Selenium alleviates chromium stress and promotes chromium uptake in As-hyperaccumulator Pteris vittata: Cr reduction and cellar distribution.

Arsenic-hyperaccumulator Pteris vittata exhibits remarkable absorption ability for chromium (Cr) while beneficial element selenium (Se) helps to reduce Cr-induced stress in plants. However, the effects of Se on the Cr uptake and the associated mechanisms in P. vittata are unclear, which were investigated in this study. P. vittata plants were grown for 14 days in 0.2-strength Hoagland solution containing 10 (Cr10) or 100 µM (Cr100) chromate (CrVI) and 1 µM selenate (Se1). The plant biomass, malondialdehyde contents, total Cr and Se contents, Cr speciation, expression of genes associated with Cr uptake, and Cr subcellular distribution in P. vittata were determined. P. vittata effectively accumulated Cr by concentrating 96-99% in the roots under Cr100 treatment. Further, Se substantially increased its Cr contents by 98% to 11,596 mg kg-1 in the roots, which may result from Se's role in reducing its oxidative stress as supported by 27-62% reduction in the malondialdehyde contents. Though supplied with CrVI, up to 98% of the Cr in the roots was reduced to insoluble chromite (CrIII), with 83-89% being distributed on root cell walls. Neither Cr nor Se upregulated the expression of sulfate transporters PvSultr1;1-1;2 or phosphate transporter PvPht1;4, indicating their limited role in Cr uptake. P. vittata effectively accumulates Cr in the roots mainly as CrIII on cell walls and Se effectively enhances its Cr uptake by reducing its oxidative stress. Our study suggests that Se can be used to enhance P. vittata Cr uptake and reduce its oxidative stress, which may have application in phytostabilization of Cr-contaminated soils.

Efficient removal of chromate from wastewater using a one-pot synthesis of chitosan cross-linked ceria incorporated hydrous copper oxide bio-polymeric composite.

Remediating hexavalent chromium [Cr(VI)] from contaminated water systems is a significant concern due to its harmful effects on human health, aquatic life, and plants. To tackle this issue, scientists have created a chitosan cross-linked hydrous ceria incorporated cupric oxide bio-polymeric composite (CHCCO) by combining chitosan biopolymer with corresponding metal ions using glutaraldehyde as a cross-linker. The composite was characterized using advanced analytical instruments such as FTIR, p-XRD, SEM, XPS, etc. The synthesized composite (CHCCO) was then tested for its efficiency in removing Cr(VI) from synthetic Cr(VI) aqueous samples. The parameters examined included pH, material dose, contact time, concentration, temperature, and co-existing ions. The experimental data showed that the kinetics and equilibrium data fit well with the pseudo-second-order and the Freundlich isotherm models, respectively. Thermodynamic analysis demonstrated that the investigated surface adsorption process is spontaneous and endothermic. Except for the SO42- ion, no other species imparts adverse influence significantly on the reaction. The CHCCO bio-composite surfaces were refreshed using a dilute NaOH (1.0 M) solution and effectively recycled five times for Cr(VI) adsorption, indicating no significant surface activity deterioration. This study highlights the high effectiveness of CHCCO bio-polymeric composites in Cr(VI) remediation and the potential for this technology as an easy-to-use technique for environmental restoration.

Au nanoparticles decorated graphitic carbon nitride nanosheets as a sensitive and selective fluorescence probe for Fe3+ and dichromate ions in aqueous medium.

Graphitic carbon nitride mutated with metal nanoparticles has captivated great interest as an effective fluorescent sensor for the detection of harmful ions present in water. In the present work, bulk-gCN was synthesized using melamine as precursor, and further Au-gCN nanocomposite were fabricated via in-situ direct reduction deposition method. The structural, morphological, compositional, stability and optical properties of bulk gCN and Au-gCN nanocomposite were examined using various scattering and spectroscopic techniques such as HRTEM, XPS, XRD and SEM. The synthesized bulk gCN straggles during selectivity studies with different cations and anions because of its uneven surface morphology, however in Au-gCN gold nanoparticles are uniformly distributed on the gCN sheets which results in its enhanced selectivity over bulk gCN. This leads to the fabrication of an optical sensor for Fe3+ and Cr2O72- ions with limit of detection of 4.62 and 2.77 µM, respectively. The sensing of Fe3+ ions corresponds to the photoinduced electron transfer (PET) mechanism, while the detection of chromate species is associated with an inner filter effect (IFE). The practical applicability of the sensor was also evaluated for different environmental water samples. The high stability, sensitivity, and specificity of Au-gCN nanocomposite make it a potential fluorescent probe for Fe3+ and Cr2O72- ions in water samples.

Evidence of turmeric adulteration with lead chromate across South Asia.

Food adulteration with toxic chemicals is a global public health threat. Lead chromate adulterated spices have been linked with lead poisoning in many countries, from Bangladesh to the United States. This study systematically assessed lead chromate adulteration in turmeric, a spice that is consumed daily across South Asia. Our study focused on four understudied countries that produce >80 % of the world's turmeric and collectively include 1.7 billion people, 22 % of the world's population. Turmeric samples were collected from wholesale and retail bazaars from 23 major cities across India, Pakistan, Sri Lanka, and Nepal between December 2020 and March 2021. Turmeric samples were analyzed for lead and chromium concentrations and maximum child blood lead levels were modeled in regions where samples had detectable lead. A total of 356 turmeric samples were collected, including 180 samples of dried turmeric roots and 176 samples of turmeric powder. In total, 14 % of the samples (n = 51) had detectable lead above 2 µg/g. Turmeric samples with lead levels greater than or equal to 18 µg/g had molar ratios of lead to chromium near 1:1, suggestive of lead chromate adulteration. Turmeric lead levels exceeded 1000 µg/g in Patna (Bihar, India) as well as Karachi and Peshawar (Pakistan), resulting in projected child blood lead levels up to 10 times higher than the CDC's threshold of concern. Given the overwhelmingly elevated lead levels in turmeric from these locations, urgent action is needed to halt the practice of lead chromate addition in the turmeric supply chain.

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.

Acute particulate hexavalent chromium exposure induces DNA double-strand breaks and activates homologous recombination repair in rat lung tissue.

Hexavalent chromium [Cr(VI)] is an established human lung carcinogen, but the carcinogenesis mechanism is poorly understood. Chromosome instability, a hallmark of lung cancer, is considered a major driver of Cr(VI)-induced lung cancer. Unrepaired DNA double-strand breaks are the underlying cause, and homologous recombination repair is the primary mechanism preventing Cr(VI)-induced DNA breaks from causing chromosome instability. Cell culture studies show acute Cr(VI) exposure causes DNA double-strand breaks and increases homologous recombination repair activity. However, the ability of Cr(VI)-induced DNA breaks and repair impact has only been reported in cell culture studies. Therefore, we investigated whether acute Cr(VI) exposure could induce breaks and homologous recombination repair in rat lungs. Male and female Wistar rats were acutely exposed to either zinc chromate particles in a saline solution or saline alone by oropharyngeal aspiration. This exposure route resulted in increased Cr levels in each lobe of the lung. We found Cr(VI) induced DNA double-strand breaks in a concentration-dependent manner, with females being more susceptible than males, and induced homologous recombination repair at similar levels in both sexes. Thus, these data show this driving mechanism discovered in cell culture indeed translates to lung tissue in vivo.

Sphingobium sp. SJ10-10 encodes a not-yet-reported chromate reductase and the classical Rieske dioxygenases to simultaneously degrade PAH and reduce chromate.

Both polycyclic aromatic hydrocarbons (PAHs) and heavy metals persist in the environment and are toxic to organisms. Their co-occurrence makes any of them difficult to remove during bioremediation and poses challenges to environmental management and public health. Microorganisms capable of effectively degrading PAHs and detoxifying heavy metals concurrently are required to improve the bioremediation process. In this study, we isolated a new strain, Sphingobium sp. SJ10-10, from an abandoned coking plant and demonstrated its capability to simultaneously degrade 92.6 % of 75 mg/L phenanthrene and reduce 90 % of 3.5 mg/L hexavalent chromium [Cr(VI)] within 1.5 days. Strain SJ10-10 encodes Rieske non-heme iron ring-hydroxylating oxygenases (RHOs) to initiate PAH degradation. Additionally, a not-yet-reported protein referred to as Sphingobium chromate reductase (SchR), with low sequence identity to known chromate reductases, was identified to reduce Cr(VI). SchR is distributed across different genera and can be classified into two classes: one from Sphingobium members and the other from non-Sphingobium species. The widespread presence of SchR in those RHO-containing Sphingobium members suggests that they are excellent candidates for bioremediation. In summary, our study demonstrates the simultaneous removal of PAHs and Cr(VI) by strain SJ10-10 and provides valuable insights into microbial strategies for managing complex pollutant mixtures.

Cooperation and competition between denitrification and chromate reduction in a hydrogen-based membrane biofilm reactor.

Competition and cooperation between denitrification and Cr(VI) reduction in a H2-based membrane biofilm reactor (H2-MBfR) were documented over 55 days of continuous operation. When nitrate (5 mg N/L) and chromate (0.5 mg Cr/L) were fed together, the H2-MBfR maintained approximately 100 % nitrate removal and 60 % chromate Cr(VI) removal, which means that nitrate outcompeted Cr(VI) for electrons from H2 oxidation. Removing nitrate from the influent led to an immediate increase in Cr(VI) removal (to 92 %), but Cr(VI) removal gradually deteriorated, with the removal ratio dropping to 14 % after five days. Cr(VI) removal resumed once nitrate was again added to the influent. 16S rDNA analyses showed that bacteria able to carry out H2-based denitrification and Cr(VI) reduction were in similar abundances throughout the experiment, but gene expression for Cr(VI)-reduction and export shifted. Functional genes encoding for energy-consuming chromate export (encoded by ChrA) as a means of bacterial resistance to toxicity were more abundant than genes encoding for the energy producing Cr(VI) respiration via the chromate reductase ChrR-NdFr. Thus, Cr(VI) transport and resistance to Cr(VI) toxicity depended on H2-based denitrification to supply energy. With Cr(VI) being exported from the cells, Cr(VI) reduction to Cr(III) was sustained. Thus, cooperation among H2-based denitrification, Cr(VI) export, and Cr(VI) reduction led to sustained Cr(VI) removal in the presence of nitrate, even though Cr(VI) reduction was at a competitive disadvantage for utilizing electrons from H2 oxidation.

Bioreduction of chromate in a syngas-based membrane biofilm reactor.

This study leveraged synthesis gas (syngas), a renewable resource attainable through the gasification of biowaste, to achieve efficient chromate removal from water. To enhance syngas transfer efficiency, a membrane biofilm reactor (MBfR) was employed. Long-term reactor operation showed a stable and high-level chromate removal efficiency > 95%, yielding harmless Cr(III) precipitates, as visualised by scanning electron microscopy and energy dispersive X-ray analysis. Corresponding to the short hydraulic retention time of 0.25 days, a high chromate removal rate of 80 µmol/L/d was attained. In addition to chromate reduction, in situ production of volatile fatty acids (VFAs) by gas fermentation was observed. Three sets of in situ batch tests and two groups of ex situ batch tests jointly unravelled the mechanisms, showing that biological chromate reduction was primarily driven by VFAs produced from in situ syngas fermentation, whereas hydrogen originally present in the syngas played a minor role. 16 S rRNA gene amplicon sequencing has confirmed the enrichment of syngas-fermenting bacteria (such as Sporomusa), who performed in situ gas fermentation leading to the synthesis of VFAs, and organics-utilising bacteria (such as Aquitalea), who utilised VFAs to drive chromate reduction. These findings, combined with batch assays, elucidate the pathways orchestrating synergistic interactions between fermentative microbial cohorts and chromate-reducing microorganisms. The findings facilitate the development of cost-effective strategies for groundwater and drinking water remediation and present an alternative application scenario for syngas.

Relationships between blood chromium exposure and liver injury: Exploring the mediating role of systemic inflammation in a chromate-exposed population.

Hexavalent chromium and its compounds are prevalent pollutants, especially in the work environment, pose a significant risk for multisystem toxicity and cancers. While it is known that chromium accumulation in the liver can cause damage, the dose-response relationship between blood chromium (Cr) and liver injury, as well as the possible potential toxic mechanisms involved, remains poorly understood. To address this, we conducted a follow-up study of 590 visits from 305 participants to investigate the associations of blood Cr with biomarkers for liver injury, including serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), and direct bilirubin (DBIL), and to evaluate the mediating effects of systemic inflammation. Platelet (PLT) and the platelet-to-lymphocyte ratio (PLR) were utilized as biomarkers of systemic inflammation. In the linear mixed-effects analyses, each 1-unit increase in blood Cr level was associated with estimated effect percentage increases of 0.82% (0.11%, 1.53%) in TBIL, 1.67% (0.06%, 3.28%) in DBIL, 0.73% (0.04%, 1.43%) in ALT and 2.08% (0.29%, 3.87%) in AST, respectively. Furthermore, PLT mediated 10.04%, 11.35%, and 10.77% increases in TBIL, DBIL, and ALT levels induced by chromate, respectively. In addition, PLR mediated 8.26% and 15.58% of the association between blood Cr and TBIL or ALT. These findings shed light on the mechanisms underlying blood Cr-induced liver injury, which is partly due to worsening systemic inflammation.

Cellular senescence mediates hexavalent chromium-associated lung function decline: Insights from a structural equation Model.

There is sufficient evidence suggesting that exposure to hexavalent chromium [Cr(VI)] can cause a decline in lung function and the onset of lung diseases. However, no studies have yet explored the underlying mechanisms of these effects from various perspectives such as systemic inflammation, oxidative stress, and cellular senescence, simultaneously. This cross-sectional study was conducted among 304 workers engaged in chromate production and processing in China. Urine was used for detection of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 8-iso-prostaglandin F2α (8-iso-PGF2α), while RNA and DNA extraction from peripheral blood cells was used for detection of mRNA, telomere length, and ribosomal DNA copy numbers (rDNA CNs). A 2.7-fold elevation in blood chromate (Cr) corresponded to a 7.86% (95% CI: 2.57%, 13.42%) rise in urinary 8-OHdG and a 4.14% (0.02%, 8.42%) increase in urinary 8-iso-PGF2α, indicating that exposure to chromates can cause oxidative stress. Furthermore, strong correlations emerged between blood Cr concentration and mRNA levels of P16, P21, TP53, and P15 in the cellular senescence pathway. Simultaneously, a 2.7-fold elevation in blood Cr associated with a -5.47% (-8.72%, -2.1%) change in telomere length, while rDNA CNs (5S, 5.8S, 18S, and 28S) changed by -3.91% (-7.99%, 0.34%), -9.4% (-15.73%, -2.6%), -8.06% (-14.01%, -1.69%), and -5.86% (-10.67%, -0.78%), respectively. Structural equation model highlighted that cellular senescence exerted significant indirect effects on Cr(VI)-associated lung function decline, with a mediation proportion of 23.3%. This study provided data supporting for 8-iso-PGF2α, telomere length, and rDNA CNs as novel biomarkers of chromate exposure, emphasizing the significant role of cellular senescence in the mechanism underlying chromate-induced lung function decline.

Immune Regulation Patterns in Response to Environmental Pollutant Chromate Exposure-Related Genetic Damage: A Cross-Sectional Study Applying Machine Learning Methods.

Exposure to hexavalent chromium damages genetic materials like DNA and chromosomes, further elevating cancer risk, yet research rarely focuses on related immunological mechanisms, which play an important role in the occurrence and development of cancer. We investigated the association between blood chromium (Cr) levels and genetic damage biomarkers as well as the immune regulatory mechanism involved, such as costimulatory molecules, in 120 workers exposed to chromates. Higher blood Cr levels were linearly correlated with higher genetic damage, reflected by urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) and blood micronucleus frequency (MNF). Exploratory factor analysis revealed that both positive and negative immune regulation patterns were positively associated with blood Cr. Specifically, higher levels of programmed cell death protein 1 (PD-1; mediated proportion: 4.12%), programmed cell death ligand 1 (PD-L1; 5.22%), lymphocyte activation gene 3 (LAG-3; 2.11%), and their constitutive positive immune regulation pattern (5.86%) indirectly positively influenced the relationship between blood Cr and urinary 8-OHdG. NOD-like receptor family pyrin domain containing 3 (NLRP3) positively affected the association between blood Cr levels and inflammatory immunity. This study, using machine learning, investigated immune regulation and its potential role in chromate-induced genetic damage, providing insights into complex relationships and emphasizing the need for further research.

A PadR family transcriptional repressor regulates the transcription of chromate efflux transporter in Enterobacter sp. Z1.

Chromium is a prevalent toxic heavy metal, and chromate [Cr(VI)] exhibits high mutagenicity and carcinogenicity. The presence of the Cr(VI) efflux protein ChrA has been identified in strains exhibiting resistance to Cr(VI). Nevertheless, certain strains of bacteria that are resistant to Cr(VI) lack the presence of ChrB, a known regulatory factor. Here, a PadR family transcriptional repressor, ChrN, has been identified as a regulator in the response of Enterobacter sp. Z1(CCTCC NO: M 2019147) to Cr(VI). The chrN gene is cotranscribed with the chrA gene, and the transcriptional expression of this operon is induced by Cr(VI). The binding capacity of the ChrN protein to Cr(VI) was demonstrated by both the tryptophan fluorescence assay and Ni-NTA purification assay. The interaction between ChrN and the chrAN operon promoter was validated by reporter gene assay and electrophoretic mobility shift assay. Mutation of the conserved histidine residues His14 and His50 resulted in loss of ChrN binding with the promoter of the chrAN operon. This observation implies that these residues are crucial for establishing a DNA-binding site. These findings demonstrate that ChrN functions as a transcriptional repressor, modulating the cellular response of strain Z1 to Cr(VI) exposure.

Efficient nitrate and Cr(VI) removal by denitrifier: The mechanism of S. oneidensis MR-1 promoting electron production, transportation and consumption.

When Cr(VI) and nitrate coexist, the efficiency of both bio-denitrification and Cr(VI) bio-reduction is poor because chromate hinders bacterial normal functions (i.e., electron production, transportation and consumption). Moreover, under anaerobic condition, the method about efficient nitrate and Cr(VI) removal remained unclear. In this paper, the addition of Shewanella oneidensis MR-1 to promote the electron production, transportation and consumption of denitrifier and cause an increase in the removal of nitrate and Cr(VI). The efficiency of nitrate and Cr(VI) removal accomplished by P. denitrificans as a used model denitrifier increased respectively from 51.3% to 96.1% and 34.3% to 99.8% after S. oneidensis MR-1 addition. The mechanism investigations revealed that P. denitrificans provided S. oneidensis MR-1 with lactate, which was utilized to secreted riboflavin and phenazine by S. oneidensis MR-1. The riboflavin served as coenzymes of cellular reductants (i.e., thioredoxin and glutathione) in P. denitrificans, which created favorable intracellular microenvironment conditions for electron generation. Meanwhile, phenazine promoted biofilm formation, which increased the adsorption of Cr(VI) on the cell surface and accelerated the Cr(VI) reduction by membrane bound chromate reductases thereby reducing damage to other enzymes respectively. Overall, this strategy reduced the negative effect of chromate, thus improved the generation, transportation, and consumption of electrons. SYNOPSIS: The presence of S. oneidensis MR-1 facilitated nitrate and Cr(VI) removal by P. denitrificans through decreasing the negative effect of chromate due to the metabolites' secretion.

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.

Simultaneous adsorption of chromate and arsenate onto ferrihydrite/alginate composite beads: Competition and mechanism.

Ferrihydrite is an effective adsorbent of chromate and arsenate. In order to gain insight into the application of ferrihydrite in water treatment, macroporous alginate/ferrihydrite beads, synthesized using two different methods (internal and encapsulation processes), were used in this work. The properties of the ferrihydrite were assessed using various techniques, including X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) theory, and zetametry. The results showed that the specific surface area of the ferrihydrite was 242 m2/g, and the PZC was pH8. The kinetic and isotherm adsorption properties of the ferrihydrite were evaluated in this study. The results indicate that the pseudo second-order and Freundlich models accurately describe the kinetic and isotherm adsorption properties of chromates and arsenates. For chromate removal, ferrihydrite exhibited a relatively high adsorption capacity (40.7 mgCr/g) compared to other adsorbents. However, the arsenate adsorption capacity of MFHB-SI (140.8 mgAs/g) was shown to be the most optimal. The internal synthesis process was suitable for arsenate retention due to the resulting arsenate precipitation. The competitive adsorption analyses indicated that the presence of chromate does not limit the adsorption of arsenate. However, the presence of arsenate almost completely inhibits the adsorption of chromate when the arsenate concentration is above 50 mg/L, due to the precipitation reaction of arsenate.

Modeling the Role in pH on Contaminant Sequestration by Zerovalent Metals: Chromate Reduction by Zerovalent Magnesium.

The role of pH in sequestration of Cr(VI) by zerovalent magnesium (ZVMg) was characterized by global fitting of a kinetic model to time-series data from unbuffered batch experiments with varying initial pH values. At initial pH values ranging from 2.0 to 6.8, ZVMg (0.5 g/L) completely reduced Cr(VI) (18.1 µM) within 24 h, during which time pH rapidly increased to a plateau value of ∼10. Time-series correlation analysis of the pH and aqueous Cr(VI), Cr(III), and Mg(II) concentration data suggested that these conditions are controlled by combinations of reactions (involving Mg0 oxidative dissolution and Cr(VI) sequestration) that evolve over the time course of each experiment. Since this is also likely to occur during any engineering applications of ZVMg for remediation, we developed a kinetic model for dynamic pH changes coupled with ZVMg corrosion processes. Using this model, the synchronous changes in Cr(VI) and Mg(II) concentrations were fully predicted based on the Langmuir-Hinshelwood kinetics and transition-state theory, respectively. The reactivity of ZVMg was different in two pH regimes that were pH-dependent at pH < 4 and pH-independent at the higher pH. This contrasting pH effect could be ascribed to the shift of the primary oxidant of ZVMg from H+ to H2O at the lower and higher pH regimes, respectively.

Forming a chromium-based interstrand DNA crosslink: Implications for carcinogenicity.

The reduction of the carcinogen chromate has been proposed to lead to three Cr(III)-containing DNA lesions: binary adducts (Cr(III) and DNA), interstrand crosslinks, and ternary adducts (Cr(III) linking DNA to a small molecule or protein). Although the structures of binary adducts have recently been elucidated, the structures of interstrand crosslinks and ternary adducts are not known. Analysis of Cr(III) binding to an oligonucleotide duplex containing a 5'-CG site allows elucidation of the structure of an oxide- or hydroxide-bridged binuclear Cr(III) assembly bridging the two strands of DNA. One Cr(III) is directly coordinated by the N-7 atom of a guanine residue, and the complex straddles the helix to form a hydrogen bond between another guanine residue and a Cr(III)-bound aquo ligand. No involvement of the phosphate backbone was observed. The properties and stability of this Cr-O(H)-Cr-bridged complex differ significantly from those reported for Cr-induced interstrand crosslinks, suggesting that interstrand crosslinks resulting from chromate reduction may be organic in nature.

HBM4EU chromates study - PFAS exposure in electroplaters and bystanders.

The study aims to reveal the exposure to perfluoroalkyl substances (PFAS) in workers in different industry sectors with exposures to hexavalent chromium (Cr(VI)). The PFAS exposure of in total 172 individuals from 4 countries was assessed by the determination of 8 perfluoroalkyl carboxylic acids and 4 perfluoroalkyl sulfonic acids in plasma samples. The participants were 52 chrome plating workers, 43 welders, 3 surface treating workers and 74 workers without any occupational Cr exposure as controls. Significant differences between workers with Cr exposure and controls were found for the perfluoroalkyl sulfonic acids, particularly for perfluorooctane sulfonic acid (PFOS). The median and maximum levels were, respectively, 4.83 and 789 µg/l for chrome plating workers, 4.97 and 1513 µg/l for welders, and 3.65 and 13.9 µg/l for controls. The considerably high PFOS exposure in Cr platers and welders can be explained by the former application of PFOS as mist suppressants in electroplating baths, which resulted in an exposure of the directly involved operators, but also of welders performing maintenance and repair service at these workplaces.