Barium compounds are absorbed via ingestion and inhalation, the extent of which depends on the individual compound. In the body, the majority of the barium is found in the bone, while small amounts exists in the muscle, adipose, skin, and connective tissue. Barium is not metabolized in the body, but it may be transported or incorporated into complexes or tissues. Barium is excreted in the urine and faeces. Chromium is absorbed from oral, inhalation, or dermal exposure and distributes to nearly all tissues, with the highest concentrations found in kidney and liver. Bone is also a major storage site and may contribute to long-term retention. Hexavalent chromium's similarity to sulfate and chromate allow it to be transported into cells via sulfate transport mechanisms. Inside the cell, hexavalent chromium is reduced first to pentavalent chromium, then to trivalent chromium by many substances including ascorbate, glutathione, and nicotinamide adenine dinucleotide. Chromium is almost entirely excreted with the urine. (A12, L16, L214)
IDENTIFICATION AND USE: Barium chromate is a heavy, pale-yellow crystalline powder. It is used as pigment, almost entirely in anticorrosion jointing pastes, to prevent electro-chemical corrosion at junctions of dissimilar metals; some use in artists' colors and in coloring glass, ceramics, porcelain. Also used in metal primers, pyrotechnic compositions. HUMAN EXPOSURE AND TOXICITY: Barium chromate is cytotoxic and genotoxic to human lung cells. Genotoxicity may not be solely mediated by Cr ions, but also involve some clastogenic activity of barium ions. The clastogenic effects of barium chromate and zinc chromate were similar. ANIMAL STUDIES: No implantation site tumors were seen in 35 rats given intramuscular implantation of 25 mg barium chromate or in their controls; no implantation tumors were observed in 34 rats given intramuscular implants and observed for 27 months; controls were also negative. Thirty-one rats implanted with intrapleural barium chromate revealed only one tumor in treated rats and none in the 34 control rats. Barium chromate produced a significant level of mutations in a transgenic, V79-derived, mammalian cell line (G12).
Barium is a competitive potassium channel antagonist that blocks the passive efflux of intracellular potassium, resulting in a shift of potassium from extracellular to intracellular compartments. The intracellular translocation of potassium results in a decreased resting membrane potential, making the muscle fibers electrically unexcitable and causing paralysis. Some of these barium's effects may also be due to barium induced neuromuscular blockade and membrane depolarization. Hexavalent chromium's carcinogenic effects are caused by its metabolites, pentavalent and trivalent chromium. The DNA damage may be caused by hydroxyl radicals produced during reoxidation of pentavalent chromium by hydrogen peroxide molecules present in the cell. Trivalent chromium may also form complexes with peptides, proteins, and DNA, resulting in DNA-protein crosslinks, DNA strand breaks, DNA-DNA interstrand crosslinks, chromium-DNA adducts, chromosomal aberrations and alterations in cellular signaling pathways. It has been shown to induce carcinogenesis by overstimulating cellular regulatory pathways and increasing peroxide levels by activating certain mitogen-activated protein kinases. It can also cause transcriptional repression by cross-linking histone deacetylase 1-DNA methyltransferase 1 complexes to CYP1A1 promoter chromatin, inhibiting histone modification. Chromium may increase its own toxicity by modifying metal regulatory transcription factor 1, causing the inhibition of zinc-induced metallothionein transcription. (A12, L16, A34, A35, A36, L214)
WEIGHT OF EVIDENCE CHARACTERIZATION: Under the current guidelines (1986), Cr(VI) is classified as Group A - known human carcinogen by the inhalation route of exposure. Carcinogenicity by the oral route of exposure cannot be determined and is classified as Group D. Under the proposed guidelines (1996), Cr(VI) would be characterized as a known human carcinogen by the inhalation route of exposure on the following basis. Hexavalent chromium is known to be carcinogenic in humans by the inhalation route of exposure. Results of occupational epidemiological studies of chromium-exposed workers are consistent across investigators and study populations. Dose-response relationships have been established for chromium exposure and lung cancer. Chromium-exposed workers are exposed to both Cr(III) and Cr(VI) compounds. Because only Cr(VI) has been found to be carcinogenic in animal studies, however, it was concluded that only Cr(VI) should be classified as a human carcinogen. Animal data are consistent with the human carcinogenicity data on hexavalent chromium. Hexavalent chromium compounds are carcinogenic in animal bioassays, producing the following tumor types: intramuscular injection site tumors in rats and mice, intrapleural implant site tumors for various Cr(VI) compounds in rats, intrabronchial implantation site tumors for various Cr(VI) compounds in rats and subcutaneous injection site sarcomas in rats. In vitro data are suggestive of a potential mode of action for hexavalent chromium carcinogenesis. Hexavalent chromium carcinogenesis may result from the formation of mutagenic oxidatitive DNA lesions following intracellular reduction to the trivalent form. Cr(VI) readily passes through cell membranes and is rapidly reduced intracellularly to generate reactive Cr(V) and Cr(IV) intermediates and reactive oxygen species. A number of potentially mutagenic DNA lesions are formed during the reduction of Cr(VI). Hexavalent chromium is mutagenic in bacterial assays, yeasts and V79 cells, and Cr(VI) compounds decrease the fidelity of DNA synthesis in vitro and produce unscheduled DNA synthesis as a consequence of DNA damage. Chromate has been shown to transform both primary cells and cell lines. HUMAN CARCINOGENICITY DATA: Occupational exposure to chromium compounds has been studied in the chromate production, chromeplating and chrome pigment, ferrochromium production, gold mining, leather tanning and chrome alloy production industries. Workers in the chromate industry are exposed to both trivalent and hexavalent compounds of chromium. Epidemiological studies of chromate production plants in Japan, Great Britain, West Germany, and the United States have revealed a correlation between occupational exposure to chromium and lung cancer, but the specific form of chromium responsible for the induction of cancer was not identified ... Studies of chrome pigment workers have consistently demonstrated an association between occupational chromium exposure (primarily Cr(VI)) and lung cancer. Several studies of the chromeplating industry have demonstrated a positive relationship between cancer and exposure to chromium compounds. ANIMAL CARCINOGENICITY DATA: Animal data are consistent with the findings of human epidemiological studies of hexavalent chromium ... /Chromium (VI)/
Evaluation: There is sufficient evidence in humans for the carcinogenicity of chromium(VI) compounds. Chromium(VI) compounds cause cancer of the lung. Also positive associations have been observed between exposure to Chromium(IV) compounds and cancer of the nose and nasal sinuses. There is sufficient evidence in experimental animals for the carcinogenicity of chromium(VI) compounds. Chromium(VI) compounds are carcinogenic to humans (Group 1). /Chromium(VI) compounds/
Elimination of chromium from mice within 48 hr after intratracheal admin of barium chromate was only 12% of the dose. Among hexavalent chromium cmpd, barium chromate showed a low absorption rate near that of trivalent chromium cmpd. The biological half-time was 18 days. The amt of chromium distributed in the body was moderate. Chromium excretion was greater in feces than in urine ... .
BaCrO4 microdiscs composed of multi-layered microplates were successfully synthesized by a facile oxalate-assisted precipitation method. Based on time-dependent experiments, a dissolution–recrystallization–self-assembly process has been proposed.
Unusual aquation of Ba<sup>2+</sup>ions in the solid state: synthesis and X-ray structural and spectroscopic characterization of the novel polymeric complex salt of empirical formula {Ba<sub>6</sub>(H<sub>2</sub>O)<sub>17</sub>[Cr(ox)<sub>3</sub>]<sub>4</sub>}·7H<sub>2</sub>O (ox = oxalate dianion)
Reaction of BaII and CrIII,VI compounds with oxalates in water affords a salt of empirical formula Ba6(H2O)17[Cr(ox)3]4}·7H2O (1), consistent with the expected 3BaII/2CrIII ratio; the triclinic structure is held together by unusual water and oxalate bridges, and compound 1 proved to be suitable for the synthesis of new salts with chiral cations and anions.
Ba II和Cr III，VI化合物与草酸盐的反应水得到经验式为Ba 6（H 2 O）17 [Cr（ox）3 ] 4 }·7H 2 O（1）的盐，与预期的3Ba II / 2Cr III比值一致；三斜结构被不寻常的结合在一起水和草酸盐桥以及化合物1被证明适用于合成具有手性的新盐阳离子 和阴离子。
A New Approach to Synthesis of Layered Fluorites Containing Molecular Anions: Synthesis of Ln<sub>2</sub>O<sub>2</sub>CO<sub>3</sub>, K(LnO)CO<sub>3</sub>, and Ln<sub>2</sub>O<sub>2</sub>CrO<sub>4</sub> via Metathesis Reactions
作者：Dmitri O. Charkin、Roman O. Grischenko、Arman A. Sadybekov、Richard J. Goff、Philip Lightfoot
DOI：10.1021/ic701558m
日期：2008.4.1
layered, structure type. In addition, significantly easier and more efficient synthetic pathways were found to the known compounds [Ln2O2]K2(CO3)2 and [La2O2]CrO4. The structure of the latter compound has been determined from neutron powder diffraction data. Factors affecting reaction pathways and products are discussed, as well as prospects for applying the approach to more complex layered compounds
Application of the Taguchi Method for Optimization Experimental Condition of Synthesized Barium Chromate Nanoparticles by a Precipitation Method
作者：Iraj Kohsari、Seiedeh Somayyeh Hajimirsadeghi
DOI：10.1080/15533174.2011.568428
日期：2011.5.1
operational parameters for the synthesis of bariumchromate nanoparticles. The effect of precipitation reaction conditions on the particle size of bariumchromate was quantitavely evaluated by the analysis of variance (ANOVA). The optimum conditions for synthesis of bariumchromate nanoparticles were proposed. The results of ANOVA showed that 0.1 mol/L chromate ion concentration, 2.5 mL/min flow rate,
这项研究检查了用于合成铬酸钡纳米粒子的操作参数。通过方差分析（ANOVA）定量评估了沉淀反应条件对铬酸钡粒度的影响。提出了合成铬酸钡纳米粒子的最佳条件。方差分析的结果表明，0.1 mol / L的铬酸根离子浓度，2.5 mL / min的流速和0°C的温度是生产铬酸钡纳米颗粒的最佳条件。此外，以生物活性蛋壳膜为指导和组装模板，合成了BaCrO 4纳米超结构。通过这种方法合成的BaCrO 4纳米棒的平均直径为125 nm。
Preparation of Inorganic Compounds at Near Room Temperature by the Direct Conversion of Borate Glass in Solutions of the Corresponding Anions
作者：Wenhai Huang、Mohamed N. Rahaman、Delbert E. Day、Xin Liu
DOI：10.1111/j.1551-2916.2008.02425.x
日期：2008.7
The preparation of alkaline‐earth chromate, selenite, and stannate compounds at near room temperature by the direct conversion of borate glass in aqueous solutions of the corresponding anions was investigated. Borate glass particles (150–300 μm) with the composition 20Na2O·20CaO·60B2O3 or 20Na2O·20BaO·60B2O3 (mol%) were prepared by conventional methods and immersed in dilute solutions of K2CrO4, K2SeO3, or K2SnO3 at 37°C. The conversion of the glasses was monitored using weight loss and pH measurements, while X‐ray diffraction (XRD), X‐ray fluorescence, and scanning electron microscopy were used to characterize the structure and composition of the products. After a reaction for 140–320 h, porous crystalline products identified by XRD as CaSeO3.H2O, CaSnO3.3H2O, BaCrO4, and BaSeO3 were obtained. The conversion of fibers (0.5–1.0 mm in diameter) of the Na2O–BaO–B2O3 glass in K2CrO4 solution was pseudomorphic. The kinetics and mechanisms of the conversion process, as well as the structure of the products, are discussed.
