Cr Transport Research Articles

Significance of Conformation Changes During the Binding and Release of Chromium(III) from Human Serum Transferrin

Abstract Objectives Transferrin, Tf, the protein that transports iron from the blood to the tissues via endocytosis, is believed to also transport chromium(III), Cr(III). Recently, the presence of multiple conformations was suggested by spectroscopic studies. The objective of this work is confirm whether various conformers of Cr(III)2-Tf exist and their potential significance for Cr(III) transport. Methods Cr(III) was added to apoTf in a buffered solution at pH 7.4 containing 25 mM bicarbonate at 37 °C. After time intervals, ultraviolet spectra were collected, or aliquots were removed and frozen for analysis by electron paramagnetic resonance (EPR) spectroscopy, which can distinguish free Cr(III) and Cr(III) bound to the two metal binding sites of Tf. To model the acidification of the endosome that triggers release of metal ions from Tf, the Cr(III)2-Tf conformer solutions were acidified by the addition of hydrochloric acid to pH 4.5 or 5.5. At time intervals after acidification, samples were again analyzed by ultraviolet and EPR spectroscopies. Results A combination of electronic and EPR studies reveal that the addition of Cr(III) to apoTf at near neutral pH in the presence of 25 mM bicarbonate results in the rapid binding of two Cr(III) accompanied and then followed by a series of conformation changes in Cr(III)2-Tf. These multiple conformations give rise to different spectroscopic properties and upon acidification different rates of Cr(III) release. Conclusions The conformer of Cr(III)2-Tf used in most previous studies and giving rise to EPR features at g ∼ 5.1, 5.4, and 5.6 forms too slowly to be physiologically relevant; however, two previously unknown conformers of Cr(III)2-Tf, giving rise to an EPR feature at g ∼2 and at g ∼ 5.4, respectively, were identified. The latter of these conformers has a lifespan similar to the turnover time of transferrin and releases Cr(III) rapidly, suggesting it is probably the most physiologically significant conformer of Cr(III)2-Tf. Funding Sources The University of Alabama College of Arts and Sciences Research Award.

Reduced NOM triggered rapid Cr(VI) reduction and formation of NOM-Cr(III) colloids in anoxic environments

Natural organic matter (NOM) can influence the toxicity and speciation of chromium (Cr) in subsurface through redox reactions and complexation. Under anoxic conditions, NOM can be reduced by microorganisms or geochemical reductants, and the reduced NOM (NOMred) represents a large reservoir of organic matter observed in anoxic sediments and water. While the current body of work has established the kinetic of Cr(VI) reduction by oxidized NOM (NOMox) under oxic conditions, much less is known about the rates and mechanisms of Cr(VI) reduction triggered by NOMred under anoxic conditions and the colloidal properties of the reaction products. This study provided new information regarding the NOMred-mediated Cr(VI) reduction and colloidal stability of reduced Cr(III) particles over a wide range of environmentally relevant anoxic conditions. We show that under dark anoxic conditions reduced humic acid (HAred) moieties (e.g., quinone) can quickly reduce Cr(VI) to Cr(III), and the reduced Cr(III) can subsequently complex with carboxyl groups of HA leading to the formation of stable HA-Cr(III) colloids. Rates of Cr(VI) reduction by HAred are 3–4 orders of magnitude higher than those by oxidized HA (HAox) due primarily to the higher reducing capacity of HAred. The stable HA-Cr(III) colloids are formed across a range of HA concentrations (8–150 mg C/L) and pH conditions (6–10) with hydrodynamic diameter in the range of 210–240 nm. Aberration-corrected scanning transmission electron microscopy (Cs-STEM) and X-ray photoelectron spectroscopy (XPS) confirmed that the particles are composed of HA-Cr(III). The high colloidal stability of HA-Cr(III) particles could be attributed to the enhanced electrosteric stabilization effect from free and adsorbed HA, which decreased particle aggregation. However, the presence of divalent cations (Ca2+ and Mg2+) promoted particle aggregation at pH 6. These new findings are valuable for our fundamental understanding of the fate and transport of Cr in organic-rich anoxic environments, which also have substantial implications for the development and optimization of subsurface Cr sequestration technology.

Enhanced removal of Cr(VI) by polymer inclusion membrane based on poly(vinylidene fluoride) and Aliquat 336

New polymer inclusion membranes (PIMs) based on poly(vinylidene fluoride) (PVDF) (polymer matrix), tricaprylmethylammonium chloride (Aliquat 336) (ion carrier) and 2-nitrophenyloctylether (2NPOE) (plasticizer) were successfully elaborated by casting evaporation method and used in selectively facilitated transport of Cr(VI) ions in an acidic aqueous medium. Obtained PIMs are dense and homogeneous and are characterized by intermolecular interactions of the membrane components (i.e. polymer matrix, ion carrier and plasticizer). The presence of ion carrier and plasticizer enhances the membrane flexibility and its hydrophilic character. The decrease of the PVDF melting point is ascribed to the strong electrostatic interactions between liquid compounds (i.e. ion carrier and plasticizer) and polymer chains. PVDF-based PIM with only 20 wt% of Aliquat 336 ensures almost complete transport of Cr(VI) ions from the donor to acceptor phase. Moreover, the addition of 5 wt% of plasticizer significantly increases the transport flux. Also, Cr(VI) ions are selectively recovered (~97%) from a mixture containing other heavy metal ions (Cd(II), Pb(II), Fe(III), Zn(II), Cu(II), Ni(II), Co(II)) with such PIM. Elaborated PVDF-based PIMs reveal improved transport properties compared to other polymer-based PIMs, exhibiting high stability (more than 190 h) and lifetime durability and so they are suitable for long term application.

Insights into the facilitated transport mechanisms of Cr(VI) in ionic liquid-based polymer inclusion membrane – Electrodialysis (PIM-ED) process

To improve the relatively low transport efficiency of ionic liquid-based polymer inclusion membrane (PIM), an integration of electrodialysis (ED) with PIM is explored for the facilitated transport of Cr(VI). Several parameters such as current density, carrier concentration, initial composition and properties of feed and stripping solutions have been systematically studied. Current intensity was crucial to the facilitating transport of Cr(VI), while a threshold of current density was observed at around 7 mA cm−2, and the highest permeability coefficient was achieved at 10 mA cm−2. By using the integrated system at optimized condition, the permeability coefficient increased from 0.62 to 3.33 μm s−1 below threshold, while from 3.33 to 23.53 μm s−1 above threshold to 10 mA cm−2. Under optimum conditions, the initial flux of Cr(VI) in our experiment can reach 116 μmol m−2 s−1. Therefore, the facilitated transport was proposed to be achieved by promoting fixed-site jumping mechanism in electric field below the threshold value, while a continuous pathway manner was hypothesized above the threshold value. The PIM exhibited high stability in PIM-ED system in 9 repeated experiments with slightly decrease for Cr(VI) transport performance. The transport efficiency can be further improved by using multistage operation which is appropriate for scale-up applications.

Evaluation of Metals Leaching in Permeable Asphalt Pavement and Conventional Asphalt Pavement

A permeable asphalt pavement (PP) and a conventional asphalt pavement (PD) have been tested regarding the potential leaching of the metals Cd, Cr, Fe, Pb, Mn, Ni and Zn during 11 rain events immediately after their construction. Water samples were picked up for the rain water and in four sampling points of both pavements during every rain, two located at the surface of the pavements (PPE and PDE), and other two after infiltration in the pavements (PPI and PDI). The results show that there was introduction and transport of Cr, Fe, Pb, Mn, Ni and Zn during surface runoff on pavements. After water infiltration in the pavements, there was significant removal of Cr in the PD pavement, Pb and Zn concentrations did not decrease in depth and concentrations of Fe and Ni increased after infiltration. However, the concentrations of all metals in the leaching water are very low comparing with the minimum standard legal values set up for irrigation and discharge on water courses.

Separation of Zn(II), Cr(III), and Ni(II) Ions Using the Polymer Inclusion Membranes Containing Acetylacetone Derivative as the Carrier.

Polymer inclusion membranes (PIMs) doped with ethylenodiamino-bis-acetylacetone as fixed carrier was applied for the investigation of the facilitated transport of Zn(II), Cr(III), and Ni(II) ions from an aqueous nitrate feed phase (cM = 0.001 mol/dm3). The optimal membrane composition (amount of carrier and o-NPPE-plasticizer) was determined. For the optimal polymer inclusion membranes doped with ethylenodiamino-bis-acetylacetone, the following patterns of transport selectivity were found: Zn(II) > Cr(III) > Ni(II). The initial flux of Zn(II), Cr(III), and Ni(II) ions was 6.37 µmol/m2∙s, 5.53 µmol/m2∙s, and 0.40 µmol/m2∙s, respectively. The selectivity coefficients equal to 1.2 and 15.9 were found for Zn(II)/Cr(III) and Zn(II)/Ni(II), respectively. After 24-h transport, the recovery factor of Zn(II), Cr(III), and Ni(II) were 90%, 65%, and 6%, respectively. The polymer inclusion membranes doped with ethylenodiamino-bis-acetylacetone were characterized by scanning electron microscopy and non-contact atomic force microscopy. The influence of membrane morphology on transport process was discussed.

Chromium, manganese, nickel, and cobalt mobility and bioavailability from mafic-to-ultramafic mine spoil weathering in western Massachusetts, USA.

Fragmented ultramafic bodies in New England were important mineral resources until the early twentieth century, yet few studies have addressed their potential to release trace metals to terrestrial and aquatic environments. Here, we evaluate the release of four trace metals (Cr, Co, Mn, and Ni) from a historic serpentine-talc "soapstone" quarry in Blandford, MA, USA. Soil pits, sediment and rock samples, and stream water samples were collected from upslope undisturbed areas, within the mine spoils and mine face, and downslope of the mine. In order to provide a bottom-up approach for understanding metal release, careful petrographic analysis, electron-dispersive spectroscopy, and wavelength-dispersive spectroscopy were employed to provide first-order insight into the mineralogy of the deposit and a determination of potential metal-bearing phases. Trace metals were primarily observed in ultramafic sheet silicates, primary Fe-oxides, and interstitial weathering-related sulfates. Bulk rock concentrations were Cr (1550mgkg-1), Co (230mgkg-1), Mn (1100mgkg-1), and Ni (1960mg kg1); Cr, Co, and Ni were elevated relative to the surrounding country rock. However, soils and sediments total concentrations were comparable to background soil concentrations: Cr (119mgkg-1), Co (73mgkg-1), Mn (894mgkg-1), and Ni (65mgkg-1). Moreover, < 0.5% of the total concentrations were bioavailable (0.1M ammonium acetate extraction), implying that metals are present as insoluble forms. However, ~ 20% of the total Cr, Mn, Ni, and Co concentrations were strong acid extractable, suggesting mobilization over the coming decades. Stream water concentrations of Mn and Cr were < 50µg L-1, below concentrations outlined by USEPA drinking water standards, and WHO water guidelines for Ni. These results suggest that transport of Cr, Mn, Ni, and Co from the serpentine-talc as dissolved compounds or sediments is limited by retention within silicate and oxides.

Chemical vapor deposition of TiN on a CoCrFeNi multi-principal element alloy substrate

The reactivity of a quaternary multi-principal element alloy (MPEA), CoCrFeNi, as a substrate in thermal halide chemical vapor deposition (CVD) processes for titanium nitride (TiN) coatings was studied. The coatings were deposited at 850 °C–950 °C using TiCl4, H2 and N2 precursors. The coating microstructures were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM) with energy dispersive X-ray spectroscopy (EDS). Thermodynamic calculations of substrate and coating stability for a gas phase environment of N2 and H2 within a temperature range relevant for the experiments showed that Cr is expected to form hexagonal Cr2N and cubic (Ti1−ε1Crε1)N or (Cr1−ε2Tiε2)N phases. These phases could however not be discerned in the samples by XRD after the depositions. Cr was detected at the grain boundaries and the top surface by EDS for a sample synthesized at 950 °C. Grain boundary and surface diffusion, respectively, were the suggested mechanisms for Cr transport into the coating and onto the top surface. Although thermodynamic calculations indicated that Cr is the most easily etched component of the CoCrFeNi alloy to form gaseous chlorides in similar concentrations to that of the residual Ti-chlorides, no sign of etching were found according to the imaging of the sample cross-sections using SEM and TEM. Cross-section and top surface images further confirmed that the choice of substrate had no significant detrimental influence on the film growth or microstructure.

Formation and Transport of Cr(III)-NOM-Fe Colloids upon Reaction of Cr(VI) with NOM-Fe(II) Colloids at Anoxic–Oxic Interfaces

Natural organic matter-iron (NOM-Fe) colloids are ubiquitous at anoxic-oxic interfaces of subsurface environments. Fe(II) or NOM can chemically reduce Cr(VI) to Cr(III), and the formation of Cr(III)-NOM-Fe colloids can control the fate and transport of Cr. We explored the formation and transport of Cr(III)-humic acid (HA)-Fe colloids upon reaction of Cr(VI) with HA-Fe(II) colloids over a range of environmentally relevant conditions. Cr(VI) was completely reduced by HA-Fe(II) complexes under anoxic conditions, and the formation of Cr(III)-HA-Fe colloids depended on HA concentration (or molar C/Fe ratio) and redox conditions. No colloids formed at HA concentrations below 3.5 mg C/L (C/Fe ratio below 1.6), but Cr(III)-HA-Fe colloids formed at higher HA concentrations. In column experiments, Cr(III)-HA-Fe(III) colloids formed under oxic conditions were readily transported through sand-packed porous media. Colloidal stability measurements further suggest that Cr(III)-HA-Fe colloids are highly stable and persist for at least 20 days without substantial change in particle size. This stability is attributed to the enrichment of free HA adsorbed on the Cr(III)-HA-Fe colloid surfaces, intensifying the electrostatic and/or steric repulsion interactions between particles. The new insights provided here are important for evaluating the long-term fate and transport of Cr in organic-rich redox transition zones.

A comprehensive investigation on the components in ionic liquid-based polymer inclusion membrane for Cr(VI) transport during electrodialysis

In order to explore the primary roles played by components in the polymer inclusion membrane (PIM) and their potential interactions which result in ion transport performance during electrodialysis (ED), the effect of different membrane components, i.e. base polymer, ionic liquid and plasticizer have been systematically investigated. Results showed that the roughest and least hydrophilic poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) based PIMs exhibited the best transport efficiency at the same current density (7 mA cm−2) compared to cellulose triacetate (CTA) and poly (vinyl chloride) (PVC) based membranes. The addition of ionic liquids decreased the crystallinity of CTA based PIMs, but increased the crystallinity of PVDF-HFP based PIMs through forming hydrogen bonds and thus supported the fixed-site jumping mechanism. Additionally, the membrane area resistance of PVDF-HFP based PIMs was the lowest (28.4 and 5.4 Ω cm−2 for Cyphos IL 101 and Aliquat 336, respectively). Furthermore, a proper amount of plasticizer can improve the transport efficiency of Cr(VI), which the stripping degree and permeability reached 95.9% and 35.8 μm s−1 at a stack voltage of only 2.6 V. The prepared PIM also exhibited good stability during 10 cycles running in ED. This study provides prospects and guidance to enhance the PIM properties for valuable ion recovery from various streams.

Occurrence and transfer of heavy metals in sediments and plants of Aegiceras corniculatum community in the Qinzhou Bay, southwestern China

Mangrove wetlands can reduce heavy metal pollution by trapping heavy metals. In this study, the concentration, transport and bioaccumulation of Cr, Cd, Cu, Zn and Pb in the sediments and different parts of Aegiceras corniculatum at four different sites in the Qinzhou Bay in southwestern China were investigated. The results showed that although the potential ecological risk of all five heavy metals was slight, the concentration of Cr was at a moderate pollution level due to the emissions of industries and aquaculture waste water. Core sediment records indicated that the concentrations of heavy metals at the depth of 0–20 cm were relatively high, showing an increasing trend of heavy metals over the past 20–30 years. Cr, Cu, Pb and Cd accumulated mainly in the roots of A. corniculatum, while Zn accumulated mainly in the stems. Aegiceras corniculatum showed the strongest transport capacity for Zn and Cu and the strongest bioaccumulation ability for Cd. Compared with other mangrove communities, A. corniculatum can be chosen as a restoration species in tropical and subtropical coastal zones polluted by Zn, Cu and Cd.

Features in cosmic-ray lepton data unveil the properties of nearby cosmic accelerators

We present a comprehensive discussion about the origin of the features in the leptonic component of the cosmic-ray spectrum. Working in the framework of a up-to-date CR transport scenario tuned on the most recent AMS-02 and Voyager data, we show that the prominent features recently found in the positron and in the all-electron spectra by several experiments are compatible with a scenario in which pulsar wind nebulae (PWNe) are the dominant sources of the positron flux, and nearby supernova remnants (SNRs) shape the high-energy peak of the electron spectrum. In particular we argue that the drop-off in positron spectrum found by AMS-02 at ∼ 300 GeV can be explained—under different assumptions—in terms of a prominent PWN that provides the bulk of the observed positrons in the ∼ 100 GeV domain, on top of the contribution from a large number of older objects. Finally, we turn our attention to the spectral softening at ∼ 1 TeV in the all-lepton spectrum, recently reported by several experiments, showing that it requires the presence of a nearby supernova remnant at its final stage.

AMS-02 beryllium data and its implication for cosmic ray transport

The flux of unstable secondary cosmic ray nuclei, produced by spallation processes in the interstellar medium, can be used to constrain the residence time of cosmic rays inside the Galaxy. Among them, $^{10}$Be is especially useful because of its relatively long half-life of 1.39 Myr. In the framework of the diffusive halo model we describe cosmic ray transport taking into account all relevant interaction channels and accounting for the decay of unstable secondary nuclei. We then compare our results with the data collected by the Alpha Magnetic Spectrometer (AMS-02) on board the International Space Station for the flux ratios Be/C, B/C, Be/O, B/O, C/O and Be/B as well as C, N and O absolute fluxes. These measurements, and especially the Be/B ratio, allow us to single out the flux of $^{10}$Be and infer a best fit propagation time of CRs in the Galaxy. Our results show that, if the cross sections for the production of secondary elements through spallation are taken at face value, AMS-02 measurements are compatible with the standard picture based on CR diffusion in a halo of size $H \gtrsim 5$ kpc. Taking into account the uncertainties in the cross sections, this conclusion becomes less reliable, although still compatible with the standard picture. Implications of our findings for alternative models of CR transport are discussed.

An Approach in EME: Development of Thermal and Electrical Conductivities of Membrane and Disable the Chemical Carrier in Transport Process

In this study, amine functional reduced graphene oxide (rGO-fNH2) and modified membrane was synthesized in an attempt to provide a thermal and mechanical contribution to their present performances by achieving more productive and stable membranes with the improvement of the membrane systems. So, the transport of the metal cation Cr(VI) was realized. The productivity of the membrane was increased by the transport process being realized without using a carrier on the membrane phase by modifying the membrane with rGO-fNH2. Thus, it was proved that a more productive division can be applied on a wider temperature range.When the conductivity values of the membrane were measured between 265–330 K and compared by adding different rGO-fNH2values (18.52–15.38–12.00%–8.33% w/w) to the membrane, it was seen that the conductivity values of all except for the one with the lowest compound was extremely high between these temperature ranges. Another point is that the membrane prepared as 8.33% w/w had a semi conductive feature. By applying electrical current to the membranes with polymer content (PIM) which are examples of liquid applications, the process transport time duration known as electromembrane extraction (EME) was reduced to minutes from hours. The optimized membrane includes 51.85% 2-nitrophenyl octyl ether (2-NPOE), 29.63% cellulose triacetate (CTA), 18.52% rGO-fNH2. Besides, in the experiment in which the membrane compound was 18.52 w/w; 0.5 A and 60 V was applied and within 90 min 97.41% Cr(VI) was removed from the donor phase. For a more stable process, we performed experiments with constant current instead of constant voltage. The fact that the membrane stability was over 90% even after 30 repetitions obviously showed the positive effect of the rGO-fNH2 added to the membrane.

Ion Transport Mechanisms in the Oxide Film Formed on 316L Stainless Steel Surfaces Studied by ToF-SIMS with 18O2 Isotopic Tracer

The composition and structure of the native and passive oxide films formed on 316 L stainless steel have been studied in situ by ToF-SIMS. High temperature re-oxidation experiments in isotopic 18O2 gas have also been done to assess the ion transport mechanisms in the native and passive oxide films. Duplex oxides with an inner Cr rich layer and an outer layer rich in Fe and Mo oxide have been observed on native and passive oxide films. Exposure of the oxide films to isotopic 18O2 tracer at 300 °C reveals that the outward cationic diffusion governs the inner oxide growth. The outer Mo-rich layer prevents the continued transport of Cr to the outermost surface. The passive film, due to its composition and structure, exhibits a markedly lower oxidation rate compared to native oxide films.

ACTIVATED POLYPROPYLENE MEMBRANES WITH ION-EXCHANGE POLYMERS TO TRANSPORT CHROMIUM IONS IN WATER

Polypropylene (PP) membranes were modified by in situ radical-polymerizations of functional monomers forming networks inside the pores. The main experimental conditions studied include the functional monomer concentration and crosslinking concentration. The modified membranes were characterized by scanning electron microscopy, charge density properties, and Donnan dialysis for chromium ion transport. The experimental data of the transport of Cr(III) and Cr(VI) ions were fitted to mathematical models (a polynomial fit as the first step and then the change in the concentration rates of both phases). The 4-order polynomial equation for the Cr(III) ions and the 7-order polynomial equation for the Cr(VI) ions provide better fits to the data and aid in predicting the chromium concentration values for any time.

Less metal fluxes than expected from fibrous marine sediments

Deposits of fibrous sediment, which include fiberbanks and fiber-rich sediments, are known to exist on the Swedish seafloor adjacent to coastally located former pulp and paper industries. These deposits contain concentrations of hazardous substances that exceed national background levels and contravene national environmental quality objectives (EQOs). In this study of metal fluxes from fibrous sediments using benthic flux chamber measurements (BFC) in situ we obtained detected fluxes of Co, Mo, Ni and Zn, but no fluxes of Pb, Hg and Cr. The absence of fluxes of some of the analyzed metals indicates particle bound transport of Pb, Cr and Hg from fiberbanks even though Hg might become methylated under anoxic conditions and, in that case, may enter the food chain. We found less metal fluxes than expected and thus emphasize the importance of in-situ flux measurements as a compliment to sediment metal concentrations within risk assessments of contaminated sediments.

Spectrally resolved cosmic ray hydrodynamics – I. Spectral scheme

Abstract Cosmic ray (CR) protons are an important component in many astrophysical systems. Processes like CR injection, cooling, adiabatic changes as well as active CR transport through the medium strongly modify the CR momentum distribution and have to be taken into account in hydrodynamical simulations. We present an efficient novel numerical scheme to accurately compute the evolution of the particle distribution function by solving the Fokker-Planck equation with a low number of spectral bins (10 − 20), which is required to include a full spectrum for every computational fluid element. The distribution function is represented by piecewise power laws and is not forced to be continuous, which enables an optimal representation of the spectrum. The Fokker-Planck equation is solved with a two-moment approach evolving the CR number and energy density. The low numerical diffusion of the scheme reduces the numerical errors by orders of magnitude in comparison to classical schemes with piecewise constant spectral representations. With this method not only the spectral evolution of CRs can be computed accurately in magnetohydrodynamic simulations but also their dynamical impact as well as CR ionisation. This allows for more accurate models for astrophysical plasmas, like the interstellar medium, and direct comparisons with observations.

Adsorption Characteristics and Transport Behavior of Cr(VI) in Shallow Aquifers Surrounding a Chromium Ore Processing Residue (COPR) Dumpsite

This study explored the stratigraphic distribution and soil/shallow aquifer characteristics surrounding a chromium ore processing residue (COPR) dumpsite at a former chemical factory in China. Total Cr levels in top soils (5–10 cm) nearby the COPR dumpsite were in the range of 8571.4–10711.4 mg/kg. Shallow aquifers (1–6 m) nearby the COPR dumpsite showed a maximum total Cr level of 9756.7 mg/kg. The concentrations of Cr(VI) in groundwater nearby the COPR dumpsite were 766.9–1347.5 mg/L. These results display that the top soils, shallow aquifers, and groundwater of the study site are severely polluted by Cr(VI). Then, three aquifers (silt, clay, and silty clay), respectively, collected from the depth of 1.4–2.4 m, 2.4–4.8 m, and 4.8–11.00 m were first used to evaluate the adsorption characteristics and transport behavior of Cr(VI) in shallow aquifers by both batch and column experiments. The adsorption of Cr(VI) on tested aquifers was well described by pseudo-second-order equation and Freundlich model. The adsorption capacities of Cr(VI) on three aquifers followed the order: clay &gt; silty clay &gt; silt. The kinetics proved that Cr(VI) is not easily adsorbed by the aquifer mediums but transports with groundwater. Thermodynamics indicated that Cr(VI) adsorption on tested aquifers was feasible, spontaneous, and endothermic. Cr(VI) adsorption on tested aquifers decreased with increasing pH. Furthermore, the transport of Cr(VI) in adsorption columns followed the sequence of clay &lt; silty clay &lt; silt. Desorption column experiments infer that the Cr(VI) adsorbed on aquifers will desorb and release into groundwater in the case of rainwater leaching. Therefore, a proper treatment of the COPR and a comprehensive management of soils are vital to prevent groundwater pollution.

Effects of chromium supplementation on body composition, human and animal health, and insulin and glucose metabolism.

Chromium(III) has been proposed to have a nutritional or pharmacological role in changing body composition and improving symptoms of insulin resistance, type 2 diabetes, and related conditions although the mode of action of Cr(III) at a molecular level has failed to be elucidated. This review details the current status of studies into Cr(III) supplementation. Clinical trials, meta-analyses and systematic reviews have failed to demonstrate clinically significant effects from Cr(III) supplementation on body composition or symptoms of insulin resistance and related conditions in humans and farm animals. Although new Cr(III) supplements continue to appear in the scientific literature, studies have failed to elucidate the mechanism of chromium action at a molecular level. Conflicting results on a role of transferrin in Cr(III) transport and detoxification have appeared. Cr(III) supplementation cannot currently be recommended in humans or farm animals. Further studies are required to probe the mechanism of Cr(III) action in increasing insulin sensitivity and glucose uptake in rodent models of insulin resistance and diabetes, with particular attention being turned to a potential role of transferrin in Cr(III) transport and detoxification.