loss, oxidative stress (OS), autophagy, intestinal barrier injury, inflammation-pyroptosis response, and enteropathogen invasion in mice. Mechanistic investigations revealed that PSMPs@Cr exacerbated the OS, resulting in intestinal barrier damage and inflammation-pyroptosis response via overactivated Notch signaling and autophagy/cathepsin B/IL-1β pathway, respectively, which ultimately elevated mortality related to bacterial pathogen infection. In vitro experiments confirmed that autophagy-mediated reactive oxygen species (ROS) overproduction resulted in severe pyroptosis and impaired intestinal stem cells differentiation alongside the overactivation of Notch signaling in PSMPs@Cr-exposed organoids. Overall, our findings provide an insight into autophagy-modulated ROS overproduction within the acidic environment of autophagosomes, accelerating the release of free Cr from PSMPs@Cr and inducing secondary OS, revealing that PSMPs@Cr is a stable hazard material that induces intestinal injury. These findings provided a potential therapeutic target for environmental MPs pollution caused intestinal disease in patients.

Fe (hydr)oxides and organic colloids mediate colloid-bound chromium mobilization in Cr(VI) contaminated paddy soil

The association of chromium (Cr) with colloidal particles transport in contaminated sites can affect hexavalent chromium (Cr(VI)) migration and transformation, which is an important mechanism for Cr pollutants in soil and groundwater systems. Here, we investigated colloid and particle-bound Cr migration and transformation effects on rice Cr accumulation during different rice growth stages and different redox conditions in Cr(VI) contaminated soil by pot experiment. Results showed that 13–29% of soil Cr was water dispersible colloid-bound (100–1000 nm) form during rice growth. Using transmission electron microscopy - energy dispersion spectroscopy and asymmetric flow field - flow separation, we identified colloid-bound organic matter (OM) and iron (Fe), most likely in the form of Fe (hydr)oxides - clay composites, as the primary Cr carrier. Specifically, colloid-bound Cr was mainly associated with 125–350 nm soil particle size. Under different redox conditions, colloid- and nanoparticle-bound Cr concentration decreased with increasing nanoparticles zero-valent iron (nZVI) dose. Soil reoxidation promoted the colloid- and nanoparticle-bound Cr release due to the weakly crystalline Fe-(hydr)oxides reprecipitation. Further quantitative analysis showed that colloid-bound Cr concentrations were positively correlated with colloid-bound Mn concentrations during the whole rice growth soils. Most important of all, Cr content in rice grain was positively correlated with colloid-bound Cr significantly. This study provides a quantitative and size-resolved understanding of particle-bound Cr in paddy soils, highlighting the importance of colloid-bound Cr and Fe interactions in Cr geochemical cycle of paddy soil.

Construction of DNA Vaccine of Extracellular Region of Vascular Endothelial Growth Factor Receptor 2 and Its Antitumor Activity in Vivo

Introduction: it constructed recombinant DNA vaccine of extracellular region of vascular endothelial growth factor receptor 2 (VEGFR2) and analyzed its in vivo activity against H22 transplanted hepatoma. Methods: the gene fragment of VEGFR2 extracellular region 1-3 was amplified, and the pcDNA3.1(+)/exVEGFR2 recombinant plasmid was constructed. The expression of exVEGFR2 was detected by Western blot. Subsequently, liposome (LP) pcDNA3.1(+)/exVEGFR2 complex (LP-pcDNA3.1(+)/exVEGFR2) was prepared and immunized to C57BL/6 mice. The cytotoxic activity mediated by cytotoxic T cells (CTLs) was analyzed by 51Cr release assay. H22 tumor bearing C57BL/6 mouse model was prepared. Quadriceps femoris muscle was injected with normal saline (saline group, AG), LP-pcDNA3.1(+) 100 μL (1 μg/μL, LP-pcDNA3.1(+) group, BG), and LP-pcDNA3.1(+)/exVEGFR2 100 μL (1 μg/μL, LP-pcDNA3.1(+)/exVEGFR2 group, CG). Tumor growth and death were recorded, and microvessel density (MVD) was evaluated by CD31 immunohistochemical staining. Results: a 1252 bp of exVEGFR2 sequence was amplified, and a specific band expressing 44 kDa molecular weight was constructed by transfecting pcDNA3.1(+)/exVEGFR2 into COS-7 cells. After immunizing C57BL/6 mice for 6 weeks, CTLs experiment suggested that LP-pcDNA3.1(+)/exVEGFR2 could effectively mediate the toxic effect of VEGFR2 positive H22 cells. The in vivo antitumor activity experiment found that as against AG and BG, the tumor volume, weight, and MVD were markedly reduced, the tumor latency time was markedly prolonged, and the average survival time was also markedly prolonged in CG (P < 0.05). Conclusion: LP-pcDNA3.1(+)/exVEGFR2 can effectively activate C57BL/6 mice to produce specific anti-VEGFR2 immune response, and then produce anti-tumor cell immunotoxicity in vitro and in vivo. Inhibiting angiogenesis can effectively prolong the survival time of H22 tumor bearing mice.

Effect of phytic acid on chemical, structural, and mechanical characteristics of nickel–titanium endodontic files

This study investigated phytic acid (IP6) effect on chemical, structural, and mechanical characteristics of nickel–titanium (NiTi) files. The tested files were equally divided into groups according to the immersion protocol: sodium hypochlorite (NaOCl), ethylenediaminetetraacetic acid (EDTA), IP6, EDTA followed by NaOCl, and IP6 followed by NaOCl. These groups were then compared in terms of Ni, Ti, and chromium (Cr) ions release from the files. Microstructural changes using field emission scanning electron microscope (Fe-SEM) and energy dispersive X-ray spectroscopy (EDX) and surface roughness were analyzed. The mechanical characterization was conducted using cyclic fatigue resistance test. Fractured segments were scanned under SEM. Statistical analysis was performed using one-way ANOVA, Tukey test, Kruskal–Wallis test and Mann–Whitney U test. Results showed that NaOCl caused significant release of Cr, followed by IP6 and EDTA (P < 0.05). When files were pre-immersed in EDTA, NaOCl tended to induce less release of Ti and Cr. EDX evaluation revealed that the main surface elements were Ni, Ti, carbon, and oxygen. EDTA group contained the highest amount of carbon, while the control group showed the lowest. Surface roughness evaluation revealed no significant differences between groups despite the minor increases after immersion in certain groups. Black areas were observed in the NaOCl group which indicated corrosion. However, the cyclic fatigue test showed no significant differences between the groups.

A Chromium-Based magnetic resonance probe for in situ gastric pH imaging

Effective monitoring of gastric fluid pH is crucial for diagnosing gastric diseases and evaluating anti-gastric-acid therapies. The invasiveness and low patient compliance with traditional gastric fluid aspiration methods highlight the need of a non-invasive, real-time technique for in situ gastric pH monitoring. This study introduces a novel chromium (Cr)-based magnetic resonance probe, Cr(OH)3@HSA, specifically designed for pH-sensitive gastric imaging. Synthesized via an albumin-mediated biomimetic mineralization process, Cr(OH)3@HSA possesses an amorphous structure that facilitates the sensitive release of paramagnetic Cr(III) ions in acidic environments. This release substantially decreases the longitudinal relaxation time of surrounding hydrogen protons, as demonstrated by an 18.29-fold increase in the longitudinal relaxation rate from pH 6.5 to pH 1.0. In vivo experiments show that Cr(OH)3@HSA accurately detects abnormal gastric pH levels and evaluates the efficacy of gastric antiacids, surpassing the performance of the conventional “always-on” contrast agent, Magnevist®. Notably, our research reveals that chromium picolinate, a common dietary supplement for diabetes, generates a “turn-on” signal in the gastrointestinal tract, suggesting potential MR signal interference in diabetic patients. Consequently, we recommend that diabetic patients avoid chromium-based dietary supplements prior to MRI procedures to prevent Cr(III)-induced signal alterations.

Effect of biochar-derived DOM on contrasting redistribution of chromate during Schwertmannite dissolution and recrystallization

Biochar-derived dissolved organic matter (BDOM), is extensively involved in the recrystallization of minerals and the speciation alteration of associated toxic metals. This study investigates how BDOM extracted from tobacco petiole (TP) or tobacco stalk (TS) biochar influences the speciation repartitioning of Cr(VI) in environments impacted by acid mine drainage (AMD), focusing on interactions with secondary minerals during Schwertmannite (Sch) dissolution and recrystallization. TP-BDOM, rich in lignin-like substances, slowed down the Cr-Sch dissolution and Cr release under acidic conditions compared to TS-BDOM. TP-BDOM's higher O/C component exerts a delayed impact on Cr-Sch stability and Cr(VI) reduction. In-situ ATR-FTIR and 2D-COS analysis showed that carboxylic and aromatic N-OH groups in BDOM could interact with Cr-Sch surfaces, affecting sulfate and Cr(VI) release. It was also observed that slight recrystallization occurred from Cr-Sch to goethite, along with increased Cr incorporation into secondary minerals within TS-BDOM. This enhances our understanding of BDOM's role in Cr(VI) speciation changes in AMD-contaminated sites.

Effects of nZVI on the migration and availability of Cr(VI) in soils under simulated acid rain leaching conditions

Hexavalent chromium, Cr(VI), is a ubiquitous toxic metal that can be reduced to Cr(III) by nano-zero-valent iron (nZVI). Finding out effects of continuous rainfall leaching on the Cr(VI) release and availability remains a problem, needing to be addressed. Whether the Cr(VI) reduction by nZVI and continuous rainfall leaching lead to localized heterogeneity in soil is unclear. Therefore, two in situ high-resolution (HR) techniques of the diffusive gradients in thin-films (DGT) and planar optode were combined with ex situ sampling experiments here. Results demonstrate that nZVI decreased Cr(VI) leaching by 5.60–8.50 % compared to control soils. DGT-measured concentrations of Cr(VI), CDGT-Cr(VI), ranged from 7.31 to 19.4 μg L-1 in the control soils, increasing with depth while CDGT-Cr(VI) in nZVI-treated soils (2.41–6.18 μg L-1) decreased or remained stable with depth. However, simulated acid-rain leaching increases CDGT-Cr(VI) by 1.61-fold in nZVI-treated soils, negatively affecting the remediation. DGT measurements in bulk soils using disc devices are better at capturing the change of Cr(VI) availability at different conditions, whereas 2D-HR DGT mappings did not characterize significant mobilization of Cr(VI) at the micro-scale. These findings emphasize the importance of monitoring Cr(VI) release and availability in remediated soil under acid-rain leaching conditions for effective environment management.

Soil flushing coupled with aminated-nanocellulose/MOF hydrogel nanocomposites adsorbents: A novel sustainable remediation strategy for Cr(VI)-contaminated agricultural soils

Soil flushing and adsorption-based soil remediation are promising options for removing heavy metals in agricultural soil. However, they encounter limitations in low removal efficiency, secondary pollution potential, or the need for a purification/recovery process. Optimizing flushing solutions or the functional properties of adsorbents could fundamentally eliminate the drawbacks of these methods. Yet, their practical application remains a formidable challenge. Herein, a new combined remediation strategy of multiple-pulse water soil flushing (MF) with novel aminated cellulose nanofibers (A-NFCs)/AEM/AM@MIL-100(Fe) nanocomposite hydrogel adsorbent (ANCMH) was adopted to remove Cr(VI) from agricultural soil. The characteristic analyses approved Cr(VI) adsorption-coupled reduction/swelling-based mechanisms on ANCMH with the maximum theoretical adsorption capacity of 338.24 mg g−1 at pH 6.8 governed by pseudo-second-order and Freundlich models. Instead of conventional MF application using environmentally problematic extractant fluids, a 5-day soil column simulation trial of MF coupled with ANCMH adsorbent layers (MF@ANCMH) was applied in medium-to-highly Cr(VI)-contaminated soil followed by easy ANCMHs separation, preventing secondary pollution. Innovatively, the water flushing-stop flux events favorably decreased the pH of neutral soil by 0.83 folds and allowed Cr(VI) release from the soil matrix to be adsorbed by ANCMHs, achieving a high Cr(VI) removal efficiency of 98.9 %. Compared to the soil treated with ANCMH individually and soil flushed with water or Na2EDTA, the MF@ANCMH-treated soil reached the corresponding regulation of permissible levels for Cr(VI) residential scenarios in agricultural soil of 5.6 ppm with 3-cycles of ANCMH reuse. The residual Cr in MF@ANCMH-remediated soil displayed minimal bioavailability at root-zoon soil of ≤4.2 ppm and a 97.66 % reduction in its exchangeable-carbonate fraction compared to untreated soil, corresponding to a risk assessment code score below 1 %. Also, the application of MF@ANCMH resulted in Cr bioaccumulation below 0.1 ppm in cultivated wheat plants, prevented the physiological phytotoxicity symptoms, and elevated their antioxidant enzyme activity, photosynthesis, growth, and yielding indicators compared to that grown in untreated soil. Furthermore, it improved soil organic matter, microbial community, diversity, and microecological functions. This study provides a promising alternative remediation strategy for neutral soil that can maintain soil/crop quality and soil health with high chemical/environmental stability of pollutants after remediation, demonstrating its sustainability and feasibility in agricultural soil.

Dual electro-/pH-responsive nanoparticle/hydrogel system for controlled delivery of anticancer peptide

An electro-chemo-responsive carrier has been engineered for the controlled release of a highly hydrophilic anticancer peptide, CR(NMe)EKA (Cys-Arg- N-methyl-Glu-Lys-Ala). Remotely controlled on demand release of CR(NMe)EKA, loaded in electro-responsive poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles, has been achieved by applying electrical stimuli consisting of constant positive (+0.50 V) or negative voltages (−0.50 V) at pre-defined time intervals. In addition, after loading CR(NMe)EKA/PEDOT nanoparticles into an injectable pH responsive hydrogel formed by phenylboronic acid grafted to chitosan (PBA-CS), the efficiency of the controlled peptide release has increased approximately by a factor of 2.6. The hydration ratio of such hydrogel is significantly lower in acidic environments than in neutral and basic media, which has been attributed to the dissociation of the boronate bonds between polymer chains. Hence, the electro-controlled peptide release from PBA-CS/CR(NMe)EKA/PEDOT hydrogels, in the acidic environment of tumors, combines the effects of the oxidation and reduction of PEDOT chains on the interactions with the peptide and the carrier, with the peptide concentration gradient at the interface between the collapsed hydrogel and the release medium. Furthermore, the peptide released by electro-stimulation preserved its bioactivity assessed by promoting human prostate cancer cells death. Overall, this work is a promising attempt to develop a carrier platform for small hydrophilic anticancer peptides, which delivery rationale is synergistically regulated by the electrical and pH responsiveness of the carrier.

Influence of vegetation on heavy metal Cr release process from bottom sediment under unidirectional flows and regular waves

As human activities become more intensive, a substantial number of heavy metals are discharged into estuarine or wetland environments. Due to the poor degradability, heavy metals are prone to adsorption and deposition on suspended particles in bottom sediments. Subsequently, under the influence of disturbances, there is a potential for their re-release, causing secondary pollution. To investigate the release process of the heavy metal Cr from sediment, laboratory experiments were conducted under both unidirectional flow and regular wave conditions. At the initial stage, the temporal trends of particulate (CrP) and dissolved (CrD) Chromium concentrations were both characterized by initial increments followed by stabilization and continuous escalation. Vertically, the stable concentrations of CrP and CrD increased with the presence of vegetation and the enhancement of hydrodynamics. The Elovich equation, pseudo-second-order kinetic equation, Double constant equation (Freundlich model), and parabolic diffusion equation were employed to predict the release process of CrD from bottom sediment. The Elovich equation proved most suitable for describing the release process of CrD, with an R2 exceeding 0.9. In order to assess the influence of vegetation on the Cr release process, the Stem-Reynolds were introduced to modify the Elovich equation. The final maximum error was 12 % (excluding the initial stage), which was much lower than that using the original Elovich equation (maximum error of 32 %). The study findings provide practical support for estuarine and wetland managers to formulate effective heavy metal management measures, which contribute to the conservation and sustainable management of aquatic ecosystems.

Fluorescence 'Turn-on' Probe for Chromium Reduction, Adsorption and Detection Based on Cellulosic Nitrogen-Doped Carbon Quantum Dots Hydrogels.

This paper proposes a new, highly effective fluorescence test for Cr(VI) detection. This method utilizes a hydrogel composed of hydroxyethyl cellulose (HEC), nitrogen-doped carbon quantum dots (N-CQDs), and poly(co-acrylamido-2-methyl-1-propane sulfonic acid) (AMPS). The N-CQDs were successfully synthesized using a simple microwave method, and then conjugated with HEC and AMPS. The higher adsorption (99.41%) and higher reduction rate in H1 likely stems from both the presence of N-CQDs (absent in HB) and their increased free functional groups (compared to H2/H3, where N-CQDs block them). This facilitates the release (desorption) of Cr(VI) from the hydrogels, making it more available for reduction to the less toxic Cr(III). The fluorescent brightness of the HEC-N-CQDs-g-poly(AMPS) hydrogel increases gradually when Cr(VI) is added in amounts ranging from 15 to 120 mg/L. The fluorescent enhancement of the HEC-N-CQDs-g-poly(AMPS) hydrogel appeared to exhibit a good linear relationship with the 15-120 mg of the Cr(VI) concentration, with a detection limit of 0.0053 mg/L, which is lower than the standard value published by WHO. Our study found that the HEC-N-CQDs-g-poly(AMPS) hydrogel served effectively as a fluorescent probe for Cr(VI) detection in aqueous solutions, demonstrating high sensitivity.

Leachability of hexavalent chromium from fly ash-marl mixtures in Sarigiol basin, Western Macedonia, Greece: environmental hazard and potential human health risk

Hexavalent chromium (Cr (VI)) is an environmental contaminant brining high concerns due to its higher toxicity and mobility in comparison with trivalent chromium Cr(III). Cr (VI) has been linked with several adverse health effects, including respiratory diseases, lung cancer, and skin irritation. The primary sources of it in the environment are industrial activities.Most of the time, fly ash made of lignite can release Cr(VI) when it comes into contact with water in an aquatic environment. The objective of this study is the investigation of Cr (VI) concentration in leachates of fly ash and marl mixtures and the determination of its solubility under different pH conditions. Samples of fly ash were collected from the Power Plant of Agios Dimitrios. Additionally, samples of marl were collected from the mine of South Field, and both samples were mixed and prepared in in different proportions (% w.t.). The leaching experiments were carried out according to the EN-12457/1-4 (2003) standard under different pH conditions and chemical analysis of the leachates were performed by spectrophotometry with diphenylcarbazide (DPC). The environmental footprint of Cr (VI) in the study area was significant, especially in mixtures containing higher concentrations of fly ash. A critical pH range between 6 to 12 is observed. At acidic pH values, a high release of Cr (VI) was observed, while at the mentioned critical values (pH 10–12), a gradual decrease in its leachability was noticed. The high concentrations of Cr (VI) in the industrial area studied require immediate actions in terms of managing and limiting the potential hazardous impacts on the environment and by extension on the public health by developing appropriate prevention strategies.Graphical abstract

Stabilization of heavy metals in solid waste and sludge pyrolysis by intercalation-exfoliation modified vermiculite

Increasing amounts of solid waste and sludge have created many environmental management problems. Pyrolysis can effectively reduce the volume of solid waste and sludge, but there is still the problem of heavy metal contamination, which limits the application of pyrolysis in environmental management. The intercalated-exfoliated modified vermiculite (IEMV) by intercalators of sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide and octadecyltrimethylammonium bromide were used to control the release of Cd, Cr, Cu, Zn and Pb during pyrolysis process of sludge or solid waste. The retention of heavy metals in sludge was generally better than that in solid waste. The IEMV by octadecyltrimethylammonium bromide as the intercalator calcined 800 °C (STAB-800) was the best additive for heavy metal retention, and the retention of Cr, Cu and Zn was significantly better than that of Pb and Cd. Cr, Cu, Zn and Pb were at low risk, while Cd had considerable risk under certain circumstances. New models were proposed to comprehensively evaluate the results of the risk and forms of heavy metals, and the increasing temperature was beneficial in reducing the hazards of heavy metals by the addition of STAB-800. The reaction mechanism of heavy metals with vermiculite was revealed by simulation of reaction sites, Fukui Function and Frontier Molecular Orbital. Thermal activation-intercalated-exfoliated modified vermiculite (T-IEMV) is more reactive and had more active sites for heavy metals. Mg atoms and outermost O atoms are the main atoms for T-IEMV to react with heavy metals. The Cr, Cu and Zn have better adsorption capacity by T-IEMV than Pb and Cd. This study provides a new insight into managing solid waste and sludge and controlling heavy metal environmental pollution.

Citric acid-induced photochemical behavior of Cr(III)-substituted ferrihydrite: Fe and Cr release, mineral transformation and reactive oxygen species generation

Cr(III)-substituted ferrihydrite (Fh-Cr(III)) is widespread in the surrounding environment of mining areas. Fh-Cr(III) is unstable and susceptible to the influence of environmental factors, such as dissolved organic matter (DOM) and light, so Cr species embedded in mineral crystal layers are likely to have more profound negative effects on the environment with the photochemical behaviors of minerals. However, the photochemical behaviors of Fh-Cr(III) in the presence of DOM remains poorly understood. For this reason, citric acid (CA) was chosen as the representative DOM to study its combined effects with visible light irradiation on Fh-Cr(III) dissolution and phase transition. The results showed that CA hindered the agglomeration of Fh-Cr(III) particles, thereby slowing the phase transition of Fh-Cr(III). However, CA exacerbated the release of Fe and Cr by maintaining Fh-Cr(III) under unstable crystal structure. Moreover, due to the occurrence of ligand-metal charge transfer (LMCT) in (CA)n-Fh-Cr(III) formed on the Fh-Cr(III) surface, the synergistic effect between CA and light irradiation greatly promoted the dissolution of Fh-Cr(III). In the mixed system of Fh-Cr(III) (3 g/L) and CA (5 mM) at initial pH 3.0, the maximum concentrations of TFe and TCr were 18.17 and 5.68 mg/L after 6 h of light reaction, which were 1.82 and 3.62 times of those in the corresponding system in the darkness. Meanwhile, the Fe(III)/Fe(II) cycling in solution and solid surfaces was affected by various reactive oxygen species (ROS) generated from the LMCT process, in which the photoproduced Fe(II) further accelerated Cr(III) dissolution under acidic solution. The fast release of Cr(III) may pose greater danger to the environment as the more toxic Cr(VI) can be easily formed through the oxidation of dissolved Cr(III). This work offers fresh insights into the migration and transformation of Cr elements in the natural environment.

Influence of environmental factors on changes in the speciation of Pb and Cr in sediments of Wuliangsuhai Lake, during the ice-covered period.

Ecological pollution caused by heavy metals released from sediments is a worldwide concern. However, the effect of changes in sediment speciation on their release of heavy metals has not been adequately reported. In this study, the research focused on Pb and Cr in the ice period of Wuliangsuhai. This study analyzed changes in the sediment speciation of Pb and Cr before and after a release experiment using four risk assessment methods while varying the temperature, pH, and salinity of the water column. The results indicated that the total concentration of Pb ranged from 11.17 to 24.25mg/kg, while for Cr it ranged from 42.26 to 69.68mg/kg. Both elements exhibited mild contamination. The release of Pb and Cr from sediments increases with increasing water temperature, mainly due to the conversion of the residual fraction of Pb to the Fe-Mn oxide fraction and Cr converting more residual fraction to the organic matter and sulfide fraction. The release of sediment Pb and Cr decreased with increasing pH, with Pb converting more acid extractable fraction to the residual fraction and Cr converting more organic matter and sulfide fraction to the residual fraction. In contrast, the release of Pb and Cr increased and then decreased with increasing salinity. For Pb, the acid extractable fraction was more susceptible to conversion to the residual fraction by environmental influences, whereas for Cr, the organic matter and sulfide fraction were susceptible to conversion to the residual fraction.

Re-yellowing of chromium-contaminated soil after reduction-based remediation: Effects and mechanisms of extreme natural conditions

Chromium (VI) in soil poses a significant threat to the environment and human health. Despite efforts to remediate Cr contaminated soil (Cr-soil), instances of re-yellowing have been observed over time. To understand the causes of re-yellowing as well as the influence of overdosed chemical reductant in remediating Cr-soil, experiments on excess reducing agent interference and soil re-yellowing mechanisms under different extreme conditions were conducted. The results show that the USEPA method 3060A & 7196A combined with K2S2O8 oxidation is an effective approach to eliminate interference from excess FeSO4 reducing agents. The main causes of re-yellowing include the failure of reducing agents, disruption of soil lattice, and interactions between manganese oxides and microorganisms. Under various extreme conditions simulated across the four seasons, high temperature and drought significantly accelerated the failure of reducing agents, resulting in the poorest remediation effectiveness for Cr-soil (91.75 %). Dry-wet cycles promoted the formation of soil aggregates, negatively affecting Cr(VI) removal. While these extreme conditions caused relatively mild re-yellowing (9.46 %–16.79 %) due to minimal soil lattice damage, the potential risk of re-yellowing increases with the failure of reducing agents and the release of Cr(VI) within the lattice. Prolonged exposure to acid rain leaching and freeze-thaw cycles disrupted soil structure, leading to substantial leaching and reduction of insoluble Cr, resulting in optimal remediation effectiveness (94.37 %–97.73 %). As reducing agents gradually and the involvement of the water medium, significant re-yellowing occurred in the remediated soil (51.52 %). Mn(II) in soil enriched relevant microorganisms, and the Mn(IV)-mediated biological oxidation process was also one of the reasons for soil re-yellowing.

PROPOLIS EXTRACT AS ANTI-CORROSIVE AGENT INHIBITS METAL IONIC RELEASE FROM ORTHODONTIC BRACKETS

Background: A combination of nickel (Ni), chromium (Cr), and iron (Fe) can be found in the stainless steel orthodontic bracket. Ion release takes place as a result of the chemical interaction between metals and the oral environment, which leads to the potential of hypersensitivity during fixed orthodontic treatment. Propolis contains phytochemicals that have the ability to reduce corrosion, making it a potential treatment option. Purpose: to determine the release of Ni, Cr, and Fe in metal brackets in an 8.2% propolis solutionMethod: Four sets of six brackets were made from 24 brackets. Artificial saliva, sodium fluoride, sterilized distilled water (aquabidest), and 8.2% propolis were applied to these brackets. After incubating at 37°C for seven days, ICP EOS measured the metal ions Ni, Cr, and Fe. The analysis revealed significant differences (p&lt;0.05) in ionic release of Ni, Cr, and Fe among groups exposed to sterilized distilled water (aquabidest) and an 8.2% propolis solution. Additionally, the Mann-Whitney test showed substantial Ni ion release differences (p&lt;0.05) between 8.2% propolis solution and sterilized distilled water. The 8.2% propolis solution and sodium fluoride solution released Cr ions differently. Fe ion levels differed between propolis solution 8.2%, sodium fluoride solution, sterilized distilled water, and fake saliva. Conclusion: Propolis affects metal bracket ionic release of Ni, Cr, and Fe. Keywords : Cr and Fe, ions of Ni, propolis solution, Stainless steel bracket

Encapsulating carboxymethyl cellulose stabilized nanoscale ferrous sulfide with layered magnesium hydroxide shell for controlled reactivity release and long-term sequestration of Cr(Ⅵ)

Nanoparticulate iron sulfide (nano-FeS) is a highly effective and environmentally-friendly reducing agent for decontamination. However, challenges such as aggregation, poor mobility, and oxidative aging limit its application of in situ groundwater and soil remediation. Herein, we present a novel approach to enhance the feasibility and effectiveness of nano-FeS for in situ remediation by encapsulating carboxymethyl cellulose stabilized FeS nanoparticles with a layered magnesium hydroxide shell (referred to as CMC-FeS@Mg(OH)2). The novel CMC-FeS@Mg(OH)2 nanoparticles, with a suitable coating ratio (10 %–50 %), demonstrate considerably increased colloidal stability and enhanced mobility in porous media. This is mainly due to steric hindrance, and decreased attachment, blocking, and straining effects. The Mg(OH)2 shell obviously protects the reactivity of FeS nanoparticles and enhances their resistance to oxidation, ensuring their longevity and long-term decontamination effectiveness during practical field applications. The preserved reactivity of FeS core can be progressively released and fully recovered by modulating the Mg(OH)2 coating ration and the extent of dissolution. After the complete dissolution of the Mg(OH)2 shell, CMC-FeS@50 % Mg(OH)2 exhibits enhanced efficiency in Cr(VI) sequestration, increasing from 58 % to 92 % compared to bare FeS. The removal of Cr(VI) by CMC-FeS@Mg(OH)2 is a synergistic process, and the main mechanisms includes adsorption, reduction, ion exchange, and subsequent precipitation. These results demonstrate a promising and effective method to improve the mobility and longevity of FeS and enable the controlled reactivity release for in situ remediation of subsurface contamination.

The Release and Migration of Cr in the Soil under Alternating Wet-Dry Conditions.

In recent decades, chromium contamination in soil has emerged as a serious environmental issue, demanding an exploration of chromium's behavioral patterns in different soil conditions. This study aims to simulate the release, migration, and environmental impact of chromium (Cr) in contaminated soils under natural rainfall conditions (wet-dry cycles). Clean soils sourced from Panzhihua were used to cultivate chromium-containing soils. Simulated rainfall, prepared in the laboratory, was applied to the cultivated chromium-containing soils in indoor simulated leaching experiments. The experiments simulated three years of rainfall in Panzhihua. The results indicate that soils with higher initial Cr contents result in higher Cr concentrations in the leachate, but all soils exhibit a low cumulative Cr release. The leachate shows similar patterns in total organic carbon (TOC), pH, electrical conductivity, and Cr content changes. An analysis of the speciation of Cr in the soil after leaching reveals a significant decrease in the exchangeable fraction for each Cr species, while the residual and oxidizable Cr fractions exhibit notable increases. The wet-dry cycle has the following effects on the soil: it induces internal reduction reactions in the soil, leading to the reduction of Cr(VI) to Cr(III); it alters the binding of Cr ions to the soil, affecting the migration of chromium; and it involves microorganisms in chemical processes that consume organic matter in the soil. After three years of rainwater leaching, chromium-containing soils released a relatively low cumulative amount of total chromium, resulting in a reduced potential risk of groundwater system contamination. Most of the chromium in the chromium-containing soil is fixed within the soil, leading to less biotoxicity.