Fluoride In Soil Research Articles

Organic manures reduce the bioavailability of fluoride in soil via different mechanisms

Fluoride (F) pollution in soils, which can be caused by long-term application of phosphate fertilizers, has serious socio-economic and ecological impacts. Therefore, it is important to find economically viable and environmentally friendly remediation technologies that mitigating the potential hazards of F-contaminated soil while maintaining crop yields. In this study, a soil incubation experiment was carried out to investigate the effects of two different organic manures at various amounts on soil F content and soil properties. We demonstrated that organic manure application at a rate of 5% was optimal to control the content of available fluoride (AE-F) in soil. Organic manure decreased the AE-F content and increased the residual or organically bound content. Furthermore, organic manure application also increased the contents of carbohydrates, proteins, and amides, which can anchor AE-F to the dissolved organic matter (DOM) in soil through physicochemical reactions, thereby reducing the migration of F. Moreover, after organic manure application, complex humus compounds were formed through microbial action, thus reducing the bioavailability of soil F. In summary, the application of organic manures can reduce the accumulation of soil AE-F, thereby reducing the absorption of F by crops in F-contaminated soil and alleviating the potential risk of F contamination.

Efficient and simultaneous immobilization of fluoride and lead in water and tea garden soil by bayberry tannin foam loaded zirconium

Nowadays, human activities intensified the combined pollution of fluoride and lead in acidic tea garden soil. The key to eliminating this combined pollution is to immobilize pollutants simultaneously, thus preventing their migration from tea garden soil to tea trees. In this paper, the natural product bayberry tannin was employed as raw material to fabricate functional materials (TF-Zr) for simultaneous adsorption of fluorine (F) and lead (Pb) in water and soil by the reactivity of tannin with Pb2+ and the affinity of Zr with F. SEM-Mapping, EDS, FT-IR, XPS were utilized to probe the immobilization mechanisms. The results showed that TF-Zr could simultaneously and efficiently adsorb F– and Pb2+ from water with the adsorption capacity of 5.02 mg/g (Pb) and 4.55 mg/g (F). The adsorption processes were both in accordance with the proposed secondary kinetic adsorption model. Besides, the presence of F– promoted the adsorption of Pb2+ by TF-Zr. The materials were applied into tea garden soil to explore its effect on the variation of F and Pb forms in the soil. It was found that the proportion of water-soluble fluorine, exchangeable fluorine and exchangeable lead in the tea garden soil decreased significantly, while the proportion of residual fluorine and lead increased evidently, illustrating TF-Zr possessed eximious fixation effect on the highly reactive fluorine and lead in the soil and facilitated their conversion to the more stable residue state. Therefore, TF-Zr can be used for the efficient and simultaneous immobilization of fluorine and lead in water and tea garden soil.

Hydro-meteorological aspects of soil fluorides in semi-arid soils using microwave remote sensing.

Soil fluoride is a critical determinant of soil fertility, human health and crop productivity. Soil fluoride can be increased by climatic conditions, irrigation water and anthropogenic activity, and it is important to control fluoride by understanding the complex relationships between atmospheric conditions and water systems. In this research, a detailed focus is on the hydrological and meteorological aspects of soil fluorides in semi-saturated and saturated soils to discuss the impact of irrigation, capillary rise and the combination of rainfall and anthropogenic activities such as fertilizer application on the soils in the dry spell and monsoon seasons of 2021 and 2022. A Sentinel-1 data can be used to estimate fluoride levels to the above soil conditions. In an effort to estimate fluoride levels in different hydro-meteorological scenarios, we have put forward a hypothesis that focuses on understanding the potential connections between hydro-meteorological factors (precipitation, groundwater levels, and temperature) and the levels of fluoride. The findings indicate that the extensive use of groundwater for irrigation leads to a rise in fluoride levels, posing a significant threat to crop health over time. Furthermore, the combined effects of irrigation and upheaval leaching on fluoride levels have shown strong statistical conformity (R2 > 0.85) with the relevant field-measured fluoride data for the year 2022. Importantly, areas affected by are more sensitive to the sand and clay percentage in the soil because potential and dispersion behaviour enlarge the capillaries to decelerate the upward movement. A region-based discussion details the factors contributing to the increase of fluoride in soil helpful in taking remedial measures and mitigation plans.

Innovative soil fluoride estimation method: dual polarimetric saline-associated fluoride for agricultural patches.

Fluoride and its constituents in soil affect plant growth and public health. In this study, soil fluoride was measured for the semi-arid regions in southern India, using Sentinel-1 data in conjunction with the dual polarimetric saline-associated fluoride model (also known as fluoride model). A loss angle was estimated from laboratory-based dielectric components of soil samples with strong electrical conductivity under high and low fluoride conditions. The conductivity loss angle and real and imaginary dielectric constants were used to study fluoride salt's dielectric behavior. The imaginary dielectric component sensitive to dielectric loss could predict fluoride across large areas over time. This was statistically analyzed with R2 = 0.86, RMSE = 1.90, and bias = 0.35 showing a promising depiction that C-band SAR data can distinguish fluoride levels over varied clay soil and soil with varying vegetation development. Moreover, the association between biomass and simulated fluoride helped to identify fluoride-tolerant and non-tolerant crops. The study found that Sorghum and Oryza sativa tolerate saline-associated fluoride, whereas Peanut and Allium do not. Furthermore, the model successfully retrieves fluoride from saline salts based on tangent loss.

Spatial Variability Characteristics and Influencing Factors of Soil Fluoride in the Western Nansihu Lake Basin

The western plain of the Nansihu Lake Basin (NLB) is an important agricultural economic zone in Shandong Province, where there is a high content of fluoride in soils. Studying the content and influencing factors of fluoride in soils is of great significance for the maintenance of regional eco-logical security and human health. This study takes the farmland soils in the west of NLB as the research focus and uses a method based on GIS and geostatistics to quantitatively analyze the spatial variation characteristics of soil total fluoride and water-soluble fluoride contents to draw a map showing their spatial distribution. The effects on the spatial distribution of soil total fluoride and water-soluble fluoride were analyzed from the aspects of geomorphological type, soil parent material (stratigraphic lithology), crop type, and groundwater fluoride concentration, among others, and the correlation between groundwater and soil fluoride contents was also analyzed. Our study results in the following findings: (1) The average content of total fluoride in topsoil in the study area is 652.8 mg/kg, the national background value is exceeded in 99.5% of the sampling sites, and the background value of Shandong Province is exceeded in 98.7% of the sampling sites. The average water-soluble fluoride is 15.2 mg/kg and exceeds 5.0 mg/kg in 94.3% of the sampling sites. Topsoils have high values of total fluoride and water-soluble fluoride. (2) The total fluoride and water-soluble fluoride in topsoils exhibit moderate spatial variability, indicating that their spatial distribution is the result of structural factors such as soil parent materials and man-made random factors such as fluorinated fertilizers. (3) In the 2 m vertical profile of shallow soils, total fluoride and water-soluble fluoride increase with the increase in soil viscosity, and the water-soluble fluoride has the characteristics of surface aggregation due to the influence of soil adsorption. Because fluoride ions as ligands are easily adsorbed and form fluoride complexes with other ions such as aluminum ions, the water-soluble fluoride shows the characteristics of surface aggregation and fractionation. (4) The analysis of influencing factors reveals that the lithology of Quaternary strata, geomorpho-logical types, and planting crop types have significant effects on the distribution of the total fluoride and water-soluble fluoride in the topsoils, and the distribution of the groundwater soluble fluoride in the topsoils is not related to that in groundwater. Our study provides data and technical support for improving both the soil environmental quality and water quality of the eastern route of the South-to-North Water Transfer Project, thus helping to promote the sustainable development of the social economy and ecological environment in the NLB.

Fluoride contents in commonly used commercial phosphate fertilizers and their potential risks in China.

The application of phosphate fertilizer is an important source of anthropogenic fluoride in agricultural soil. However, relatively few studies have examined the fluoride content of phosphate fertilizers, and that has limited our understanding of the phosphate fertilizer contribution to soil fluoride accumulation and distribution. To examine this problem, we first quantified the total fluoride (TF) and water-soluble fluoride (WF) contents of six of the most commonly used commercial phosphate fertilizers in China (potassium dihydrogen phosphate (MKP), calcium superphosphate (SSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), ternary compound fertilizer (NPK), and water-soluble macroelement fertilizer (WSF)). After calculating the [P2O5]/TF ratio for each of those fertilizers, we used those ratios and the average P2O5 application per crop of five typical crops grown in China (apples, greenhouse vegetables, wheat, corn, and rice) to estimate the annual fluoride accumulations in their soils after application of each type of phosphate fertilizer. Among the six fertilizer types, SSP, DAP, and NPK had much higher total fluoride and water-soluble fluoride contents than MKP, MAP, and WSF had. During crop production, the risk of fluoride accumulation was lower with MKP, MAP, and WSF (high [P2O5]/TF ratios) and higher with SSP, DAP, and NPK (low [P2O5]/TF ratios), especially in cash crops (fruit and greenhouse vegetables), which traditionally have unreasonably high P2O5 applications. Based on our findings, we proposed steps that should be taken to help effectively mitigate fluoride accumulation in China's agricultural soils.

Potential Ecological Risk Assessment and Source Analysis of Heavy Metals in Soil-crop System in Xiong'an New District

In order to evaluate the distribution characteristics of fluorine geochemistry in the surface soil and human health risk in Xiong'an New District, GIS spatial analysis and correlation analysis were used to analyze the depleted and enriched features and influencing factors of soil fluoride and to carry out the soil fluoride health risk assessment. The uncertainty of the health risk assessment results was studied based on the Monte Carlo stochastic simulation. The results showed that the average content of fluorine was 641 mg·kg-1, which was 1.34 times the background value of the national A-layer soil. The excess fluorine and high-grade samples accounted for more than 85%, and the overall soil fluorine content was relatively high. The average content of fluoride of the irrigation water samples was 0.85 mg·L-1, the spatial distribution characteristics of which were affected by the hydrochemical type and flow direction of shallow groundwater. The vertical spatial variation of soil fluoride, mainly affected by the vertical distribution of soil physicochemical properties such as soil organic carbon and texture, was not obvious. The depletion and enrichment of topsoil fluorine was mainly controlled by the geological background, and its spatial distribution was affected by external inputs, such as human factors (agricultural irrigation water, fertilization, and atmospheric dry and wet deposition). The soil fluoride content was significantly correlated with the iconic indicators of the geomorphological environment, including the content of Al2O3, Fe2O3, MgO, K2O, soil organic carbon (Corg.), cation exchange capacity (CEC), clay, and silt (P<0.01). The results of human health risk assessment showed that oral intake was the main exposure risk route of soil fluoride. The non-carcinogenic health risk index HQ of adults was less than 1, and the harm could be ignored. The probability of non-carcinogenic health risk exceeding the threshold for adults and children was 34.3% and 27.6%, respectively, and daily soil intake was the most sensitive parameter.

Influence of Modified Biochar on Soil Fluoride and Cadmium Speciation and Their Bioavailability to Tea Seedling (Camellia Sinensis L.)

ABSTRACT Biochar is widely used as a good soil amendment, while knowledge of modified biochar application in tea garden soils contaminated by fluoride (F) and cadmium (Cd) is insufficient. The tea seedling (Camellia sinensis L.) growth assay was performed to evaluate interaction of soil Cd and F and the improving effect of aluminum trichloride-modified corn stalk biochar (Al-BC) on their speciation, phytoaccumulation and phytotoxicity. Results showed that soil F speciation ratio sequence was as follows: residual > exchangeable > organic-bound > water-soluble > Fe/Mn oxide-bound. Soil exchangeable Cd was the largest Cd speciation (>35.6%), probably due to the low pH values in the acid tea gardens. Root F contents showed a strong significant relationship with soluble F contents (r = 0.92, P < .01) and similarly root Cd highly connected with exchangeable Cd (r = 0.86, P < .01). Seedling height, fresh and dry weight, root surface area, length, and photosynthetic pigment showed different sensitivities to F or Cd oxidative stress and toxicity effects, and only root F contents significantly inversely correlated with them (r = 0.74–0.80, P < .01). The interaction of Cd and F, could influence their speciation distribution and antagonized each other in root accumulation. Meanwhile, joint simulation models showed that antagonistic effects were observed in the F and Cd mixture soils for most cases at Enshi. Biochar application reduced bioavailable F and Cd contents, and thus decreased F and Cd accumulation in tea roots and obviously alleviated toxicity effects. For instance, biochar application significantly reduced root F contents, which had 33.2% to 62.2% declines at Enshi and 39.7% to 77.2% declines at Huanggang. Meanwhile, the soil properties were improved as biochar added, with an increase in soil pH, EC, CEC and organic matter. Overall, Al-modified biochar was beneficial environmental materials for reducing both F and Cd bioavailability.

Effects of calcium supplements on oral bioavailability of fluoride in soil based on In Vivo and In Vitro methods

Dietary calcium (Ca) intake can alleviate fluoride (F) induced fluorosis to maintain bone health. However, it is unclear whether calcium supplements can reduce the oral bioavailability of F present in contaminated soils. Here we evaluated the effects of Ca supplements on F bioavailability in three soils using an in vitro method (Physiologically Based Extraction Test) and an in vivo mouse model. Seven Ca salts, commonly used in calcium supplements, significantly reduced the F bioaccessibility in the gastric and small intestinal phases. Particularly for Ca phosphate at 150 mg Ca supplementation, F bioaccessibility in the small intestinal phase was reduced from 35.1–38.8% to 0.7–1.9% where soluble F concentrations were less than 1 mg/L. Overall, the eight Ca tablets tested in this study showed greater efficiency at decreasing F solubility. The in vitro bioaccessibility after Ca supplementation was consistent with the relative bioavailability of F. As supported by X-ray photoelectron spectroscopy, a possible mechanism is that freed F can be bound by Ca to form insoluble CaF2 and exchanged with OH groups from Al/Fe hydroxide to strongly adsorb F. These findings provide evidence of Ca supplementation in reducing health risks associated soil F exposure.

Fluoride and Metals in the Agricultural Soils of Mica Mining Areas of Jharkhand, India: Assessing the Ecological and Human Health Risk

ABSTRACT The concentration of metals and fluoride in the agricultural soils of the mica mining areas of Jharkhand was estimated for human health risk assessment and source apportionment studies. The elemental concentrations of As, Co, Cu, Fe, Ni, Pb and Zn in the study area exceeded the world average values. The sources of the metals and fluoride in soil were suggested to be from both natural and human-induced activities as per principal component analysis (PCA) and cluster analysis (CA). The sources of Al, Fe, Mn and F in the soil were ascribed to the mica mining–related activities as indicated by PCA and CA. Potential ecological risk assessment suggested moderate risk with respect to Cd, Cu and Pb at few locations. Considering metals and fluoride content of the soils, non-cancer risk assessment suggested considerable risk to the child population which was largely due to Al and Fe. Taking into account all the pathways and elements, the HIs for the study area were calculated to be 0.586 and 3.58 for the adult and child residents, respectively. The carcinogenic risk assessment evaluated the cancer risk to be within the target risk of 1 × 10−4, suggesting insignificant cancer risk to the residents.

Fluoride risk assessment from agricultural soils in India: a study based on vertical, spatial and geochemical distribution.

Fluoride (F) in agricultural soil is increasing continuously due to injudicious application of F-laden fertilizers, causing global concern about fluorosis disease. The objective of the study was to assess F risk in humans due to soil ingestion, dermal contact, and particulate inhalation during various agricultural activities. The study also emphasized chemical fractionation, distribution, and geochemical understanding of high F incidence. Agricultural surface soil was sampled randomly from 5km × 5km square grids besides soil profile samples for studying the vertical distribution of F. Various F fractions in soil (1:1 soil:water ratio, calcium chloride extractable F, hot water soluble F, exchangeable F, Fe-Mn oxide bound F, organic matter bound F, residual F, and total F) were estimated using the sequential fractionation method. Multivariate geochemical analysis and soil F risk were also assessed in humans. The water soluble F (F1:1) and CaCl2 extractable F (FCa) varied between 0.11 to 6.73mgkg-1 and 1.02 to 6.94mg F kg-1 soil, respectively. Total fluoride (TF) however, ranged between 115 to 456mg F kg-1. A higher average of FCa/TF moving down the soil profile indicated a propensity for F endemicity. Weathering, ion-exchange, alkalinity, and clay were found to control the soil geochemistry of the area. The F contamination index explained > 82% variance of F contamination, but the hazard quotient of F for an adult was found < 1, indicating no potential fluorosis risk in the area. This study is the first of its kind in India, where ecological risk due to F from agricultural soil was assessed in humans and will be a benchmark for future researchers.

Determination of Perfluorooctane Sulfonyl Fluoride and Perfluorohexane Sulfonyl Fluoride in Soil by Chemical Derivatization and Liquid Chromatography-Tandem Mass Spectrometry.

Perfluorooctane sulfonyl fluoride (PFOSF) and perfluorohexane sulfonyl fluoride (PFHxSF) were listed as persistent organic pollutants by the Stockholm Convention in 2009 and 2022, respectively. To date, their concentrations in environmental samples have not been reported due to the lack of sensitive methods. Herein, a novel chemical derivatization was developed for quantitative analysis of trace PFOSF and PFHxSF in soil by derivatizing them to the corresponding perfluoroalkane sulfinic acids. The method showed good linearity in the range from 25 to 500 ng L-1 with correlation coefficients (R2) better than 0.99. The detection limit of PFOSF in soil was 0.066 ng g-1 with recoveries in the range of 96-111%. Meanwhile, the detection limit of PFHxSF was 0.072 ng g-1 with recoveries in the range of 72-89%. Simultaneously, perfluorooctane sulfonic acid (PFOS) and perfluorohexane sulfonic acid (PFHxS) were also detected accurately without being affected by the derivative reaction. By applying this method in an abandoned fluorochemical manufacturing facility, PFOSF and PFHxSF were successfully detected at concentrations ranging from 2.7 to 357 ng g-1 and 0.23 to 26 ng g-1 dry weight, respectively. It is very interesting that 2 years after factory relocation, there still exists high concentrations of PFOSF and PFHxSF, which is of concern.

Fluoride accumulation characteristics in a northern China apple orchard that has had long-term phosphate fertilization

Phosphate fertilizer can cause fluoride accumulation in the soil and excessive fluoride poses potential risks to soil and food crop safety. However, the effects of fertilization on soil and fruit fluoride accumulations through long-term positioning trials, especially in high-fertilizer application situations such as apple orchards, have received little attention. To close this knowledge gap, we conducted a field experiment to demonstrate the effects among five long-term (13-year) fertilizer treatments on fluoride accumulations at different soil depths and in the fruits of an apple orchard in Baishui, Shaanxi, China. The five treatments included no fertilization (CK); manure application (M); nitrogen and phosphate fertilization (NP); nitrogen, phosphorus, and potassium fertilization (NPK); and groundcover with nitrogen and phosphate fertilization (GNP). The results confirmed that all phosphate fertilizer treatments (NP, NPK, and GNP) had significant increases in total fluoride (TF) and water-soluble fluoride (WF) accumulations in the topsoil (0–20 cm). Among the phosphate fertilizer treatments, NP topsoil accumulated the most TF and WF, 79.4 and 7.7 mg kg−1 more than CK, respectively, and an average annual TF increase of 6 mg kg−1. However, the M treatment both experienced reduced fluoride content in the topsoil and had TF and WF contents 8.1 and 0.67 mg kg−1 lower than CK, respectively. There was no significant difference between all fertilizer treatments and CK in apple fluoride content. Furthermore, TF and WF accumulated mainly in the topsoil and the differences in soil fluoride content among the treatments decreased with soil depth. These findings showed that long-term phosphate fertilization increases the risk of fluoride accumulation in orchard topsoil. Altogether, these results improve the understanding of the characterization of soil and fruit fluoride accumulations in apple orchards under long-term fertilizer conditions and provide new insights into the use of manure as a possible alternative fertilization strategy that reduces fluoride accumulation.

Predicting and modelling availability of fluoride in soil from sorption properties

AbstractUsage of alkaline and saline groundwater with elevated concentrations of fluoride (F−) for irrigation of pastures requires an assessment of the mobility of F− within the plant‐water‐soil continuum. Factors influencing F− sorption and desorption in 95 Australian soils were examined. Pronounced differences in F− sorption were observed across the soils, but these differences could not be explained by differences in soil pH, electrical conductivity or organic carbon. Rather, sorption was correlated with the content of Fe/Al hydrous oxides and kaolinite in soil. Sorption of F− onto soils increased the solution pH and the ratio of (F− adsorbed) to (OH− desorbed) was consistently below 1, thereby indicating that adsorption of F− results in the release of water and hydroxyl groups from, or co‐adsorption of protons to, the sorbent surface. Maximum sorption occurred at pH values of approximately 5–6, whilst sulphate slightly increased (&lt;5%) F− sorption. Desorption was slightly decreased (~3%–7%) in presence of sulphate anions. Hence, it is unlikely that irrigation of soil with alkaline and saline groundwater, in combination with soil applications of gypsum and sulphur to limit pH fluctuations, would increase mobility of F− in soil. Finally, the irrigation of soil columns with 1200–1500 mm of alkaline and saline groundwater containing 0.18 mM F−, as would commonly occur in irrigation systems using coal seam gas associated water in Australia, resulted in a F− concentration of 0.05 mM at 10 cm depth and the measured values were in excellent agreement with modelled F− movement based on sorption parameters. Thus, sorption parameters can be used to identify soils which minimize movement of F− because of their strong F− sorption. Based on these results, safe limits for irrigation of soil can be established which avoid F− toxicity risks to plants, animals and contamination of water resources.

Soil exposure is the major fluoride exposure pathways for residents from the high-fluoride karst region in Southwest China

In the karst areas of southwest China, soil fluoride levels are higher than in China (478 mg kg−1) and world (200 mg kg−1). High levels of F in the environment might pose a health risk to humans. The comprehensive exposure risk must be studied in this area. Herein, samples of crops and soil were collected from Bijie City, a typical karst area in southwest China, to investigate the pollution level and evaluate the comprehensive F exposure risk. The single-factor index (PFw) and the geological accumulation index (Igeo) were used. The hazard index (HI) was applied to assess exposure risk from multiple exposure routes. The results revealed that there is considerable F contamination in soil and crops in the study area. Average soil total fluorine (Ft) was 1139.13 mg kg−1, and soil water soluble F (Fw) was 3.792 mg kg−1. In corn, rice, wheat, and potatoes, F contents were 1.167–9.585, 1.222–6.698, 1.587–9.976, and 1.797–9.143 mg kg−1, respectively. The mean values of HI were 4.45 and 2.42 for children and adults, respectively, > 1, showing potential health risk exists. Youngsters are at a greater exposure risk than adults. From the results of contribution ratios of different exposure routes for health risk, the major exposure risk was determined to be from soil exposure. Based on this, we suggest that risk managers mainly strive to control the soil fluoride level and implement the risk education and communication.

Remediation of Soils Contaminated by Fluoride Using a Fermentation Product of Seaweed (Eucheuma cottonii)

This study investigated the efficacy of fermented seaweed (Eucheuma cottonii) on the remediation of fluoride-contaminated soil. The soil was amended with either 1.25, 3.0, or 5.0% (w/w) fermented seaweed (FSW), parallel with the controls (0%). The amendment improved the physicochemical properties of the soil particularly pH regulated from strong alkaline (9.3) to neutral (7.0) which is essential for germination, crop growth, and yield. The amount of water soluble-fluoride (Ws-F) dropped from 81.7 ± 3.1 mg/kg to 42.7 ± 2.4, 33.7 ± 1.2, 19.6 ± 0.9, and 12 ± 1.3 mg/kg following 0, 1.25, 3, and 5% amendment dosage, respectively. Most of the Ws-F was converted into exchangeable fluoride (Ex-F) and to fluoride-bound to iron and manganese (Fe/Mn-F). Furthermore, the amendment also enhanced microbial mass and diversity in the soil. The FSW contains organic acids which participate in ionic bonding with the multivalent cations in the soil. The formed compound participates in ion exchange with clay or with anionic adsorption to positively charged clay sites at the edges. This interaction is further essential for enhancing the fluoride holding capacity of the soil. The use of seaweed reduced the bioavailability of fluoride in the agricultural soils and had positive effects on promoting soil fertility. However, further studies to observe its effects on crop performance is of significance.

Anchoring H-Bond Donating/Accepting Pyrrolic Derivatives on Preorganized Scaffolds: Conformationally Switchable Bipedal/Tripodal and Locked Molecular Cage Ionophores for Potentiometric Sensing of Phosphate and Fluoride.

The ionophore properties of a myriad of conformationally switchable bipedal/tripodal receptors and locked molecular cages were evaluated here for the first time to fabricate potentiometric sensors for the determination of environmentally important phosphate and fluoride. Owing to the competent ionophore properties such as high binding selectivity and affinity, the developed ion-selective electrodes displayed response preference for phosphate and fluoride with a selectivity pattern that differs distinctly from traditional Hofmeister series. Binding constants of the ionophore-anion complexes are determined to underscore how modifications in the preorganization and H-bond donating/accepting ability of a given series of ionophores can be exploited to improve the performance for potentiometric sensing. While conformationally switchable bipedal/tripodal ionophores prefer tetrahedral oxyanions, locked molecular cages shift their preference to spherical halides gradually. Nernstian potential responses with good reversibility to target anions can be observed when shifting the optimized membrane electrodes in aqueous solutions within the concentration range of 10-6.5-10-2.0 M. Moreover, potentiometric determination of phosphate and fluoride in mineral water, soil, and tap water samples was achieved in a low μM concentration range with high accuracy, confirming their promising utility in real world applications.

Metabolome and transcriptome analyses of plants grown in naturally attenuated soil after hydrogen fluoride exposure

Accidental chemical leaks and illegal chemical discharges are a global environmental issue. In 2012, a hydrogen fluoride leak in Gumi, South Korea, killed several people and contaminated the environment. This leak also led to a significant decline in crop yield, even after the soil concentration of hydrogen fluoride decreased to below the standard level following natural attenuation. To determine the cause of this decreased plant productivity, we designed direct and indirect exposure tests by evaluating the metabolome, transcriptome, and phenome of the plants. In an indirect exposure test, soil metabolomics revealed downregulation of metabolites in vitamin B6, lipopolysaccharide, osmolyte, and exopolysaccharide metabolism. Next-generation sequencing of the plants showed that ABR1 and DREB1A were overexpressed in response to stress. Plant metabolomics demonstrated upregulation of folate biosynthesis and nicotinate and nicotinamide metabolism associated with detoxification of reactive oxygen species. These results demonstrate impaired metabolism of soil microbes and plants even after natural attenuation of hydrogen fluoride in soil. The novel chemical exposure testing used in this study can be applied to identify hidden damage to organisms after natural attenuation of chemicals in soil, as well as biomarkers for explaining the decline in yield of plants grown in soil near pollutant-emitting industrial facilities.

Hydro-geochemical control of high arsenic and fluoride groundwater in arid and semi-arid areas: A case study of Tumochuan Plain, China

Globally, groundwater with high fluoride and arsenic receives extensive concern because of its wide distribution and great harm to human health caused by drinking water. In this paper, taking Tumochuan Plain in China as an example, based on hydrogeological investigation, groundwater flow system theory and hydro-chemical analysis methods were applied to reveal the mechanism of high fluoride and high arsenic in arid and semi-arid regions. In unconfined and confined groundwater of Tumochuan Plain, the highest concentration of fluoride is 7.2 and 11.2 mg/L respectively, and the highest concentration of total arsenic is 200.3 and 162.3 μg/L respectively. Fluoride in groundwater is mainly derived from the soluble fluoride in soil and aquifer medium. Because of the water-rock interaction, the alkaline environment caused by the hydrolysis of feldspar minerals in the central part of the plain has an important influence on the accumulation of F and As in this area. High fluoride water is formed in the alkaline environment (high pH values) of high concentration of Na+ and low concentration of Ca2+. The high arsenic groundwater is distributed in the alkaline reducing environment that the content of soluble salt in aquifer media is high (>200 mg/100 g dry soil). The reductive dissolution of iron and manganese oxides and competitive adsorption of HCO3− all contribute to a high level of arsenic in both unconfined and confined aquifers. The research results have important guiding significance for water supply safety and water quality improvement in arid-semiarid areas in the world with high fluoride and high arsenic groundwater distribution.

Spatio-temporal variation of fluoride in groundwater and agricultural soil and crops of Unnao district, UP: Monitoring and assessment

Fluoride (F−) contamination in groundwater of Unnao district, Uttar Pradesh was reported for the first time in 1994, however comprehensive monitoring of F− in different environmental matrices remains to be undertaken. The presented study reports spatio-temporal monitoring of F− content in groundwater, crops and soil from F− affected district Unnao, in pre-monsoon (PRM), monsoon (MO) and post-monsoon (PMO), to establish F− groundwater-soil-plant continuum. More than 80% of groundwater samples were contaminated with F−> 1.0 mg L−1 with highest level (mg L−1), at Patiyara (3.6 ± 0.64), during PRM > Pathakpur (2.73 ± 0.57) during PMO > Sarukheda (2.40 ± 0.43) during PRM. High Cr in groundwater was observed in Jajmau (7.08 ± 1.42). The level of F− (mg Kg−1) in agricultural soils followed 3.4 ± 0.71 at Patiyara (MO) > 2.9 ± 0.14 at Badlikheda (PRM) 1.89 ± 0.28 at Jagatkhera (PRM). Among the different edible parts of crops in selected sites, highest F− content (mg Kg−1), F− level in grains of Oryza sativa ranged between 0.23 ± 0.02 to 2.01 ± 0.24. Whereas in the edible fruit of Trichosanthes diocia contained 1.47 ± 0.32 and Momordica charantia 1.47 ± 0.02. Leaf of spinach (1.03 ± 0.22) and seed of Brassica juncea (0.73 ± 0.08). Overall, comparing across all the three seasons, level of F− was highest in all the plants during MO, as compared to PRM and PMO. The regression analysis of physiochemical properties of groundwater show negative relationship between Na+ and F− whereas soil alkalinity exhibited strong influence in soil F−. The high F− content in soil and groundwater at Patiyara and Shekhpur also coincided with presence of several brick kilns, possibly contributing to the high F−.