Cr Contamination Research Articles

Chitosan hydrogel microspheres loaded with Bacillus subtilis promote plant growth and reduce chromium uptake

Cr contamination can lead to reduced crop yields and threaten food security. Eliminating soil Cr contamination or improving crop resistance to Cr is challenging in terms of costly, environment and biodiversity risk. Here, we used chitosan hydrogel microspheres loaded with Bacillus subtilis to cope with plant stress caused by Cr contamination. The addition of chitosan hydrogel microspheres loaded with Bacillus subtilis increased shoot biomass by 88 % and decreased the plant Cr concentration by 17 %. The bacterial chitosan hydrogel microsphere treatment enhanced the decomposition of organic matter and facilitated the uptake of nutrients by the plants. It also significantly increased the abundance of anti-heavy metal stress functional bacteria (Proteobacteria, Actinobacteria, and Chloroflexi), strongly promoting interactions and correlations between microbes. This technology of bacterial-chitosan hydrogel microspheres presents promising opportunities for sustainable strategies for addressing heavy metal pollution and enhancing agricultural productivity.

Effect of Tannery Organic Matter on the Migration and Transformation of Chromium in Soil

ABSTRACT Chromium (Cr) contamination is one of the main pollution issues in the soils of tanning industries. Nevertheless, it is unclear how tannery organics affect the movement and transformation of Cr in soil. Column leaching tests were carried out to investigate the impact of various tannery organics, such as phenol, dyes, and surfactants on Cr mobility in tannery soil. The cumulative release of Cr from the soil was less in the presence of tannery organics than that from the non-tannery organics treated group. This suggests that the tannery organics enhanced the fixing of Cr in the soil. Cr was poured from the top of the soil column in the form of Cr (III) solution for leaching, and the concentration of Cr decreased with the increase of soil depth regardless of the presence of tannery organic matter. After leaching, the residual Cr concentration in the soil was 59%−78% of the total Cr concentration. The potential risk of Cr in the soil/groundwater system decreased in the presence of the tannery organics, which decreased the bioavailability of Cr and increased the percentage of Cr in residual state. Understanding the relationship between Cr migration and tannery organics in soil is helpful for soil environment risk assessment of tannery site.

Heavy metal pollution and evaluation of health risk of amaranth around Don Bosco wastewater treatment plant, Iringa, Tanzania

One of the world’s most significant sources of environmental pollution is heavy metals contamination of soil, water, and agricultural products. Liver cancer, kidney damage, anaemia, coma, hypertension and sporadic fever are among the illnesses that might result from consuming plants contaminated with heavy metals. This study assesses heavy metals (Cu, Mn, Cd, Cr, Ni and Pb) contamination and associated human health risks in amaranth (Amaranthus hybridus) grown near Don Bosco wastewater treatment plant in Iringa municipal, Tanzania. The study measured the concentration of heavy metals in amaranth vegetables using AAS. The level of Mn in the vegetables ranged between 67.90 and 493.44 mg/kg. The mean concentration of Mn obtained was 280.67 mg/kg, lower than the permissible levels set by FAO/WHO but above the limit as set by TBS. The Cu levels in amaranth ranged between 6.37 and 7.90 mg/kg, with a mean concentration of 7.24 mg/kg lower than the permissible limits set by FAO/WHO and TBS. The Cd levels in amaranth ranged between 0.05 and 0.35 mg/kg, and the mean concentration was 0.20 mg/kg below the permissible limit set by FAO/WHO and TBS. The calculated daily intake consumption fell in the following sequence: Mn>Cu>Cd. The hazard quotient (HQ) for Mn and Cd is 261.66 and 6.45, respectively, higher than the allowed limit (HQ <1), and the hazard index (HI) for all samples was HI>1, which indicates the consumption of these veggies could pose a harm to one’s health. Additionally, the assessment of cancer risks revealed that Mn and Cd levels exceeded the USEPA recommended threshold of 1E-04, indicating a risk of one additional cancer case for every 10,000 individuals consuming amaranth vegetables. Thus, regularly checking for heavy metal contamination in vegetables is critical to minimize health hazards.

Successful hexavalent chromium removal introducing a novel system composed of aminated polyacrylonitrile nanofiber coated with polysulfide

This study investigates the adsorption removal of hexavalent chromium (Cr(VI)), a hazardous contaminant commonly found in industrial wastewater, using aminated polyacrylonitrile (APAN) nanofibers coated with polysulfide (PS). Cr(VI) contamination, often originating from industries like leather tanning, poses serious health and environmental risks. The APAN/PS nanofibers achieved a maximum Cr(VI) adsorption capacity of 172.4 mg/g at pH 3, with a removal efficiency of 94.49 %, compared to 86.54 % for uncoated APAN. Characterization by FTIR and FESEM confirmed the successful modification of the nanofiber surface, with an average fiber diameter of 328 nm. Adsorption kinetics followed a pseudo-second-order model (R2 > 0.98), suggesting chemisorption as the primary mechanism, and the process aligned closely with the Langmuir isotherm model. Thermodynamic parameters indicated an endothermic and spontaneous process, with favorable ∆G values. These results demonstrate APAN/PS nanofibers as an effective and sustainable adsorbent for Cr(VI) removal in industrial wastewater treatment.

Trace Metal Levels in Seawater, Suspended Particulate Matter and Sediment in Mersin Bay, Turkey

The concentrations and distributions of trace metals in surface sediment, water and suspended particulate matter (SPM) in coastal area of Mersin Bay were studied to determined the anthropogenic inputs from surrounding activities. Elevated zinc levels (275 ppm) represent the trace metal with the highest concentration, as measured in suspended particulate matter samples collected from the Kazanlı and Karaduvar areas. The high concentrations are associated with terrestrial inputs from the anthropogenic (domestic +industrial) sources. An important observation is that increasing concentrations are found in dissolved phase, sediment and particulate phase, respectively. But this is not the case for Cr which is higher in sediment. This is related to intense activity of chromium processing plant working for many years. Moreover, Cd and Cr concentrations in surface sediments are above the shale average. Heavy metal concentrations in surface sediments are Cr&gt;Zn&gt;Cu&gt;Pb&gt;Cd, respectively. The elevated copper level relative to cadmium in surface sediments is likely attributable to the higher stability of surface complexes with clay minerals, which constitute the primary components of the sediments. Adsorption of zinc to iron and manganese oxide compounds in the sediment is a possible explanation for the high amounts of zinc that were found in the sediments. The estimated index values (enrichment factor, geoacumulation index and pollution load index) indicated widespread contamination of Cr and Cd in Mersin Bay. The origins of these trace metals in the sediments were caused by human activity, and the region was categorized as a moderately severely polluted area.

Machine learning models with innovative outlier detection techniques for predicting heavy metal contamination in soils

Machine learning (ML) models for accurately predicting heavy metals with inconsistent outputs have improved owing to dataset outliers, which influence model reliability and accuracy. A comprehensive technique that combines machine learning and advanced statistical methods was applied to assess data outlier’s effects on ML models. Ten ML models with three outlier detection methods predicted Cr, Ni, Cd, and Pb in Narayanganj soils. XGBoost with density-based spatial clustering of applications with noise (DBSCAN) improved model efficacy (R2). The R2 of Cr, Ni, Cd, and Pb was considerably enhanced by 11.11 %, 6.33 %, 14.47 %, and 5.68 %, respectively, indicating that outliers affected the model's HM prediction. Soil factors affected Cr (80 %), Ni (72.61 %), Cd (53.35 %), and Pb (63.47 %) concentrations based on feature importance. Contamination factor prediction showed considerable contamination for Cr, Ni, and Cd. LISA revealed Cd (55.4 %), Cr (49.3 %), and Pb (47.3 %) as the significant pollutant (p < 0.05). Moran's I index values for Cr, Ni, Cd, and Pb were 0.65, 0.58, 0.60, and 0.66, respectively, indicating strong positive spatial autocorrelation and clusters with similar contamination. Finally, this work successfully assessed the influence of data outliers on the ML model for soil HM contamination prediction, identifying crucial regions that require rapid conservation measures.

Using trees to monitor airborne Cr pollution: Effects of compass direction and woody species on Cr uptake during phytoremediation

Among the heavy metals (HMs) whose concentrations in natural environments have risen considerably in the last era, chromium (Cr) is one of the most toxic. Because of the risks it poses to human and environmental health, it is of great importance to screen the variation in Cr contamination in the atmosphere and decrease the pollution. This study aimed to determine the proper tree species that can be used to monitor and reduce Cr contamination. For this aim, studies were conducted on Tilia tomentosa, Robinia pseudoacacia, Cedrus atlantica, Pseudotsuga menziesii, and Fraxinus excelsior species growing in Düzce, which is among the 5 most contaminated European towns according to the World Air Pollution report. Samples taken from these trees were examined, and changes in Cr concentration depending on species, organs, compass direction, and age range in the last 60 years were evaluated. Results indicated higher Cr pollution in recent years, consistent with higher traffic density, but that there was no consistent effect of compass direction. It was also determined that the tree species most appropriate for screening the variation in Cr contamination in the airborne were Tilia tomentosa, and the most appropriate species for decreasing pollution were Robinia pseudoacacia and Cedrus atlantica.

Synchronous bioremediation of vanadium(V) and chromium(VI) using straw in a continuous-flow reactor

Vanadium (V) and chromium (Cr) are key resources widely used in industrial production. However, mining causes V(V) and Cr(VI) contamination in groundwater, posing health and environmental risks. Straw is an important byproduct and considered waste, however, it could be a solid carbon source. Therefore, the feasibility of V(V) and Cr(VI) bioremediation in groundwater was determined using straw as the carbon source in this study. A continuous-flow reactor able to resist fluctuations in pollutant concentrations in groundwater was constructed. V(V) and Cr(VI) were completely removed (100%, 10–34 d) in the reactor, and the maximum Cr(VI) removal rate from effluent was 1.19 mg/(L·h) (34–64 d). After long-term reactor operation (114 d), the V(V) and Cr(VI) removal rates reached almost 100%. Moreover, the formation of humus and tryptophan contributed to V(V) and Cr(VI) bioremediation. The extracellular polymeric substance content increased from 108.28 to 113.98 mg/g VSS, and combined with V(V) and Cr(VI) to reduce their concentrations. Moreover, functional microbes associated with heavy metal removal (Bacillus and Pseudobacteroides) and straw decomposition (Paludibacter) were found. The findings of this study offer empirical evidence that support the utilization of straw for mitigating composite heavy metal pollution, thereby laying a foundation for its practical engineering applications.

A nitrogen-enriched strategy to accelerate the remediation of Cr(VI)-contaminated soil by iron-based materials in microwave fields

The existing remediation technologies for Cr(VI) contamination soil suffer from long processing times. Microwave catalysis is an efficient environmental remediation technology, and the reasonable design of microwave catalysts can enable a microwave catalytic system to rapidly complete the remediation of Cr(VI). In this study, a microwave catalyst, NRFC-3, with high microwave absorption performance and electron density was designed via a nitrogen enrichment strategy. Density functional theory (DFT) calculations verified that the electron density of the material was increased by nitrogen-enriched strategy. Under the experimental conditions, the electrons (e−) of NRFC-3 originate from “hot spots” and the current density is not lower than 3.78 × 109 e·g−1·s−1. In addition, the reduction of Cr(VI) in the MW/NRFC-3 system is feasible through DFT predictions, and this conclusion was experimentally verified. The MW/NRFC-3 system has a remediation efficiency of 100 % for Cr(VI)-contaminated soil within 25 min, significantly reduced the toxicity of Cr(VI) to the environment and humans, and had long-term stability. The potential application of the MW/NRFC-3 system was verified by remediation experiments on Cr(VI)-contaminated soils of different degrees. This study provides a new technology for the rapid and harmless treatment of Cr(VI)-contaminated soil.

Heavy metal (Pb, Cd and Cr) contamination and human health risk assessment of groundwater in Kuakata, southern coastal region of Bangladesh

This study investigates the quality of groundwater in Kuakata, a coastal area in southwestern Bangladesh, by analyzing the levels of lead (Pb), cadmium (Cd), and chromium (Cr) in 50 groundwater samples. The concentrations of these heavy metals were determined using atomic absorption spectrometry. The results indicated that while cadmium was not detected, significant levels of lead and chromium exceeded recommended safety thresholds. The contamination was evaluated using several indices, including the heavy metal evaluation index (HEI), heavy metal pollution index (HPI), and degree of contamination (Cd). Health risk assessments for adults and children revealed potential non-carcinogenic and carcinogenic risks, particularly from lead. This study provides essential data to guide groundwater management and improve public health in the region. The groundwater samples contain traces of additional heavy metals including lead and chromium. The lead concentration ranges from 0.0003 to 0.1049 mg/L, while chromium ranges from 0.00074 to 0.1828 mg/L. The levels of certain substances in groundwater exceeded the maximum limit set by international and local health authorities for safe drinking water. Heavy metal evaluation index (HEI), along with the degree of contamination (Cd) and heavy metal pollution index (HPI), were used to assess the pollution load. The results of HEI and HPI revealed that a significant portion of the samples in the study area, specifically 34% and 38%, were found to be strongly and seriously affected, whereas 38% samples were within the highest values (>4) of Cd. Based on the hazard index (HI) and incremental lifetime cancer risk (ICLR) values, the deep groundwater in the coastal area presents a notable health risk to the local population, particularly children. This study provides essential data that can be used as a foundation for developing effective groundwater management strategies in the coastal region, with the ultimate goal of ensuring the availability of safe drinking water.

Spatial and seasonal variations in trace metals in marine sediments from the Dubai coastal environment.

This study was conducted to assess sediment trace metals (Cd, Cr, Cu, Pb, Ni and Zn) contamination using a systematic approach by collecting sediment samples from 8 transects along the Dubai coastline, each 10 km long, and each transect included its nearshore sediment sampling station. Additionally, 10 sediment samples were collected from the Dubai creek and other potential sources of metal pollution. The sediment samples were collected in December and again in August. However, no significant difference in sediment metal concentration was found between the two sampling campaigns. The sediment trace metal concentrations (0.92-1.31mg Cd/kg, 2.82-176.6mg Cr/kg, 2.27-621.67mg Cu/kg, 0.88-23.6mg Pb/kg, 1.92-192.2mg Ni/kg and 9.1-391.05mg Zn/kg) showed considerable variability, except for Cd (1.08 ± 0.06mg/kg, 5.55% variability). Despite this, no significant differences in sediment metal concentrations were found between the sampled transects. However, significant variations in Cr, Cu, Pb and Zn were evident between distances from the shoreline to offshore stations along the Dubai coast, and the nearshore locations presented clear evidence of elevated/maximum sediment metal concentrations. Most of the sediment trace metal concentrations, however, were found well within the sediment quality guidelines (SQGs) for nearshore sediments. Trace metal contamination hotspots, nonetheless, were identified at some nearshore stations as determined by metal level exceedance over the SQGs, background levels and the pollution load index, with limited potential ecological risk. Overall, the findings suggest that sediments in the Dubai coastal environment are mainly influenced by anthropogenic activities in stations located in the proximity of ship maintenance, ports, and industrial areas such as Dry Dock, Jaddaf, Jebel Ali Port, Wharfage, Hamriya and DUBAL.

Remediation of hexavalent chromium in water and soil by pristine and chemically modified pine barks: Effects and mechanisms

Chemical modification can greatly improve the adsorption performance of materials. In this study, pristine pine bark (PB) was modified by phosphoric acid (PA-PB), dodecyl trimethylammonium bromide (DTAB-PB) and cetyl trimethylammonium bromide (CTAB-PB) to test their influence on remediating hexavalent chromium [Cr(Ⅵ)] contamination in water and soil systems. Under the optimal experimental conditions in solution, the reduction/adsorption capacities and removal rates of Cr(Ⅵ) follow the order of CTAB-PB > PA-PB > DTAB-PB > PB, with CTAB-PB showing the highest capacity of 88.1 mg g−1. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) indicated that adsorption coupled with reduction were the responsible mechanisms for Cr(Ⅵ) removal by pristine and modified PB, and modification with CTAB greatly improved Cr(Ⅵ) removal, especially the reduction of Cr(Ⅵ). When CTAB-PB and PB were applied in soil for a 30-day microcosm experiment, more than 93 % of Cr(Ⅵ) was converted into Cr(Ⅲ) at four different addition levels (2, 5, 10, and 15 wt%) with CTAB-PB exhibiting a faster immobilization rate than PB. In conclusion, CTAB-PB showed better performance than PB and is a promising material for the remediation of Cr(Ⅵ) contamination in water and soil.

Ultra-efficient removal of aqueous hexavalent chromium by activated biochar nanoparticles derived from squid ink

Biochar have been recognized as efficient and renewable carbon sorbents, which attracted much attention on Cr contamination remediation in wastewater. In this study, we propose a cost-effective one-step strategy to synthesize activated biochar nanoparticles derived from squid ink (AS-BC) for aqueous Cr(VI) removal. The results demonstrated that AS-BC achieved a removal rate of 24.29 h−1 at 700 °C (400-times higher than the unmodified one). This was also a state-of-the-art removal performance for aqueous Cr(VI) compared to other reported materials. AS-BC possessed an enormous specific surface (2408 m2/g at 700 °C) with abundant O- and N-containing groups, condensed aromatic structures, and high electron transfer capacity (3.64 and 2.13 mmol e−/g for EAC and EDC at 700 °C), contributing to the ultra-efficient removal of Cr(VI) by synergistic adsorption and reduction. AS-BC absorbed Cr(VI) in the form of HCrO4− by electrostatic attraction with protonated amine-N and hydroxy (-NH3+ and -OH2+) groups and Cr(III) in the form of Cr3+ by complexation with amine-N and hydroxy groups. With a hydroxy-quinone and conjugated π-electron system, AS-BC served as mediator and shuttle to accelerate electron transfer in Cr(VI) reduction with an electron donor. Therefore, our findings highlight the immense potential of AS-BC biochar nanoparticles represent a potential alternative for high-performance Cr(VI) remediation in wastewater.

Biochar solutions: Slow and fast pyrolysis effects on chromium stress in rapeseed roots

Chromium (Cr) contamination in agricultural soils, largely due to industrial activities, poses a significant threat to plant growth and productivity. This study examines the effects of Cr stress at concentrations of 100 and 200 mg of K2Cr2O7 per kg soil on rapeseed (Brassica napus) roots and evaluates the mitigating potential of biochar. Biochar, produced through both slow and fast pyrolysis and applied at 30 g per kg soil, was investigated for its ability to neutralize Cr toxicity. Our findings indicate that Cr stress significantly decreased the growth and physiological functions of rapeseed roots. However, biochar application improved soil pH, cation exchange capacity, and the uptake of essential nutrients such as nitrogen, phosphorus, potassium, calcium, and magnesium. Additionally, biochar enhanced the production of osmotic regulators like glycine betaine and soluble proteins, as well as indole acetic acid, promoting better root growth and water uptake under Cr stress. Notably, biochar reduced Cr availability and absorption in rapeseed roots, leading to lower levels of stress-related hormones such as abscisic acid, salicylic acid, and jasmonic acid. Among the biochars tested, slow pyrolysis biochar was more effective than fast pyrolysis biochar in mitigating Cr toxicity. These results highlight the potential of slow pyrolysis biochar as a sustainable strategy to alleviate Cr pollution and enhance plant resilience in contaminated soils.

Chromium cycle in Red Soil Critical Zone constrained by chromium isotopes

Chromium (Cr) isotopic system has been used to trace Cr pollution in the modern surface environment and redox change in the paleoenvironment. However, the transformation mechanism of Cr in soil and the accompanied Cr isotopic fractionation have not been clarified clearly. Here we measured Cr isotopic compositions (δ53Cr) of two paddy field profiles from the Red Soil Critical Zone Observatory in South China. The δ53Cr values of the young paddy fields, which have been cultivated for about 20 years, range from −0.34 ‰ to −0.22 ‰. The old paddy fields have been cultivated for >100 years and have more positive Cr isotopic compositions than the young paddy fields, from −0.20 ‰ to −0.06 ‰. The results of three-step leaching experiments show that iron and manganese oxides are enriched in heavy Cr isotopes, while organic matters have much lower Cr isotopic compositions, likely resulting from back reduction of Cr(VI). Our results suggest that Cr isotopic fractionation during the oxidation of Cr(III) is not the only reason for the depletion of heavy isotopes during oxidative weathering, and the partial back-reduction of generated Cr(VI) by organic matter plays an important role in Cr isotopic fractionation during weathering. Comparison between the old and young paddy fields further indicates that cultivation can significantly affect the Cr cycle in red soils. Paddy fields could be a potential sink for the Cr(VI) contaminant, and soils with a long history of cultivation would be more susceptible.

Potential functional profiling of soil microbial communities under long-term application of tannery sludge

This study investigated the impact of Cr contamination on the functional profiling of bacterial and archaeal communities in a tropical soil. The contaminated soil contained ∼300 mg kg⁻¹ of Cr due to the long-term application of tannery sludge. The FAPROTAX database was used to assess the potential functional profiling of bacterial and archaeal communities based on 16S rRNA gene phylogeny. The results showed a higher relative abundance of Actinobacteria, Proteobacteria, and Firmicutes. Additionally, an increased relative abundance of Bacillaceae and Paenibacillaceae was observed in Cr-contaminated soil. The functional profiling predicted eleven potential functions, with Cr contamination negatively affecting chemoheterotrophy, nitrification, ammonia oxidation, and nitrogen fixation. This study reveals that Cr contamination significantly impacts the functional profiling of soil bacterial and archaeal communities, emphasizing the importance of monitoring and mitigating Cr contamination to preserve soil function.

Chromium contamination affects the fungal community and increases the complexity and stability of the network in long-term contaminated soils

Chromium (Cr) contamination can adversely affect soil ecology, yet our knowledge of how fungi respond to Cr contamination at heavily contaminated field sites remains relatively limited. This study employed high-throughput sequencing technology to analyze fungal community characteristics in soils with varying Cr concentrations. The results showed that Cr contamination significantly influenced soil fungi's relative abundance and structure. Mantel test analysis identified hexavalent chromium (Cr(VI)) as the primary factor affecting the structure of the soil fungal community. In addition, FUNGuild functional prediction analysis exhibited that Cr contamination reduced the relative abundance of Pathotroph and Symbiotroph trophic types. High concentrations of Cr may lead to a drop in the relative abundance of Animal Pathogens. Molecular ecological network analysis showed that Cr contamination increased interactions among soil fungi, thereby enhancing the stability and complexity of the network. Within these networks, specific keystone taxa, such as the genus Phanerochaete, exhibited properties capable of removing or reducing the toxicity of heavy metals. Our studies suggest that Cr contamination can alter indigenous fungal communities in soil systems, potentially impacting soil ecosystem function.

Chromium removal from concentrated ammonium-nitrate solution: Electrocoagulation with iron in a plug-flow reactor

Highly concentrated ammonium nitrate (AN) solutions are characteristic of explosives manufacturing wastewaters and liquid fertilizer commodities, but chromium (Cr) contamination from corroding metal infrastructure or source impurities can pose problems. Technologies are needed to decontaminate AN from Cr without chemical alterations if AN is to be recovered as a resource. Iron-based electrocoagulation is a proven way to produce Fe(II) for reducing dissolved Cr(VI) to the less soluble and less toxic form of Cr(III), but is an untested technology for AN brines. This work examined Cr removal from synthetic wastewater with high concentrations of AN (400 g/L) by electrocoagulation in a flow-through reactor, where the effects of time, solution flow rate, applied current, and coexisting ions were analyzed. This method not only reduces Cr(VI) to Cr(III) using the produced Fe(II), but also promotes complete Cr removal from solution with the formation of insoluble Fe-Cr precipitates. A slower flow rate and higher applied current increased the removal efficiency of the reactor; furthermore, the reactor took up to one hour to reach steady state conditions, depending on the flow rate. Cr concentrations along the anode length were modeled using a simplified advection–dispersion-reaction model, providing reaction rate coefficients for various flow rates and currents. Overall, the results of this work showed that electrocoagulation with iron can be used for treatment of AN solution contaminated with Cr(VI). This work also provides design guidelines with a corresponding model for field applications in future work.

Tracking the Molecular-Scale Mechanistic Pathway of Trapping-Bonding CTAB/Fe3O4-AS for High-Performance Cr(VI) Adsorption

Cr(VI) contamination threatens the environment and health, necessitating urgent, sustainable removal solutions. Composite biological adsorbents are promising, yet the molecular-level adsorption mechanisms remain unclear. This gap in understanding hinders the development and application of more efficient biological adsorbent materials. Here, we propose a magnetic composite adsorbent based on Aspergillus niger spores (CTAB/Fe3O4-AS) to track the trapping-bonding mechanisms of Cr(VI) on its surface. Characterization analysis showed that Fe3O4 nanoparticles and CTAB form a stable magnetic shell and an outermost quaternary ammonium layer on the spore surface. This synergistic structure enhanced the Cr(VI) adsorption capacity to 186 mg·g−1 at pH 2.0 in solution and achieved a Cr(VI) removal rate exceeding 99 % in electroplating wastewater, with dosage of 1.8 g·L−1 after 180 min. CTAB/Fe3O4-AS selectively removes Cr(VI) from acidic wastewater, with selectivity coefficients of KCr/Zn = 1334 and KCr/Cu = 2661. Cr(VI) removal occurs mainly through chemical adsorption via heterogeneous processes. DFT calculations and MD simulations visualize reaction pathways and interaction strengths at the molecular scale. The quaternary ammonium cation group ((CH3)4-N+) in CTAB traps Cr(VI) ions electrostatically, transferring them to the spore surface. Electron-donating groups (–COO, –NH-) on the spores reduce Cr(VI) to Cr(III). Amide groups in chitin create optimal coordination sites for Cr(III) by twisting, with nitrogen atoms forming stable complexes through coordination bonds with Cr(III)’s vacant orbitals. This study not only developed an efficient microbial-based composite adsorbent but also proposed a novel synergistic adsorption mechanism: electrostatic trapping–reduction–coordination bonding. This provides valuable insights for developing more efficient and applicable heavy metal ion adsorbent materials in the future.

Phosphorus and selenium compounding mitigates Cr stress in peanut seedlings by enhancing growth homeostasis and antioxidant properties.

Peanut is an economically important crop, but it is susceptible to Cr contamination. In this study, we used peanut as experimental material to investigate the effects of exogenous P, Se interacting with Cr on the nutrient growth and antioxidant system of peanut seedlings by simulating Cr (0μM, 50μM, and 100μM) stress environment. The results showed that exogenous P, Se supply could mitigate irreversible damage to peanut seedlings by altering the distribution of Cr in roots and aboveground, changing root conformation, and repairing damaged cells to promote growth. When the Cr concentration is 100μM, it exhibits the highest toxicity. Compared to the control group P and Se (0 MM), the treatment with simultaneous addition of P + Se (0.5 + 6.0) resulted in a significant increase in root length and root tip number by 248.7% and 127.4%, respectively. Additionally, there was a 46.9% increase in chlorophyll content, a 190.2% increase in total surface area of the seedlings, and a respective increase of 149.1% and 180.3% in soluble protein content in the shoot and roots. In addition, by restricting the absorption of Cr and reducing the synthesis of superoxide dismutase SOD (Superoxide dismutase), CAT (Catalase), POD (Peroxidase), and MDA (Malonaldehyde), it effectively alleviates the oxidative stress on the antioxidant system. Therefore, the exogenous addition of P (0.5 MM) and Se (6.0 MM) prevented the optimal concentration of chromium toxicity to peanuts. Our research provides strong evidence that the exogenous combination of P and Se reduces the risk of peanut poisoning by Cr, while also exploring the optimal concentration of exogenous P and Se under laboratory conditions, providing a basis for further field experiments.