Fluoride Accumulation Research Articles

Spondias mombin, a potential bioindicator of potassium fluoride pollution

Ecological contamination by air pollutants is a worldwide problem. Fluoride-based compounds are released in large proportions into the atmosphere, soil and water from various industrial sources. These compounds are more phytotoxic to various plants than are other pollutants. The objective of this work was to determine the effects of fluoride in the form of potassium fluoride (KF)-simulated rain, on morphological and physiological responses, macronutrient content and fluoride accumulation in Spondias mombin leaves. S. mombin seedlings were transplanted to 5-liter pots containing Bioplant® substrate in a greenhouse. After acclimatization, the plants were subjected to KF, through simulated rain, at concentrations of 0, 10, 20 and 30 mg L−1, for a period of 9 days. Subsequently, visual and anatomical evaluations, chlorophyll a fluorescence variables, gas exchange, fluoride accumulation and macronutrient content were performed in all plants. KF-treated S. mombin developed necrosis on leaf surfaces with damage of up to 70%, followed by parenchymal tissue alterations characterized by cellular collapse and accumulation of phenolic compounds. We observed photochemical and macronutrient content changes that may compromise development of these plants. The correlation between the analyses suggested that noninvasive characteristics are important tools for detecting environmental pollution, and that S. mombin is an important bioindicator of KF-contaminated environments.

Deciphering the molecular mechanism behind stimulated co-uptake of arsenic and fluoride from soil, associated toxicity, defence and glyoxalase machineries in arsenic-tolerant rice

The current study elucidates the uncharacterized biohazard associated with rice growth in arsenic and fluoride co-contaminated sites. Analysis of the arsenic-tolerant rice cultivar, Muktashri (known to restrict arsenic uptake) revealed that fluoride largely stimulated arsenic bioaccumulation in the stressed tissues and vice versa. Gene expression studies revealed that high arsenic uptake was facilitated by the fluoride-dependent up regulation of phosphate transporter2 (PT2), PT8 and low silicon rice1 (Lsi1), and elevated fluoride accumulation was stimulated by the arsenic-mediated induction of chloride channels (CLCs). The endogenous accumulation of fluoride and arsenic increased reactive oxygen species (ROS), O2−, membrane peroxidation and arsenic localization within tissues. This inhibited plant growth by triggering chlorosis, electrolyte leakage, malondialdehyde production (due to high lipoxygenase activity), protein carbonylation, protease activity and methylglyoxal accumulation due to inhibited glyoxylase activity. Metabolic analysis showed inhibited proline biosynthesis along with increased channelization of glutathione towards phytochelatin synthase and glutathione-S-tranferase-dependent pathways. Inhibition of the antioxidant enzymes like catalase, ascorbate peroxidase and guaiacol peroxidase validated the inefficient scavenging of H2O2 during combined stress. In silico analyses predicted the ecotoxicological risks of arsenic-fluoride complex formed during joint stress. Overall, our investigation illustrated the underlying mechanism of arsenic-fluoride co-uptake which resulted in complete suppression of the ‘tolerant’-phenotype in Muktashri seedlings.

Synthesis and evaluation of 6-[18F]fluoro-3-(pyridin-3-yl)-1H-indole as potential PET tracer for targeting tryptophane 2, 3-dioxygenase (TDO)

IntroductionThe increase in expression of tryptophan 2, 3-dioxygenases (TDO) and indoleamine 2,3-dioxygenase (IDO) have been reported as potential tumor biomarkers. TDO and IDO are enzymes that catalyze the first and rate-limiting step of the kynurenine pathway. Positron emitting tomography (PET) tracers investigating the kynurenine pathway may allow for the detection of different disease pathologies in vivo including cancer. However, current PET tracers being developed for TDO and IDO have suffered from either multi-step low yielding syntheses or de-fluorination of the tracer in vivo. ResultsTDO inhibitors based on 6-fluoroindole with C3 substituents are a class of small molecules that have been shown to bind to TDO effectively, restore tryptophan concentration and decrease the production of immunosuppressive metabolites. The compound 6-fluoro-3-(pyridine-3-yl)-1H-indole has been reported to have high in vitro affinity for TDO. Herein we report the fully automated radiosynthesis of 6-[18F]fluoro-3-(pyridine-3-yl)-1H-indole [18F]4 using a copper-mediated nucleophilic 18F-fluorination resulting in a non-corrected yield of 5 to 6% of the tracer with a radiochemical purity of >99% after 4 h. Small animal dynamic PET/CT imaging of [18F]4 intravenously injected into normal C57BL/6 mice revealed rapid accumulation in heart and brain, reaching maximum occupancy in heart (10.9% ID/g) and brain (8.1% ID/g) at 1.75 min and 2.25 min, respectively. Furthermore, these in vivo studies revealed no de-fluorination of the tracer, as evidence by the absence of [18F]fluoride accumulation in bone. ConclusionIn vitro studies demonstrate that 4 has good affinity for hTDO and the radiolabeled analogue [18F]4 can be synthesized with suitable radiochemical yields. [18F]4 demonstrates good uptake in the brain and the radiolabeled compound shows no de-fluorination in vivo in C57BL/6 mice.

Thyroid gland pathology in children population exposed to the combination of iodine deficiency and fluoride pollution of environment

The article presents results of study of the impact of iodine deficiency and technogenic fluoride on the state of the thyroid gland in children. On the example of two districts of the city of Bratsk there were executed dynamic investigations (2002 and 2012), including the estimation of the pollution of ambient air and soil by fluorine compounds, levels of iodine intake by the body, the clinical examination of children aged from 5 to 7 years d and interviewing of their parents. In the course of the medical examination there were executed: physical examination by the pediatrician, endocrinologist, ultrasound examination of the thyroid gland, the determination both of serum hormone content by radioimmunoassay and urinary excretion offluorine and iodine. Concentrations of hydrogen fluoride and a solidfluorides in ambient air led to the accumulation offluoride ion in the soil. The iodine entering with drinking water and food, was established to provide only 37.5-50% of the daily requirement of iodine. Increased fluoride ion content in urine and milk teeth in children is associated with the concentrations of the fluorine-containing pollutants in the ambient air and soil. The fluoride pollution against the background of the natural iodine deficiency was established to increase the frequency of functional and morphological disorders of the thyroid gland in children.

Nitrate and Phosphate Transporters Rescue Fluoride Toxicity in Yeast.

Organisms are exposed to fluoride in the air, water, and soil. Yeast and other microbes utilize fluoride channels as a method to prevent intracellular fluoride accumulation and mediate fluoride toxicity. Consequently, deletion of fluoride exporter genes (FEX) in S. cerevisiae resulted in over 1000-fold increased fluoride sensitivity. We used this FEX knockout strain to identify genes, that when overexpressed, are able to partially relieve the toxicity of fluoride exposure. Overexpression of five genes, SSU1, YHB1, IPP1, PHO87, and PHO90, increase fluoride tolerance by 2- to 10-fold. Overexpression of these genes did not provide improved fluoride resistance in wild-type yeast, suggesting that the mechanism is specific to low fluoride toxicity in yeast. Ssu1p and Yhb1p both function in nitrosative stress response, which is induced upon fluoride exposure along with metal influx. Ipp1p, Pho87p, and Pho90p increase intracellular orthophosphate. Consistent with this observation, fluoride toxicity is also partially mitigated by the addition of high levels of phosphate to the growth media. Fluoride inhibits phosphate import upon stress induction and causes nutrient starvation and organelle disruption, as supported by gene induction monitored through RNA-Seq. The combination of observations suggests that transmembrane nutrient transporters are among the most sensitized proteins during fluoride-instigated stress.

Differential fluoride uptake induces variable physiological damage in a non-aromatic and an aromatic indica rice cultivar

The current study illustrates the systemic damages caused by increasing concentration of fluoride in non-aromatic rice variety, IR-64 and aromatic rice Gobindobhog (GB). Analysis of the physiological parameters like shoot length, root length and electrolyte leakage along with crucial damage indices like chlorophyll, malondialdehyde, H2O2 and protease activity indicated higher fluoride adaptation in GB compared to IR-64. IR-64 exhibited unregulated fluoride bioaccumulation when exposed to 25 mg L−1 NaF stress, whereas fluoride uptake in GB was much regulated. Gene expression studies proposed that CLC2 rather than CLC1 mediated the fluoride import. Fluoride also triggered higher P-H+/ATPase accumulation in GB compared to IR-64, thus highlighting efficient homeostasis in stressed GB. Unlike IR-64, GB could maintain photosynthesis (RuBisCo expression), sugar metabolism (α-amylase expression and activity), glycolysis and Krebs cycle even under high concentration of fluoride stress. Fluoride also inhibited nitrate reductase activity in both the cultivars. The present research illustrates differential phytotoxicity emerging out of fluoride accumulation in rice seedlings, highlighting that IR-64 is a highly susceptible variety, whereas GB exhibits physiological plasticity and is better adapted to higher concentrations of fluoride.

Removal of Fluoride and Arsenic by a Hybrid Constructed Wetland System.

A pilot-scale hybrid wetland system was constructed for the removal of fluoride and arsenic from synthetic wastewater. After five months of operation, the fluoride and arsenic removal rate were at the value of 65 % and 90 %, respectively. Through calculation, the accumulation of fluoride in plants only accounted for 1.63 % of the accumulation in substrates, and the accumulation of arsenic in plants accounted for 3.3 % of that in substrates. Both the accumulation of fluoride and arsenic in plants were much higher in roots than that in leaves. And for substrates, the accumulation in the first layer was higher than the second layer. The changes of microbial community in the substrate of the wetland during the operation were also analyzed to investigate the effects of operating condition on the microbial community and to study the role of microorganism on the removal of fluoride and arsenic. The results showed that the relative abundance of Firmicutes reduced, while the relative abundance of Proteobacteria increased, indicating that the fluoride and arsenic in solution had a great influence on the microbial community. Findings of this study suggest that the hybrid constructed wetland system may be a promising process for the removal of fluoride and arsenic from synthetic wastewater.

USE HERBAL PLANTS (CHAMAENERION ANGUSTIFOLIUM AND TANACETUM VULGARE) FOR MONITORING OF TERRITORIES POLLUTED BY FLUORINE-CONTAINING EMISSIONS

Specific features of fluoride accumulation by two species of herbaceous plants – Chamerion angustifolium (L.) Holub and Tanacetum vulgare L., were found at different distances from the aluminum smelter located in the Baikal region. The highest fluorine content was recorded at the distance of 3 km from the smelter: 433 mg / kg of dry weight in C. angustifolium, 306 mg / kg in T. vulgare. According to the level of accumulation of fluorine, the organs of C. angustifolium were arranged in the following order (as the concentration decreases): leaves> roots> stems ≥ flowers, for T. vulgare the another sequence was typical: roots> leaves> flowers ≥ stems. Calculation of the root barrier coefficient for different organs of C. angustifolium and T. vulgare indicates the existence of barrier mechanisms that prevent the entry of fluorine from the soil into the aerial part of plants. A feature of the accumulation of fluoride in the leaves of C. angustifolium is its active foliar absorption and barrier-free intake from the soil. It has been established that the rate of fluoride accumulation by the reproductive organs of both species is much lower than by the assimilation organs. The data obtained make it possible to recommend using C. angustifolium for monitoring air fluorine pollution, and T. vulgare – for soil fluorine pollution.

Accumulation, fractionation and health risk assessment of fluoride and heavy metals in soil-crop systems in northwest China

Untreated industrial sewage and domestic wastewater irrigation has led to agricultural soil-crop system contamination by heavy metals and fluoride in Dongdagou and Xidagou stream basins, Baiyin city, China. A total of 36 pairs of soil and wheat samples (roots, stalks, leaves, husks, and grains) and 42 pairs of soil and maize samples (roots, stalk1, stalk2, stalk3, leaves, husks, corncobs and grains) were collected from Dongdagou and Xidagou stream basins to examine the accumulation, fractionation, correlation of heavy metals and F in soil-crop systems. Risks posed by heavy metals and F in this system to human health was also assessed. The total contents of F and heavy metals (Cd, Cu, Pb, Mn Zn, Cr and Ni), as well as the fraction distribution in soil, were determined. The total contents of F and heavy metals in crop tissues were also determined. The results indicated that the average contents of Cd, Cu, Pb, Mn Zn, F and Cr in Dongdagou and Xidagou stream basins exceeded the soil background value. Heavy metals and F more easily accumulated in the male inflorescence of maize. Correlation analysis showed that content of water soluble F positively were correlated with the contents of Cd, Cu, Pb, Mn Zn, Cr and Ni in exchangeable and carbonate fractions (P < 0.05). Stepwise discriminant analysis showed that the combined stresses of soil total Cu and Ni accounts for 100% effect on water soluble F accumulation in soil and crop roots. The hazard index indicated that noncancerous risk is likely to occur through maize grains and wheat grains consumption by children and adults.

Effects of Fluoride of Antarctic Krill (&amp;lt;i&amp;gt;Euphausia superba&amp;lt;/i&amp;gt;) Meal on Accumulation and Weight of Mice

Antarctic krill (<i>Euphausia superba</i>) possesses rich nutritional value, large fishing capacity and potentials for processing and utilization. However, the development and utilization of Antarctic krill is impeded by its high fluorine contents. In this study, Antarctic krill meal and sodium fluoride solution (300 mg/L) were selected as the study objects to feeding mice, and the effects of fluoride on accumulation and weight gained in small intestine, blood, liver, and kidney femur of mice were investigated. The results showed that the contents of small intestine, blood, liver and kidney in the group of the mice fed with Antarctic krill and sodium fluoride remained less than 1 mg/kg, which was slightly higher than that of the blank control group (<i>p</i>＜0.05). The fluoride contents in the femur of mice fed with Antarctic krill meal and sodium fluoride solution were ten times higher than that of the blank control group, indicating that the fluorine in Antarctic krill meal was likely different from the chemical fluorine in sodium fluoride. No signification difference on accumulation of fluoride was found in the small intestine, blood, liver and kidney of mice, but fluorine from Antarctic krill meal and sodium fluoride was obviously deposited in the femur of mice. On the other hands, the weight gained rate of mice in the sodium fluoride group was 3.22%, and that of mice in Antarctic krill meal group was 7.81%, both of that were significantly lower than that in the blank group (12.87%). The results showed that the fluorine in Antarctic krill meal inhibited the growth of mice, but its specific absorption, metabolism and transformation process in the body still needed to be further studied.

Fluoride toxicity triggered oxidative stress and the activation of antioxidative defence responses in Spirodela polyrhiza L. Schleiden

ABSTRACT The present study was designed to assess the fluoride mediated antioxidant defence responses in Spirodela polyrhiza, grown under hydroponic conditions. The plants of S. polyrhiza were exposed to different fluoride concentrations (0, 5, 10, 15, 20, 25, 50 ppm) for the time period 24, 72, 120 and 168 h. Fluoride was observed to be readily accumulated by S. polyrhiza at all the exposure periods. Increased accumulation of fluoride triggered the oxidative stress that was quite evident from enhanced electrolyte leakage, proline, anthocyanin and phenolic content To counterbalance the stress, plant responded by the alterations in the activities of antioxidative enzymes (SOD, CAT, APOX, POD, GR), that was also supposed to confer tolerance ability to plant. Moreover, SEM-EDX, CLSM and FT-IR studies were also performed to confirm oxidative damage. Hence, it can be elucidated that this plant can act as an efficient fluoride accumulator and antioxidant defence system minimized fluoride toxicity.

PECULIARITIES OF STORAGE OF FLUORINE IN SOIL AND PLANTS IN THE ZONE OF THE INFLUENCE OF TECHNOGENESIS

The article is devoted to the study of the features of the accumulation of fluorine in soil and plantsin the zone of influence of technogenesis. The topicality of the study of fluorine in the soil is due to theproperties of this element negatively to affect on human health through the trophic chains. The purposeof the research was to determine the technogenic sources of fluorine intake in the agricultural area of theDonetsk region and to study the factors affecting the ways and levels of fluoride accumulation in soil andplants. The methodological basis of the study consists of the following methods: field, laboratory, measuring,calculation and comparison, graphical data display. Along with the well-known methods used somespecial: analysis and synthesis. The studies were conducted using certified and standardized in Ukrainemethodologies and methodological approaches. Analytical measurements of fluoride content were carriedout in straw, grain and soil samples, which were taken from the arable layer at the same time as the plantsamples. Selection of soil and plant samples was carried out from the arable layer in accordance with thecurrent requirements and recommendations. Statistical processing of the results was carried out in accordancewith the «Methodology of field experience» B.A. Dospehova.Based on the analysis of statistical data on emissions from industrial enterprises, it is determinedthat technogenic sources of fluorine pollution of agrolandscapes of Donetsk region are metallurgy andpower engineering. These enterprises supply around 200 tons of fluorine per year to the environment. Ata distance of up to 5 km, the concentration of water-soluble form of fluorine in the soil exceeds the MPC(10 mg/kg) by 1,5 to 3 times. When removed, the content of soluble forms is reduced. Outside the technogenicimpact (10–15 km), the concentration of water-soluble form of fluorine in the soil practically doesnot exceed the MPC. It is established that the greatest amount of fluorine is contained in the vegetativemass and least of all in the grain. High sensitivity to fluorine was observed in barley and corn, for whichthe fluorine content exceeded the recommended standard by 2-2,5 times. Winter wheat and sunflower wereless sensitive to fluorine. The content of the element in the grain of these crops did not exceed the norm orwas on the verge. There was no excess of the normative content of fluorine (15 mg/ kg) in the by-productsof agricultural crops that were studied.

Fluoride movement into and out ofBacillusspores and growing cells and effects of fluoride accumulation on spore properties

To investigate effects of fluoride ion (F- ) on, and kinetics of its movement into and out of, spores and growing cells of Bacillus species. Effects of F- on Bacillus cell growth, spore germination and outgrowth and heat resistance were investigated, as well as F- movement into and out of spores using 19 F-NMR. F- inhibited Bacillus subtilis spore germination and outgrowth, and YhdU, now named FluC, was crucial to prevent F- accumulation in growing cells and to minimize F- inhibition of spore germination. Dormant wild-type, yhdU and coat defective B. subtilis spores, and Bacillus cereus spores incubated in 40mmoll-1 NaF for 48h accumulated 2-2·6mol l-1 F- and its movement into Bacillus spores was highest at low pH. Bacillus subtilis spores lacking Ca-dipicolinic acid accumulated higher F- levels than wild-type spores. These results are consistent with F- incorporation into the dormant spore core, and as HF and/or NaF, but not CaF2 . YhdU played no significant role in F- uptake or efflux in dormant spores, but assisted in F- export early in spore germination. This knowledge provides new insight into effects of F- on Bacillus cells and spores and how this anion moves into, and out of spores.

Chromium and fluoride contamination in groundwater around leather tanning industries in southern India: Implications from stable isotopic ratio δ53Cr/δ52Cr, geochemical and geostatistical modelling

This study investigates the contamination of groundwater by chromium and fluoride around leather tanning industries. Major ions, chromium, δ53Cr/δ52Cr and fluoride were analyzed by advanced analytical methods. High degree of variation was observed in the concentration of chloride in groundwater, which ranged between 205 and 3310 mg/L, around 56% of the samples were recorded above the acceptable limit indicating the quality of groundwater is fresh to saline and it could be due to mixing of tannery effluents with freshwater aquifers. The chromium in the groundwater around 40% of the sampling wells exceeds the permissible limit whereas, 37% of wells were with fluoride above the accepted limit. Geochemical modelling using Phreeqc suggest that the saturation index of minerals such as calcite, dolomite, fluoride, gypsum and anorthite is affected by precipitation, dissolution and ion exchange processes. Concentration of chromium isotopes δ53Cr and δ52Cr reveals the source of Cr in the groundwater is more likely from tannery effluents. Accumulation of fluoride in groundwater is contributed by bedrock, charnockite, granite, epidote hornblende gneiss, fissile hornblende biotite gneiss in the study area. Groundwater contamination in this area is caused by both natural as well as anthropogenic sources. Around 37% of the samples exceeds HQI limit (HQI>1), which indicates possible health problems to the public upon prolonged use of untreated groundwater for drinking. To overcome this situation, it's essential to improve the performance of the effluent treatment plants and recharge structure to recover the quality of groundwater.

When less is more: a comparison of models to predict fluoride accumulation in free-ranging kangaroos

Vegetation contaminated by industrial fluoride emissions can cause disease in herbivorous mammals. Spatially explicit exposure models offer a quantitative approach for evaluating and managing the potentially toxic effects of chronic fluoride consumption on wildlife. We monitored eastern grey kangaroos (Macropus giganteus) inhabiting a high-fluoride environment in the buffer zone of an aluminium smelter in southeastern Australia between 2010 and 2013. We measured fluoride levels at 19 pasture sites and determined the foraging range of 37 individual kangaroos. A series of generalised linear models were developed to estimate bone fluoride accumulation as a function of pasture exposure. Model outputs were compared to identify the most appropriate predictive tool for kangaroo bone fluoride accumulation relative to exposure. Accounting for age there was a negative association between bone fluoride concentration and distance of the central emission point from both the mean centre of foraging range and the point of death. The mean foraging range centre was the best predictor, with point of death just as suitable (and simpler), whereas more complex parameters such as monthly and cumulative fluoride exposure were poor predictors of bone fluoride concentration. The more complex dietary fluoride exposure estimates did not improve predictive capability compared with the simple, spatial models. We conclude that in actively managed wildlife populations, simple, locally validated models can provide estimates of bone fluoride accumulation sufficient to support decision-making.

Geochemical Evolution of Fluoride and Implication for F− Enrichment in Groundwater: Example from the Bilate River Basin of Southern Main Ethiopian Rift

Groundwater is the most important source of drinking water. Fluoride was found in high concentrations in the groundwater from deep wells of the water supply in the southern main Ethiopian rift. The high concentration of fluoride is dominantly geogenic rather than anthropogenic in origin, as the agricultural area was not found to be contaminated with NO3−. Knowledge of fluoride enrichment will help to provide management plans for developing deep groundwater and minimizing the health risks of exposure to fluoride. The chemical processes of fluoride were investigated in the waters in the Bilate River basin using hydrochemical and isotopic tools. The F− concentration ranged from 0.5 to 1.29 mg/L in water from shallow wells and from 0.48 to 5.61 mg/L in water from deep wells. Seventy percent of deep well samples had F− &gt; 1.5 mg/L higher than the World Health Organization potable guideline. The high fluoride concentration in the groundwater was mainly situated in the rift valley of the Bilate River basin, in contrast with low F− groundwater in the highland. The concentration of fluoride was lowest in Ca-Mg-HCO3 type groundwater and highest in Na-HCO3 type groundwater. Moreover, F− was positively correlated with HCO3−, Na+, Na+/Ca2+ and pH in groundwater and Na+/Ca2+ ratios were increased along the flow path. Hydrogeological, hydrodynamic and hydrochemical conditions are responsible for fluoride accumulation in the deep aquifers. Strong dynamic flow in highland areas flush away weathered chemical components (e.g., F−). Thus, surficial weathering is not a major controlling factor for high concentrations of Fluoride in deep groundwater but the combination of silicate hydrolysis and ion exchange mainly control fluoride enrichment in stagnant flow environments.

Effect of Fe3O4 NPs application on fluoride (F) accumulation efficiency of Prosopis juliflora

Fluoride (F) pollution is a major worldwide problem affecting approximately 200 million people. Hyperaccumulator plant Prosopis juliflora has been used for the removal of F from contaminated soils; however it’s low F accumulation efficiency and low biomass limits the phytoremediation efficiency. Present study deals with enhancement of F uptake efficiency of plant P. juliflora through iron oxide nanoparticles (Fe3O4 NPs) application for remediation of agricultural soils. For the study, Fe3O4 NPs were synthesized through green route using waste jojoba leaves. The application of Fe3O4 NPs significantly increased the shoot and root length of plant P. juliflora. Fe3O4 NPs treatment also promoted the F accumulation in shoot and root tissues upto 28.43 and 34.64 mg kg−1, respectively. Microscopic (FESEM and light microscopic) and EDX spectrum analysis of plant tissues confirmed the accumulation and translocation of Fe3O4 NPs and F in plant tissues This nano-phytoremediation approach could be a better option for F remediation for agricultural and commercial purpose.

Removal of fluoride in aqueous medium under the optimum conditions through intracellular accumulation in Bacillus flexus (PN4)

ABSTRACTThe removal of fluoride is essential for water contaminated with fluoride before being utilized since the unsafe concentration of fluoride with respect to the permissible limits. In the present study, there are 61 bacterial strains belonging to fluoride tolerance were isolated from the contaminated soil of Dharmapuri District, Tamil Nadu, India and they were evaluated for different characterization. Among the strains isolated, the strain PN4 showed a high tolerance to fluoride ranging from 500 to 2500 ppm under different stress conditions. The strain PN4 was selected as a possible organism for the degradation and removal of fluoride in an aqueous medium. Based on the morphology, biochemical characteristics and the 16S rRNA sequencing, the bacterium PN4 was identified as Bacillus flexus. In batch mode studies, the glucose was showed the maximum removal of fluoride (86%) followed by beef extract (82%) and a significant level of defluoridation was observed at pH 7.0 and the temperature at 35°C. In the antibiotic-resistance pattern, the strain Bacillus flexus PN4 was shown sensitive to three different antibiotics. Intracellular accumulation of fluoride by the bacterial cell was characterized by SEM- EDAX, TEM and FTIR analysis.

Insights into fluoride-induced oxidative stress and antioxidant defences in plants

Fluoride is a common pollutant which occurs in various environmental matrices considered as one of the most phytotoxic pollutants. It is essential to the living organisms in trace quantities but at its higher concentration it becomes poisonous. Excess amount of fluoride in environment not only exerts its toxic effects on human beings and animals but also on plants. Toxicological impacts of fluoride on plants have been largely debated due to reduction of growth parameters, inhibition of metabolic activities and decreased photosynthetic activity. The signs of fluoride impacts on plants may be severe, acute or chronic and toxicity of fluoride depends on dose, frequency of exposure, duration and genotype of plant. This article overviews understanding of transport, uptake and fluoride accumulation in plants and provide insights into the fluoride-induced oxidative stress and regulatory mechanisms to cope up with it. The main objective of this article is to prospect new research avenues to unravel the mechanisms explaining fluoride toxicity in various plant species.

Enhanced fluoride adsorption of aluminum humate and its resistance on fluoride accumulation in tea leaves

ABSTRACTTea trees (Camellia sinensis) can take in fluorine from soil and the content of fluorine in tea increases with maturity, leading to high content of fluoride in tea leaves and tea products. Long-term consumption of high fluoride tea products could result in chronic fluoride intoxication. Confining the fluoride in the earth with absorbents to reduce the fluoride accumulation of the tea trees during the growth period which could radically control the fluoride level in tea product. Humic acid (HA), a kind of organic matter in the earth was used as raw material to prepare adsorbent aluminum humate (HAA) by aluminum modification. The HAA absorbent presented excellent absorption performance to the fluoride in a wide pH range (4–10), and the maximum adsorptive capacity can reach to 62.5 mg/g. The absorption isotherm demonstrated the adsorption of fluoride was the monomolecular adsorption and the absorption was in accordance with the pseudo-second order kinetic equation. Fluoride content in real soil solution decreased significantly by 53.03% by using the HAA absorbent. The utilization of HAA adsorbent in the culture and field plots experiments also obviously adsorb the soluble fluoride in solution and soil, which could significantly suppress the fluoride accumulation in tea leaves. In September, the fluoride accumulation in tea leaves has been reduced 74.29% in the field plots experiments.