Hexavalent chromium exposure alters bone remodeling in the developing tooth alveolus and delays tooth eruption / La exposición a cromo hexavalente altera la remodelación ósea del alvéolo dental en desarrollo y retarda la erupción dentaria

ABSTRACT Although it has been demonstrated that exposure of lactating rats to CrVI delays tooth eruption, the effects of CrVI exposure on bone remodeling in the developing alveolus during tooth eruption remain unknown. Our purpose was to analyze the effect of CrVI in the alveolus of the first lower molar of rats. Thirty-two suckling Wistar rats were divided into two groups. The experimental group received 12.5 mg/kg body weight/day of potassium dichromate dissolved in saline solution by oral gavage as of day 4 of the experiment; the control group received an equal dose of saline solution. Each group was divided into two sub-sets and euthanized at the ages of 9 and 15 days, respectively. Histochemical and histomorphometric studies of the bone surfaces of the developing tooth alveolus were performed. The percentage of bone formation surfaces was lower in experimental animals than in age-matched controls. The percentage of bone resorption surfaces was significantly lower in 9-day-old experimental rats than in controls and significantly higher in 15-day-old experimental rats than in controls. Exposure to CrVI during lactation alters the sequence of bone resorption and formation in the walls of the developing alveolus, both of which are necessary for tooth eruption, thus causing a delay.

RESUMEN Si bien ya ha sido demostrado que la exposición a CrVI de ratas lactantes retrasa la erupción dentaria, aún se desconocen los efectos de la exposición a CrVI que se producen sobre la modelación y remodelación de las paredes del alvéolo en formación que ocurren en los diferentes estadios de la erupción dentaria. Por tal motivo, el propósito de este trabajo fue estudiar el efecto del CrVI sobre la formación y la reabsorción óseas del alvéolo del primer molar inferior en desarrollo en ratas, a los 9 y a los 15 días de edad, que corresponden a los estadios intraóseo y de penetración mucosa de la erupción dentaria, respectivamente. El grupo experimental recibió una dosis diaria de 12,5 mg/kg de peso corporal de dicromato de potasio disuelto en solución salina por sonda bucal a partir del 4° día; mientras que el grupo control, un volumen equivalente de solución salina. Cada grupo fue dividido en 2 subgrupos de acuerdo al tiempo experimental en el que se llevó a cabo la eutanasia: 9 y 15 días de edad. Se llevaron a cabo estudios histoquímicos e histomorfométricos de las superficies óseas de los alveólos dentarios en formación. Los datos fueron analizados estadísticamente utilizando la prueba t de Student; estableciéndose un valor de p<0,05 como estadísticamente significativo. El porcentaje de superficies en formación fue menor en los animales experimentales de 9 y de 15 días de edad que en los respectivos controles. El porcentaje de superficies en reabsorción en los animales experimentales de 9 días de edad fue significativamente menor y en los animales de 15 días de edad fue significativamente mayor con respecto a sus controles. La exposición al cromo hexavalente durante la lactancia altera la secuencia de la reabsorción y la formación ósea de las paredes del alvéolo en desarrollo necesarias para que la pieza dentaria erupcione, causando su retraso. Los hallazgos obtenidos muestran la importancia del control de sustancias tóxicas en el agua potable, ya que sus efectos pueden alterar la remodelación ósea y por ende, el crecimiento y el desarrollo de los individuos que fueron expuestos durante la infancia temprana.

Evaluation of Sample Preparation Procedures for Determination of Cr(VI) in Cr2O3 Pigments by Vis Spectrophotometry

Abstract Six sample preparation procedures were evaluated for selective extraction of Cr(VI) from commercial samples of chromium oxide green (Cr2O3) pigments prior to formation of its diphenylcarbazone complex [CrDPCO]- for determination by visible spectrophotometry: (I) water-soluble chromium; (II) EPA method 3060A without Mg2+; (III) EPA method 3060A with Mg2+; (IV) Na3PO4 based extraction; (V) method IRSA16 based on acidic extraction and; (VI) Na2CO3 based extraction. Evaluation of the influence of concomitant Cr(III) ions, time and stability of the [CrDPCO]- complex was investigated. Recoveries of soluble and insoluble Cr(VI) species were 86% and 80%, respectively, using procedure (VI). Direct calibration against aqueous standards prepared in the extraction medium was successful for Cr(VI) in the concentration range 0.05-1.50 μg L-1. Limits of detection and quantitation were 0.3 µg g-1 and 1.0 µg g-1, respectively, for 250 mg subsamples/25 mL. Procedure (VI) was applied to the analysis of four commercial samples of Cr2O3 pigments, three determined to have Cr(VI) within compliance limits below 1.0 µg g-1, but one at 16.6 ± 0.6 µg g-1, prohibiting use of this pigment in cosmetic formulations. This sample was conveniently employed to evaluate the accuracy of the method. The recommended procedure is simple and accurate and has been adopted by Tecpar's laboratory of Parana Institute of Technology (Curitiba, Brazil).

Cr(VI) toxicity inhibits microbe enhanced plant growth promotion without affecting bioremediation potential

Hexavalent Chromium [Cr(VI)], a toxic inorganic pollutant of agriculture soil derived from variousanthropogenic industrial sources, disturbs vegetation and contaminates the food chain. Chromate microbialtoxicity was studied using plant growth-promoting chromate reducing Pseudomonas aeruginosa ATCCP15442 (P15). With a minimum inhibitory concentration of 1,250 µg/ml Cr(VI), the isolate is capable of 98%bioreduction of 100 µg/ml Cr(VI) in 24 hours and 83% of 500 µg/ml Cr(VI) in 72 hours. Additionally, P15shows tolerance to cross heavy metal pollutants (Cd, Pb, and Zn), halotolerance, and the production of plantgrowth-promoting substance, such as indole acetic acid (IAA), siderophore, and phosphate solubilization in thepresence and absence of Cr(VI). This study also reports that 100 and 250 µg/ml Cr(VI) decreases the productionof IAA, siderophore, and phosphate solubilization without affecting the growth or Cr(VI) bioreduction ability.In Vigna mungo seed bacterization assay, P15 is capable of enhancing root and shoot length in absence ofCr(VI) and reversing toxic effects of 100 µg/ml Cr(VI). No enhancement of plant parameters was observed athigher Cr(VI) concentrations, except reversal of Cr toxicity. These data are indication of the detrimental effectof Cr(VI) pollution on rhizospheric microbial flora associated with plant growth-promoting activities.

Diversidad bacteriana en el biocátodo reductor de Cr(VI) de una Celda de Combustible Microbiana con puente salino / Bacterial diversity in the Cr(VI) reducing biocathode of a Microbial Fuel Cell with salt bridge

Although Cr(VI)-reducing and/or tolerant microorganisms have been investigated, there is no detailed information on the composition of the microbial community of the biocathode microbial fuel cell for Cr(VI) reduction. In this investigation, the bacterial diversity of a biocathode was analyzed using 454 pyrosequencing of the 16S rRNA gene. It was found that most bacteria belonged to phylum Proteobacteria (78.8%), Firmicutes (7.9%), Actinobacteria (6.6%) and Bacteroidetes (5.5%), commonly present in environments contaminated with Cr(VI). The dominance of the genus Pseudomonas (34.87%), followed by the genera Stenotrophomonas (5.8%), Shinella (4%), Papillibacter (3.96%), Brevundimonas (3.91%), Pseu-dochrobactrum (3.54%), Ochrobactrum (3.49%), Hydrogenophaga (2.88%), Rhodococcus (2.88%), Fluviicola (2.35%), and Alcaligenes (2.3%), was found. It is emphasized that some genera have not previously been associated with Cr(VI) reduction. This biocathode from waters contaminated with tannery effluents was able to remove Cr(VI) (97.83%) in the cathodic chamber. Additionally, through use of anaerobic sludge in the anodic chamber, the removal of 76.6% of organic matter (glucose) from synthetic waste water was achieved. In this study, an efficient biocathode for the reduction of Cr(VI) with future use in bioremediation, was characterized.

Aunque se ha investigado sobre los microorganismos reductores y/o tolerantes de Cr(VI), no hay información detallada sobre la composición de la comunidad microbiana del cátodo de una Celda de Combustible Microbiana para la reducción de Cr(VI). En esta investigación se analizó la diversidad bacteriana de un biocátodo usando pirosecuenciación 454 del gen 16S rRNA. Se encontró que la mayoría de las bacterias pertenecieron a los filos Proteobac-teria (78,8%), Firmicutes (7,9%), Actinobacteria (6,6%) y Bacteroidetes (5,5%), comúnmente presentes en ambientes contaminados con Cr(VI). Se encontró como género dominante a Pseudomonas (34,87%), seguido por los géneros Stenotrophomonas (5,8%), Shinella (4%), Papil-libacter (3,96%), Brevundimonas (3,91%), Pseudochrobactrum (3,54%), Ochrobactrum (3,49%), Hydrogenophaga (2,88%), Rhodococcus (2,88%), Fluviicola (2,35%) y Alcaligenes (2,3%). Se destaca que algunos géneros no han sido previamente asociados con la reducción de Cr(VI). Este biocátodo procedente de aguas contaminadas con efluentes de curtiembres fue capaz de remover Cr(VI) (97,83%) en la cámara catódica. Adicionalmente, a través del uso de lodo anaeróbico en la cámara anódica, se logró la remoción del 76,6% de materia orgánica (glucosa) a partir de agua residual sintética. En este estudio se caracterizó un eficiente biocátodo para la reducción de Cr(VI) con futuro uso en biorremediación.

Melanin-embedded materials effectively remove hexavalent chromium (Cr) from aqueous solution

BACKGROUND@#Currently, it is recognized that water polluted with toxic heavy metal ions may cause serious effects on human health. Therefore, the development of new materials for effective removal of heavy metal ions from water is still a widely important area. Melanin is being considered as a potential material for removal of heavy metal from water.@*METHODS@#In this study, we synthesized two melanin-embedded beads from two different melanin powder sources and named IMB (Isolated Melanin Bead originated from squid ink sac) and CMB (Commercial Melanin Bead originated from sesame seeds). These beads were of globular shape and 2-3 mm in diameter. We investigated and compared the sorption abilities of these two bead materials toward hexavalent-chromium (Cr) in water. The isotherm sorption curves were established using Langmuir and Freundlich models in the optimized conditions of pH, sorption time, solid/liquid ratio, and initial concentration of Cr. The FITR analysis was also carried out to show the differences in surface properties of these two beads.@*RESULTS@#The optimized conditions for isotherm sorption of Cr on IMB/CMB were set at pH values of 2/2, sorption times of 90/300 min, and solid-liquid ratios of 10/20 mg/mL. The maximum sorption capacities calculated based on the Langmuir model were 19.60 and 6.24 for IMB and CMB, respectively. However, the adsorption kinetic of Cr on the beads fitted the Freundlich model with R values of 0.992 for IMB and 0.989 for CMB. The deduced Freundlich constant, 1/n, in the range of 0.2-0.8 indicated that these beads are good adsorption materials. In addition, structure analysis data revealed great differences in physical and chemical properties between IMB and CMB. Interestingly, FTIR analysis results showed strong signals of -OH (3295.35 cm) and -C=O (1608.63 cm) groups harboring on the IMB but not CMB. Moreover, loading of Cr on the IMB caused a shift of broad peaks from 3295.35 cm and 1608.63 cm to 3354.21 cm and 1597.06 cm, respectively, due to -OH and -C=O stretching.@*CONCLUSIONS@#Taken together, our study suggests that IMB has great potential as a bead material for the elimination of Cr from aqueous solutions and may be highly useful for water treatment applications.

Remediación de residuos sólidos contaminados con Cr(vi) por un hongo filamentoso / Remediation of waste contaminated with Cr (VI) by a filamentous fungus

La biotecnología ambiental recurre a organismos capaces de reducir los niveles de metales pesados, entre ellos el Cr(VI), contenido en residuos y efluentes agroindustriales. El objetivo del trabajo fue estudiar la biorremediación de un residuo como pulpa de limón contaminada con Cr(VI) y el efecto del metal sobre el crecimiento fúngico. Se utilizaron tres hongos filamentosos como Aspergillus niger; Penicillium expansum y P. islandicum para remediar pulpa de limón (residuo) contaminada con Cr(VI) (50 mg/L) que se realizó en las siguientes condiciones de cultivo: la pulpa se suplementó con urea, 0,006; (NH4) 2SO4, 0,012; KH2PO4,0,003 y KCl, 0,001 g/ g; 105 conidios/g, a pH 2,5, 30°C y 96 h de incubación. Se estudió el efecto tóxico de diferentes concentraciones (5; 10; 20 y 50 mg/L) del metal sobre el desarrollo del hongo de mayor eficiencia de remediación (Ef. por ciento). Aspergillus niger; obtuvo mayor EF. de remediación (97 por ciento) respecto a Penicillium expansum (95 por ciento) y P. islandicum (94 por ciento), del residuo contaminado con 50 mg/L de Cr(VI). Se determinó que la presencia de Cr(VI) y no su concentración estimuló la maduración temprana (48 h) de los conidios (blancos a negros) de A. niger, sin que se observe alteraciones en el micelio con respecto al control (72h), desarrollado en la pulpa sin el metal. En conclusión, A. niger fue más resistente y presentó altas Ef. de remediación de Cr(VI) de residuos sólidos, este proceso es una alternativa a las tecnologías físico-químicas, debido que los microorganismos pueden remover selectivamente diferentes iones de zonas contaminadas.

Environmental biotechnology uses organisms capable of reducing levels of heavy metals, including the Cr (VI), contained in waste and agro-industrial effluents. The objective of this work was to study bioremediation of waste contaminated with Cr(VI) lemon pulp and the effect of the metal on the fungal growth. We used three filamentous fungi such as Aspergillus niger; Penicillium expansum and P. islandicum to remedy pulp from lemon (residue) contaminated with Cr(VI) (50 mg/L) that was conducted in the following conditions of cultivation: the pulp is supplemented with urea, 0.006; (NH4) 2SO4, 0.012; KH2PO4, 0.003 and KCl, 0.001 g / g; 105 conidia/g, at pH 2.5, 30 ° C and 96 h of incubation. We studied the toxic effect of different concentrations (5, 10, 20 and 50 mg/L) of the metal on the development of the fungus increased efficiency of remediation (Ef. percent). Aspergillus niger; obtained greater EF. remediation (97 percent) with respect to Penicillium expansum (95 percent) and P. islandicum (94 percent), 50 mg/L of Cr (VI)-contaminated waste. It was determined that the presence of Cr (VI) and not its concentration stimulated early maturation (48 h) of conidia (white on black) from A. niger, unless you observe alterations in the mycelium as compared to the control (72 h), developed in the pulp without the metal. In conclusion, A. niger was stronger and presented high Ef. remediation of Cr (VI) waste, this process is an alternative to physico-chemical technologies, due to the micro-organisms be removed selectively different ions from contaminated areas.

Adsorción de Cr(VI) por Cocos nucífera L. en residuales de Fibrocemento en Santiago de Cuba / Cr(VI) adsorption by Cocos nucífera L. in wastewater of fibrocement from Santiago de Cuba

La adsorción y/o formación de complejos de metales pesados basados en la actividad química de la biomasa, es el proceso conocido como biosorción y es la base de una nueva tecnología para su remoción en efluentes industriales y su posterior recuperación. En esta tecnología se pueden utilizar diferentes tipos de biomasas tales como: algas, microorganismos y sub-productos agrícolas. Este trabajo estudió la adsorción de Cr(VI) utilizando la cáscara del fruto de la planta Cocos nucífera L. como biomasa orgánica. Los valores óptimos de adsorción de Cr(VI) son: pH de 3 unidades; tamaño de partícula menor que 0,074 mm; dosis de adsorbente de 5 g.dm-3 y tiempo contacto de 1 hora. A valores bajos de concentración del metal (1,0; 1,5 y 1,84 mg.dm-3) se obtuvo porcentaje de remoción superiores a 90, sin embargo a altos valores de concentración (2,5 y 3 mg.dm-3), se obtienen valores inferiores al 90 %. El proceso pudo ser estudiado a través de los modelos de Langmuir y de Freundlich, ya que el coeficiente de correlación para ambos modelos fue de 0,994 y 0,991 respectivamente. Se logra remover los iones Cr(VI) a valores de pH de 3 y 7 unidades en una matriz real, alcanzando valores de remoción de 96,85 % y 93,71 % respectivamente.

Adsorption and/or formation of complexes of heavy metals based on the chemical activity of the biomass, it is the process known as biosorption and it is the base of a new technology for its removal in industrials effluent and its posterior recuperation. In this technology, different kinds of biomasses can be utilized such as: algae, microorganisms and agricultural subproducts. In this work, the adsorption of Cr(VI) was studied utilizing the nutshell of the fruit of the plant Cocos nucífera L as organic biomass. The optimal values of adsorption of Cr(VI) are: pH of 3 units, size of particle smaller than 0.074 mm, doses of adsorbent of 5 g.dm-3 and contact time of 1 hour. At low values of concentration of the metal (1.0, 1,5 and 1.84 mg.dm-3) percentage of removal superior to 90% were obtained, however, at high values of concentration (2.5 and 3 mg.dm-3) values inferior to 90 % are obtained. The process can be studied by the models of both, Langmuir and of Freundlich, because the , coefficient of correlation for these two models was 0.994 and 0.991 respectively. The ions Cr(VI) can be removed at values of 3 and 7 units in a real matrix, reaching removal values of 96.85% and 93.71% respectively.

Impact of environmental stress on biochemical parameters of bacteria reducing chromium

Chromium pollution is produced in connection with industrial processes like in tanneries. It has been suggested that bioremediation could be a good option for clean up. The stress effect of variable chromate levels, pHs and growth temperatures on biochemical parameters of two Cr(VI) reducing bacterial strains Pseudomonas aeruginosa Rb-1 and Ochrobactrum intermedium Rb-2 was investigated. Transmission electrone microscopy (TEM) was performed to study the intracellular distribution of Cr(VI). It was observed that initial stress of 1000 µgmL-1 caused significant enhancement of all studied biochemical parameters at pH 7.0 and growth temperature of 37 °C showing great bioremediation potential of the strains. Transmission electron microscopy revealed that the distribution of chromium precipitates was not uniform as they were distributed in the cytoplasm as well as found associated with the periplasm and outer membrane. Fourier transform infrared spectroscopy showed the possible involvement of carboxyl, amino, sulpohonate and hydroxyl groups present on the bacterial cell surface for the binding of Cr(VI) ions. Cr(VI) stress brought about changes in the distridution of these functional groups. It can be concluded that the investigated bacterial strains adjust well to Cr(VI) stress in terms of biochemical parameters and along that exhibited alteration in morphology.

Evaluation of in vitro Reduction of Hexavalent Chromium by Cell-Free Extract of Arthrobacter sp. SUK 1201.

Aims: This study aims at to evaluate the hexavalent chromium [Cr(VI)] reduction potential of crude cell-free extracts of chromium resistant and reducing bacterium Arthrobacter sp. SUK 1201 and determination of optimum conditions for Cr(VI) reduction for possible bioremediation of Cr pollutants. Place and Duration of Study: Chromium reduction studies with Arthrobacter sp. SUK 1201, was undertaken in the Microbiology Laboratory, Department of Botany, University of Calcutta, Kolkata during 2010-2012. Methodology: Cell-free extract was prepared from freshly grown cell mass of Arthrobacter sp. SUK 1201 following the standard procedure. Cell mass suspended in Tris-HCl was sonicated (120 KHz for 30 min), centrifuged (12,000×g at 4ºC for 10 min) and the supernatant (S12) was used as the cell- free extract (CFE). Chromate reductase activity of the CFE was assayed colorimetrically using 1, 5-diphenylcarbazide as the complexing reagent. Results: Chromate reductase activity of CFE of Arthrobacter sp. SUK 1201 was constitutive in nature and reduced Cr(VI) with decreasing efficiency as the concentration of Cr(VI) was increased. Its Km and Vmax were 263.45 M Cr(VI) and 17.5 U mg-1 protein respectively. Reduction of Cr(VI) was optimal at pH 7 and 32ºC but was extremely thermolabile. NADH was the most suitable electron donor, and the chromate reduction was enhanced by Cu(II) and Fe(III), but inhibited by Hg(II). Among the different inhibitors tested, 2, 4-dinitrophenol (DNP) restored nearly 96.4% reductase activity, while carbonyl cyanidem- chloro phenyl hydrazone (CCCP) was most inhibitory to the process. Conclusion: It has been established that the Cr(VI) reduction potential of the cell-free extract of Arthrobacter sp. SUK 1201 is promising and could be exploited in the bioremediation of toxic hexavalent chromium.

Hexavalent chromium reduction by immobilized cells of Bacillus sphaericus AND 303

Bacillus sphaericus AND 303, a Cr(VI)-resistant and reducing bacterium reported from serpentine outcrops of Andaman was evaluated for Cr(VI) reduction using immobilized cells under batch culture. Screening of inert matrices for entrapment of whole cells indicated that polyvinyl alchohol-alginate was the most effective one reducing 87.5% of 20 µM Cr(VI) in 24 h. The rate of chromate reduction was dependent on initial Cr(VI) and biomass concentrations. The PVA cell beads were recycled three times without cell leakage and disintegration. The reduction efficiency was improved in the presence of glucose and glycerol as electron donors leading to complete reduction. However, the presence of additional metal ions was inhibitory to Cr(VI) reduction. It could be emphasized that PVA-alginate immobilized cells of B. sphaericus AND 303 could be used as a continuous bioprocess in treating Cr(VI) contaminated effluents.

Adsorção de cromo (VI) por carvão ativado granular de soluções diluídas utilizando um sistema batelada sob pH controlado

In Amazonia, chromium is mainly used in the leather and wood industries. It is responsible for many health problems, because of its toxicity. These industries remove chromium waste by various processes, such as adsorption. This work shows the results of Cr(VI) adsorption by commercial granular activated carbon (GAC) as adsorbent from diluted solutions, and batch systems with controlled pH. The functional groups on the CAG surface was carried out by the Boehm method. In addition, effect of pH on the Cr(VI) adsorption, adsorption equilibrium, and kinetic were studied under experimental conditions (pH = 6, MA = 6g, for 90min.). On the GAC surface, carboxylic groups were found to be in higher concentrations (MAS=0,43 mmol/gCAG), which increase the Cr(VI) adsorption, principally in acidic pH values. The adsorption capacity is dependent on the pH of the solution, due to its influence on the surface properties of the CAG and different ionic forms of the Cr(VI) solutions. The adsorption equilibrium data was adjusted satisfactorily by the Langmuir isotherm (R²=0,988), favorable type. From kinetics adsorption of 20 mg/L and 5 mg/L, the results were compatible with the national legislation (Res. nº 357/05). Therefore, the experimental system using (CAG) was efficient in removing the Cr(VI) from liquid streams containing low concentrations of the metal.

Na Amazônia o cromo é empregado principalmente na indústria de couro e de madeira, sendo responsável por vários problemas de saúde porque é tóxico para os seres vivos. A remoção de cromo de efluentes industriais é feita por meio de diversos processos como a adsorção. Este trabalho mostra os resultados da adsorção de Cr(VI) por carvão ativado granular comercial (CAG) como adsorvente de soluções diluídas empregando um sistema de adsorção batelada com controle de pH. Os grupos funcionais da superfície do CAG foram determinados pelo método de Boehm. Além disso, o efeito do pH na adsorção de Cr(VI), o equilíbrio e a cinética de adsorção foram estudados nas condições experimentais (pH = 6, MA = 6g, tempo de adsorção 90min.). Na superfície do CAG, os grupos carboxílicos foram determinados em maior concentração (MAS=0,43 mmol/gCAG), estes, presentes em concentrações elevadas aumentam a adsorção do metal, principalmente em valores de pH ácidos. A capacidade de adsorção é dependente do pH da solução, devido a sua influência nas propriedades de superfície do CAG e nas diferentes formas iônicas das soluções de Cr(VI). Os dados de equilíbrio da adsorção foram ajustados satisfatoriamente pela isoterma de Langmuir (R²=0,988), tipo favorável. A partir da cinética de adsorção a 5mg/L e 20mg/L, os resultados obtidos foram compatíveis com o valor limite preconizado na legislação nacional (Res. nº 357/05). Portanto, para o sistema experimental utilizando CAG foi eficiente na remoção de Cr(VI) a partir de correntes líquidas contendo baixas concentrações do metal.