Toxic Cr Research Articles

Inhibitory mechanism of Cr(VI) on sulfur-based denitrification: Bio-toxicity, bio-electron characteristics, and microbial evolution

Sulfur-based denitrification is a promising technology for efficient nitrogen removal in low-carbon wastewater, while it is easily affected by toxic substances. This study revealed the inhibitory mechanism of Cr(VI) on thiosulfate-based denitrification, including bio-toxicity and bio-electron characteristics response. The activity of nitrite reductase (NIR) was more sensitive to Cr(VI) than that of nitrate reductase (NAR), and NIR was inhibited by 21.32 % and 19.86 % under 5 and 10 mg/L Cr(VI), resulting in 10.12 and 15.62 mg/L of NO2--N accumulation. The biofilm intercepted 36.57 % of chromium extracellularly by increasing 25.78 % of extracellular polymeric substances, thereby protecting microbes from bio-toxicity under 5 mg/L Cr(VI). However, it was unable to resist 20–30 mg/L of Cr(VI) bio-toxicity as 19.95 and 14.29 mg Cr/(g volatile suspended solids) invaded intracellularly, inducing the accumulation of reactive oxygen species by 165.98 % and 169.12 %, which triggered microbial oxidative-stress and damaged the cells. In terms of electron transfer, S2O32- oxidation was inhibited, and parts of electrons were redirected intracellularly to maintain microbial activity, resulting in insufficient electron donors. Meanwhile, the contents of flavin adenine dinucleotide and cytochrome c decreased under 5–30 mg/L Cr(VI), reducing the electron acquisition rate of denitrification. Thermomonas (the dominant genus) possessed denitrification and Cr(VI) resistance abilities, playing an important role in antioxidant stress and biofilm formation. Environmental ImplicationSulfur-based denitrification (SBD) is a promising method for nitrate removal in low-carbon wastewater, while toxic heavy metals such as Cr(VI) negatively impair denitrification. This study elucidated Cr(VI) inhibitory mechanisms on SBD, including bio-toxicity response, bio-electron characteristics, and microbial community structure. Higher concentrations Cr(VI) led to intracellular invasion and oxidative stress, evidenced by ROS accumulation. Moreover, Cr(VI) disrupted electron flow by inhibiting thiosulfate oxidation and affecting electron acquisition by denitrifying enzymes. This study provided valuable insights into Cr(VI) toxicity, which is of great significance for improving wastewater treatment technologies and maintaining efficient and stable operation of SBD in the face of complex environmental challenges.

Multiplicative effects of co-incineration of sewage sludge and wasted oyster shells in air, CO2, and steam atmospheres on P speciation and bioavailability and metal ecotoxicity

The study was aimed at the reutilization of oyster shells (OS) as a calcium-based additive to turn sewage sludge ash into phosphate fertilizer, employing the oxygen-enriched combustion technology. This process transformed all non-apatite inorganic phosphorus into apatite phosphorus with the incorporation of a 7.5% Ca-based additive. OS demonstrated comparable effectiveness to CaO in catalyzing this transformation in the oxygen-steam atmosphere. The amount of OS added and the atmosphere type significantly influenced the P bioavailability of sewage sludge ash. The oxygen-steam atmosphere, with its increased water vapor concentration, facilitated the decomposition of CaCO3 and initiated reactions with calcium phosphate to form hydroxyapatite, thus substantially enhancing P bioavailability. The oxygen-steam atmosphere increased not only metal volatilization but also the ecological toxicity of residual metals, particularly Pb, mainly in the form of F2. Excessive OS addition appeared to elevate the toxicity of Cr. Therefore, additional strategies for metal removal or passivation are needed to improve the safety of sewage sludge ash with high metal content.

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.

Metagenomes from microbial populations beneath a chromium waste tip give insight into the mechanism of Cr (VI) reduction

Dumped Chromium Ore Processing Residue (COPR) at legacy sites poses a threat to health through leaching of toxic Cr(VI) into groundwater. Previous work implicates microbial activity in reducing Cr(VI) to less mobile and toxic Cr(III), but the mechanism has not been explored. To address this question a combined metagenomic and geochemical study was undertaken. Soil samples from below the COPR waste were used to establish anaerobic microcosms which were challenged with Cr(VI), with or without acetate as an electron donor, and incubated for 70 days. Cr was rapidly reduced in both systems, which also reduced nitrate, nitrite then sulfate, but this sequence was accelerated in the acetate amended microcosms. 16S rRNA gene sequencing revealed that the original soil sample was diverse but both microcosm systems became less diverse by the end of the experiment. A high proportion of 16S rRNA gene reads and metagenome-assembled genomes (MAGs) with high completeness could not be taxonomically classified, highlighting the distinctiveness of these alkaline Cr impacted systems. Examination of the coding capacity revealed widespread capability for metal tolerance and Fe uptake and storage, and both populations possessed metabolic capability to degrade a wide range of organic molecules. The relative abundance of genes for fatty acid degradation was 4× higher in the unamended compared to the acetate amended system, whereas the capacity for dissimilatory sulfate metabolism was 3× higher in the acetate amended system. We demonstrate that naturally occurring in situ bacterial populations have the metabolic capability to couple acetate oxidation to sequential reduction of electron acceptors which can reduce Cr(VI) to less mobile and toxic Cr(III), and that microbially produced sulfide may be important in reductive precipitation of chromate. This capability could be harnessed to create a Cr(VI) trap-zone beneath COPR tips without the need to disturb the waste.

Efficient and low-cost mesoporous magnetic carbon composites derived from date palm stones for environmental remediation of hexavalent chromium

This study was performed to achieve two important scientifically challenging goals, environmental remediation of toxic heavy metals and utilization of agricultural lignocellulosic wastes. In this work, a series of mesoporous magnetic carbon (MMC) adsorbents were synthesized by carbothermic reduction at different temperatures employing date palm (Phoenix dactylifera L.) stones as the carbon source. The synthesized adsorbents were characterized by different technquies and the results confirmed the presence of zero-valent iron (ZVI) nanoparticles and other iron oxides as products of the carbothermal reduction. The nature of phases present, crystallite size and the surface properties were found to be dependent on the calcination temperature. The adsorbent MMC700 exhibited the smallest (ZVI) crystallite size 36 nm and the largest SBET 341 m2/g. All adsorbents showed mesoporous structure with mesopore average diameter lower than 6 nm. The performance was evaluated in the removal process of toxic Cr(VI) in an aqueous medium, and the optimum conditions of the process were reported. The removal process was dependant of solution pH where best results was achieved at pH = 2. Complete removal of chromium was achieved in less than 5 min by MMC700. The results were better fitted with pseudo-second-order kinetics and followed the Freundlich model isotherm. The maximum adsorption capacity was found to be 265.25 mg/g for MMC700, suggesting its application as an efficient, low-cost, and easily separable adsorbent for the toxic Cr(VI) removal process. The prepared adsorbents exhibited superior performance in the removal process compared to other agricultural wastes or biomass - derived adsorbents reported in literature.

The influence of Mn(II) on transformation of Cr-absorbed Schwertmannite: Mineral phase transition and elemental fate

Schwertmannite (Sch) is considered as an effective remover of Chromium (Cr) due to its strong affinity for toxic Cr species. Since the instability of Sch, the environmental fate of Cr deserves attention during the transformation of Sch into a more stable crystalline phase. The ubiquitous manganese(II) (Mn(II)) probably affects the transformation of Sch and thus the environmental fate of Cr. Therefore, this study investigated the impact of Mn(II) on the transformation of Cr-absorbed Sch (Cr-Sch) and the associated behavior of SO42− and Cr. We revealed that the transformation products of Cr-Sch at pH 3.0 and 7.0 were goethite and Sch, respectively. The presence of Mn(II) weakened the crystallinity of the transformation products, and the trend was positively correlated with the concentration of Mn(II). However, Mn(II) changed the transformation products of Cr-Sch from hematite to goethite at pH 10.0. Mn(II) replaced Fe(III) in the mineral structures or formed Mn-O complexes with surface hydroxyl groups (-OH), thereby affecting the transformation pathways of Sch. The presence of Mn(II) enhanced the immobilization of Cr on minerals at pH 3.0 and 7.0. Sch is likely to provide an channel for electron transfer between Mn(II) and Cr(VI), which promotes the reduction of Cr(VI). Meanwhile, Mn(Ⅱ) induced more -OH production on the surface of secondary minerals, which played an important role in increasing the Cr fixation. In addition, part of the Mn(Ⅱ) was oxidized to Mn(Ⅲ)/Mn(Ⅳ) at pH 3.0 and pH 7.0. This study helps to predict the role of Mn(II) in the transformations of Cr-Sch in environments and design remediation strategies for Cr contamination.

Non-carcinogenic risk assessment and sources apportionment of heavy metals in pomegranate in Anhui, China

This study examined the concentrations, sources, and health risks associated with 7 heavy metals in Chinese pomegranates. The results showed that the heavy metal in pomegranates was within standard limits, and the accumulation of heavy metals was low. PCA showed that Cd and Hg in pomegranates originate from irrigation water, Zn, As, and Cu from soil, and Cr and Pb from fertilizers. MLR and Monte Carlo sensitivity analysis showed that soil and irrigation water were the primary sources of heavy metals in pomegranates, with Zn, As, Cu, and Pb primarily originating from soil, and Cd, Cr, and Pb predominantly coming from irrigation water. The presence of organic matter and Ca in soil influenced heavy metal accumulation in pomegranates, other properties (Mg, Fe, and pH value in soil) have minor effects. The TTHQ for both adults and children remained below 1, while the TTRisk exceeded 1×10−4, mainly due to the hazardous impact of As in water. The upper 95% uncertainty limit indicated that residents were exposed to both non-carcinogenic and carcinogenic risks, primarily due to the toxicity of Cr in soil and As in water. Strengthening heavy metal screening in soil and water and enhancing pollution management policies are imperative.

Efficient removal of Cr(VI) from wastewater by composite adsorptive membrane modified with polyethyleneimine (PEI)

The development of an efficient and economical method to remove the toxic Cr(VI) from water is a global challenge. This study developed a new composite adsorptive membrane by combining polyacrylonitrile (PAN) as a substrate with crosslinked polyethyleneimine (PEI) to efficiently remove Cr(VI) from wastewater. After optimizing the preparation conditions of the material, the Cr(VI) removal by PEI/GMA@PAN was investigated using batch adsorption and longer-term filtration experiments. The composite adsorptive membrane exhibited a high adsorption capacity, reaching a maximum of 89.16 mg/g, along with fast adsorption kinetics that achieved equilibrium within 100 min for Cr(VI) removal. Even in the presence of coexisting ions, PEI/GMA@PAN membrane maintained a high efficiency in removing Cr(VI). The removal mechanism mainly relied on electrostatic interactions and the reduction of Cr(VI) to Cr(III). Notably, long-term filtration experiments substantiated the membrane's effectiveness in removing Cr(VI) from synthetic wastewater, with an impressive treatment volume of 342 L/m2. The optimized PEI/GMA@PAN membrane also demonstrated low PEI leaching across a wide pH range and the potential for re-utilization through four-round cycles, underscoring its promising applicability in wastewater treatment. Therefore, the newly synthesized composite membranes show potential for the removal of Cr(VI) from wastewater.

Salinity-Induced Changes in Heavy Metal Behavior and Mobility in Semi-Arid Coastal Aquifers: A Comprehensive Review

Semi-arid coastal aquifers face critical challenges characterized by lower rainfall, higher evaporation rates, and looming risk of over-exploitation. These conditions, coupled with climate change, are conducive to seawater intrusion and promote mechanisms associated with it. The understanding of metal behavior in such environments is limited, and hence, an attempt is made through this review to bridge the knowledge gap. A study on the behavior of trace metals within a specific context of semi-arid coastal aquifers was carried out, and 11 aquifers from 6 different countries were included. The review observed that trace metals within semi-arid coastal aquifers exhibit distinctive behaviors influenced by their surrounding environment. The prevalence of evaporation and continuous seawater intrusion played a pivotal role in shaping trace metal dynamics by curtailing groundwater flux. The findings suggest that the formation of stable Cl and organic ligands under increased alkaline conditions (pH > 8) has higher control over Zn, Pb, and Cd toxicity in a highly ionic reactive condition. In addition, dominant control of Fe/Mn-hydroxide association with Pb and high organic affinity of Zn played a pivotal role in controlling its bioavailability in aquifers such as WFB, Saudi Arabia NW-C and India. On the contrary, under prevailing acidic conditions (pH < 6), carbonate and SO4-ligands become more dominant, controlling the bioavailability/desorption of Cu irrespective of its origin. The behavior of Ni is found to be controlled by stable organic ligands increasing salinity. An increase in salinity in the considered aquifers shows an increase in bioavailability of Ni, except UmC, South Africa, where organic ligands act as a sink for the metal, even at low pH conditions (pH < 5.5). This study indicates that factors such as mineral saturation, carbonate complexes, pH variations (pH > 8), and chloride complexes govern the distribution of trace metals further enhanced by prolonged water residence time. Nonetheless, specific conditions, such as a reducing and acidic environment, could potentially elevate the solubility of highly toxic Cr (VI) released from anthropogenic sources.

Impact of fly ash deposition on plants diversity, metal content, and associated risk on grazing ruminants in the vicinity of Morupule power station, Botswana

Fly ash (FA) deposition originating from power stations and unprotected dumpsites, have been found to affect plant communities, potentially causing environmental degradation and food chain contamination. An analysis of plant composition, heavy metal concentration in plants and soil within 40 kilometers of the Morupule dumpsite was conducted to evaluate the impact of FA disposal. In addition, risks to the ruminants grazing in this area, were assessed. The windward transect had significantly higher species diversity and richness than the leeward transect, especially in areas closer to the dumpsite. This could be attributed to the inability of some plants to tolerate higher concentrations of toxic metal and alkalinity in areas near the dumpsite. In this study, average concentrations in plants of Cr (546.11 mg kg−1), Mn (905.69 mg kg−1), and Cu (128 mg kg−1) were above toxicity levels of 75-100 mg kg−1 for Cr, 400 mg kg−1 for Mn, and 100 mg kg−1 for Cu. Although the quantities of these metals were above the maximum allowable daily consumption, calculations of the daily plant intake by grazing animals in this area revealed a potential danger of exposure to Cr and Cu. Particularly in areas that were nearest to the FA dumpsite, ruminants grazing on the leeward transect were more exposed to Cu than Cr toxicity. Overall, it was found that FA deposition damaged the plant community and put grazing ruminants at greater danger. However, more investigation is required to pinpoint the precise level of hazardous metals found in the grazing animals in this area.

Visible-light photocatalytic O2-to-H2O2 via nitrogen-graphene quantum dots-modified Bi2Fe4O9 for synchronizing the reduction of Cr(VI) and oxidation of organic contaminants: Kinetics, mechanism, and performance

Synergistic coexistence of toxic chromium and organic contaminants in wastewater has made treatments highly complicated. As solar-driven wastewater treatments become increasingly environmentally and economically attractive, a photocatalyst (denoted as N-GQDs/Bi2Fe4O9) is developed for photocatalytic reduction of Cr(VI) and simultaneous oxidation of organic contaminants in wastewater. Incorporating N-GQDs (as electron reservoir) into Bi2Fe4O9 modulates the band structure (from 2.40 to 2.24 eV), facilitating charge transfer and electron accumulation at N-GQDs. Due to the photo-Fenton synergistic reaction between N-GQDs/Bi2Fe4O9 photocatalysis process, N-GQDs/ Bi2Fe4O9 demonstrates excellent H2O2 generation (1.64 μM min−1) and H2O2 activation (0.0063 min−1) performance, leading to generation of more highly reactive species (i.e., OH radicals), achieving BPA removal of 99.9 % under visible-light irradiation for 100 min. Interestingly, the photo-Fenton synergistic reaction enhances the reduction of Cr(VI) (99.8 %), while the Fe(II) active sites on the N-GQDs/Bi2Fe4O9 can also promote the synchronized Cr(VI) reduction. Also, the accumulated electron around N-GQDs enhances redox cycles of Fe(II)/Fe(III) reactions to realize the sustainable photo-Fenton catalytic reaction. This new N-GQDs/Bi2Fe4O9 photocatalyst demonstrates the feasibility of concurrent reduction of toxic Cr(VI)-to-Cr(III) and oxidation of organic contaminants in wastewater with a simple process via nearly unlimited solar energy.

Identification of the single and combined acute toxicity of Cr and Ni with Heterocypris sp. and the quantitative structure-activity relationship (QSAR) model.

Mining wastewater with heavy metals poses a serious threat to the ecological environment. However, the acute single and combined ecological effects of heavy metals, such as chromium (Cr) and nickel (Ni), on freshwater ostracods, and the development of relevant prediction models, remain poorly understood. In this study, Heterocypris sp. was chosen to investigate the single and combined acute toxicity of Cr and Ni. Then, the quantitative structure-activity relationship (QSAR) model was used to predict the combined toxicity of Cr and Ni. The single acute toxicity experiments revealed high toxicity for both Cr and Ni. In addition, Cr exhibited greater toxicity compared to Ni, as evidenced by its lower 96-hour half-lethal concentration (LC50) of 1.07 mg/L compared to 4.7 mg/L for Ni. Furthermore, the combined acute toxicity experiments showed that the toxicity of Cr-Ni was higher than Ni but lower than Cr. Compared with the concentration addition (CA) and independent action (IA) models, the predicted results of the QSAR model were more consistent with the experimental results for the Cr-Ni combined acute toxicity. So, the high accuracy of QSAR model identified its feasibility to predict the toxicity of heavy metal pollutants in mining wastewater.

Mechanism of Cr(VI) removal by polyphenols-rich bacterial cellulose gel produced from fermented wine pomace

Hexavalent chromium (Cr(VI)) is still a common contaminant in water. In this work, we studied the Cr(VI) adsorption by polyphenol-rich bacterial cellulose(BC) gel, synthesized by the Komagataeibacter rhaeticus K15 using wine pomace. The results showed that the equilibrium removal capacity was 473.09 ± 1.41 mg g−1 (dry weight). The quasi-second-order kinetics model and the Langmuir removal isotherm model was the most suitable for describing the Cr(VI) removal process. Toxic Cr(VI) was converted to the low toxic Cr(III) during the removal process via the reduction of Cr(VI) to Cr(III) by polyphenols released into the solution by the BC gel. The FTIR, XRD, XPS, SEM-EDX results indicated the physical adsorption on the surface of BC and the reduction reaction between polyphenol groups and Cr(VI) is the critical mechanism of Cr(VI) removal by BC. The finding of this study demonstrates that polyphenols-rich BC gel produced from wine pomace has a superior feature for future Cr(VI)-wastewater purification.

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.

A sustainable redox-active electrocatalyst utilizing natural quercetin-infused MWCNT for ultra-sensitive detection of environmental Cr(VI) contaminants

Hexavalent chromium (Cr(VI)), classified as a Group 1 carcinogen, is a widely acknowledged water pollutant, posing significant public health risks. The persisting challenge involves the development of sensitive and cost-effective methods for the detection and monitoring of Cr(VI) species at the concentration level recommended by the World Health Organization (WHO), which is 50 ppb (960 nM), in water sources. In the electrochemical detection of Cr(VI), modified electrodes utilizing precious metals (Au and Ag) and toxic organic redox mediators (Thionine, methylene blue, quionone, bisphenol and phenosafranine) have been employed. In this work, as an new platform, green electrochemical approach based on parsley-plant based natural quercetin (Qn-Redox) infused MWCNT modified glassy carbon electrode, designated as GCE/MWCNT@Qn-Redox, has been introduced for highly-effective electrocatalytic reduction and sensing of Cr(VI) species in pH 2 KCl-HCl solution. The as prepared GCE/MWCNT@Qn-Redox showed highly redox active surface confined peak at Eo = 0.550 V vs Ag/AgCl with surface excess value, 10.31 × 10−9 mol cm−2. Extensive physicochemical, spectroscopic, molecular characterization, and electrochemical control experiments confirm the identity of the entrapped molecular species in the green electrode as quercetin. By using scanning-electrochemical technique, the electroactive site of the green-electrode was imaged using Fe(CN)63−/Fe(CN)64− redox couple. The green-electrode showed excellent electrocatalytic Cr(VI) reduction signal where the Qn-Redox peak appears without any fouling problem. As a practical application, a portable batch-injection analysis coupled with three-in-one screen-printed electrode modified with MWCNT@Qn-Redox, which exhibitted a detection limit of 203 nM (S/N = 3), has been demonstrated for real time monitoring of toxic Cr(VI) species in tannery industries contaminated water samples. Given the electrochemical foundation of this approach, it holds promise for various sustainable electroanalytical assays in the future.

Co-application of titanium nanoparticles and melatonin effectively lowered chromium toxicity in lemon balm (Melissa officinalis L.) through modifying biochemical characteristics.

Chromium (Cr) toxicity can negatively affect plant growth and development, impacting agricultural productivity and posing risks to human health. Metallic nanoparticles (MNPs) such as titanium dioxide (TiO2) and natural growth regulators such as melatonin (MT) become a promising technology to manage heavy metal-contaminated soils and promote safe food production. The present work was conducted to find the effect of foliar application of TiO2 NPs (15 mg L-1) and MT (100 µM) on growth, biochemical attributes, and Cr accumulation in plant tissues of Melissa officinalis L. under Cr toxicity (50 and 100 mg Cr kg-1 soil). The results showed that Cr toxicity led to decreased plant performance, where 100 mg Cr kg-1 soil led to notable decreases in shoot weight (28%), root weight (27%), essential oil (EO) yield (34%), chlorophyll (Chl) a + b (33%), while increased malondialdehyde (MDA, 30%), superoxide dismutase (SOD) activity (51%), and catalase (CAT) activity (122%). The use of TiO2 NPs and MT, particularly their co-application, remarkably reduced Cr toxicity by enhancing plant weight, Chl content, and lowered MDA and antioxidant activity. Total phenolic content (TPC), total flavonoid content (TFC), EO percentage, and rosmarinic acid in plants treated with Cr at 50 mg Cr kg-1 soil and co-application of TiO2 NPs and MT were relatively higher than in other treatments. Under 100 mg Cr kg-1 soil, the synergic effect of TiO2 NPs and MT-enhanced rosmarinic acid content (22%) but lowered Cr accumulation in roots (51%) and shoots (72%). Heat map analysis showed that CAT, SOD, MDA, and EO yield had the maximum variability under Cr, TiO2 NPs, and MT. Exogenous TiO2 NPs and MT can be recommended to modulate Cr toxicity in lemon balm under soil Cr toxicity.

Transcriptomic analysis reveals particulate hexavalent chromium regulates key inflammatory pathways in human lung fibroblasts as a possible mechanism of carcinogenesis

Hexavalent chromium [Cr(VI)] is considered a major environmental health concern and lung carcinogen. However, the exact mechanism by which Cr(VI) causes lung cancer in humans remains unclear. Since several reports have demonstrated a role for inflammation in Cr(VI) toxicity, the present study aimed to apply transcriptomics to examine the global mRNA expression in human lung fibroblasts after acute (24 h) or prolonged (72 and 120 h) exposure to 0.1, 0.2 and 0.3 μg/cm2 zinc chromate, with a particular emphasis on inflammatory pathways. The results showed Cr(VI) affected the expression of multiple genes and these effects varied according to Cr(VI) concentration and exposure time. Bioinformatic analysis of RNA-Seq data based on the Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and MetaCore databases revealed multiple inflammatory pathways were affected by Cr(VI) treatment. qRT-PCR data corroborated RNA-Seq findings. This study showed for the first time that Cr(VI) regulates key inflammatory pathways in human lung fibroblasts, providing novel insights into the mechanisms by which Cr(VI) causes lung cancer.

Interaction of titanium dioxide nanoparticles with PVC-microplastics and chromium counteracts oxidative injuries in Trachyspermum ammi L. by modulating antioxidants and gene expression

The emergence of polyvinyl chloride (PVC) microplastics (MPs) as pollutants in agricultural soils is increasingly alarming, presenting significant toxic threats to soil ecosystems. Ajwain (Trachyspermum ammi L.), a plant of significant medicinal and culinary value, is increasingly subjected to environmental stressors that threaten its growth and productivity. This situation is particularly acute given the well-documented toxicity of chromium (Cr), which has been shown to adversely affect plant biomass and escalate risks to the productivity of such economically and therapeutically important species. The present study was conducted to investigate the individual effects of different levels of PVC−MPs (0, 2, and 4 mg L−1) and Cr (0, 150, and 300 mg kg−1) on various aspects of plant growth. Specifically, we examined growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress responses, antioxidant compound activity (both enzymatic and nonenzymatic), gene expression, sugar content, nutritional status, organic acid exudation, and Cr accumulation in different parts of Ajwain (Trachyspermum ammi L.) seedlings, which were also exposed to varying levels of titanium dioxide (TiO2) nanoparticles (NPs) (0, 25, and 50 µg mL−1). Results from the present study showed that the increasing levels of Cr and PVC−MPs in soils significantly decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. Conversely, increasing levels of Cr and PVC−MPs in the soil increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation pattern in the roots of T. ammi seedlings. Interestingly, the application of TiO2−NPs counteracted the toxicity of Cr and PVC−MPs in T. ammi seedlings, leading to greater growth and biomass. This protective effect is facilitated by the NPs' ability to sequester reactive oxygen species, thereby reducing oxidative stress and lowering Cr concentrations in both the roots and shoots of the plants. Our research findings indicated that the application of TiO2−NPs has been shown to enhance the resilience of T. ammi seedlings to Cr and PVC−MPs toxicity, leading to not only improved biomass but also a healthier physiological state of the plants. This was demonstrated by a more balanced exudation of organic acids, which is a critical response mechanism to metal stress.

A stable Zn-MOF with anthracene-based linker for Cr(VI) photocatalytic reduction under sunlight irradiation

The highly desired goal is to employ visible light for the photocatalytic reduction of toxic Cr(VI) to environmentally friendly Cr(III). Metal-organic frameworks (MOFs) are considered one of the most promising materials for the photoreduction of Cr(VI). Nevertheless, developing MOFs with high stability and activity is still challenging. Herein, we report a stable Zn-based MOF (named DZU-64) with an anthracene functionalized ligand, and its reduction of Cr(VI) under sunlight irradiation was investigated. DZU-64 exhibits excellent chemical stability in pH range of 2−14 aqueous solution, and remarkable thermal stability to 570 °C. For the photoreduction of Cr(VI) under visible light irradiation, DZU-64 gives a record rate constant of 0.467 min−1 and a high Cr(VI) reduction rate of 6.68 mg Cr(VI) g−1cata min−1 at pH 2. Moreover, under real solar light, DZU-64 can also efficiently reduce Cr(VI) to Cr(III) while retaining its catalytic activity throughout 5 cycles without any notable decline, further demonstrating its great application prospect. By combining the photovoltaic performance tests and electron spin resonance test, the possible photoreduction of Cr(VI) mechanism in DZU-64 was analyzed.

Efficient green Cr(VI) adsorbent from sorghum waste: Eco-designed functionalized mesoporous silica FDU-12

This paper presents an eco-design approach to the synthesis of a highly efficient Cr(VI) adsorbent, utilizing a positively charged surface mesoporous FDU-12 material (designated as MI-Cl-FDU-12) for the first time. The MI-Cl-FDU-12 anion-exchange adsorbent was synthesized via a facile one-pot synthesis approach using sodium silicate extracted from sorghum waste as a green silica source, 1-methyl-3-(triethoxysilylpropyl) imidazolium chloride as a functionalization agent, triblock copolymer F127 as a templating or pore-directing agent, trimethyl benzene as a swelling agent, KCl as an additive, and water as a solvent. The synthesis method offers a sustainable and environmentally friendly approach to the production of a so-called “green” adsorbent with a bimodal micro-/mesoporous structure and a high surface area comparable with the previous reports regarding FDU-12 synthesis. MI-Cl-FDU-12 was applied as an anion exchanger for the adsorption of toxic Cr(VI) oxyanions from aqueous media and various kinetic and isotherm models were fitted to experimental data to propose the adsorption behavior of Cr(VI) on the adsorbent. Langmuir model revealed the best fit to the experimental data at four different temperatures, indicating a homogeneous surface site affinity. The theoretical maximum adsorption capacities of the adsorbent were found to be 363.5, 385.5, 409.0, and 416.9 mg g−1 at 298, 303, 308, and 313 K, respectively; at optimal conditions (pH=2, adsorbent dose=3.0 mg, and contact time of 30 min), surpassing that of most previously reported Cr(VI) adsorbents in the literature. A regeneration study revealed that this adsorbent possesses outstanding performance even after six consecutive recycling.