A review on chromium health hazards and molecular mechanism of chromium bioremediation

Exploring bio-remediation strategies by a novel bacteria Micrococcus sp. strain HX in Cr(VI)-contaminated groundwater from long-term industrial polluted

Hexavalent chromium (Cr(VI)) has emerged as a contaminant of heavy metal, owing to its wide use in industry. This study focuses on elucidating the interaction between microbial communities and environmental parameters in Cr(VI)-contaminated groundwater near a factory in Henan Province, and evaluating the bio-remediation potential of microorganisms toward Cr(VI) reduction. The highest concentration of Cr(VI) in the groundwater is 208.08 mg/L. The dominant microbes were Proteobacteria and Bacteroidota, closely positively related to Cr(VI) and SO42-. Many of these genus have been proven to be chromium tolerant or have the ability to reduce Cr(VI). Two strains, Micrococcus sp. HX and Bacillus sp. HX-2, were isolated from contaminated groundwater, and Micrococcus sp. HX was used for the first time to reduce Cr(VI) in groundwater. The reduced ability of HX reached 90.18 % at a Cr(VI) concentration of 100 mg/L, while HX-2 achieved a reduction capacity of 63.8 %. Micrococcus sp. HX shows the best reduction efficiency in alkaline environments (ph=8), which is close to the tannery industry wastewater. The reduction efficiency by Micrococcus sp. HX reached 67.26 % in groundwater samples (Cr(VI)= 26.08 mg/L). Transcriptome analyses revealed oxidoreductase activity, ATP binding and the NAD(P) binding region protein-related gene expression were up-regulated. Binding reduction experiments indicated that most of the Cr(III) was detected extracellular, which suggests that the reduction of Cr(VI) by HX was mainly extracellular enzyme-catalyzed.

Highly Efficient Reduction of Cr (VI) with C4H6O6

In this paper, tartaric acid (C4H6O6) was used as a reductant to treat chromium (VI)-containing solution. Several independent experimental parameters, including reaction temperature, concentration of H2SO4, concentration of C4H6O6 and reaction time, on the reduction process were studied. The results showed that 100% of the Cr (VI) could be reduced by C4H6O6 in a strong acidic environment under a high reaction temperature. All of the experimental parameters showed positive effects on the reduction process and followed the order [H2SO4] > [C4H6O6] > reaction temperature > reaction time. A higher concentration of tartaric acid and higher reaction temperature could facilitate the reduction process and reduce reaction time.

Cr(VI) induced hepatocyte apoptosis through the CTH/H2S/Drp1 signaling pathway

Hexavalent chromium [Cr(VI)] is a highly hazardous heavy metal with multiple toxic effects. Occupational studies indicate that its accumulation in humans can lead to liver damage. However, the exact mechanism underlying Cr(VI)-induced hepatotoxicity remains unknown. In this study, we explored the role of CTH/H2S/Drp1 pathway in Cr(VI)-induced oxidative stress, mitochondrial dysfunction, apoptosis, and liver injury. Our data showed that Cr(VI) triggered apoptosis, accompanied by H2S reduction, reactive oxygen species (ROS) accumulation, and mitochondrial dysfunction in both AML12 cells and mouse livers. Moreover, Cr(VI) reduced cystathionine γ-lyase (CTH) and dynamin related protein 1 (Drp1) S-sulfhydration levels, and elevated Drp1 phosphorylation levels at Serine 616, which promoted Drp1 mitochondrial translocation and Drp1-voltage-dependent anion channel 1 (VDAC1) interactions, ultimately leading to mitochondria-dependent apoptosis. Elevated hydrogen sulfide (H2S) levels eliminated Drp1 phosphorylation at Serine 616 by increasing Drp1 S-sulfhydration, thereby preventing Cr(VI)-induced Drp1-VDAC1 interaction and hepatotoxicity. These findings indicated that Cr(VI) induced mitochondrial apoptosis and hepatotoxicity by inhibiting CTH/H2S/Drp1 pathway and that targeting either CTH/H2S pathway or Drp1 S-sulfhydration could serve as a potential therapy for Cr(VI)-induced liver injury.

Simulation study on heavy metals, phthalate esters, and organic halogens: Content and distribution characteristics during waste paper recycling

Imported waste paper and recycled pulp may contain pollutants, posing potential environmental risks to the ecosystem of China. This study examined the presence and distribution patterns of heavy metals, phthalate esters (PAEs), and adsorbable organic halogens (AOX) in recycled pulp and production wastewater after various recycling processes of three typical restricted types of imported waste paper. The results indicated that the concentration ranges of heavy metals, PAEs, and AOX in the three types of imported recycled waste paper were 21.61-40.38 mg/kg, 15.35-27.88 mg/kg, and 19.21-57.72 mg/kg, respectively. The comparative analysis with the initial waste paper demonstrated a reduction in heavy metal content in the recycled pulp by 17.80-49.75%, PAEs by 65.42-90.55%, and AOX by 32.80-42.34%. The average concentrations of these pollutants in wastewater were 0.85-1.66 mg/L, 27.28-59.86 mg/L, and 1.15-3.34 mg/L, respectively. Chromium and lead were identified as the primary heavy metals present in the waste paper. Following pulping, No. 1 and No. 2 met the arsenic and lead levels specified in the "Reuse Fiber Pulp" standard (GB/T24320-2021), whereas No. 3 met these criteria after de-inking only. The main PAEs detected in the waste paper were dibutyl phthalate and di(2-ethylhexyl) phthalate, most of which were removed during the pulping stage. Significantly higher levels of AOX were observed in No. 2 and No. 3 than in No. 1, with a minimal impact on AOX removal from the pulp during the recycling process.

"Efficient novel fungal-enriched biochar formulation for hexavalent chromium bioremediation"

Chromium (Cr), a key element in industrial processes such as leather tanning, poses severe environmental hazards, particularly its hexavalent form, Cr(VI), which is highly toxic and prevalent in tannery effluents/sludge. The persistence and toxicity of Cr(VI) necessitate the development of effective remediation strategies to mitigate its environmental impact. This study investigated the potential of Trichoderma yunnanense (NBRICRF_97) and its combination with 0.5% sugarcane bagasse biochar (SBC) for the reduction of Cr(VI). The results demonstrated that T. yunnanense alone achieved a 91.04% reduction of 50 mg L-1 Cr(VI) within 72 h. Combined with 0.5% SBC, the reduction efficiency increased to 99.65% within 48 h. However, the efficiency decreased at higher concentrations (200 mg L-1). The combination also improved fungal growth and increased extracellular ChrR enzyme activity (13.07 U mg-1 protein compared to the control). Total glutathione activity was boosted by 161.07% at 100 mg L-1 Cr(VI). Antioxidant enzymes (SOD, POD, CAT) and proline mitigated oxidative stress and FTIR analysis revealed changes in fungal cell wall functional groups (-OH and -NH) upon Cr(VI) exposure. SEM-EDX confirmed chromium deposition on fungal surfaces. These results underscore the Cr(VI) detoxification capabilities of T. yunnanense and the synergistic benefits of SBC, suggesting a promising bioremediation strategy for Cr(VI)-contaminated environments. The integration of T. yunnanense with SBC offers a sustainable and cost-effective approach for the bioremediation of Cr(VI)-contaminated sites, with potential for implementation in large-scale environmental cleanup efforts.

Role of PERK-Mediated Endoplasmic Reticulum Stress in Ferroptosis Caused by Hexavalent Chromium in Chicken Hepatocytes

This study aimed to investigate whether Cr(VI) can induce ferroptosis in chicken hepatocytes and determine the role of PERK-mediated endoplasmic reticulum stress (ERS). First, a model of Cr(VI) poisoning was established by exposing chicken hepatocytes to Cr(VI). The levels of ferroptosis-related proteins, meanwhile, GSH, SOD, MDA, and lipid ROS, were measured. Furthermore, the expression of GRP78 and PERK proteins was examined. Changes in ERS and ferroptosis were evaluated by silencing the PERK gene. Results showed that Cr(VI) led to the accumulation of lipid ROS, decreased expression of GPX4 and HSP27, increased expression of COX2, and induced ferroptosis in chicken hepatocytes. Exposure to Cr(VI) increased the protein expression of GRP78 and PERK, and silencing of PERK worsened Cr(VI)-induced ferroptosis. In conclusion, Cr(VI) can induce ferroptosis in chicken hepatocytes, and PERK plays an important role as a negative regulator.

Efficient removal of Cr(VI) from contaminated kaolin and anolyte by electrokinetic remediation with foamed iron anode electrode and acetic acid electrolyte

Combined electrokinetic remediation employing reducing agents represents an extensively utilized approach for the remediation of hexavalent chromium (Cr(VI))-contaminated soil. In this investigation, electrokinetic remediation of artificially contaminated kaolin was conducted utilizing a separate circulation system for the anolyte, with a 0.5M solution of acetic acid (HAc) as the electrolyte and foamed iron serving as the anode. The experimental outcomes demonstrated that employing HAc as the electrolyte enhances the electromigration of Cr(VI) and establishes an acidic milieu conducive to the reduction of Cr(VI) by foamed iron, thereby facilitating the rapid reduction of Cr(VI) accumulated in the anolyte through electrokinetic remediation. In the self-prepared contaminated kaolin, the initial concentration of Cr(VI) was 820.26 mg/L. Following the remediation process under optimal experimental conditions, the concentration was significantly reduced to 11.6 mg/L, achieving a removal efficiency of Cr(VI) in the soil of 98.59%. In the optimal experimental setup, the Cr(VI) concentration in the anolyte was reduced to 0.05 mg/L, which is below the EPA's Safe Drinking Water Act standard for Cr(VI) content of 0.1 mg/L. The removal mechanism of Cr(VI) from the electrolyte primarily involves reduction, precipitation, and co-precipitation, with the foamed iron playing a predominant role. HAc and foamed iron exhibit a synergistic effect. The findings of this study substantiate that the integration of foamed iron with HAc is efficacious for the electrokinetic remediation of soil contaminated with Cr(VI).

Heavy metals and elderly kidney health: A multidimensional study through Enviro-target Mendelian Randomization

Chronic Kidney Disease (CKD), closely linked to environmental factors, poses a significant public health challenge. This study, based on 529 triple-repeated measures from key national environmental pollution area and multiple gene-related public databases, employs various epidemiological and bioinformatics models to assess the impact of combined heavy metal exposure (Chromium [Cr], Cadmium [Cd], and Lead [Pb]) on early renal injury and CKD in the elderly. Introducing the novel Enviro-Target Mendelian Randomization method, our research explores the causal relationship between metals and CKD. The findings indicate a positive correlation between increased levels of metal and renal injury, with combined exposure caused renal damage more significantly than individual exposure. The study reveals that metals primarily influence CKD development through oxidative stress and metal ion resistance pathways, focusing on three related genes (SOD2, MPO, NQO1) and a transcription factor (NFE2L2). Metals were found to regulate oxidative stress levels in the body by increasing the expression of SOD2, MPO, NQO1, and decreasing NFE2L2, leading to CKD onset. Our research establishes a new causal inference framework linking environmental pollutants-pathways-genes-CKD, assessing the impact and mechanisms of metal exposure on CKD. Future studies with more extensive in vitro evidence and larger population are needed to validate.

Microbial mediated remediation of heavy metals toxicity: mechanisms and future prospects

Heavy metal pollution has become a serious concern across the globe due to their persistent nature, higher toxicity, and recalcitrance. These toxic metals threaten the stability of the environment and the health of all living beings. Heavy metals also enter the human food chain by eating contaminated foods and cause toxic effects on human health. Thus, remediation of HMs polluted soils is mandatory and it needs to be addressed at higher priority. The use of microbes is considered as a promising approach to combat the adverse impacts of HMs. Microbes aided in the restoration of deteriorated environments to their natural condition, with long-term environmental effects. Microbial remediation prevents the leaching and mobilization of HMs and they also make the extraction of HMs simple. Therefore, in this context recent technological advancement allowed to use of bioremediation as an imperative approach to remediate polluted soils. Microbes use different mechanisms including bio-sorption, bioaccumulation, bioleaching, bio-transformation, bio-volatilization and bio-mineralization to mitigate toxic the effects of HMs. Thus, keeping in the view toxic HMs here in this review explores the role of bacteria, fungi and algae in bioremediation of polluted soils. This review also discusses the various approaches that can be used to improve the efficiency of microbes to remediate HMs polluted soils. It also highlights different research gaps that must be solved in future study programs to improve bioremediation efficency.

Recent advances in alginate-based composite gel spheres for removal of heavy metals

The discharge of heavy metal ions from industrial wastewater into natural water bodies is a consequence of global industrialisation. Due to their high toxicity and resistance to degradation, these heavy metal ions pose a substantial threat to human health as they accumulate and amplify. Alginate-based composite gels exhibit good adsorption and mechanical properties, excellent biodegradability, and non-toxicity, making them environmentally friendly heavy metal ion adsorbents for water with promising development prospects. This paper introduces the basic properties, cross-linking methods, synthetic approaches, modification methods, and manufacturing techniques of alginate-based composite gels. The adsorption properties and mechanical strength of these gels can be enhanced through surface modification, multi-component mixing, and embedding. The main production processes involved are sol-gel and cross-linking methods. Additionally, this paper reviews various applications of alginate composite gels for common heavy metals, rare earth elements, and radionuclides and elucidates the adsorption mechanism of alginate composite gels. This study aimed to provide a reference for synthesising new, efficient, and environmentally friendly alginate-based adsorbents and to contribute new ideas and directions for addressing the issue of heavy metal pollution.

Microbial innovations in chromium remediation: mechanistic insights and diverse applications

The ubiquity of hexavalent chromium (Cr(VI)) from industrial activities poses a critical environmental threat due to its persistence, toxicity and mutagenic potential. Traditional physico-chemical methods for its removal often entail significant environmental drawbacks. Recent advancements in remediation strategies have emphasized nano and bioremediation techniques as promising avenues for cost-effective and efficient Cr(VI) mitigation. Bioremediation harnesses the capabilities of biological agents like microorganisms, and algae to mitigate heavy metal contamination, while nano-remediation employs nanoparticles for adsorption purposes. Various microorganisms, including E. coli, Byssochlamys sp., Pannonibacter phragmitetus, Bacillus, Aspergillus, Trichoderma, Fusarium, and Chlorella utilize bioreduction, biotransformation, biosorption and bioaccumulation mechanisms to convert Cr(VI) to Cr(III). Their adaptability to different environments and integration with nanomaterials enhance microbial activity, offering eco-friendly solutions. The study provides a brief overview of metabolic pathways involved in Cr(VI) bioreduction facilitated by diverse microbial species. Nitroreductase and chromate reductase enzymes play key roles in nitrogen and chromium removal, with nitroreductase requiring nitrate and NADPH/NADH, while the chromium reductase pathway relies solely on NADPH/NADH. This review investigates the various anthropogenic activities contributing to Cr(VI) emissions and evaluates the efficacy of conventional, nano-remediation, and bioremediation approaches in curbing Cr(VI) concentrations. Additionally, it scrutinizes the mechanisms underlying nano-remediation techniques for a deeper understanding of the remediation process. It identifies research gaps and offers insights into future directions aimed at enhancing the real-time applicability of bioremediation methods for mitigating with Cr(VI) pollution and pave the way for sustainable remediation solutions.

Enhanced chromium removal from tannery wastewater through electrocoagulation with iron electrodes: Leveraging the Box-Behnken design for optimization

This study is focused on reducing total chromium level in tannery wastewater through the electrocoagulation process, in order to comply with the maximum permissible limits (MPL) and to determine the effects from its main operating factors. For this purpose, a batch electrocoagulation reactor was manufactured using iron electrodes. Next, the response surface methodology was applied in the experimental design using a Box-Behnken design (BBD) with three factors: current intensity, treatment time, and p H level. In addition, the total chromium removal percentage was taken as a response variable. The corresponding statistical analysis revealed that the treatment time, current intensity, and p H level variables were significant at a confidence level of P - v a l u e < 0.05 . Obtained in this study for a 99 % total chromium removal were: current intensity ( I ) = 2.9 A , time ( t ) = 18.1 min , and p H = 5.6 . Our results indicated that the electrocoagulation process effectively removes total chromium from tannery effluents up to MPL values.

One step synthesis of highly photoluminescent red light-emitting carbon dots from O-phenylenediamine and 2,4-diaminophenol as fluorescent probes for the detection of pH and Cr(VI)

In this study, new red light-emitting carbon dots (R-CDs) that can selectively recognize Cr(VI) were prepared using a strategy that utilizes 2,4-diaminophenol to enhance the fluorescence of O-phenylenediamine based carbon dots. The results showed that 2,4-diaminophenol increased the quantum yield (QY) of the carbon quantum dots (CDs), and that the QY of the CDs increased from their original value of 8.7% to 20.1% (R-CDs). The R-CDs show sensitivity to acidic conditions and maintain good linearity between pH = 1.00-4.00, making them useful as pH probes. Furthermore, the prepared R-CDs possess good solubility in water and are responsive to changes in Cr(VI) concentrations in aqueous environments. The quenching of the R-CDs fluorescence was linearly correlated with the Cr(VI) concentration within a range of 0-20 μM, with a lower detection limit of 66 nM. The detection mechanism is attributed to the formation of hydrogen bonds between Cr(VI) and the R-CDs, resulting in the fluorescence quenching of the R-CDs. The R-CDs can be considered effective multifunctional fluorescent probes for both pH and Cr(VI) in aqueous environments. This study will provide new R-CD design strategies for probes that selectively identify specific target substances.

Serum cobalt and chromium concentration following total hip arthroplasty: a Bayesian network meta-analysis

The present systematic review investigated the concentration of chromium (Cr) and cobalt (Co) in serum in patients who have undergone total hip arthroplasty (THA). The first outcome of interest was to investigate the mean concentration in serum of Cr and Co using different material combinations and to verify whether their concentrations change significantly using different patterns of head and liner in THA. The second outcome of interest was to investigate whether the time elapsed from the index surgery to the follow-up, BMI, sex, and side exert an influence on the mean concentration of Cr and Co in serum in patients who have undergone THA. The following material combinations were investigated (head-liner): Ceramic-Co Cr (CoCr), CoCr-CoCr, CoCr-Polyethylene, CoCr high carbide-CoCr high carbide. Data from 2756 procedures were retrieved. The mean length of follow-up was 69.3 ± 47.7 months. The ANOVA test evidenced good comparability in age, length of follow-up, BMI, and sex (P > 0.1). In patients who have undergone THA, the mean concentration in the serum of Co ranged between 0.5 µg/L and 3.5 µg/L, and the mean concentration of Cr from 0.6 to 2.6 µg/L. The difference in the concentration of Co and Cr in serum is strictly related to the implant configuration, with the coupling CoCr-CoCr showing the highest and CoCr-Polyethylene showing the lowest concentration. Patient characteristics, BMI, sex, side and the time elapsed from the index surgery to the last follow-up did not exert a significant influence on the concentration of Co and Cr in serum in patients who have undergone total hip arthroplasty (THA).

Sensitivity of Zea mays and Soil Microorganisms to the Toxic Effect of Chromium (VI)

Chromium is used in many settings, and hence, it can easily enter the natural environment. It exists in several oxidation states. In soil, depending on its oxidation-reduction potential, it can occur in bivalent, trivalent or hexavalent forms. Hexavalent chromium compounds are cancerogenic to humans. The aim of this study was to determine the effect of Cr(VI) on the structure of bacteria and fungi in soil, to find out how this effect is modified by humic acids and to determine the response of Zea mays to this form of chromium. A pot experiment was conducted to answer the above questions. Zea mays was sown in natural soil and soil polluted with Cr(VI) in an amount of 60 mg kg-1 d.m. Both soils were treated with humic acids in the form of HumiAgra preparation. The ecophysiological and genetic diversity of bacteria and fungi was assayed in soil under maize (not sown with Zea mays). In addition, the following were determined: yield of maize, greenness index, index of tolerance to chromium, translocation index and accumulation of chromium in the plant. It has been determined that Cr(VI) significantly distorts the growth and development of Zea mays, while humic acids completely neutralize its toxic effect on the plant. This element had an adverse effect on the development of bacteria of the genera Cellulosimicrobium, Kaistobacter, Rhodanobacter, Rhodoplanes and Nocardioides and fungi of the genera Chaetomium and Humicola. Soil contamination with Cr(VI) significantly diminished the genetic diversity and richness of bacteria and the ecophysiological diversity of fungi. The negative impact of Cr(VI) on the diversity of bacteria and fungi was mollified by Zea mays and the application of humic acids.