CrCl3 Concentration Research Articles

Catalytic conversion of sucrose to 5-hydroxymethylfurfural in green aqueous and organic medium

5-Hydroxymethylfurfural (HMF) is one of the promising chemicals, which can serve as a platform chemical to produce various energy chemicals. HMF can be produced from different lignocellulosic biomass derived sugars employing different catalytic processes. In this study, the synthesis of HMF was investigated from excessively available sucrose using environment friendly and cost-effective technology. Among the various solvents applied, dimethyl sulfoxide (DMSO) was found as an efficient organic solvent medium. The results elucidated the combination of p-toluenesulfonic acid (pTSA) and chromium chloride (CrCl3.6H2O) as the best dehydrating catalyst. A relatively higher HMF yield of 55% was achieved at a lower temperature (120 ℃) while at 150 ℃ (higher temperature) oxalic acid with higher concentration of CrCl3.6H2O gave a maximum yield of 59.21%. The time, temperature, and concentrations affected the yields. The positive impact was found with a rise in temperature from 100 to 120 ℃ in pTSA while oxalic acid affected the yield until 150 ℃. HMF yields were reported in descending order as pTSA > oxalic acid > maleic acid > malonic acid > succinic acid > blank at 120 ℃. It was observed that the isomerization of glucose to fructose is the major barrier to achieve the high process yield. Therefore, more efforts should be made to achieve the high rate of isomerization of glucose (part of sucrose disaccharide) in order to improve the HMF selectivity by depressing the humin formation.

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.

Структурные и электрофизические свойства пленок PbS, легированных Cr-=SUP=-3+-=/SUP=- в процессе химического осаждения

The evolution of the morphology, composition, structural characteristics (lattice constant, microstrains, texturing), optical and photoelectric properties of the PbS films obtained by chemical bath deposition in the presence of ammonium iodide and chromium (III) chloride at a concentration of up to 0.02 M has been studied. According to the elemental analysis by an energy dispersive X-ray spectroscopy, the chromium content in the PbS films has a nonmonotonic dependence on the CrCl3 concentration, and the largest amount is 1.08 at%. The particle size distribution is monomodal, and the average size of the particles forming the films varies from ~ 100 to ~ 225 nm with a content of 2–6% of nanoparticles. The introduction of NH4I and CrCl3 into the reactor preserves the cubic B1 structure of lead sulfide and results in an increase in the band gap Eg by 0.16–0.20 eV, a decrease in the dark resistance Rd, and an increase in the voltage sensitivity Us. The dependences of Eg and Us on the concentration of the chromium salt in the reaction bath have an extreme character with a maximum at 0.016 M, which is associated with the nonmonotonic incorporation of chromium into the PbS lattice. The results of studying the current-voltage characteristics of thin-film PbS(I) and PbS(I, Cr) layers are in good agreement with the results of the structural, optical, and photosensitive properties.

Chromium Electroplating from Cr(III) in Deep Eutectic Solvents

Hard chromium coatings are often used to improve the wear and corrosion resistance of different tools and components. Often electrolytes based on hexavalent chromium compounds, which are highly oxidative and carcinogenic, are still used to plate hard chromium layers. A key challenge is the development of an alternative baths free of Cr(VI). Such an alternative could be chromium coatings from a Cr(III)-based electrolyte.Over the last years alternative electrolytes besides water were studied for electroplating. One of these alternatives are the deep eutectic solvents, DES, of which ethaline is a prominent candidate. It is 1:2 molar ratio mixture of choline chloride and ethylene glycol. This DES show good solubility for various metal salts. The electrochemical potential window of most DES is typically in the range of 3 V. Ethaline has excellent physical and chemical properties, such as: it is stable under ambient conditions, easy to prepare and handle, cheap (manufactured on the M tons scale globally) and biodegradable (used as a B-vitamin in animal food), requires no additional registration for process applications, it has good conductivity and low viscosity.This paper will discuss the electroplating of Cr layers from ethaline on steel substrates. Different concentrations of CrCl3 × 6 H2O in the DES were investigated. The influence of LiCl, NaCl, KCl, formic acid and oxalic acid in the electrolyte as well as the influence of temperature were also investigated. Furthermore, the role of deposition technique (direct current or pulsed current) and of the hydrodynamic conditions on the quality of the chromium layers were evaluated.The electrodeposition of some µm thick and adherent chromium films was proved to be possible from ethaline. The hardness of the deposited Cr layers was up to 2500 N/mm2, depending on the process parameters.

Tribological property of MoS2-Cr3O4 nanocomposite films prepared by PVD and liquid phase synthesis

MoS2-Cr3O4 composite films were prepared by the combination method of PVD and liquid phase synthesis. The microstructure and tribological properties of films have been investigated. The results indicate that the size of Cr3O4 varied from 5 nm to 500 nm and the shape of Cr3O4 changed from nanospheres to nanorods by adjusting concentration of CrCl3. The MoS2-Cr3O4 composite films developed excellent wear resistance and much lower friction coefficient than sputtered MoS2 both in vacuum and 45%RH air. During friction, the Cr3O4@MoS2 core-shell structure with Cr3O4 core of high hardness and soft MoS2 shells were formed and played the role of nano-bearing, which reduced the friction and wear of the composite film. Besides, better oxidation resistance and tribological property of the MoS2-Cr3O4 composite films in humid air were attributed to the Cr3O4 nanoparticles, which occupied the most of dangling bond sites.

Effects of Process Parameters and CrCl3 Concentration on the Structure, Surface Morphology, Composition and Corrosion Resistance of Electrodeposited NiCrP Amorphous Alloy Coatings

Herein, NiCrP amorphous alloy coatings were prepared on copper substrates by electrodeposition. The aim of this paper is to replace Cr6+ with Cr3+ to prepare NiCrP amorphous alloy coating, which can reduce environmental pollution. By studying the influence of pH, temperature (T), current density (DK), and CrCl3 concentration on the structure, surface morphology, composition, and corrosion resistance of the alloy coatings, the optimum bath formulation and process parameters were determined as follows: 25 g·L−1 NiSO4·6H2O, 100 g·L−1 CrCl3·6H2O, 20 g·L−1 NaH2PO2·H2O, 80 g·L−1 Na3C6H5O7·2H2O (sodium citrate), 40 g·L−1 H3BO3, 50 g·L−1 NH4Cl, 1 g·L−1 KF, 5 g·L−1 C7H5O3NS (saccharin), 0.05 g·L−1 C12H25SO4Na (sodium dodecyl sulfate), and 40 mL·L−1 HCOOH and T: 30 °C, DK: 15 A·dm−2, and pH: 3.5, respectively. NiCrP amorphous alloy coatings with high corrosion resistance were prepared under the abovementioned conditions. The crystal cells of the coating surface are uniform and fine. The corrosion resistance of the NiCrP amorphous alloy coatings was characterized by polarization curves, electrochemical impedance spectroscopy, and an immersion corrosion test and compared with that of the NiP amorphous alloy coating. The results show that Ni91.9P8.1 and Ni83.5Cr8.3P8.2 corrosion potential and corrosion current density are −0.68, −0.44 V, and 36, 7 μA·cm−2 in 3.5 wt.% NaCl, respectively. With Ni91.9P8.1 and Ni83.5Cr8.3P8.2, the maximum weight loss is 61.67 and 15.42 mg·dm−2 in a 1 mol·L−1 HCl, respectively. The corrosion resistance of the NiCrP amorphous alloy coatings in 3.5 wt.% NaCl and 1 mol·L−1 HCl solutions is better than that of the NiP alloy coating.

Preparation of Ganoderma lucidum polysaccharide‑chromium (III) complex and its hypoglycemic and hypolipidemic activities in high-fat and high-fructose diet-induced pre-diabetic mice

Polysaccharide from Ganoderma lucidum is one of the best metal-ion chelating agents because of its structural characteristics and excellent functional activities. In this study, we synthesized and characterized a novel G. lucidum polysaccharide‑chromium (III) [GLP-Cr(III)] complex. Response surface methodology (RSM) was used to optimize the reaction conditions for the maximum chelation rate of GLP-Cr(III) complex. The optimal reaction conditions obtained from RSM were as follows: concentration of CrCl3 5.71 mg/mL, pH 6.36, temperature 66.4 °C and time 2.0 h, respectively. The pH was the most significant factor, followed by reaction temperature and CrCl3 concentration. Under the optimal conditions, the experimental chelation rate was 94.17 ± 1.0% for GLP-Cr(III) complex, which agreed closely with the predicted value (94.60%). Fourier transform infrared (FT-IR) spectroscopy revealed that the primary sites of chromium (III)-binding in G. lucidum polysaccharide were OH and CO groups, which induce the morphology change from flat sheet to rough surface. Meanwhile, according to the result of X-ray diffraction (XRD), the crystal degree of GLP was disappeared after chelation with Cr(III). The presence of a “blind zone” in the 1H NMR spectrum obviously indicated the binding of Cr(III) to GLP. Additionally, the effects of GLP-Cr(III) complex on hyperglycemia and hyperlipidemia in high fructose and fat diet-induced pre-diabetic mice were also investigated. Results showed that the serum total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), fasting blood glucose levels and glucose tolerance in mice supplemented with GLP-Cr(III) complex (50 mg/kg day) were significantly lower than the model group (P < 0.01). More importantly, the GLP-Cr(III) complex had no significant adverse effects on the physiological metabolism, organ index, and liver tissue morphology of mice fed a normal diet. These results suggest that GLP-Cr(III) complex could be used as potential functional food ingredients for the prevention or treatment of hyperglycemia and hyperlipidemia.

Brønsted and Lewis acid catalyzed conversion of pulp industry waste biomass to levulinic acid

Enormous amounts of fiber sludge are generated annually by the pulp industry as a by-product. As a cellulose-rich material, its current usage, mainly as fuel, is inefficient from a material efficiency point of view. This work studied the utilization of fiber sludge from a Finnish and a Swedish pulp mill as a potential feedstock to produce levulinic acid, a valuable platform chemical. The conversion experiments of fiber sludge to levulinic acid were performed in a microwave reactor with a mixture of H2SO4 and Lewis acid as the catalyst. The reaction conditions, which included reaction time and temperature as well as the H2SO4 and Lewis acid concentrations, were studied in detail. The highest levulinic acid yield, 56%, was obtained with Swedish fiber sludge after 60 min at 180 °C with the H2SO4 concentration of 0.3 mol/L and a CrCl3 concentration of 7.5 mmol/L which indicated that the fiber sludge had the potential to be used as feedstock for levulinic acid production.

Preparation of a novel Grifola frondosa polysaccharide-chromium (III) complex and its hypoglycemic and hypolipidemic activities in high fat diet and streptozotocin-induced diabetic mice.

Polysaccharide from Grifola frondosa is one of the best metal-ion chelating agents because of its structural characteristics and excellent functional activities. In this study, we synthesized and characterized a novel Grifola frondosa polysaccharide-chromium (III) [GFP-Cr(III)] complex. Response surface methodology (RSM) was used to optimize the reaction conditions for the maximum chelation rate of GFP-Cr(III) complex. The optimal reaction conditions obtained from RSM were as follows: concentration of CrCl3 6.97 mg/mL, pH 7.75 and temperature 71.73 °C, respectively. The pH was the most significant factor, followed by reaction temperature and concentration of CrCl3. Under the deduced optimal conditions (CrCl3 7.0 mg/mL, pH 7.7 and temperature 70.0 °C), the experimental chelation rate was 28.01% ± 0.18% for GFP-Cr(III) complex, which agreed closely with the predicted value (27.61%). Fourier transform infrared (FTIR) spectroscopy revealed that the primary sites of chromium (III)-binding in polysaccharides were OH and CN groups, leading to the structure of GFP-Cr(III) complex was loose than the original polysaccharide. Nevertheless, Cr(III) did not make a fundamental change in the structure of GFP when comparing the FTIR spectra of GFP and GFP-Cr(III) complex. Additionally, the effects of GFP-Cr(III) complex on hyperglycemia and hyperlipidemia in high-fat diet (HFD) and streptozotocin (STZ)-induced diabetic mice were also investigated. Results showed that the serum total cholesterol (TC), total triglyceride (TG), low density lipoprotein cholesterol (LDL-C), fasting blood glucose levels and glucose tolerance in diabetic mice fed a high-fat diet (HFD) supplemented with GFP-Cr(III) complex (900 mg/kg day) were significantly lower than the diabetic group (P < 0.01). These results suggest that GFP-Cr(III) complex could be used as potential functional food ingredients for the prevention or treatment of hyperglycemia and hyperlipidemia.

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.

Effects of chromic chloride on chick embryo fibroblast viability

The objective of this study is to evaluate the effects of chromic chloride (CrCl3) on chick embryo fibroblast (CEF) viability. The cells were incubated with CrCl3 (0.02, 0.1, 0.5, 2.5, 12.5, and 62.5μM), and the viability was determined using MTT assay, morphological detection and flow cytometry. The results show that lower concentrations of CrCl3 (0.02, 0.1, and 0.5μM) did not damage CEF viability. At 0.1μM, CrCl3 can increase CEF viability (P<0.05). However, at higher concentrations of CrCl3 (2.5, 12.5, and 62.5μM), the number of apoptotic and necrotic cells (P<0.01) and intracellular reactive oxygen species (P<0.01) increased. In addition, decreased mitochondrial membrane potential (P<0.01) and enhanced intracellular calcium levels (P<0.01) were observed after the exposure. Moreover, apoptotic morphological changes induced by these processes in CEF were confirmed using Hoechst 33258 staining. Cell death induced by higher concentrations of CrCl3 was caused by an apoptotic and a necrotic mechanism, whereas the main mechanism of oxidative stress and induced mitochondrial dysfunction was apoptotic death. The induced apoptotic death in CEF is concentration- and time-dependent.

Electrode processes and their kinetic parameters in the reduction and oxidation of Cr(III) and Cr(II) in molten CsCl

The reduction of chromium ions in the CsCl-CrCl3 melt in wide concentration and temperature ranges is reported. It is assumed that the melt contains polynuclear chromium complexes. The reduction of Cr(III) to Cr(II) is a reversible one-electron process. The electroreduction of divalent chromium to chromium metal is an irreversible process involving dinuclear and mononuclear chromium complex ions. The electron transfer rate constant has been calculated for various temperatures and chromium chloride concentrations in the salt melt. The activation energy of electron transfer and its dependence on the CrCl3 concentration in the electrolyte have been determined for the Cr(III) ↔ Cr(II) process.

Potential for desalination using lower critical solution temperature polymers: Concentration of salt solutions by pluronic PE6200

AbstractA commercially available lower critical solution temperature (LCST) polymer was demonstrated to preferentially adsorb water containing a reduced ion concentration, from CrCl3 salt solutions and release some of this scavenged water at higher temperatures. The scavenging ability of the polymer was demonstrated to be dependent on the bulk salt concentration. The volume of water scavenged and the concentration of the remaining CrCl3 solution increased linearly with the amount of LCST polymer (Pluronic PE 6200) used. Both the volume of water removed and the amount by which the remaining CrCl3 solution was concentrated decreased with increasing CrCl3 concentration. Implications for research into a novel method for sea water desalination are addressed. We also show water extraction from dilute sodium chloride and sea water, and that these results are consistent with the CrCl3 model system. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Bioeffects of chromium(III) on the growth of Spirulina platensis and its biotransformation

AbstractBACKGROUND: In this study the bioeffects of chromium(III) (Cr(III)) on the growth of Spirulina platensis and its biotransformation were investigated. Spirulina platensis was batch cultured in Zarrouk medium containing different concentrations of CrCl3 · 6H2O. Total and organic Cr contents in S. platensis were determined by inductively coupled plasma mass spectrometry (ICP‐MS), and Cr speciation was assayed by high‐performance liquid chromatography/ICP‐MS.RESULTS: Results based on the dry weight, growth curve, chlorophyll yield and morphology change of S. platensis indicated that the growth of S. platensis was facilitated by Cr(III) below 4.51 mol L−1 and inhibited by a higher concentration of Cr(III). It was found that Cr(III) could be accumulated efficiently in S. platensis, with a highest Cr yield of 173.17 g kg−1 and a highest organic Cr proportion of 50.19 g kg−1 (96.04% of the total concentration of Cr). No evidence of oxidation of Cr(III) to Cr(VI) in S. platensis cells was found.CONCLUSION: The results of this study suggest that S. platensis could potentially be used as a safe food carrier to accumulate Cr(III) through some metabolic process. Copyright © 2009 Society of Chemical Industry

Effect of chromium chloride on the mechanical and dielectric properties of EPDM rubber

Measurements of Young’s modulus, dielectric loss and a.c. conductivity have been carried out on EPDM rubber samples loaded with different concentrations of CrCl3 (0,2,4 and 6 phr). The values of Young’s modulus was found to be linearly dependent on the CrCl3 content. Variation of the dielectric loss with temperature showed that CrCl3 may act as plasticizer. However, at higher frequencies the dielectric loss was found to be independent of frequency and the rubber samples may behave as non-polar dielectric. Investigations of the a.c conductivity suggested that the conduction in these rubber samples can be described by small polaron tunneling. In addition, conductivity was found to increase with CrCl3 content.

The use of positron annihilation lifetime technique to study the effect of doping metal salts on polyhydroxamic acid polymers

Polyhydroxamic acid (PHA) from polymethacrylamide (PMAA) was prepared. Chromium chloride (CrCl3) and ferric chloride (FeCl3) salts were added to the polymer in order to increase its electrical conductivity, i.e., the dopants help produce semiconducting properties. The positron annihilation lifetime technique spectroscopy (PALS) was used to study the changes in the free volume as a function of FeCl3 and CrCl3 concentrations. ortho-Positronium lifetime components were used to estimate the free volume parameters. It was found that the hole size and the total free volume fraction decreased with FeCl3 concentration. On the other hand, the hole size increased slightly with CrCl3 concentration and then decreased, while the total free volume fraction increased continuously. The free volume distributions were determined from ortho-positronium distributions. The electric conductivity as a function of FeCl3 and CrCl3 concentrations showed fluctuation behavior and showed a continuous increase with the increase in temperature. The correlation between positron annihilation parameters and electric conductivity were discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2095–2101, 2001

Electrochemistry of molten LiCl–KCl–CrCl3 and LiCl–KCl–CrCl2 mixtures

Chemical reactions during dissolution of CrCl3 or CrCl2 in molten LiCl–KCL eutectic have been demonstrated to occur, but the nature of the reactions is not yet well understood. Reduction of CrCl3 to chromium metal occurs through two well-characterized electrochemical steps, at approximately +0.1 and –0.9 V vs Ag/AgCl. Each step was studied in the 0.025–0.085 molar CrCl3 concentration range, at various temperatures between 375 and 550 °C. The Cr(iii)/Cr(ii) electron transfer step exhibited reversible behaviour under all the experimental conditions studied. In contrast, the Cr(ii)/Cr(0) step could involve Cr(ii) adsorbed species and initial chromium electrocrystallization phenomena, mainly depending on the nature of the substrate.

Induction of 8-hydroxydeoxyguanosine in DNA by chromium(III) plus hydrogen peroxide and its prevention by scavengers.

The capability of Cr(III) to induce DNA lesions generated by oxidative damage was investigated in this study by examining the formation of 8-hydroxydeoxyguanosine (8-OHdG) in calf thymus DNA by CrCl3 and/or H2O2 in 10 mM phosphate buffer. In the presence of 0.5 mM H2O2, the formation of 8-OHdG markedly increased with increasing CrCl3 concentration. In contrast, H2O2 or CrCl3 alone did not cause any increase in 8-OHdG level above background. The amount of 8-OHdG induced by CrCl3 plus H2O2 was time dependent; its generation increased linearly over an incubation period of 90 min. The formation of 8-OHdG was unfavorable in an acidic solution (pH < 6); the highest level of 8-OHdG was observed at pH 7-8. Scavengers of reactive oxygen species markedly inhibited the formation of 8-OHdG by CrCl3 plus H2O2; the inhibition effect was sodium azide > D-mannitol > Tris-HCl at an equal concentration. The induction of 8-OHdG by CrCl3 plus H2O2 remained unchanged in D2O. Moreover, an addition of catalase (2.2 U/ml) to the reaction mixture completely inhibited the formation of 8-OHdG by CrCl3/H2O2, whereas only 22% of that formation was inhibited by superoxide dismutase (11 U/ml). A large amount of bovine serum albumin (1.1 mg/ml) could reduce the formation of 8-OHdG by CrCl3 plus H2O2, thereby implying that Cr(III)-mediated DNA-protein crosslinks are unfavorable for 8-OHdG formation. Furthermore, ascorbate could prevent the formation of 8-OHdG by CrCl3 plus H2O2; the extent of prevention increased with increasing ascorbate concentration (10 microM-3 mM). Thus, ascorbate acts as a free radical scavenger in the CrCl3/H2O2 system. The above findings suggest that Cr(III)/H2O2 could generate oxidative damage to DNA, possibly through a Fenton-like reaction, i.e. Cr(III)+H2O2-->Cr(IV)+.OH+OH-. This study also indicates that Cr(III), previously considered as the ultimate kinetically stable species of Cr(VI) metabolites, is capable of inducing carcinogenic lesions through interaction with a cellular oxygen species.

Genotoxicity of chromiumin vitroon yeast: Interaction with DNA†

The genotoxicity of chromium chloride was investigated in cells of D7 strain of Saccharomyces cerevisiae harvested either from logarithmic or stationary growth phase. A weak induction of mifotic gene conversion and point reverse mutation was obtained when the incubations were performed using phosphate buffer. No genetic effect was observed when the incubations were performed using Tris‐HCl buffer. The experiments with 51Cr radiotracer demonstrated that Cr3+ ion enters the yeast cells and binds to DNA even if the incubation mixture was performed with Tris HCl buffer. This behaviour could be due to the highest concentration of CrCl3 that cause some damages to cytoplasmatic membrane.

Sister chromatid exchanges in Chinese hamster V79 cells treated with the trivalent chromium compounds chromic chloride and chromic oxide.

The induction of sister chromatid exchanges (SCEs) in Chinese hamster V79 cells exposed to soluble CrCl3 and insoluble Cr2O3, compounds of trivalent chromium (Cr3+), was determined. Their ability to induce SCEs was compared with those of three hexavalent chromium (Cr6+) compounds: K2CrO4, Na2CrO4 and Na2Cr2O7. Both the delay in progression through the cell cycle induced by Cr3+ compounds and the SCE frequencies in the delayed cells were also evaluated. The exposure for 28 h to CrCl3 and Cr2O3 at concentrations of 9.7-39 micrograms and of 34-136 micrograms of Cr3+ per ml, respectively, induced a statistically significant (p less than 0.001) dose-dependent increase in SCEs up to 1.9-fold (CrCl3) and 4-fold (Cr2O3) over control levels. Compared with the effective concentrations of Cr6+ compounds, which produced up to 4-fold increase of SCEs, inducing concentrations of CrCl3 and Cr2O3 were 300- and 1000-fold higher in terms of chromium. By prolongation of treatment time up to 48 h, a progressive dose- and time-related enhancement in SCE frequencies induced by Cr3+ compounds in delayed cells was observed. Lower concentrations of Cr2O3, without effect after 28 h of treatment, induced an increase of SCEs by prolongation of exposure time.