Climatic condition, geology, and geochemical processes in an area play a major role on groundwater quality. Impact of these on the fluoride content of groundwater was studied in three regions-part of Nalgonda district in Telangana, Pambar River basin, and Vaniyar River basin in Tamil Nadu, southern India, which experience semi-arid climate and are predominantly made of Precambrian rocks. High concentration of fluoride in groundwater above 4 mg/l was recorded. Human exposure dose for fluoride through groundwater was higher in Nalgonda than the other areas. With evaporation and rainfall being one of the major contributors for high fluoride apart from the weathering of fluoride rich minerals from rocks, the effect of increase in groundwater level on fluoride concentration was studied. This study reveals that groundwater in shallow environment of all three regions shows dilution effect due to rainfall recharge. Suitable managed aquifer recharge (MAR) methods can be adopted to dilute the fluoride rich groundwater in such regions which is explained with two case studies. However, in deep groundwater, increase in fluoride concentration with increase in groundwater level due to leaching of fluoride rich salts from the unsaturated zone was observed. Occurrence of fluoride above 1.5 mg/l was more in areas with deeper groundwater environment. Hence, practicing MAR in these regions will increase the fluoride content in groundwater and so physica or chemical treatment has to be adopted. This study brought out the fact that MAR cannot be practiced in all regions for dilution of ions in groundwater and that it is essential to analyze the fluctuation in groundwater level and the fluoride content before suggesting it as a suitable solution. Also, this study emphasizes that long-term monitoring of these factors is an important criterion for choosing the recharge areas.

Excessive enrichment of fluoride threatens ecological stability and human health. The high-fluoride groundwater in the Chagan Lake area has existed for a long time. With the land consolidation and irrigation area construction, the distribution and migration process of fluoride have changed. It is urgent to explore the evolution of fluoride under the dual effects of nature and human. Based on 107 groundwater samples collected in different land use periods, hydrogeochemistry and isotope methods were combined to explore the evolution characteristics and hydrogeochemical processes of fluoride in typical high-fluoride background area and elucidate the impact of anthropogenic activities on fluoride migration. The results indicate that large areas of paddy fields are developed from saline-alkali land, and its area has increased by nearly 30%. The proportion of high-fluoride groundwater (>2 mg/L) has increased by nearly 10%, mainly distributed in the new irrigation area. Hydrogeochemical processes such as dissolution of fluorine-containing minerals, precipitation of carbonate minerals and exchange of Na⁺, Ca²⁺ on the water-soil interface control the enrichment of fluoride. The groundwater d-excess has no obvious change with the increase of TDS, and human activities are one of the reasons for the increase of fluoride. The concentration of fluoride is diluted due to years of diversion irrigation in old irrigation area, whereas the enrichment of δ²H, δ¹⁸O and Cl⁻ in new irrigation area indicates that the vertical infiltration of washing alkali and irrigation water brought fluoride and other salts to groundwater. Fertilizer and wastewater discharges also contribute to the accumulation of fluoride, manifesting as co-increasing nitrate and chloride salts. The results of this study provide a new insight into fluoride migration under anthropogenic disturbance in high-fluoride background areas.

Fluoride (F) is an emerging pollutant that originates from multiple sources and adversely affects plant growth and nutrient bioavailability in soil. This greenhouse study investigated the effects of soil F (0, 10, 20, 50, 100, 200 mg kg⁻¹) on morpho-physiological growth characteristics of wheat, soil F contents, and bioavailability and uptake of F, phosphorus (P), sulphur (S), potassium (K), calcium (Ca), magnesium (Mg), aluminium (Al), iron (Fe), manganese (Mn), silicon (Si) and zinc (Zn) by wheat. Higher F significantly reduced plant height and number of leaves particularly at early growth stages and increased visible leaf injury index. Powdery mildew infestation coincided with leafy injury and was higher in elevated soil F treatments. Fluoride treatments (>50 mg kg⁻¹) significantly increased water (H₂O)- and calcium chloride (CaCl₂)-extractable F contents in soil. Water-extractable soil F contents from soil in all concentration were higher than CaCl₂-extractable F. This increased F bioavailability resulted in significantly higher F uptake and accumulation in live leaves, dead leaves and grains of wheat which followed order: live leaves > dead leaves > grains. Leaf injury index and number of dead leaves correlated significantly positively with soil H₂O- and CaCl₂-extractable F contents. Patterns of nutrient (P, K, S) and trace metals (Al, Ca, Mg, Fe, Mn, Si, Zn) varied significantly with F concentrations and between live and dead leaves, and grains except for Zn. Dead leaves generally had higher nutrients and trace metals than live leaves and grains. Fluoride contents in live leaves, dead leaves and grains showed positive correlations with nutrient elements but negative with trace metals. Number of dead leaves correlated negatively with Al, Ca, Fe, Mg, S and Si but positively with P and Zn contents in dead leaves whereas leaf injury index showed positive correlation with Fe, K, P, Si, Zn, S but negative with Al, Ca and Mg contents. These observations provided evidence of higher F uptake and associated impairment in nutrient and trace metal accumulation which caused leaf injury accompanied by powdery mildew infestation in wheat. However, further research in the region is required to confirm the relationship between F pollution, leaf injury and trace metal accumulation in crops under field conditions.

The increasing salinization of groundwater renders it challenging to maintain the water quality. Moreover, knowledge regarding the characteristics and mechanism of groundwater salinization in mining areas remains limited. This study represents the first attempt of combining the hydrochemical, isotope (δD, δ¹⁸O, δ³⁷Cl, and ⁸⁷Sr/⁸⁶Sr) and multivariate statistical analysis methods to explore the origin, control, and influence of fluoride enrichment in mining cities. The TDS content of groundwater ranged from 275.9 mg/L to 2452.0 mg/L, and 54% of the groundwater samples were classified as class IV water according to China's groundwater quality standards (GB/T 14848–2017), indicating a decline in the water quality of the study area. The results of the groundwater ion ratio and isotope discrimination analysis showed that dissolution and evaporation involving water-rock interactions and halite were the main driving processes for groundwater salinization in the study area. In addition to the hydrogeological and climatic conditions, mine drainage inputs exacerbated the increasing salinity of the groundwater in local areas. The mineral dissolution, cation exchange, and evaporation promoted the F⁻ enrichment, while excessive evaporation and salinity inhibited the F⁻ enrichment. Gangue accumulation and infiltration likely led to considerable F⁻ enrichment in individual groundwater regions. Extensive changes in the groundwater salinity indicated differences in the geochemical processes that controlled the groundwater salinization. Given the particularity of the study area, the enrichment of salinization and fluoride triggered by mining activities cannot be ignored.

Urbanization is conducive to promoting social development and improving living standards. However, the changing land use attributed to urbanization has placed both the environment and humans at risk. Based on the long-term monitoring and the land use change during 2010–2017, we investigated the exposure of fluoride (F) and arsenic (As) in groundwater. We analyzed the temporal and spatial variation of F and As from different land use changes. The study assessed health risk for children by calculating carcinogenic risk and non-carcinogenic risk. Furthermore, we mapped the distribution pattern of F and As using GIS. For the 768 water samples collected from 2010 to 2017, F concentrations ranged between 0.10 and 5.70 mg L⁻¹ (M = 0.68 ± 0.02 mg L⁻¹), As concentrations ranged between 0.50 and 71.50 μg L⁻¹ (M = 4.28 ± 0.28 μg L⁻¹). A concerning result showed that 6.77% of F concentrations larger than 1.5 mg L⁻¹ and 11.46% of As concentrations larger than 10 μg L⁻¹ based on the recommendation by WHO, respectively. Results proved that land use change caused by human activity increased groundwater pollution and placed human health at risk. High F and As risk were found in southern Taiyuan City. In particular, the groundwater of industrial land suffered from more severe pollution, especially at the frontier of urban and suburban areas in the southern part of Taiyuan City. Land use change attributed to industrial land resulted in major increases in the F and As concentrations in groundwater across 2010–2017. Both carcinogenic risk and non-carcinogenic risk in 2016–2017 were higher than that in 2010–2015. Rational land use planning, strict groundwater protection policies and the regular monitoring of pollution levels are necessary in order to prevent the adverse health of residents.

The high concentration of fluoride (F) in soils has become a rising concern for its toxicity to microbes, plants, animals and human health. In the present study, the spatial and vertical distribution, health risk assessment and anthropogenic sources of F in farmland soils in an industrial area dominated by phosphate chemical plants were studied. Concentrations of total fluoride (TF) and water soluble fluoride (WSF) in the surface soils decreased with distance within the range of 2500 m at the prevailing downwind of the industrial area. The soil TF and WSF concentrations in 0–40 cm profiles were higher than those in 40–100 cm layers in the industrial area. At the prevailing downwind of the industrial area within 700 m, the hazard quotient values of human exposure to surface soils were higher than 1, indicating that a potential risk may exist for human health in this area. The main exposure pathway for children and adults was oral ingestion and particulate inhalation, respectively. The source apportionment model of soil F was modified based on years’ historical data and experimental data. The results showed that the proportion of anthropogenic sources of soil F was dustfalls (69%) > irrigation water (23%) > air (5%) > chemical fertilizers (3%) in the industrial area. The high F concentration of dustfalls was mainly due to the phosphate rock, phosphogypsum, and surface soils with high F contents from the factories. In order to safeguard human health and alleviate hazards of F to surroundings, the control of pollutants emission from factories was a basic and vital step to reduce F in the soils in industrial areas.

Hydrogeochemistry and isotope hydrology were carried out to investigate the spatial distribution of fluoride (F−) and the mechanisms responsible for its enrichment in the western region of the Ordos basin, northwestern China. Sixty-two groundwater samples from the unconfined aquifer and fifty-six from confined aquifer were collected during the pre-monsoon (June 2016). Over 77% of groundwater samples from the unconfined aquifer (F− concentration up to 13.30 mg/L) and approximately 66% from confined aquifer (with a maximum F− concentration of 3.90 mg/L) exhibit F− concentrations higher than the Chinese safe drinking limit (1.0 mg/L). High-F− groundwater presents a distinctive hydrochemical characteristic: a high pH value and HCO3− concentration with Ca-poor and Na-rich. Mineral dissolution (e.g., feldspar, calcite, dolomite, fluorite), cation exchange and evaporation in the aquifers predominate the formation of groundwater chemistry, which are also important for F− enrichment in groundwater. Mixing with unconfined groundwater is a significant mechanism resulting in the occurrence of high-F− groundwater in confined aquifer. These findings indicate that physicochemical processes play crucial roles in driving F− enrichment and that may be useful for studying F− occurrence in groundwater in arid and semi-arid areas.