Chemical properties and toxicity of chromium(III) nutritional supplements

Nanocomposites Based on Magnetic Nanoparticles and Metal-Organic Frameworks for Therapy, Diagnosis, and Theragnostics

In the last two decades, metal-organic frameworks (MOFs) with highly tunable structure and porosity, have emerged as drug nanocarriers in the biomedical field. In particular, nanoscaled MOFs (nanoMOFs) have been widely investigated because of their potential biocompatibility, high drug loadings, and progressive release. To enhance their properties, MOFs have been combined with magnetic nanoparticles (MNPs) to form magnetic nanocomposites (MNP@MOF) with additional functionalities. Due to the magnetic properties of the MNPs, their presence in the nanosystems enables potential combinatorial magnetic targeted therapy and diagnosis. In this Review, we analyze the four main synthetic strategies currently employed for the fabrication of MNP@MOF nanocomposites, namely, mixing, in situ formation of MNPs in presynthesized MOF, in situ formation of MOFs in the presence of MNPs, and layer-by-layer methods. Additionally, we discuss the current progress in bioapplications, focusing on drug delivery systems (DDSs), magnetic resonance imaging (MRI), magnetic hyperthermia (MHT), and theragnostic systems. Overall, we provide a comprehensive overview of the recent advances in the development and bioapplications of MNP@MOF nanocomposites, highlighting their potential for future biomedical applications with a critical analysis of the challenges and limitations of these nanocomposites in terms of their synthesis, characterization, biocompatibility, and applicability.

Trophodynamics and potential health risk assessment of heavy metals in the mangrove food web in Yanpu Bay, China

Mangroves are the cradle of coastal water biodiversity and are susceptible to heavy metal pollution. However, the trophic transfer mechanism of heavy metals in the mangrove food web and the resulting human health risks are not fully understood. Heavy metal concentration (Cr, Ni, Cu, Zn, As, Cd, Pb, V, Co) and stable isotope ratios of carbon and nitrogen (δ13C and δ15N) were evaluated in sediments and particulate organic matter, litter, and aquatic organisms (plankton, arthropods, mollusks, omnivorous fish, and carnivorous fish) from the Yanpu Bay mangroves. The results revealed that heavy metals exhibited different trophic transfer patterns. As and Hg were efficiently biomagnified, with trophic magnification factors of 1.17 and 1.42, respectively; while Cr, Ni, Cu, Cd, Pb, V, and Co were efficiently biodiluted. Zn exhibited a trophic magnification factor > 1 and was not significantly correlated with δ15N (p > 0.05), suggesting no biomagnification or biodilution. The heavy metals in the important fishery species (omnivorous fish and carnivorous fish) were below the permissible limits, except for Zn in Ophichthus apicalis. The assessment of probabilistic health risks revealed that fish consumption in adults and children posed an acceptable risk (total target hazard quotient <1).

Trophic transfer of heavy metals across four trophic levels based on muscle tissue residuals: a case study of Dachen Fishing Grounds, the East China Sea

In this study, we collected 56 species of fishery organisms (including fish, crustaceans, cephalopods, gastropods, and bivalves) from four seasonal survey cruises at the Dachen fishery grounds. We measured the concentrations of seven heavy metals (Cd, Zn, Cu, Pb, Cr, As, and Hg) in these fisheries organisms. We determined their trophic levels using carbon and nitrogen stable isotope techniques. We analyzed the characteristics of heavy metal transfer in the food chain. The results showed significant differences in heavy metal concentrations among different species. Among all biological groups, bivalves and gastropods exhibited higher levels of heavy metal enrichment than other biological groups, while fish had the lowest levels of heavy metal enrichment. Heavy metals exhibited different patterns of nutritional transfer in the food chain. While Hg showed a biomagnification phenomenon in the food chain, it was not significant. Cd, Zn, Cu, Pb, Cr, and As exhibited a trend of biodilution with increasing nutritional levels, except for As, which showed no significant correlation with δ15N.

Simultaneous binding characterization of different chromium speciation to serum albumin

The binding process between three species of chromium and serum albumin (SA) was investigated, as well as the interaction between K2Cr2O7 and bovine serum albumin (BSA) under coexistence of different chromium forms. CrCl3, K2Cr2O7 and Crpic bound to SA spontaneously through Van der Waals force, and their binding constants were 103-104 M-1 at 298 K, respectively. K2Cr2O7 and Crpic both had strong binding affinity for BSA, and significantly affected the secondary structure of BSA and the microenvironment surrounding amino acid residues. Chromium exhibited a greater fluorescence quenching constant towards HSA than toward BSA, and K2Cr2O7 induced greater conformational changes in human serum albumin (HSA) than in BSA. A weak binding of CrCl3 to BSA had no significant effect on the binding affinity of K2Cr2O7 to BSA. K2Cr2O7 and BSA have a greater binding affinity when coexisting with Crpic, and K2Cr2O7 induces a greater conformational change in BSA.

Trophic transfer of heavy metals through aquatic food web in the largest mangrove reserve of China

Understanding the mechanism of trophic transfer of heavy metal through the aquatic food web is critical to ecological exposure risk assessments in mangrove ecosystems. Zhanjiang Mangrove National Nature Reserve (ZMNNR) is the largest and biologically richest mangrove reserve in China, but has been exposed to heavy metal pollutants caused by the progressive industrialization and urbanization. We collected a variety of aquatic consumers, and primary producers, as well as sediments from the ZMNNR and analyzed them for heavy metal (Cd, Cr, Cu, Ni, Pb and Zn) concentrations, and for both δ13C and δ15N values to establish the trophic levels. The trophic magnification factors (TMF) of Cd, Cu and Zn are 0.19 (p < 0.01), 0.07 (p < 0.01) and 0.33 (p < 0.05), respectively, indicating significant biodilution in a simplified food web composed of bivalves, crustaceans and fish. There are also potential tendencies of biodilution for Cr, Ni and Pb. Comparison of heavy metals in representative fish and shrimp in the ZMNNR with those in worldwide mangroves indicate a low risk level for aquatic consumers in our ecosystem. Quantitative source tracking is conducted based on principal component analysis and cluster analysis, which indicate that Cr, Ni and Pb are mainly originated from natural geological processes, Cu and Zn from shrimp farming and agriculture activities, and Cd from the deposition of aerosol released by regional metal smelting industry.

Chromium (III) and chromium (VI) removal and organic matter interaction with nanofiltration

Chromium (Cr) is a toxic inorganic contaminant for drinking water, in which the concentration has to be controlled for human health and safety. Cr retention was investigated with stirred cell experiments using sulphonated polyethersulfone nanofiltration (NF) membranes of different molecular weight cut-off (MWCO). Cr(III) and Cr(VI) retention follow the order of the MWCO of the studied NF membranes; HY70-720 Da > HY50-1000 Da > HY10-3000 Da with a pH dependency, especially for Cr(III). The importance of the charge exclusion was highlighted when Cr(OH)₄^- (for Cr(III)) and CrO₄^2- (for Cr(VI)) was the predominant species in the feed solution. In presence of organic matter, namely humic acid (HA), Cr(III) retention increased by 60 %, while no influence of HA was observed for Cr(VI). HA did not induce major modifications on the membrane surface charge for these membranes. Solute-solute interaction, in particular Cr(III)-HA complexation, was the responsible mechanism for the increase in Cr(III) retention. This was confirmed by asymmetric flow field-flow fractionation, coupled with inductively coupled plasma mass spectrometry (FFFF-ICP-MS) analysis. Cr(III)-HA complexation was significant at HA concentrations as low as 1 mgC/L. The chosen NF membranes were able to achieve the EU guideline (25 μg/L) for Cr in drinking water for a feed concentration of 250 μg/L.

Novel insight on chemo-specific detection of toxic environmental chromium residues existing as recalcitrant Cr(III)-carboxyl complexes using plasmonic silver nanoplatform bi-functionalized with citrate and PVP

Chromium (Cr) is a toxic environmental pollutant that majorly exists in trivalent and hexavalent forms. Though Cr(VI) is more dangerous than Cr(III), the trivalent Cr forms complexes with environmentally-available organic molecules. This makes them potentially harmful and difficult to detect. In this study, we have designed an ultrasensitive plasmonic nanosensor using citrate and PVP functionalized Ag nanoparticles (Ag-citrate-PVPNPs) for the detection of trivalent chromium organic complexes such as Cr(III)-EDTA (Cr-E), Cr(III)-acetate (Cr-A), Cr(III)-citrate (Cr-C) and Cr(III)-tartrate (Cr-T). The nanoparticles (NPs) were structurally characterized by XRD, SEM, HRTEM, SAED, EDX and elemental mapping. The citrate and PVP molecules played a vital role in the detection mechanism and stability of the sensor. Upon detection, the yellow-colored Ag-citrate-PVP NPs turned into different shades of brown depending on the type of the Cr complex and concentration. It was accompanied by diminishing and/or shifting UV-Visible absorbance peaks due to the aggregation of Ag-citrate-PVP NPs. Further, a linear relationship was observed between absorbance reduction and analyte concentration. The selectivity tests showed that the sensor was non-functional to other metal ions and inorganic anions. The sensor was optimized using pH and temperature studies. The mechanism of detection was elucidated with the help of characterization techniques such as Raman spectroscopy, FTIR, XPS and UV-visible spectrophotometer. The limit of detection (LOD) was found to be 3.29, 4.87, 1.76 and 1.79 nM for Cr-E, Cr-A, Cr-C and Cr-T complexes respectively. This study provides a rapid and sensitive approach for the detection of multiple Cr(III)-organic complexes present in an aqueous solution.

Distribution and accumulation of metals and metalloids in planktonic food webs of the Mediterranean Sea (MERITE-HIPPOCAMPE campaign)

Particle-size classes (7 fractions from 0.8 to 2000 μm) were collected in the deep chlorophyll maximum along a Mediterranean transect including the northern coastal zone (bays of Toulon and Marseilles, France), the offshore zone (near the North Balearic Thermal Front), and the southern coastal zone (Gulf of Gabès, Tunisia). Concentrations of biotic metals and metalloids (As, Cd, Cr, Cu, Fe, Mn, Ni, Sb, V, Zn) bound to living or dead organisms and faecal pellets were assessed by phosphorus normalisation. Biotic metals and metalloids concentrations (except Cr, Mn, and V) were higher in the offshore zone than in the coastal zones. In addition, biotic Sb and V concentrations appeared to be affected by atmospheric deposition, and biotic Cr concentrations appeared to be affected by local anthropogenic inputs. Essential elements (Cd, Cu, Fe, Mn, Ni, V, Zn) were very likely controlled both by the metabolic activity of certain organisms (nanoeukaryotes, copepods) and trophic structure. In the northern coastal zone, biomagnification of essential elements was controlled by copepods activities. In the offshore zone, metals and metalloids were not biomagnified probably due to homeostasis regulatory processes in organisms. In the southern coastal zone, biomagnification of As, Cu, Cr, Sb could probably induce specific effects within the planktonic network.

Induction of zincophore pseudopaline secretion by Cr(VI) and intracellular formation of granules from nanocrystal aggregation by Cr(III) in Pseudomonas aeruginosa

When microorganisms are challenged with toxic metals, intracellular granules are commonly observed, however, the exact nature of these granules is poorly understood. Here we show that when Pseudomonas aeruginosa CCTCC AB93066 were exposed to Cr(VI), Cr can enter the cell in the form of both Cr(VI) and Cr(III), and intracellular granules of several hundred nanometers were formed in the nucleoid region and were built up by aggregation of nanocrystals. We suggested that these nanocrystals are organic crystals. Transcriptomic profiles and liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis indicated that pseudopaline (a metallophore that can complex with Zn²⁺) production and pseudopaline-Zn²⁺ import into bacterial cells were enhanced upon Cr(VI) exposure. It was proposed that pseudopaline can scavenge Zn²⁺ which is essential for transcription alteration and DNA repair. Excessive pseudopaline might precipitate as nanospheres in the nuclear region that are further agglomerated by Cr(III) to form larger granules. During this process, Cr(III) is sequestered and immobilized. Hence we revealed pseudopaline production and zinc acquisition is crucial for alleviation of Cr(VI) toxicity and intracellular granules are composed of organic nanospheres which are aggregated by Cr(III).

A Comparative Study of Chromium: Therapeutic Uses and Toxicological Effects on Human Health

Chromium is an essential trace element whose deficiency can cause impairment of glucose tolerance, growth and various biological functions. There are two isotopes of chromium-trivalent chromium and hexavalent chromium. Both the isotopes of chromium have quite different effects on the human body. The objective of this narrative review is to compile the different effects of the two isotopes of chromium and give a comprehensive analysis of the effects of hexavalent and trivalent chromium. Data from various studies across different forums were compared to provide a concrete analysis of the therapeutic and harmful effects of two isotopes of chromium on human health. Chromium plays a vital role in the biological functions of the body. It might be helpful in balancing the glycaemic levels, triglyceride levels and cholesterol levels in the body. Excessive intake of chromium is harmful for health. Overexposure to chromium can lead to carcinogenic effects. Consumption of an insufficient amount of chromium might not be adequate as well. Trivalent chromium can be quite beneficial if taken in proper quantities. Hexavalent chromium can cause cancer. Trivalent chromium is beneficial, while hexavalent chromium is harmful to human health.

Flexible and easy-handling pristine polypyrrole membranes with bayberry-like vesicle structure for enhanced Cr(VI) removal from aqueous solution

Polypyrrole has been extensively explored for Cr(VI) removal from wastewater towing to the advantages of superior performance, low cost, facile synthesis, and high environmental stability. However, the unsatisfactory adsorption capacity and complicated process of adsorbent separation from aqueous solutions remain a huge challenge, limiting its practical application. Herein, a flexible PPy membrane with bayberry-like vesicle structures (PPy-B) was prepared via template-assisted interfacial polymerization. It was found that sodium sulfosalicylate not only improved the flexibility and strength of the PPy-B membrane for easy-handling but also participated in the polymerization of PPy as a dopant to improve the specific surface area and doping level for increasing adsorption sites. Benefiting from these, the easy-handling PPy-B membrane exhibited a high adsorption capacity (586.90-682.50 mg/g at 298-318 K), a high reusability (five adsorption-desorption cycles), and a high ultimate adsorption capacity after adsorption-desorption cycles until membrane failure (1174.86 mg/g at 298 K). The proposed mechanisms of the enhanced Cr(VI) removal involve electrostatic adsorption, reduction, and ion exchange. This flexible PPy membrane therefore shows attractive advantages in wastewater treatment.

Heavy metals in marine food web from Laizhou Bay, China: Levels, trophic magnification, and health risk assessment

Heavy metals in ocean may accumulate in seafood through food web and pose risks to human health. This study investigated the occurrence, trophic magnification, and health risks of 7 heavy metals in 20 marine organisms (n = 222) in Laizhou Bay (LZB), China. Results showed that Zn was the most abundant metal, followed by Cu, As, Cd, Cr, Ni and Pb. The total concentrations of 7 heavy metals in the organisms ranked in the order of crab ˃ shellfish ˃ algae ˃ fish ˃ starfish. Interspecific differences were found in the concentrations of Cr, Ni, Cu and Cd in marine organisms from LZB. Crab and shellfish showed much higher enrichment ability of heavy metals than that of algae, starfish and fish. Cd is the most biological accumulated element with the mean biota-sediment accumulation factor (BSAF) of 12.9. Stable isotope analysis showed a significant difference of δ¹⁵N among these five species (p < 0.01), and a food web was constructed accordingly. A biodilution pattern was found for Pb, As and Ni and no trophic interference in metal uptake was observed for Zn, Cu, Ni and Cr in the food web of LZB. The estimated daily intake (EDI) and target hazard quotients (THQs) of As and Cd indicated an adverse health effect on consumption of the seafood. The mean lifetime cancer risks (LCRs) for Cd and As suggested a potential carcinogenic effect on consumption of these seafood. This study provides a basis for health risk assessment of heavy metals in marine foods.

Synthesis, Characterization, and Bioactivities of Polysaccharide Metal Complexes: A Review

Natural polysaccharides are critical to a wide range of fields (e.g., medicine, food production, and cosmetics) for their various remarkable physical properties and biological activities. However, the bioactivities of naturally acquired polysaccharides may be unsatisfactory and limit their further applications. It is generally known that the chemical structure exhibited by polysaccharides lays the material basis for their biological activities. Accordingly, possible structural modifications should be conducted on polysaccharides for their enhancement. Recently, polysaccharides complexed with metal ions (e.g., Fe, Zn, Mg, Cr, and Pt) have been reported to be possibly used to improve their bioactivities. Moreover, since the properties exhibited by metal ions are normally conserved, polysaccharides may be endowed with new applications. In this review, the synthesis methods, characterization methods, and bioactivities of polysaccharide metal complexes are summarized specifically. Then, the application prospects and limitations of these complexes are analyzed and discussed.

Relationships Between Biological Heavy Metals and Breast Cancer: A Systematic Review and Meta-Analysis

Introduction

Heavy metals were classified as essential, probably essential, and potentially toxic in the general population. Until now, it has been reported inconsistently on the association between heavy metals and BC. In this meta-analysis, we aimed to assess the association between heavy metals and BC and review the potential mechanisms systematically.

Methods

We searched for epidemiological studies in English about the association between heavy metals and BC published before September 2020 in PubMed, Web of Science, and Embase databases. In total 36 studies, comprising 4,151 individuals from five continents around the world were identified and included.

Results

In all biological specimens, Cu, Cd, and Pb concentrations were higher, but Zn and Mn concentrations were lower in patients with BC than in non-BC participants [SMD (95% CIs): 0.62 (0.12, 1.12); 1.64 (0.76, 2.52); 2.03 (0.11, 3.95); −1.40 (−1.96, −0.85); −2.26 (−3.39, −1.13); p = 0.01, 0.0003, 0.04, <0.0001, <0.0001]. Specifically, higher plasma or serum Cu and Cd, as well as lower Zn and Mn, were found in cases [SMD (95% CIs): 0.98 (0.36, 1.60); 2.55 (1.16, 3.94); −1.53 (−2.28, −0.78); −2.40 (−3.69, −1.10); p = 0.002, 0.0003, <0.0001, 0.0003]; in hair, only lower Zn was observed [SMD (95% CIs): −2.12 (−3.55, −0.68); p = 0.0004]. Furthermore, the status of trace elements probably needs to be re-explored, particularly in BC. More prospective studies, randomized clinical trials, and specific pathogenic studies are needed to prevent BC. The main mechanisms underlying above-mentioned findings are comprehensively reviewed.

Conclusion

For BC, this review identified the current knowledge gaps which we currently have in understanding the impact of different heavy metals on BC.

Systematic Review Registration

www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020176934, identifier: CRD42020176934.

Sources, trophodynamics, contamination and risk assessment of toxic metals in a coastal ecosystem by using a receptor model and Monte Carlo simulation

Heavy metal (HM) pollution in coastal ecosystems have posed threats to organisms and human worldwide. This study comprehensively investigated the concentrations, sources, trophodynamics, contamination, and risks of six HMs in the coastal ecosystem of Jiaozhou Bay, northern China, by stable isotope analysis, positive matrix factorization (PMF), and Monte Carlo simulation. Overall, Co, Cu, Ni, Pb, and Zn were significantly bio-diluted in the food web, while Cr was significantly biomagnified with a trophic magnification factor of 1.23. In addition, trophodynamics of the six HMs was different among fish, mollusk, and crustacean. Furthermore, detailed transfer pathways of six HMs in the food web including eight trophic levels were different from one another. Bioaccumulation order of the six HMs was Cu > Zn > Co, Cr, Ni, and Pb. Zinc concentrations were the highest in seawater, sediments, and organisms. Anthropogenic sources contributed to 71% for Zn, 31% for Cu and Pb, and 27% for Co, Cr, and Ni in the sediment, which was moderately contaminated with moderate ecological risk. However, the human health risk of HMs from eating seafood was relatively low. To protect the Jiaozhou Bay ecosystem, HM contamination should be further controlled in future.

Heavy Metals Presence in the Soil and Their Content in Selected Varieties of Chili Peppers in Slovakia

Capsicum chili peppers are popular vegetables in Slovakia. They provide a supply of health-promoting substances, but contaminated vegetables can pose a serious health risk to the people who consume them. Therefore, the aim of this study was to determine the content of heavy metals (Mn, Zn, Cr, Cu, Ni, Cd, Pb and Hg) in the soil as well as in selected varieties of the genus Capsicum grown in southern Slovakia. The results were compared with the limit values given by the Law no. 220/2004 (valid in the SR) as well as threshold values proposed by the European Commission (EC) (2006). The gained result showed that the total content of Cd (1.64 mg/kg) as well as the available mobile forms of Cd (0.12 mg/kg) and Pb (0.26 mg/kg) was exceeded on the soil on which Capsicum cultivars were grown. The limit values of other monitored heavy metals (Mn, Zn, Cr, Cu, Ni, and Hg) were not exceeded. The studied species of the genus Capsicum did not accumulate monitored heavy metals. It can be stated that consumption of chili peppers does not pose any risk for human health.

Direct embryotoxicity of chromium (III) exposure during preimplantation development

Chromium in its trivalent form (chromium (III)) is an essential component of a balanced diet, and its deficiency disturbs glucose and lipid metabolism in humans and animals. The prevailing view is that chromium (III) is notably less toxic than chromium (VI), which is genotoxic and carcinogenic. Thus, the biotransformation of environmental chromium (VI) to chromium (III) is a promising and environmentally friendly detoxification method. However, increasing evidence suggests that chromium (III) induces considerable cytotoxicity. However, the toxicity of chromium (III) to early embryos remains largely unknown. In the present study, we used in vitro fertilization (IVF) to produce mouse embryos and identified the direct embryotoxicity of chromium (III). On exposure to high concentrations of CrCl₃, blastocyst formation almost completely failed and a large proportion of embryos were arrested at the 2- to 4-cell stage. At low concentrations of CrCl₃, IVF embryos showed a significant decrease in blastocyst formation, reduced total cell numbers, aberrant lineage differentiation, increased oxidative stress, and apoptosis. We also found that chromium (III) exposure during the preimplantation stage, even at low concentrations, led to impaired post-implantation development. Thus, our study substantiates the direct embryotoxicity of chromium (III) during preimplantation development and prolonged impairment of development potential. The results further highlight the potential adverse effects of chromium (III) on public reproductive health with respect to increased environmental enrichment of and dietary supplementation with chromium (III) complexes.

Identification of metal binding motifs in protein frameworks to develop novel remediation strategies for Hg2+ and Cr(VI)

Amino acid sequences in metal-binding proteins with chelating properties offer exciting applications in biotechnology and medical research. To enhance their application in bioremediation studies, we explicitly aimed to identify specific metal-binding chelating motifs in protein structures for two significant pollutants, such as mercury (Hg²⁺) and chromium Cr(V1). For this purpose, we have performed an extensive coordination chemistry approach by retrieving Hg²⁺ and Cr(V1) binding protein structures from the protein database and validated using the B-factor, a term defining uncertainty of the atoms and with occupancy to obtain the best binding motifs. Our analysis revealed that acidic amino acids like aspartic acid, glutamic acid, and basic amino acids such as cysteine and histidine are predominant in coordinating with these metals. The order of preference in Hg²⁺-bound structures is predicted to be Cys > His > Asp > Glu, and for Cr(V1) is His > Asp > Glu. Examination of the atomic coordinates and their distance from each metal revealed that the sulfur atoms of cysteine showing more preference towards Hg²⁺coordination with an atomic distance ranging from 1.5 to 2.9 Å. Likewise, oxygen atoms of aspartic acid, glutamic acid and nitrogen atoms of histidine are within 2 Å of Cr(V1) coordination. Based on these observations, we obtained C-C-C, C-X(2)-C-C-(X)2-C, H-C-H motifs for Hg²⁺, and D-X(1)-D, H-X(3)-E motif for Cr(V1) to be shared within the coordination space of 3 Å. As a future scope, we propose that the identified metal-binding chelating motifs are oligopeptides and can display on the surface of microorganisms such as Escherichia coli and Saccharomyces cerevisiae for effective removal of natural Hg²⁺ and Cr(V1) through biosorption. Hence, our results will provide the basis for futuristic bioremediation.

On-Line Separation and Determination of Trivalent and Hexavalent Chromium with a New Liquid Membrane Annular Contactor Coupled to Inductively Coupled Plasma Optical Emission Spectrometry

We describe a new on-line sensitive and selective procedure for the determination of trivalent and hexavalent chromium in liquid samples by a tailor-made contactor (TMC), specifically a liquid membrane annular TMC, coupled with inductively coupled plasma with optical detection. The TMC was designed and developed to integrate the extraction and stripping phases of the analyte in one module to minimize the membrane solvent’s consumption and maximize the speed of transport through the liquid membrane. Moreover, the particular geometry studied, which consists of two coaxial hollow fibers, allows the TMC to be used for both separating and preconcentrating purposes. Both (−)-N-dodecyl-N-methylephedrinium bromide (30 mM) in dichloroethane and HNO3 (0.75 M) were used as the liquid membrane and receiving solution, respectively. The proposed method’s performance was evaluated in terms of the hexavalent chromium extraction efficiency and the coefficient of variation percentages; these were higher than 85% and less than 5%, respectively. In addition, the proposed procedure was applied to two real samples: a tap water sample and an eluate from solid urban waste. In both cases, the analytical performances were good and comparable to those obtained using synthetic standard solutions.

Effects of Different Chromium Compounds on Hematology and Inflammatory Cytokines in Rats Fed High-Fat Diet

The aim of the study was to determine how a high-fat diet supplemented with various forms of chromium affects hematological and immune parameters of the blood of rats. The rats received a standard diet or a high-fat diet supplemented with chromium at 0.3 mg/kg body weight (BW) in the form of chromium(III) picolinate, chromium(III)-methionine or nano-sized chromium. Selected hematological parameters were determined in the blood of the rats, including total white blood cell (WBC) count, leukogram, red blood cell (RBC) count, hemoglobin level (HGB), hematocrit (HCT), platelet count (PLT) and platelet percentage (PCT), as well as immune parameters: levels of immunoglobulins A and E (IgA and IgE), interleukin-6 (IL-6), interleukin-2 (IL-2), and tumor necrosis factor α (TNF-α); activity of ceruloplasmin (Cp); and levels of caspase 3 and 8 (Casp3 and Casp8). Feeding rats a high-fat diet increased blood markers of induction of inflammation, ie pro-inflammatory cytokines IL-6 and TNF-α, and also significantly increased IgE. The diet had no effect on the blood count, except for an increase in the number of neutrophils. The chromium compounds tested, particularly Cr-Met and Cr-NPs, stimulated the immune system of the rats, as indicated by increased concentrations of IgA, IgE, IL-2, IL-6, TNF-α, and Cp. Given the increase in inflammatory mediators induced by chromium, it should not be used to mitigate the effects of a high-fat diet. Moreover, chromium picolinate and chromium nanoparticles were shown to increase the content of caspase 3 and 8 in the blood of rats, which indicates a pro-apoptotic effect. The effects of the use of chromium nanoparticles include reductions in the WBC count and in the thrombocyte count (leuko- and thrombopenia). Taking account these data the use of chromium as dietary supplement should be reconsidered.

High-Affinity Sulfate Transporter Sultr1;2 Is a Major Transporter for Cr(VI) Uptake in Plants

Chromate (Cr[VI]) is a highly phytotoxic contaminant that is ubiquitous in soils. However, how Cr(VI) is taken up by plant roots remains largely unknown. Here, we show that the high-affinity sulfate transporter Sultr1;2 is responsible for Cr(VI) uptake by the roots of Arabidopsis thaliana. Sultr1;2 showed a much higher transport activity for Cr(VI) than Sultr1;1 when expressed in yeast cells. Knockdown of Sultr1;2 expression in Arabidopsis markedly reduced the Cr(VI) uptake rate, whereas knockout of Sultr1;1 had no or little effect. A double-knockout mutant (DKO) of the two genes lost the ability of Cr(VI) uptake almost completely. The Sultr1;2 knockdown mutant or DKO plants displayed higher resistance to Cr(VI) under normal sulfate conditions as a consequence of the lower tissue Cr accumulation. Overexpression of Sultr1;2 substantially increased Cr(VI) uptake with shoot Cr concentration being 1.6-2.0 times higher than that in the wild-type. These results indicate that Sultr1;2 is a major transporter responsible for Cr(VI) uptake in Arabidopsis, while Sultr1;1 plays a negligible role. Taken together, our study has identified a major transporter for Cr(VI) uptake in plants, providing potential strategies for engineering plants with low Cr accumulation and consequently enhanced Cr(VI) resistance and also plants with enhanced accumulation of Cr for the purpose of phytoremediation.

The Double Face of Metals: The Intriguing Case of Chromium

Chromium (Cr) is a common element in the Earth’s crust. It may exist in different oxidation states, Cr(0), Cr(III) and Cr(VI), with Cr(III) and Cr(VI) being relatively stable and largely predominant. Chromium’s peculiarity is that its behavior relies on its valence state. Cr(III) is a trace element in humans and plays a major role in glucose and fat metabolism. The beneficial effects of Cr(III) in obesity and types 2 diabetes are known. It has been long considered an essential element, but now it has been reclassified as a nutritional supplement. On the other hand, Cr(VI) is a human carcinogen and exposure to it occurs both in occupational and environmental contexts. It induces also epigenetic effects on DNA, histone tails and microRNA; its toxicity seems to be related to its higher mobility in soil and swifter penetration through cell membranes than Cr(III). The microorganisms Acinetobacter sp. Cr1 and Pseudomonas sp. Cr13 have been suggested as a promising agent for bioremediation of Cr(VI). This review intends to underline the important role of Cr(III) for human health and the dangerousness of Cr(VI) as a toxic element. The dual and opposing roles of this metal make it particularly interesting. An overview of the recent literature is reported in support.

Toward the Development of Ultrasensitive Detectors for Environmental Applications: A Kinetic Study of Cr(III) Monitoring in Water Using EDTA and SERS Techniques

We report for the first time kinetic studies on chromium(III) detection in aqueous solution using citrate-capped silver nanoparticles (AgNPs) and the surface-enhanced Raman spectroscopy (SERS) technique. Moreover, we have shown an important effect of adding ethylenediaminetetraacetic acid (EDTA) on the enhancement and the stability of the Raman signal. The origin of the SERS signal was attributed to the coordination of Cr(III) by citrate/EDTA molecules and the formation of hot spots on aggregated AgNPs. Depending on the mixing method of Cr(III) and EDTA with AgNPs, the temporal SERS spectral features reveal a Prout-Tompkins or a Langmuir kinetic detection model. The UV-visible data, the temporal response of the Raman signal, and the scanning electron microscopy analysis have allowed us to elucidate the mechanism of Cr(III) detection. We observed that mixing simultaneously Cr(III), AgNPs, and EDTA leads to the most stable and intense time-dependent SERS signal. The obtained results should open the way to perform kinetic studies on different host-guest interactions in solution using the SERS technique.

Elemental Composition and Associated Health Risk of Honey Obtained from Apiary Farms in Southeast Nigeria

ABSTRACT

This study investigated the levels of lead, selenium, arsenic, iron, manganese, copper, zinc, chromium, cadmium, and nickel in honey and their potential health risks to consumers, using standard protocols. The honey samples were obtained from apiary farms at nine different locations in southeast Nigeria. They were digested at optimal conditions and analyzed using a flame atomic absorption spectrophotometer. Levels of the studied elements in the honey were found to vary relative to the sample source; however, all were below European Commission maximum permissible limits, with the exception of lead, whose level in some samples exceeded the recommended set limit. Estimated daily intakes of the elements via ingestion of the honey were all below the maximum permissible limit set by the European Food Safety Authority, with the exception of arsenic, whose values in some samples slightly exceeded the set limit. For all samples, estimated health risk values for the elements quantified were higher in children than in adults. The hazard quotient for arsenic, hence, the hazard index for the elements, indicated a significant risk (>1) for children for some of the honey samples studied. Arsenic was the major contributor to incremental lifetime cancer risk; its estimated value for children in all the honey samples exceeded the U.S. Environmental Protection Agency (EPA) threshold limit (>1.0 × 10-4); hence, the total cancer risk values for the carcinogenic elements indicated an absolute unacceptable risk level for children based on EPA threshold limit.

HIGHLIGHTS

Association between concentrations of chromium in drinking water and mortality due to suicide in Alabama

Preclinical studies and clinical data from case series and placebo-controlled trials suggest that chromium might have antidepressant effects. We conducted an observational study in order to assess the association between concentrations of chromium in drinking water and mortality due to suicide in Alabama. Publicly available databases were used to determine both county-level concentrations of chromium in drinking water and county-level rates of mortality due to suicide in the years 2005-2015. Data analyses comparing county-level concentrations of total chromium in drinking water with mortality rate due to suicide were conducted using a two-tailed nonparametric Spearman's rank correlation, with statistical significance set at p ≤ 0.01 and 99% confidence interval. Sub-analyses were conducted examining males, females, whites, and blacks/other minorities. There were no statistically significant findings concerning concentrations of chromium and suicide rate in the general population (p = 0.35, r = -0.12); however, there was a statistically significant inverse relationship between the concentration of chromium and suicide deaths in whites (p = 0.009, r = -0.32). There were no statistically significant findings in the remaining demographic subgroups. Chromium in drinking water might have a protective effect against mortality due to suicide, at least in the Caucasian population.

Evaluation on the biomagnification or biodilution of trace metals in global marine food webs by meta-analysis

The transmission and accumulation of trace metals in marine food webs have a profound influence on the structure and function of marine environment. In order to quantitatively assess the trophic transfer behaviors of eight common metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) in simplified five-trophic level marine food webs, a total of 9929 biological samples from 61 studies published between 2000 and 2019, involving 154 sampling sites of 33 countries/regions, were re-compiled using meta-analysis. Based on concentration-trophic level weighted linear regression and predator/prey comparison, the food web magnification factor (FWMF) and the biomagnification factor (BMF) were calculated, respectively. The results showed dissimilar trophic transfer behaviors of these metals in global marine food webs, in which As and Ni tended to be efficiently biodiluted with increasing trophic levels (FWMFs < 1, p < 0.01), while Hg, Pb and Zn trophically biomagnified (FWMFs > 1, p < 0.05). However, Cd, Cr and Cu presented no biomagnification or biodilution trend (p > 0.05). The values of FWMFs were ranked as: Hg (2.01) > Pb (1.81) > Zn (1.15) > Cu (1.13) > Cr (0.951) > Cd (0.850) > Ni (0.731) > As (0.494). In terms of specific predator-prey relationship, Pb showed significant biodilution from tertiary consumers (TC) to top predators (BMF < 1, p < 0.05), whereas Cd and Cu displayed obvious biomagnification from primary consumers (PC) to secondary consumers (SC) (BMFs >1, p < 0.05). Additionally, when Cu and Zn were transferred from SC to TC, and primary producers to PC, clear biodilution and biomagnification effects were observed, respectively (p < 0.05). Further analysis indicated that the average concentration of Hg in five-trophic level marine food webs of developed countries (0.904 mg kg^-1 dw) was more noticeable (p < 0.05) than that of developing countries (0.549 mg kg^-1 dw).

An overview of palladium supported on carbon-based materials: Synthesis, characterization, and its catalytic activity for reduction of hexavalent chromium

Palladium plays a pivotal role in most of the industrial heterogeneous catalysts, because of its unique properties such as well-defined structure, great intrinsic carrier, outstanding electronic, mechanical and thermal stability. The combination of palladium and various porous carbons (PCs) can widen the use of heterogeneous catalysts. This review highlights the advantages and limitations of carbon supported palladium-based heterogeneous catalyst in reduction of toxic hexavalent chromium (Cr^(VI)). In addition, we address recent progress on synthesis routes for mono and bimetallic palladium nanoparticles supported by various carbon composites including graphene-based materials, carbon nanotubes, mesoporous carbons, and activated carbons. The related reaction mechanisms for the Cr^(VI) reduction are also suggested. Finally, the challenge and perspective are proposed.

Chromium (III) coordination capacity of chitosan

Polycationic chitosan has a strong coordination to heavy metal ions due to its multifunctional hydroxyl and amino groups. However, due to the fast and facile dissolution of chitosan in acidic medium, it is difficult to measure the exact adsorption amount or coordination capacity accurately. In this work, a simple method of lyophilization plus ethanol-washing was employed to separate and purify chitosan/Cr(III) complex for further determining the coordination capacity. Meanwhile, the coordination structure of Bridge-chitosan-N(OH)₃(H₂O) and morphology of regenerated fibrillar sponge of CS/Cr(III) were further certified. The coordination capacity of Cr(III) on chitosan increased with the rising concentration of Cr(III) ions till the maximum coordination capacity was reached up to 355.03 mg/g. The mechanisms and characteristic parameters of the adsorption process were fit using two-parameter isotherm models which revealed the following order (based on the coefficient of determination) of Langmuir > Halsey > Freundlich > Temkin > Dubinin-Radushkevich. A proposed coordination formula of CS/Cr (III) might be a good certificate for the homogeneous chemical combination nature of Cr(III) on the monolayer surface of chitosan in a molecular scale.

Trophic transfer, biomagnification and risk assessments of four common heavy metals in the food web of Laizhou Bay, the Bohai Sea

This study investigated the trophic transfer of four common toxic metals (Cd, Cr, Cu and Hg) in the food web and assessed their potential ecological risks in Laizhou Bay, a spawning area for fishery populations in the Bohai Sea, North China. Based on the predation relations of 43 species that were representatives of the main trophic levels (TLs), a simplified food web was constructed using stomach content analysis and stable nitrogen isotope ratio (δ¹⁵N) analysis. Using copepods as the baseline species (TL = 2.00), the TLs of the organisms ranged from 1.96 (Polychaeta) to 4.47 (Japanese flounder) and showed the following ranking order: predatory pelagic or demersal fish > medium demersal fish > crustacean, cephalopod, small pelagic or demersal fish > zooplankton and Polychaeta. The metals showed different trophic transfer behaviors in the food web. Hg and Cr tended to be efficiently biomagnified between TLs, along the main food chains and in the food web. Cu biodiluted significantly with increasing TLs, while Cd showed no biomagnification or biodilution trends in the food web. At low or moderate levels of Cd and Hg, potential ecological risks were detected in the water and sediments at only a few sites, indicating their overall low ecological risks in the environment. The metals in the important fishery species (four top predatory fish, two cephalopods and eight crustaceans) were below the permissible limits, except for Cd in octopus and paddle crab, which reached or exceeded the most restrictive criteria. Based on the provisional tolerable weekly intake (PTWI) criteria, the safe weekly human consumption levels by humans of the predatory fish, cephalopods and crustaceans were species-specific (0.20-4.44 kg) and should be cautiously assessed.

Melatonin protects against chromium(VI)-induced cardiac injury via activating the AMPK/Nrf2 pathway

Chromium (Cr) threatens health by causing oxidative stress. However, effective therapy for cardiac damage mediated by potassium dichromate (K₂Cr₂O₇) still has not been defined. Melatonin (MT) possesses a number of biological activities. Our study was performed to explore the effect and mechanism of MT on Cr(VI)-induced cardiac damage by conducting both in vitro and in vivo studies. Twenty eight male Wistar rats were randomly assigned to four groups: control, MT (20 mg/kg subcutaneously), K₂Cr₂O₇ (4 mg/kg intraperitoneally), and K₂Cr₂O₇ + MT. We measured biomarkers of oxidative stress and cardiac function, and performed histopathological analysis, assay of terminal deoxynucleotidyl transferase-mediated deoxyuracil nucleoside triphosphate nick end labeling and protein levels, and the viability assay of cultured cardiomyocytes in vitro. Our results showed that MT ameliorated K₂Cr₂O₇-induced oxidative stress, apoptosis, and the release of inflammatory mediators in the rat heart. MT also promoted adenosine monophosphate-activated protein kinase (AMPK) phosphorylation, upregulated expression of proteins that nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1, and nicotinamide adenine dinucleotide phosphatase: quinone-acceptor 1, and inhibited nuclear factor kappa B in the heart of rats exposed to K₂Cr₂O₇. Furthermore, MT increased B-cell lymphoma gene 2 (Bcl-2) and B-cell lymphoma extra large protein levels and decreased cleaved caspase 3, P53, and Bcl-2-associated X protein levels. Furthermore, the experiment in vitro showed that MT increased the cells viability and protein levels of Nrf2 and phosphorylated-AMPK in H9C2 cells treated with K₂Cr₂O₇. Collectively, our results demonstrate that MT protects against Cr-induced cardiac damage via activating the AMPK/Nrf2 pathway.

Effect of pH on Cr(III) accumulation, biomass production, and phenolic profile in 2 Salvinia species

We analyzed the effect of pH on Cr(III) accumulation, biomass production, and phenolic profile of Salvinia rotundifolia and Salvinia minima plants grown in the presence of increasing concentrations of CrCl₃ . Biomass accumulation, metal tolerance index, and photosynthetic pigment contents indicate that Salvinia rotundifolia seems to be more tolerant of Cr(III) than S. minima at different pHs. Increased metal accumulation by Salvinia species under increasing pH could be explained by changes of the protonation status of cell wall functional groups because both the highest and the lowest pH values used in the present study were outside of the levels at which Cr(III) species start to precipitate. The metal translocation factor indicates that in buffered conditions S. rotundifolia tend to retain more Cr(III) in lacinias than S. minima, probably through the involvement of insoluble phenolics. The results of the present study could be useful to the management of solution pH to maximize the removal of Cr(III) by aquatic plants. Environ Toxicol Chem 2019;38:167-176. © 2018 SETAC.

Efficient bifunctional reactivity of K-doped CrO(OH) nanosheets: exploiting the combined role of Cr(iii) and surface –OH groups in tandem catalysis

Layered K-α-CrO(OH) nanosheets as a non-noble metal based tandem catalyst for sequential oxidation and coupling/condensation reactions.

Dietary intake of cadmium, chromium, copper, manganese, selenium and zinc in a Northern Italy community

This study provides the dietary intakes of six trace elements (cadmium, chromium, copper, manganese, selenium and zinc), generally characterized by both nutritional and toxicological features depending on their exposure. Being diet the most relevant source of exposure to trace elements in non-professionally exposed subjects, we measured content of these trace elements in foods composing the typical Italian diet using inductively coupled plasma-mass spectrometry, and assessing dietary habits using a validated semi-quantitative food frequency questionnaire we eventually estimated dietary daily intake of trace elements in a Northern Italian community. In the 890 analyzed food samples, the main contributors to cadmium intake are cereals, vegetables and sweets, while cereals, beverages and vegetable are to primary source of manganese. The primary contributors for copper are cereals, fresh fruits and vegetables, while for chromium are beverages, cereals and meat. The main source of selenium intake are cereals and meat, followed by fish, seafood and milk and dairy products, while of zinc intake are meat, cereals, milk and dairy products. In our Italian population sample, the estimated median (interquartile range) dietary daily intakes are 5.00 (3.17-7.65), 56.70 (36.08-86.70) and 66.53 (40.04-101.32) μg/day for cadmium, chromium and selenium, and corresponding figures are 0.98 (0.61-1.49), 2.34 (1.46-3.52) and 8.50 (5.21-12.48) mg/day for copper, manganese and zinc. The estimated intakes are generally within the average intake reported in other European populations, and in such cases well above the daily dietary intakes recommended by national international agencies, avoiding the risk of excess or deficiency. The present estimated intake data can be used to examine a specific trace element of interest and would afford enhanced health protection from those trace elements characterized by both nutritional and toxicological effects.

Use of SU8 as a stable and biocompatible adhesion layer for gold bioelectrodes

Gold is the most widely used electrode material for bioelectronic applications due to its high electrical conductivity, good chemical stability and proven biocompatibility. However, it adheres only weakly to widely used substrate materials such as glass and silicon oxide, typically requiring the use of a thin layer of chromium between the substrate and the metal to achieve adequate adhesion. Unfortunately, this approach can reduce biocompatibility relative to pure gold films due to the risk of the underlying layer of chromium becoming exposed. Here we report on an alternative adhesion layer for gold and other metals formed from a thin layer of the negative-tone photoresist SU-8, which we find to be significantly less cytotoxic than chromium, being broadly comparable to bare glass in terms of its biocompatibility. Various treatment protocols for SU-8 were investigated, with a view to attaining high transparency and good mechanical and biochemical stability. Thermal annealing to induce partial cross-linking of the SU-8 film prior to gold deposition, with further annealing after deposition to complete cross-linking, was found to yield the best electrode properties. The optimized glass/SU8-Au electrodes were highly transparent, resilient to delamination, stable in biological culture medium, and exhibited similar biocompatibility to glass.

Effects of chromium(III) on enzyme activities and bacterial communities during swine manure composting

The present study investigated the effects of different concentrations of chromium (i.e., 200 and 700mgkg^-1 Cr corresponding to Cr200 and Cr700, respectively) on the microorganisms in swine manure compost. The results demonstrated that a high concentration of Cr(III) could inhibit the activity of key microbial enzymes (i.e., dehydrogenase, cellulase, and urease) in the early composting stages, with maximal inhibition rates of 54.9%, 32.8%, and 46.7% for cellulase, urease, and dehydrogenase, respectively. Furthermore, the bacterial abundances were determined by quantitative PCR and their compositions were evaluated by denaturing gradient gel electrophoresis. Cr200 and Cr700 had significant inhibitory effects on the abundances of bacteria. The DGGE results showed that Cr200 and Cr700 changed the bacterial community structure and diversity, where Cr(III) might enhance the abundance of pathogenic bacteria (e.g., Saccharomonospora) and decrease the abundances of bacteria that degrade cellulose and lignin (e.g., Paenibacillus) during composting.

Accumulation and detoxification dynamics of Chromium and antioxidant responses in juvenile rare minnow, Gobiocypris rarus

Hexavalent chromium (Cr⁶⁺) compounds are hazardous via all exposure routes. To explore the dynamics of Cr accumulation and elimination and to reveal the mechanisms underlying detoxification and antioxidation in juvenile Gobiocypris rarus, one-month old G. rarus larvae were exposed to 0.1mgL^-1 Cr⁶⁺ for four weeks for accumulation and subsequently placed to clean water for another week for depuration. The contents of Cr were measured weekly in the whole body of G. rarus juveniles. The activities of catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione S-transferase (GST) and glutathione reductase (GR), and contents of glutathione (GSH) and malonaldehyde (MDA), and transcripts of cat, Cu/Zn-sod, Mn-sod, gpx1, gstpi, gr, mt1, nrf2 and uba52 were determined. The results indicated that G. rarus juveniles had a strong ability to resist the Cr accumulation by Cr⁶⁺ exposure and to remove Cr from the body in clean water. In addition, GST and MT proteins may be involved in the detoxification of Cr⁶⁺. Moreover, Cr⁶⁺-induced GST detoxification in G. rarus juveniles might be accomplished through the Nrf2-mediated regulation of gene expressions. The antioxidant enzyme systems exhibited a response mechanism of the protective enzymes in organisms when they are subjected to external environmental stress. Two weeks of Cr⁶⁺ treatments could have led to the damage and consecutive degradation of antioxidant enzymes via ubiquitination, and MT proteins could be involved in protecting the activity of these enzymes. The capability of antioxidant enzyme systems to recover from the Cr⁶⁺-induced damage was strong in G. rarus juveniles after Cr⁶⁺ was removed from the water.

Carcinogenicity of chromium and chemoprevention: a brief update

Chromium has two main valence states: hexavalent chromium (Cr[VI]) and trivalent chromium (Cr[III]). Cr(VI), a well-established human carcinogen, can enter cells by way of a sulfate/phosphate anion-transport system, and then be reduced to lower-valence intermediates consisting of pentavalent chromium (Cr[V]), tetravalent chromium (Cr[IV]) or Cr(III) via cellular reductants. These intermediates may directly or indirectly result in DNA damage or DNA–protein cross-links. Although Cr(III) complexes cannot pass easily through cell membranes, they have the ability to accumulate around cells to induce cell-surface morphological alteration and result in cell-membrane lipid injuries via disruption of cellular functions and integrity, and finally to cause DNA damage. In recent years, more research, including in vitro, in vivo, and epidemiological studies, has been conducted to evaluate the genotoxicity/carcinogenicity induced by Cr(VI) and/or Cr(III) compounds. At the same time, various therapeutic agents, especially antioxidants, have been explored through in vitro and in vivo studies for preventing chromium-induced genotoxicity/carcinogenesis. This review aims to provide a brief update on the carcinogenicity of Cr(VI) and Cr(III) and chemoprevention with different antioxidants.