Isolation and identification of a new Bacillus glycinifermentans strain from date palm rhizosphere and its effect on barley seeds under heavy metal stress.

Soil contamination by heavy metals is one of the major problems that adversely decrease plant growth and biomass production. Inoculation with the plant growth-promoting rhizobacteria (PGPR) can attenuate the toxicity of heavy metals and enhancing the plant growth. In this study, we evaluated the potential of a novel extremotolerant strain (IS-2 T) isolated from date palm rhizosphere to improve barley seedling growth under heavy metal stress. The species-level identification was carried out using morphological and biochemical methods combined with whole genome sequencing. The bacterial strain was then used in vitro for inoculating Hordeum vulgare L. exposed to three different Cr, Zn, and Ni concentrations (0.5, 1, and 2 mM) in petri dishes and different morphological parameters were assessed. The strain was identified as Bacillus glycinifermentans species. This strain showed high tolerance to pH (6-11), salt stress (0.2-2 M), and heavy metals. Indeed, the minimum inhibitory concentrations at which bacterium was unable to grow were 4 mM for nickel, 3 mM for zinc, more than 8 mM for copper, and 40 mM for chromium, respectively. It was observed that inoculation of Hordeum vulgare L. under metal stress conditions with Bacillus glycinifermentans IS-2 T stain improved considerably the growth parameters. The capacity of the IS-2 T strain to withstand a range of abiotic stresses and improve barley seedling development under lab conditions makes it a promising candidate for use as a PGPR in zinc, nickel, copper, and chromium bioremediation.

A comparative study on chromium-induced micronuclei assessment in the peripheral blood of Hsd:ICR mice.

This study investigated the genotoxic effects of chromium (Cr) in Hsd:ICR mice, considering factors such as oxidative state, apoptosis, exposure pathway, duration, pregnancy, and transplacental exposure. Genotoxicity was assessed using the erythrocytes' micronucleus (MN) assay, while apoptosis was evaluated in nucleated blood cells. The results showed that Cr(III) (CrK(SO4 )2 and CrCl3 ) did not induce any marked genotoxic damage. However, Cr(VI) (CrO3 , K2 Cr2 O7 , Na2 Cr2 O7 , and K2 CrO4 ) produced varying degrees of genotoxicity, with CrO3 being the most potent. MN frequencies increased following 24-h exposure, with a greater effect in male mice. Administering 20 mg/kg of CrO3 via gavage did not lead to significant effects compared to intraperitoneal administration. Short-term oral treatment with a daily dose of 8.5 mg/kg for 49 days elevated MN levels only on day 14 after treatment. Pregnant female mice exposed to CrO3 on day 15 of pregnancy exhibited reduced genotoxic effects compared to nonpregnant animals. However, significant increases in MN levels were found in their fetuses starting 48 h after exposure. In summary, data indicate the potential genotoxic effects of Cr, with Cr(VI) forms inducing higher genotoxicity than Cr(III). These findings indicate that gender, exposure route, and pregnancy status might influence genotoxic responses to Cr.

Alleviation of chromium toxicity in mung bean (Vigna radiata L.) using salicylic acid and Azospirillum brasilense.

BACKGROUND: Chromium (Cr) contamination in soil poses a serious hazard because it hinders plant growth, which eventually reduces crop yield and raises the possibility of a food shortage. Cr's harmful effects interfere with crucial plant functions like photosynthesis and respiration, reducing energy output, causing oxidative stress, and interfering with nutrient intake. In this study, the negative effects of Cr on mung beans are examined, as well as investigate the effectiveness of Azospirillum brasilense and salicylic acid in reducing Cr-induced stress. RESULTS: We investigated how different Cr levels (200, 300, and 400 mg/kg soil) affected the growth of mung bean seedlings with the use of Azospirillum brasilense and salicylic acid. Experiment was conducted with randomized complete block design with 13 treatments having three replications. Significant growth retardation was caused by Cr, as were important factors like shoot and root length, plant height, dry weight, and chlorophyll content significantly reduced. 37.15% plant height, 71.85% root length, 57.09% chlorophyll contents, 82.34% crop growth rate was decreased when Cr toxicity was @ 50 µM but this decrease was remain 27.80%, 44.70%, 38.97% and 63.42%, respectively when applied A. brasilense and Salicylic acid in combine form. Use of Azospirillum brasilense and salicylic acid significantly increased mung bean seedling growth (49%) and contributed to reducing the toxic effect of Cr stress (34% and 14% in plant height, respectively) due to their beneficial properties in promoting plant growth. CONCLUSIONS: Mung bean seedlings are severely damaged by Cr contamination, which limits their growth and physiological characteristics. Using Azospirillum brasilense and salicylic acid together appears to be a viable way to combat stress brought on by Cr and promote general plant growth. Greater nutrient intake, increased antioxidant enzyme activity, and greater root growth are examples of synergistic effects. This strategy has the ability to reduce oxidative stress brought on by chromium, enhancing plant resistance to adverse circumstances. The study offers new perspectives on sustainable practices that hold potential for increasing agricultural output and guaranteeing food security.

Biomass production and uptake of sulfur, chromium and micronutrients by Tanzania guinea grass grown with sulfur and chromium.

Soil contamination caused by improper waste disposal can affect plant growth. Tropical forage plants have rapid growth, high biomass production and vigorous regrowth. Chromium (Cr) is one of the most common contaminants in the environment. Sulfur (S) is a nutrient involved in various cell detoxification processes. The objective was to assess the effects of excess Cr on biomass production and concentrations of this metal, S and cationic micronutrients, under conditions of varying supply of S for Tanzania guinea grass. The experiment was conducted in randomized complete blocks in a 3 × 4 factorial scheme, corresponding to three levels of S (0.1, 1.9 and 3.7 mmol L-1) and four levels of Cr (0.0, 0.5, 1.0 and 2.0 mmol L-1) in three replicates. Root surface area, shoot and root biomass production, concentrations of total S, sulfate-S, Cr and cationic micronutrients, and Cr transport factor were determined. S level of 1.9 mmol L-1 reduced the toxicity by Cr in Tanzania guinea grass, expressed by the higher shoot and root dry weight production, greater stability in the cellular concentration of sulfate-S and higher concentrations of micronutrients. It was concluded that the high availability of S reduced the toxicity by Cr(VI) in Tanzania guinea grass, expressed by the higher shoot and root dry weight production, greater stability in the cellular concentration of sulfate-S and higher concentration of micronutrients in the grass shoots.

Isolation and screening of chromium resistant bacteria from industrial waste for bioremediation purposes / Isolamento e triagem de bactérias resistentes ao cromo de resíduos industriais para fins de biorremediação

Chromium (VI) a highly toxic metal, a major constituent of industrial waste. It is continuously release in soil and water, causes environmental and health related issues, which is increasing public concern in developing countries like Pakistan. The basic aim of this study was isolation and screening of chromium resistant bacteria from industrial waste collected from Korangi and Lyari, Karachi (24˚52ʹ46.0ʺN 66˚59ʹ25.7ʺE and 24˚48ʹ37.5ʺN 67˚06ʹ52.6ʺE). Among total of 53 isolated strains, seven bacterial strains were selected through selective enrichment and identified on the basis of morphological and biochemical characteristics. These strains were designated as S11, S13, S17, S18, S30, S35 and S48, resistance was determined against varying concentrations of chromium (100-1500 mg/l). Two bacterial strains S35 and S48 showed maximum resistance to chromium (1600 mg/l). Bacterial strains S35 and S48 were identified through 16S rRNA sequence and showed 99% similarity to Bacillus paranthracis and Bacillus paramycoides. Furthermore, growth condition including temperature and pH were optimized for both bacterial strains, showed maximum growth at temperature 30ºC and at optimum pH 7.5 and 6.5 respectively. It is concluded that indigenous bacterial strains isolated from metal contaminated industrial effluent use their innate ability to transform toxic heavy metals to less or nontoxic form and can offer an effective tool for monitoring heavy metal contamination in the environment.(AU)

O cromo (VI), metal altamente tóxico, é um dos principais constituintes dos resíduos industriais. É liberado no solo e na água, causa problemas ambientais e de saúde de crescente preocupação pública em países em desenvolvimento como o Paquistão. O objetivo básico deste estudo foi o isolamento e a triagem de bactérias resistentes ao cromo de resíduos industriais coletados em Korangi e Lyari, Karachi (24˚5246,0”N 66˚5925,7”E e 24˚4837,5”N 67˚0652,6”E). Do total de 53 cepas isoladas, sete cepas bacterianas foram selecionadas por enriquecimento seletivo e identificadas com base em características morfológicas e bioquímicas. Essas cepas foram designadas como S11, S13, S17, S18, S30, S35 e S48, apresentaram alta resistência aos metais contra concentrações variáveis (100-1500 mg / l) de cromo. Já as cepas S35 e S48 foram identificadas por meio da sequência 16S rRNA e apresentaram 99% de similaridade com Bacillus paranthracis e Bacillus paramycoides. Além disso, as condições de crescimento incluindo temperatura e pH foram otimizadas e ambas as cepas bacterianas apresentaram crescimento máximo na temperatura de 30ºC, enquanto seu pH ótimo foi observado em 7,5 e 6,5, respectivamente. Conclui-se que o potencial de resistência dessas bactérias resistentes ao cromo pode ser efetivamente utilizado na remoção de cromo de efluentes industriais contaminados. Técnicas de base biológica usando bactérias ajudarão a fornecer métodos mais baratos e ecológicos de remoção, recuperação e desintoxicação de cromo.(AU)

Isolation and screening of chromium resistant bacteria from industrial waste for bioremediation purposes / Isolamento e triagem de bactérias resistentes ao cromo de resíduos industriais para fins de biorremediação

Chromium (VI) a highly toxic metal, a major constituent of industrial waste. It is continuously release in soil and water, causes environmental and health related issues, which is increasing public concern in developing countries like Pakistan. The basic aim of this study was isolation and screening of chromium resistant bacteria from industrial waste collected from Korangi and Lyari, Karachi (24˚52ʹ46.0ʺN 66˚59ʹ25.7ʺE and 24˚48ʹ37.5ʺN 67˚06ʹ52.6ʺE). Among total of 53 isolated strains, seven bacterial strains were selected through selective enrichment and identified on the basis of morphological and biochemical characteristics. These strains were designated as S11, S13, S17, S18, S30, S35 and S48, resistance was determined against varying concentrations of chromium (100-1500 mg/l). Two bacterial strains S35 and S48 showed maximum resistance to chromium (1600 mg/l). Bacterial strains S35 and S48 were identified through 16S rRNA sequence and showed 99% similarity to Bacillus paranthracis and Bacillus paramycoides. Furthermore, growth condition including temperature and pH were optimized for both bacterial strains, showed maximum growth at temperature 30ºC and at optimum pH 7.5 and 6.5 respectively. It is concluded that indigenous bacterial strains isolated from metal contaminated industrial effluent use their innate ability to transform toxic heavy metals to less or nontoxic form and can offer an effective tool for monitoring heavy metal contamination in the environment.

O cromo (VI), metal altamente tóxico, é um dos principais constituintes dos resíduos industriais. É liberado no solo e na água, causa problemas ambientais e de saúde de crescente preocupação pública em países em desenvolvimento como o Paquistão. O objetivo básico deste estudo foi o isolamento e a triagem de bactérias resistentes ao cromo de resíduos industriais coletados em Korangi e Lyari, Karachi (24˚52’46,0”N 66˚59’25,7”E e 24˚48’37,5”N 67˚06’52,6”E). Do total de 53 cepas isoladas, sete cepas bacterianas foram selecionadas por enriquecimento seletivo e identificadas com base em características morfológicas e bioquímicas. Essas cepas foram designadas como S11, S13, S17, S18, S30, S35 e S48, apresentaram alta resistência aos metais contra concentrações variáveis (100-1500 mg / l) de cromo. Já as cepas S35 e S48 foram identificadas por meio da sequência 16S rRNA e apresentaram 99% de similaridade com Bacillus paranthracis e Bacillus paramycoides. Além disso, as condições de crescimento incluindo temperatura e pH foram otimizadas e ambas as cepas bacterianas apresentaram crescimento máximo na temperatura de 30ºC, enquanto seu pH ótimo foi observado em 7,5 e 6,5, respectivamente. Conclui-se que o potencial de resistência dessas bactérias resistentes ao cromo pode ser efetivamente utilizado na remoção de cromo de efluentes industriais contaminados. Técnicas de base biológica usando bactérias ajudarão a fornecer métodos mais baratos e ecológicos de remoção, recuperação e desintoxicação de cromo.

Ellagic acid ameliorates hexavalent chromium-induced renal toxicity by attenuating oxidative stress, suppressing TNF-α and protecting mitochondria.

Nephrotoxicity is an important adverse effect of oxidative stress induced by hexavalent chromium [Cr(VI)]. The effect of ellagic acid, a dietary polyphenolic compound with potent antioxidant activity, was investigated in Cr(VI)-induced kidney injury. Six groups of male Wistar rats were treated intragastrically with vehicle or ellagic acid (15 and 30 mg/kg) for 10 days. On day 10, rats received saline or Cr(VI) (K2Cr2O7 15 mg/kg) subcutaneously. Cr(VI) significantly increased kidney weight, affected kidney function assessed by biomarkers in blood and urine (protein, creatinine and urea nitrogen), caused histological changes (tubular injury and glomerular capillary tuft damage), increased markers of oxidative stress and reduced the activity of antioxidant enzymes. In addition, Cr(VI) altered mitochondrial ultrastructure, impaired mitochondrial respiration, increased lipid peroxidation, and inhibited the function of mitochondrial enzymes. Pretreatment with ellagic acid (30 mg/kg) attenuated all the aforementioned alterations. Furthermore, we explored whether ellagic acid might regulate the tumor necrosis factor-alpha (TNF-α)/receptor-interacting protein kinase 3 (RIPK3) pathway, reducing Cr(VI)-induced tubular necrosis. Cr(VI) upregulated both TNF-α and RIPK3, but ellagic acid only decreased TNF-α levels, having no effect on RIPK3 content. Therefore, understanding the mechanisms through which Cr(VI) promotes necroptosis is crucial for future studies, in order to design strategies to mitigate kidney damage. In conclusion, ellagic acid attenuated Cr(VI)-induced renal alterations by preventing oxidative stress, supporting enzymatic activities, suppressing TNF-α, and preserving mitochondrial ultrastructure and function, most likely due to its antioxidant properties.

Protective Effect of Resveratrol against Hexavalent Chromium-Induced Genotoxic Damage in Hsd:ICR Male Mice.

The aim of this study is to examine the ability of resveratrol to counteract hexavalent chromium [Cr(VI)]-induced genetic damage, as well as the possible pathways associated with this protection. Hsd:ICR male mice are divided into groups of the following five individuals each: (a) control 1, distilled water; (b) control 2, ethanol 30%; (c) resveratrol, 50 mg/kg by gavage; (d) CrO3, 20 mg/kg intraperitoneally; (e) resveratrol + CrO3, resveratrol administered 4 h prior to CrO3. The assessment is performed on peripheral blood. Micronuclei (MN) kinetics are measured from 0 to 72 h, while 8-hydroxydeoxyguanosine (8-OHdG) adduct repair levels, endogenous antioxidant system biomarkers, and apoptosis frequency were quantified after 48 h. Resveratrol reduces the frequency of Cr(VI)-induced MN and shows significant effects on the 8-OHdG adduct levels, suggesting that cell repair could be enhanced by this polyphenol. Concomitant administration of resveratrol and Cr(VI) results in a return of the activities of glutathione peroxidase and catalase to control levels, accompanied by modifications of superoxide dismutase activity and glutathione levels. Thus, antioxidant properties might play an important role in resveratrol-mediated inhibition of Cr(VI)-induced oxidant genotoxicity. The increase in apoptotic cells and the decrease in necrosis further confirmed that resveratrol effectively blocks the actions of Cr(VI).

Individual and Combined Effects of Manganese and Chromium on a Freshwater Chlorophyceae.

Manganese (Mn), an essential metal in trace amounts, and chromium (Cr), a nonessential metal to algae, are often found in effluent discharges and may co-occur in contaminated aquatic environments. Therefore, we investigated the effects of Mn and Cr, and their mixtures, on a freshwater Chlorophyceae, Raphidocelis subcapitata, using a multiple endpoint approach. Regarding the single exposure of metals, Mn was 4 times more toxic (median inhibitory concentration at 72 h [IC5072 h ] = 4.02 ± 0.45 µM Mn) than Cr (IC5072 h = 16.42 ± 4.94 µM Cr) for microalgae, considering the effects on the relative growth rate. Moreover, this species was the most sensitive to Mn, according to the species sensitivity distribution curve. Overall, the tested metals did not lead to significant changes in reactive oxygen species production, cellular complexity, and cell relative size but significantly decreased the algal growth and the mean cell chlorophyll a (Chl a) fluorescence at the highest concentrations (3.64-14.56 µM of Mn and 15.36-19.2 µM of Cr). The decreased mean cell Chl a fluorescence indicates an impact on pigment synthesis, which may be related to the observed growth inhibition. In the mixture tests, the reference models concentration addition and independent action were used to analyze the data, and the independent action model was the best fit to describe our results. Therefore, the Mn and Cr mixture was noninteractive, showing additive effects. This is the first study to address the combined toxicity of Mn and Cr regarding freshwater Chlorophyceae. Environ Toxicol Chem 2022;41:1004-1015. © 2022 SETAC.

Occupational risk assessment of exposure to metals in chrome plating workers.

Inhalation of xenobiotics during manufacture process in chrome plating bath produce hazards to workers' health. Chromium (Cr) is a metal widely used by industry, and its hexavalent (VI) form has been classified as mutagenic and carcinogenic. This study aimed to evaluate the occupational risk of exposure to metals in chrome plating workers. Biological monitoring was performed through quantification of Cr, Pb, As, Ni, and V in blood by ICP-MS in 50 male chrome-plating workers from the exposed group and 50 male non-exposed workers. The inflammatory parameters assessed were ß-2 integrin, intercellular adhesion molecule-1 (ICAM-1), and L-selectin expression in lymphocytes. The genotoxicity was evaluated with comet and micronucleus (MN) assays and as a biomarker of oxidative damage the lipid peroxidation (MDA) and protein carbonyl (PCO). The results demonstrated that Cr levels in blood and urine were increased in the exposed group compared to the non-exposed group. Although the biomarkers of exposure proved to be within the levels considered safe in exposed individuals, chrome plating workers presented significantly increase in the percentage of lymphocytes expressing ß-2 integrin, ICAM-1, and L-selectin as well as DNA damage (comet assay) and plasmatic MDA and PCO levels. Therefore, it is possible also assign the injuries caused to lipids, proteins, and DNA assessed due to the increased presence of other metals such as Pb, As, Ni, and V in exposed subjects. These results suggest that exposure to xenobiotics present in the occupational environment in chrome plating industry could play a crucial role toward the inflammation, genetic, and oxidative damage.

Bioaccumulation of heavy metals in the tissues of Schizothorax plagiostomus at River Swat / Bioacumulação de metais pesados nos tecidos de Plagiostomo esquizotórax em River Swat

Snow trout (Schizothorax plagiostomus) is an economically important freshwater fish, mostly found in northern areas of water reservoirs of Pakistan. The current study was conducted in River Swat to analyze the bioaccumulation of heavy metals (Pb, Cr, Ni, and Zn) in tissues of Schizothorax plagiostomus. Tissues were extracted and dissolved in perchloric acid (HClO4) and nitric acid (HNO3) along with hotplate. The heavy metals, zinc (Zn), lead (Pb), chromium (Cr), and Nickel (Ni) were determined using Perkin Elmer 2380 atomic absorption spectrophotometer. Results shows great variation in the content of the metal related to tissue type and sampling sites. A high concentration of bioaccumulation was reported at Charbagh, whereas lowest at Odigram: Charbagh>Landakai>Odigram. In the same way, Cr was the most accumulated heavy metal followed by lead, nickel, and Zinc.(AU)

A truta das neves (Schizothorax plagiostomus) é um peixe de água doce economicamente importante, encontrado principalmente nas áreas ao norte de reservatórios de água do Paquistão. O presente estudo foi realizado em River Swat para analisar a bioacumulação de metais pesados (Pb, Cr, Ni e Zn) em tecidos de Schizothorax plagiostomus. Os tecidos foram extraídos e dissolvidos em ácido perclórico (HClO4) e ácido nítrico (HNO3) com placa de aquecimento. Os metais pesados zinco (Zn), chumbo (Pb), cromo (Cr) e níquel (Ni) foram determinados usando espectrofotômetro de absorção atômica Perkin Elmer 2380. Os resultados mostram grande variação no conteúdo do metal relacionado ao tipo de tecido e locais de amostragem. Uma alta concentração de bioacumulação foi relatada em Charbagh, enquanto a mais baixa, em Odigram: Charbagh > Landakai > Odigram. Da mesma forma, Cr foi o metal pesado mais acumulado, seguido por Pb, Ni e Zn.(AU)

Bioaccumulation of heavy metals in the tissues of Schizothorax plagiostomus at River Swat / Bioacumulação de metais pesados nos tecidos de Plagiostomo esquizotórax em River Swat

Snow trout (Schizothorax plagiostomus) is an economically important freshwater fish, mostly found in northern areas of water reservoirs of Pakistan. The current study was conducted in River Swat to analyze the bioaccumulation of heavy metals (Pb, Cr, Ni, and Zn) in tissues of Schizothorax plagiostomus. Tissues were extracted and dissolved in perchloric acid (HClO4) and nitric acid (HNO3) along with hotplate. The heavy metals, zinc (Zn), lead (Pb), chromium (Cr), and Nickel (Ni) were determined using Perkin Elmer 2380 atomic absorption spectrophotometer. Results shows great variation in the content of the metal related to tissue type and sampling sites. A high concentration of bioaccumulation was reported at Charbagh, whereas lowest at Odigram: Charbagh>Landakai>Odigram. In the same way, Cr was the most accumulated heavy metal followed by lead, nickel, and Zinc.

A truta das neves (Schizothorax plagiostomus) é um peixe de água doce economicamente importante, encontrado principalmente nas áreas ao norte de reservatórios de água do Paquistão. O presente estudo foi realizado em River Swat para analisar a bioacumulação de metais pesados (Pb, Cr, Ni e Zn) em tecidos de Schizothorax plagiostomus. Os tecidos foram extraídos e dissolvidos em ácido perclórico (HClO4) e ácido nítrico (HNO3) com placa de aquecimento. Os metais pesados zinco (Zn), chumbo (Pb), cromo (Cr) e níquel (Ni) foram determinados usando espectrofotômetro de absorção atômica Perkin Elmer 2380. Os resultados mostram grande variação no conteúdo do metal relacionado ao tipo de tecido e locais de amostragem. Uma alta concentração de bioacumulação foi relatada em Charbagh, enquanto a mais baixa, em Odigram: Charbagh > Landakai > Odigram. Da mesma forma, Cr foi o metal pesado mais acumulado, seguido por Pb, Ni e Zn.

Novel Biochemical Properties and Physiological Role of the Flavin Mononucleotide Oxidoreductase YhdA from Bacillus subtilis.

Cr(VI) is mutagenic and teratogenic and considered an environmental pollutant of increasing concern. The use of microbial enzymes that convert this ion into its less toxic reduced insoluble form, Cr(III), represents a valuable bioremediation strategy. In this study, we examined the Bacillus subtilis YhdA enzyme, which belongs to the family of NADPH-dependent flavin mononucleotide oxide reductases and possesses azo-reductase activity as a factor that upon overexpression confers protection on B. subtilis from the cytotoxic effects promoted by Cr(VI) and counteracts the mutagenic effects of the reactive oxygen species (ROS)-promoted lesion 8-OxoG. Further, our in vitro assays unveiled catalytic and biochemical properties of biotechnological relevance in YhdA; a pure recombinant His10-YhdA protein efficiently catalyzed the reduction of Cr(VI) employing NADPH as a cofactor. The activity of the pure oxidoreductase YhdA was optimal at 30°C and at pH 7.5 and displayed Km and Vmax values of 7.26 mM and 26.8 µmol·min-1·mg-1 for Cr(VI), respectively. Therefore, YhdA can be used for efficient bioremediation of Cr(VI) and counteracts the cytotoxic and genotoxic effects of oxygen radicals induced by intracellular factors and those generated during reduction of hexavalent chromium.IMPORTANCE Here, we report that the bacterial flavin mononucleotide/NADPH-dependent oxidoreductase YhdA, widely distributed among Gram-positive bacilli, conferred protection to cells from the cytotoxic effects of Cr(VI) and prevented the hypermutagenesis exhibited by a MutT/MutM/MutY-deficient strain. Additionally, a purified recombinant His10-YhdA protein displayed a strong NADPH-dependent chromate reductase activity. Therefore, we postulate that in bacterial cells, YhdA counteracts the cytotoxic and genotoxic effects of intracellular and extracellular inducers of oxygen radicals, including those caused by hexavalent chromium.

Mechanisms and individuality in chromium toxicity in humans.

With regards to health, chromium (Cr) is an ambiguous chemical element. Although it is considered to be an important micronutrient, it also is connected with several pathologies, including carcinogenicity. The mechanism of action of Cr and its compounds in humans is not yet fully understood. Currently, three possible mechanisms have been proposed for carcinogenesis: Cr(VI)-induced multistage carcinogenesis, genomic instability, and epigenetic modification. Therefore, in addition to the toxicity of this metal and its ions, human susceptibility to Cr-induced pathologies depends on external factors and individual characteristics, such as enzymatic polymorphisms, carriers, endogenous reducing system, adduct formation and stability, and efficiency of DNA repair mechanisms, among other factors. In fact, the variability of individual molecular constitutive factors, such as individual polymorphisms, creates an individualized environment for Cr toxicity. This mini-review contemplates the essential variables in this process.

Use of Nanoscale Zero-Valent Iron for Remediation of Clayey Soil Contaminated with Hexavalent Chromium: Batch and Column Tests.

This study investigated the reduction of hexavalent chromium (Cr(VI)) in a clayey residual soil using nanoscale zero-valent iron (nZVI). Five different ratios between nZVI and Cr(VI) were tested in batch tests (1000/11; 1000/23; 1000/35; 1000/70, and 1000/140 mg/mg) with the soil. With the selected proportion resulting best efficiency, the column tests were conducted, with molded specimens of 5 cm in diameter and 5 cm in height, with different nZVI injection pressures (10, 30, and 100 kPa). The soil was contaminated with 800 mg/kg of Cr(VI). The Cr(VI) and Cr(III) analyses were performed following the USEPA 3060A and USEPA 7196A standards. The results show that the reduction of Cr(VI) is dependent on the ratio between nZVI and Cr(VI), reaching 98% of efficiency. In column tests, the pressure of 30 kPa was the most efficient. As pressure increased, contaminant leaching increased. The permeability decreased over time due to the gradual increase in filtration and formation of oxyhydroxides, limiting nZVI mobility. Overall, nZVI is efficient for soil remediation with Cr(VI), but the injection process can spread the contaminated if not properly controlled during in situ application.

Evaluation of the effectiveness of a bioremediation process in experimental soils polluted with chromium and lindane.

Bioremediation using actinobacterium consortia proved to be a promising alternative for the purification of co-contaminated environments. In this sense, the quadruple consortium composed of Streptomyces sp. M7, MC1, A5, and Amycolatopsis tucumanensis AB0 has been able to remove significant levels of Cr(VI) and lindane from anthropogenically contaminated soils. However, the effectiveness of the bioremediation process could not be evaluated only by analytical monitoring, which is complex mainly due to the characteristics of the matrix, producing non-quantitative analyte recoveries, or interferences in the detection stage and quantification. However, the effectiveness of the bioremediation process cannot be evaluated only through analytical monitoring, which is complex due mainly to the characteristics of the matrix, to the recoveries of non-quantitative analytes or to interferences in the detection and quantification stage. For this reason, it is essential to have tools of ecological relevance to assess the biological impact of pollutants on the environment. In this context, the objective of this work was to establish the appropriate bioassays to evaluate the effectiveness of a bioremediation process of co-contaminated soils. For this, five model species were studied: four plant species (Lactuca sativa, Raphanus sativus, Lycopersicon esculentum, and Zea mays) and one animal species (Eisenia fetida). On plant species, the biomarkers evaluated were inhibition of germination (IG) and the length of hypocotyls/steam and radicles/roots of the seedling. While on E. fetida, mortality (M), weight lost, coelomocyte concentration and cell viability were tested. These bioindicators and the battery of biomarkers quantified in them showed a different level of sensitivity, from maximum to minimum: E. fetida > L. esculentum > L. sativa > R. sativus ≫>Z. mays. Therefore, E. fetida and L. esculentum and their respective biomarkers were selected to evaluate the effectiveness of the bioremediation process due to the capability of assessing the effect on the flora and the fauna of the soil, respectively. The joint application of these bioindicators in a field scale bioremediation process is a feasible tool to demonstrate the recovery of the quality and health of the soil.

Roles of Bacillus subtilis RecA, Nucleotide Excision Repair, and Translesion Synthesis Polymerases in Counteracting Cr(VI)-Promoted DNA Damage.

Bacteria deploy global programs of gene expression, including components of the SOS response, to counteract the cytotoxic and genotoxic effects of environmental DNA-damaging factors. Here we report that genetic damage promoted by hexavalent chromium elicited the SOS response in Bacillus subtilis, as evidenced by the induction of transcriptional uvrA-lacZ, recA-lacZ, and P recA-gfp fusions. Accordingly, B. subtilis strains deficient in homologous recombination (RecA) and nucleotide excision repair (NER) (UvrA), components of the SOS response, were significantly more sensitive to Cr(VI) treatment than were cells of the wild-type strain. These results strongly suggest that Cr(VI) induces the formation in growing B. subtilis cells of cytotoxic and genotoxic bulky DNA lesions that are processed by RecA and/or the NER pathways. In agreement with this notion, Cr(VI) significantly increased the formation of DNA-protein cross-links (DPCs) and induced mutagenesis in recA- and uvrA-deficient B. subtilis strains, through a pathway that required YqjH/YqjW-mediated translesion synthesis. We conclude that Cr(VI) promotes mutagenesis and cell death in B. subtilis by a mechanism that involves the formation of DPCs and that such deleterious effects are counteracted by both the NER and homologous recombination pathways, belonging to the RecA-dependent SOS system.IMPORTANCE It has been shown that, following permeation of cell barriers, Cr(VI) kills B. subtilis cells following a mechanism of reactive oxygen species-promoted DNA damage, which is counteracted by the guanine oxidized repair system. Here we report a distinct mechanism of Cr(VI)-promoted DNA damage that involves production of DPCs capable of eliciting the bacterial SOS response. We also report that the NER and homologous recombination (RecA) repair pathways, as well as low-fidelity DNA polymerases, counteract this metal-induced mechanism of killing in B. subtilis Hence, our results contribute to an understanding of how environmental pollutants activate global programs of gene expression that allow bacteria to contend with the cytotoxic and genotoxic effects of heavy metals.

Ecotoxicological risk assessment of contaminated soil from a complex of ceramic industries using earthworm Eisenia fetida.

The aim of this study was to determine ecotoxicological parameters for biomonitoring of environmental risk of native soils from a ceramic industrial area that had been contaminated with cadmium (Cd) and chromium (Cr) by using the earthworm, Eisenia fetida. Initially, lab tests were conducted to compare earthworm (Eisenia fetida) growth, survival, morphology, behavior, and reproduction rates following exposure to six concentrations of contaminated soil at 0%, 6.25%, 12.5%, 25%, 50%, or 100% mixed in artificial soil and cow dung following a 28-d incubation period. The second experiment consisted of utilizing Eisenia fetida in a predetermined lowest observed effect concentration to measure heavy metals bioaccumulation from superficial soil collected from a ceramic industrial area following a 56-d exposure. Data demonstrated that in the lab earthworms maintained at 6.25% of contaminated soil, exhibited significant increase in mean weight, bioaccumulation of Cd and Cr associated with a significant decrease in the amount of Cd and Cr in the soil. At field testing, similar results that were observed as in the lab as evidenced by rise in mean weight, higher levels of Cd and Cr in the earthworm tissue accompanied by significant fall in soil levels of Cd and Cr. In conclusion, at tested relevant environmental concentrations, the use of Eisenia fetida for assessing ecotoxicological risk arising from contaminated soil due to ceramic industrial pollutant emissions was found to be an effective tool for biomonitoring program.

Mutagenic and histopathological effects of hexavalent chromium in tadpoles of Lithobates catesbeianus (Shaw, 1802) (Anura, Ranidae).

The potential mutagenic and histopathological effects of the hexavalent chromium were investigated in Lithobates catesbeianus tadpoles. These larvae (GS 25-31) were exposed to three nominal concentrations of potassium dichromate (4, 12, and 36 mg L-1) and 5 mg L-1 of Cyclophosphamide as a positive control (PC), for 24 h. A negative control (NC) was also added to the experiment. Our results showed that, in general, the micronuclei (MN) were less frequent than the erythrocyte nuclear abnormalities (ENA); there was a significant difference in the frequency of MN between the NC and all treated groups (p < 0.05) in a concentration-dependent curve, in addition the PC did not differ from the chromium treatments. Also, only PC and the group treated with potassium dichromate at 36 mg L-1 showed significantly higher frequencies of ENA than NC (p < 0.05). Chromium treatments promoted cell retention in the Sub-G1 phase and a decrease of cells in the S and G2/M phases indicating inhibition of the cell cycle. All treatments with chromium led to liver and kidney histopathological lesions, especially with 36 mg L-1 (greater number of lesions). In conclusion, hexavalent chromium was mutagenic to L. catesbeianus tadpoles and its toxic effects also resulted in anti-mitotic activity, besides inducing histopathological alterations in liver and kidney. Amphibians have been proven to be useful bioindicators, and we suggest that tadpoles of different species can be used to represent the environmental impacts in aquatic ecosystems.

Physiological, ultrastructural, biochemical and molecular responses of young cocoa plants to the toxicity of Cr (III) in soil.

The objective of this study was to evaluate Cr toxicity in young plants of the CCN 51 Theobroma cacao genotype at different concentrations of Cr3+ in the soil (0, 100, 200, 400 and 600 mg kg-1) through physiological, ultrastructural, antioxidant and molecular changes. Doses of 400 and 600 mg Cr3+ kg-1 soil severely affected foliar gas exchange, promoted by damages in photosynthetic machinery evidenced by the decrease in CO2 fixation. Decreased expression of psbA and psbO genes, changes in enzymatic activity and lipid peroxidation also affected leaf gas exchange. A hormesis effect was observed at 100 mg Cr3+ kg-1 soil for the photosynthetic activity. As a metal exclusion response, the roots of the cocoa plants immobilized, on average, 75% of the total Cr absorbed. Ultrastructural changes in leaf mesophyll and roots, with destruction of mitochondria, plasmolysis and formation of vesicles, were related to the oxidative stress promoted by excess ROS. The activity of the antioxidant enzymes SOD, APX, GPX and CAT and the amino acid proline coincided with the greater expression of the sod cyt gene demonstrating synchronicity in the elimination of ROS. It was concluded, therefore, that the tolerance of the cocoa plants to the toxicity of Cr3+ depends on the concentration and time of exposure to the metal. Higher doses of Cr3+ in the soil promoted irreversible damage to the photosynthetic machinery and the cellular ultrastructure, interfering in the enzymatic and non-enzymatic systems related to oxidative stress and gene expression. However, the low mobility of the metal to the leaf is presented as a strategy of tolerance to Cr3+.