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Ecotoxicological insights into fluoride pollution affecting soil, plant and human health.
| Ecotoxicology and Environmental Safety | Ur Rahman Farooqi Z, Karim A, Qadir AA, Sonia A, Mohy-Ud-Din W, Wambu EW, Ali Q, Haider FU, Gururani MA, Zulfiqar U. | 119:120295. | Online before print publication.
Agriculture Bioavailability Crops Irrigation Soil-F Review
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Abstract

Original full-text study online at
https://www.sciencedirect.com/science/article/pii/S014765132600624X


Highlights

  • Fluoride moves via water–soil–plant pathways, impacting agroecosystems.
  • Bioavailability, not total fluoride, governs crop uptake and risk.
  • Elevated fluoride impairs soil microbes, crop growth, and yields.
  • Contaminated food and water increase human fluorosis risks.
  • Ca-based amendments and bio-approaches reduce fluoride mobility.
Fluoride contamination impacts the water–soil–plant continuum, with consequences for soil functions, crop performance, and dietary exposure. Although fluoride occurrence data are extensive, interpretation and cross-study comparability remain constrained by inconsistent reporting of total fluoride versus fluoride fractions up taken in edible plant parts, limited co-measurement across matched water–soil–plant compartments, and a shortage of long-term field evaluations of mitigation impacts on soil fertility and ecosystem services. To address these limitations, we (i) consolidate dominant sources and transfer pathways linking groundwater, soils, crops, and food webs; (ii) summarize the geochemical and soil controls governing the fluoride mobility and uptake, including pH/alkalinity, major-ion chemistry, Ca/Al/Fe-mediated complexation and precipitation, and sorption to clays and metal (hydr)oxides; (iii) integrate ecotoxicological evidence for soil processes and crop-relevant physiological endpoints; and (iv) critically assess the remediation and management options. Across the literature, a central finding is that risk is governed less by total soil fluoride inventories than by the fluoride concentrations up-taken in edible plant parts, which increases under alkaline conditions and in bicarbonate-, and sodium-rich systems and can be sustained through chronic irrigation loading. Evidences indicate that elevated fluoride suppresses microbial activity and enzyme functions essential for nutrient cycling, disrupts Ca–P homeostasis, reduces photosynthetic capacity in sensitive crops, and transfers to edible tissues and beverages, thereby increasing dietary exposure, including in vulnerable populations such as children. Hotspot assessments require explicit consideration of co-contaminant stressors and confounding geochemical conditions. We conclude that effective management should emphasize source control, mechanism-based immobilization (e.g., Ca-based amendments and targeted sorbents), and integrated approaches validated through multi-season field trials. Future priorities include standardized fraction metrics, matched compartment monitoring, crop dose–response datasets, and evaluation of remediation durability, agronomic trade-offs, and cost-effectiveness.

Keywords: Fluoride pollution; Human health; Agriculture; Pesticides; Fluorite; Apatite

1. Introduction

Fluoride is the dominant environmental form of fluorine, the smallest and most electronegative halogen (Group 17). It is encountered primarily as dissolved fluoride or fluoride-bearing minerals and salts rather than as elemental fluorine (RSC, https://periodic-table.rsc.org/element/9/fluorine). Although fluoride is abundant in the Earth’s crust and is widely distributed across natural matrices (Thippeswamy et al., 2021), it becomes an agricultural and public-health concern when geochemical conditions and human activities increase plant-available fluoride in groundwater, soils, and plants, ultimately making its way to edible plant tissues e.g., grains. Elevated fluoride burdens have been reported in agricultural soils up to 1000mg kg-1 (Muthu Prabhu et al., 2023), highlighting the potential for long-term accumulation when inputs are sustained and removal is limited. In agroecosystems, fluoride contamination is driven by both geogenic and anthropogenic sources i.e., geogenic inputs arise from weathering of fluoride-bearing minerals and from groundwater–rock interactions that mobilize fluoride into aquifers (Tong et al., 2023) (Fig. 1A); when such groundwater is used for irrigation, it acts as a chronic loading pathway to cultivated soils (LaFayette et al., 2020). Anthropogenic inputs commonly include phosphate fertilizers and associated by-products, industrial emissions and atmospheric deposition (including coal-related sources), and mining/smelting activities that elevate fluoride loads in surrounding landscapes (Ramteke et al., 2018). The resulting soil fluoride levels vary widely by region; for example, Polish soils have been reported to contain up to 88.9 mg kg-1 (Kupiec et al., 2019b), while Chinese soils averaging ~453 mg kg-1 of fluorides, and the sources are linked to mineral weathering and groundwater-mediated transfer into soils (Li et al., 2023). Regions with extensive rice (Oryza sativa L.) cultivation, such as China, India, Pakistan, and Bangladesh, have also been identified as key areas where groundwater fluoride contamination intersects with irrigated agriculture (Yadav et al., 2019), which underscore that fluoride contamination risk in agriculture is not defined solely by total presence, but its bioavailable forms to edible plant tissues e.g., grains.

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Fig. 1. Environmental pathways and transformations of fluoride in coupled aquatic–terrestrial systems. (A) conceptual schematic showing major geogenic (volcanism, rock weathering) and anthropogenic (industrial emissions/effluents, agricultural runoff, urban inputs) sources, with delivery to surface waters via rainfall/atmospheric deposition, runoff, and direct discharge. In aquatic systems, fluoride undergoes partitioning and exchange with sediments through adsorption, ion exchange, complexation with organic matter, co-precipitation, diffusion across the sediment–water interface, resuspension/entrapment in pore water, and long-term burial; biological uptake by organisms is depicted alongside volatilization/evaporation and microbial mediation. Plant uptake and food-chain transfer are illustrated, together with phytoremediation-relevant processes (rhizofiltration, phytostabilization, phytoaccumulation). (B) geochemical and soil factors controlling the mobility and uptake of fluoride, including pH/alkalinity, major-ion chemistry, Ca/Al/Fe-mediated complexation and precipitation, and sorption to clays and metal (hydr)oxides. Created inwww.BioRender.com.

Once introduced, fluoride transport and transformation in soils are governed by interacting physicochemical controls, including soil texture, pH, organic matter, and elemental composition (Kupiec et al., 2019a). These controls regulate sorption to clays and metal (hydr)oxides, complexation/precipitation behavior, and ultimately the soil-solution fluoride fraction that determines leaching potential and plant exposure. Fluoride can move from natural and anthropogenic sources into both biotic and abiotic compartments of the environment (Fig. 1B), creating coupled risks for soil function, crop productivity, and dietary exposure. Plants, particularly food crops, can accumulate fluoride via root uptake from soil solution and via foliar entry following atmospheric deposition and uptake through roots (Kazi et al., 2019). These fluorides concentrations, when moved to edible parts of the plants, cause human health repercussions when consumed as food (Rehman et al., 2026). In plants, fluoride has been linked to chloroplast degradation and reduced photosynthesis rates; e.g., Bano et al. (2020) reported that exposing hemp (Cannabis sativa L.) plants to 30–50 ppm of fluoride resulted in a 74.6% reduction in chlorophyll content with disruption to the mineral balance of plants by inhibiting the uptake of essential divalent cations, due to the formation of insoluble complexes, e.g., calcium (Ca) and magnesium (Mg). Due to these constraints, plant growth and biomass production is affected. Beyond direct crop impacts, elevated fluoride has been reported to inhibit soil microbial activity and metabolisms, and disrupt key processes involved in nutrient cycling and soil organic matter (SOM) decomposition, with potential consequences for fertility and resilience (Ropelewska et al., 2016). Fluoride can also alter soil chemistry and affect nutrient availability (Muthu Prabhu et al., 2023), and has been associated with soil health degradation via disturbed soil ecology and associated processes (Shahab et al., 2017). These soil-mediated effects are particularly relevant for sustainable intensification, because they link contamination not only to toxic endpoints but also to core agroecosystem services e.g., nutrient cycling, water regulation, and structural stability.

Human exposure is tightly connected to these agricultural pathways i.e., fluoride is widely used in oral health interventions and can help prevent tooth decay and support bone mineralization under appropriate exposure conditions (Kanduti et al., 2016b). However, excessive fluoride exposure remains a concern in regions with elevated drinking-water fluoride and/or significant dietary contributions from contaminated crops and beverages. Children are especially vulnerable to fluoride toxicity due to higher intake relative to body weight and developmental sensitivity (Wang et al., 2023). The World Health Organization (WHO) has set a guideline value of 1.5 mg L–1 for fluoride in drinking water (Naaz et al., 2015), and a toxicity threshold of 30 and 30.2 mg kg–1 for animal feed and raw materials (Wang et al., 2023). Accordingly, fluoride is increasingly regarded as an emerging contaminant that can constrain crop production and pose threats to food security in high-loading agroecosystems (Rizzu et al., 2021).

Despite substantial monitoring and growing concern, several gaps continue to limit risk-relevant interpretation and field management. First, many studies report total fluoride without distinguishing between the soluble/exchangeable or plant-available fractions, which more directly predict crop uptake and ecological effects, making cross-study comparisons and mechanistic inference difficult. Second, the relative importance of exposure pathways (irrigation water, soil fractions, and atmospheric deposition) remains inconsistently quantified across crop types and management systems. Third, while multiple remediation approaches have been proposed, soil washing, chemical immobilization, and electrokinetic methods, field deployment is frequently constrained by cost, secondary waste generation, durability under variable pH/salinity regimes, and potential trade-offs with nutrient availability and soil biota (Muthu Prabhu et al., 2023). These gaps collectively prevent a clear translation from measured concentrations to actionable management decisions. Unlike prior summaries that largely compile concentration ranges and general impacts, we organize the evidence around plant-uptake-controlled exposure, explicitly distinguishing total fluoride from risk-relevant fractions and linking these metrics to crop uptake, subsequent plant and human health repercussions, soil functional changes, and range of mitigation technologies. In doing so, we highlight priority research needs, all of which are necessary to strengthen mechanistic understanding and support practical risk reduction of fluorides contamination in agroecosystems.

This review synthesizes current knowledge on fluoride contamination in agricultural soils by (i) consolidating dominant sources and transfer pathways linking groundwater, soils, crops, and food webs; (ii) summarizing the key soil and geochemical controls governing fluoride mobility, speciation, and its uptake in edible plant tissues; (iii) integrating evidence on ecotoxicological impacts for soil functioning and crop-relevant endpoints, alongside implications for dietary exposure and vulnerability; and (iv) critically evaluating remediation and management strategies in terms of mechanism, feasibility, and field durability. This scientific overview serves as a foundation for further research and sustainable environmental management, emphasizing the urgency of addressing fluoride contamination for ecosystem health and human well-being.

2. Review methodology

This review was synthesized through a systematic literature search and thematic analysis i.e., a comprehensive search of peer-reviewed literature was conducted across several scientific databases, including Web of Science, Scopus, PubMed, Google Scholar, ScienceDirect, and the agricultural-focused databases such as AGRICOLA and Agris. The search strategy employed Boolean combinations of keywords, including core terms such as ‘‘fluorides pollution’’ OR ‘‘fluoride contamination’’ AND ‘‘environment’’ alongside source-specific terms like ‘‘fluoride sources’’, ‘‘soil pollution’’, ‘‘water pollution’’ and ‘‘groundwater’’ to capture media-specific occurrences. To address exposure pathways and impacts, the search included ‘‘fluoride’’ AND ‘‘plant productivity’’, ‘‘crop production’’, ‘‘fluoride uptake’’ AND ‘‘plants’’, ‘‘human health’’, ‘‘toxicity’’ and ‘‘soil microbiome’’. Remediation and management strategies were explored using combinations such as ‘‘fluoride’’ AND ‘‘remediation’’, ‘‘microbial’’, ‘‘biochar’’, ‘‘phytoremediation’’, ‘‘soil amendments’’, ‘‘defluoridation’’ and ‘‘crop protection’’. Finally, the mechanistic insights were targeted with keywords including ‘‘organic amendments/biochar mechanisms’’, ‘‘fluoride bioavailability’’ and ‘‘fluoride mobility’’ AND ‘‘soil’’. To supplement the database searches, manual searches of the relevant articles from institutional websites were explored, including agricultural research centers, environmental protection agencies, and pollutants-focused organizations. This step ensured the inclusion of pertinent grey literature, technical reports, and policy documents not captured by standard academic databases. The search was restricted to publications from 2015 (unless any historic/ mechanistic finding which was not found in recent literature was required) to onwards and the publications selection process prioritized peer-reviewed original research articles, authoritative review papers, and empirical studies with robust experimental designs. We excluded the conference proceedings, opinion-based commentaries, and non-English publications. Studies were included if they met the following criteria: (i) were peer-reviewed original research or comprehensive reviews; (ii) provided experimental evidence on fluorides pollution and its subsequent influence on environment; and (iii) detailed mechanisms and challenges posed by fluorides to soil, plant, and humans. Conversely, studies were excluded if they: (i) were purely theoretical or lacked empirical data; (ii) focused exclusively on water pollution by fluorides, unless they offered mechanistic insights directly applicable to soil entry and subsequent impacts to soil, plant, and humans; (iii) and were duplicate publications or exhibited insufficient methodological rigor. To mitigate selection bias, the screening of titles, abstracts, and full texts was performed independently by at least two reviewers. Disagreements regarding inclusion were resolved through consensus-based discussion and collaborative re-evaluation. Each selected study was critically appraised to evaluate its limitations, methodological soundness, and potential for replication. The extracted data were then synthesized thematically, structured around the core sections of fluorides pollution and its impacts on soil, plant and humans. Key insights, research gaps, methodological constraints, and future recommendations were identified and presented in the section ‘‘Research gaps and future strategies’’.

3. Sources of fluorides in water-soil-plant system

Fluoride is a highly reactive and usually exists in a bound form with other inorganic materials and constitutes 0.06–0.09% of the earth’s crust by weight (Kanduti et al., 2016a). The most common source of fluoride in environment are igneous, sedimentary, metamorphic, volcanic rocks, alkaline igneous, and coal (Supplementary Table S1). Volcanic eruptions containing hydrogen fluoride (HF) are the second most common natural source of fluoride (Kabir et al., 2020). During volcanic activity, fluoride emissions reach the soil surface through particulate fluorine fallout during atmospheric deposition and rainfall (Brindha and Elango, 2011). Prominent anthropogenic sources of fluorides are coal combustion, steel manufacturing, chemical, clay, aluminum, glass, enamel, brick, and ceramics production, as well as the utilization of pesticides and fertilizers containing fluoride, sewage and sludge wastes, and thermal power plants (Jangid et al., 2024). Fertilizers and soil conditioners, such as phosphate fertilizers and phosphogypsum, typically contain 1–4% fluorides as impurities, leading to higher soil concentrations through repeated applications and subsequent uptake by plant roots (Cui et al., 2021). Calcium fluoride (CaF2), sodium fluoride (NaF), HF, and sulfur hexafluoride (SF6) are also sources of fluoride contamination (Wang et al., 2023). Moreover, the application of fumigants and insecticides containing barium fluorosilicate (BaSiF6), sodium silicofluoride (Na2SiF6), sulfuryl fluoride (SO2F2), and fluralin (C13H16F3N3O4) also adds substantial amounts of fluoride to soil (Alexandrino et al., 2022). Fluorides are also taken up by the soil–plant system through water (Mukherjee and Singh, 2018a). Geochemical processes, including cation exchange under high-sodium and alkaline pH conditions, influence fluoride movement to groundwater (Bowes et al., 2020). Vertical leaching by irrigation return flow and mixing with pore water are dominant processes driving fluoride movement in groundwater flow systems (Bowes et al., 2020). The mobility of fluoride in soils is influenced by its association with different soil fractions. In some cases, fluoride is mainly found in the residual and water-soluble fractions, making it readily leachable into groundwater (Dehbandi et al., 2017a).

4. Fluorides entry into the water–soil–plant system

4.1. Water resources

Water is amongst the significant routes of fluoride entry into the soil and food chain through plant uptake (Table 1). Water with fluoride concentrations up to 1.5 mg L–1 is deemed safe (Bharti et al., 2018), while higher levels are considered highly contaminated (Shaji et al., 2024). Higher bicarbonate (HCO3–) and sodium concentrations, coupled with elevated pH resulting from water–rock interactions, play a crucial role in the release of fluoride from the aquifer matrix into the groundwater (Al Sabti et al., 2023). The relatively higher OH– content can readily replace exchangeable fluoride- or fluoride-bearing minerals, thereby increasing its concentration in groundwater (Mondal and Gupta, 2015). In natural waters, fluoride forms strong complexes with aluminum (Al), and therefore, fluorine chemistry is largely regulated by Al concentration and pH level (Gong et al., 2012). There is also a positive correlation between fluoride and arsenic (As) (González-Horta et al., 2015). Higher bicarbonate concentrations in groundwater can serve as a strong competitor, leading to enrichment of fluoride and As in groundwater (Khair et al., 2014). Climate also affects fluoride solubility, as temperature directly influences the solubility of fluorine-bearing minerals. For instance, the equilibrium constant for fluorite rises from 10 to 10.8 at 10ºC to 10–10.5 at 25ºC (Jha et al., 2011), resulting in approximately 30% more fluoride dissolution in dilute solutions. The level of fluoride in groundwater is much higher than in surface water because fluoride percolates from soil to groundwater through leaching, which involves dissolution, desorption, and transport of fluoride ions from soil and rock minerals into groundwater (Mukherjee and Singh, 2020). Mineral dissolution occurs when fluoride-containing minerals, e.g., fluorite (CaF2), apatite (Ca5(PO4)3 F), biotite, and amphiboles, are dissolved into water and release fluorides;

Table 1. Concentrations of fluoride in water–soil–plant system of various countries.

Country Fluoride concentration (mg L-1 For instance, the equilibrium 1 or mg kg–1) Reported sources References
Fluorides in water resources
India 20.6 – (Narsimha et al., 2020)
Afghanistan 15.0 – (Kumari and Khan, 2018)
Pakistan 22.8 – (Sahu, 2019)
Turkey 1.20 Geological origins (Yesilnacar et al., 2016)
China 14.1 Shallow groundwater leakage, gypsum and mirabilite dissolution (Li et al., 2015)
China 7.35 Over-exploitation of groundwater (Li et al., 2020)
India 2.80 Natural (Ali et al., 2019)
Sweden 7.4 Fluorine-rich granitoid rocks (Berger et al., 2016)
Italy 6.1 Volcanic-sedimentary aquifer (Parrone et al., 2020)
Kenya 74.98 Natural sources (Olaka et al., 2016)
Serbia 1.0 Lithium-bearing ores (Veskovic et al., 2024)
Romania 0.13 Natural (Dobrinas et al., 2022)
Fluorides in soil system
South Korea 222.0 Spillage of HF (An et al., 2015)
India 189.0 Zinc smelter plant (Bhat et al., 2015)
Tanzania 133.10 Fluoride-contaminated river water is used for irrigation (Rizzu et al., 2020)
India 280.0 Fluoride-contaminated irrigation water (Devi et al., 2022)
China 330.36 Irrigation water (Zhang et al., 2019)
China 883.0 Industrial and municipal wastewater for irrigation (Li et al., 2019)
China 265.0 Anthropogenic sources (Chen et al., 2017)
Tunisia 1431 Phosphatic fertilizers (Boukhris et al., 2015)
Iran 355.0 Soil and shale rocks (Dehbandi et al., 2018)
Kenya 3.47 Irrigation water (Gevera et al., 2022)
Fluorides in plant system
India Radish
63.0		 Irrigation water (Bhattacharya et al., 2017)
India Rice
Shoot: 127.2
Root: 203.0		 Irrigation water (Mondal, 2017)
China Wheat
Roots: 539.4
Leaves: 129.2
Husk: 40.2
Grains: 2.9		 Atmospheric deposition (Li et al., 2017)
Iran Mint
4.7		 Anthropogenic sources (Ghassemi-Golezani and Farhangi-Abriz, 2023)
China Tea
81.7		 Tea manufacturing process (Cai et al., 2016)
India Rice
Shoot: 38.4
Root: 47.6		 Irrigation water (Banerjee et al., 2019)
Tunisia Olive
Leaves: 220.77
Roots: 1000.43		 Anthropogenic sources (Zouari et al., 2017)
India Pigeon pea
6.5		 Anthropogenic sources (Yadu et al., 2018)
HF: hydrofluoric acid.

Similarly, ion exchange and adsorption-desorption reactions also cause their entry into water, i.e., fluoride competes with hydroxyl ions (OH–) for adsorption sites on clay minerals and oxides (e.g., alumina, iron oxides), and OH– Chinese soils averagin replaces F– on mineral surfaces, causing F– release into the groundwater;

Under alkaline soil conditions, carbonate and bicarbonate ions cause fluoride release through breaking fluorapatite. Moreover, higher soil sodium levels promote fluoride leaching by disrupting Ca equilibrium. Table 2 shows the ranges of fluoride concentrations in groundwater from various countries. Several factors, including rock type, soil consistency, temperature, soil pH, the chelating action of other elements, shallow water leakage, well depth, and the physical and chemical characteristics of water, contribute to fluoride presence in natural groundwater (Shaji et al., 2024). When fluoride enter into the water, especially in drinking or irrigation water, it subsequently work as carrier of fluorides into human food chain via entering into soil and then food grown using it as irrigational water (Fig. 2).

Table 2. Framework of fluorides entry in water, plant uptake, and biological endpoints.

Fluoride concentration in water (mg/L) Concentration moved in soil (mg/kg) Concentration up taken in food/edible parts (mg/kg) References
0.3–4.0 110.5 Tomato: 2.38
Onion: 1.89
Cucumber: 0.39		 (Asgari et al., 2025a)
1.63 2.63 Jowar grains: 1.43 (Naik et al., 2017)
– 126 Onion: 43 (De et al., 2021a)
– 883 Maize grain: 0.3 (Li et al., 2019)
15.1 1572 Lettuce: 5.76
Cabbage: 2.70		 (Dagnaw et al., 2017)
36.3 2540.3 Wheat grains: 2.9 (Li et al., 2017)
32.4 478 Wild cucumis: 186
Indian squish: 113.2
Cluster bean: 68.6		 (Kazi et al., 2019)
– Rice soil: 1.23
Red gram soil: 1.23
Jowar soil: 1.21		 Rice: 0.79
Red gram: 4.26
Jowar: 8.8		 (Havale et al., 2022)
4.0 280 Potato: 127 (Devi et al., 2022)
Limit = 1.5 Limit = 200–4000 Limit = 4.0

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Fig. 2. Entry of fluorides into water and soils and subsequent uptake and internal transport in plants. Fluoride inputs to water arise from rock weathering (fluoride-bearing minerals, as illustrated), volcanic eruptions, and industrial/agricultural/domestic sources, followed by transfer to soils via water movement and transport with eroded soil. In soils, fluoride fate is regulated by adsorption onto clays, Fe/Al oxides, and organic matter, and by Ca-associated immobilization (CaF2 precipitation). Plant exposure occurs through root uptake (passive diffusion and channel-mediated/active transport) and foliar entry (stomata and cuticular penetration), followed by xylem loading/translocation and tissue deposition; movement across the root is depicted via apoplastic and symplastic pathways constrained by the Casparian strip. Created inwww.BioRender.com.

4.2. Soil system

The fluorine content in soil are reported up to 1000 mg kg-1 (Muthu Prabhu et al., 2023), but in areas in the vicinity of phosphatic fertilizer production units are relatively higher. Fluorine in soils predominantly exists within minerals or is adsorbed to clays and oxy-hydroxides, with only a small percentage is dissolved in the soil solution (Du et al., 2024). The release of fluoride from soil is constrained by its strong association with soil components. Various factors influence fluoride release, including chemical speciation, soil chemistry, and climate. Factors governing the mobility of fluoride in soils include soil pH, exchangeable sodium percentage, clay type, and the presence of CaCO3 (Fig. 1B). Excessive fluoride concentrations in soil can alter its physicochemical properties, affecting nutrient cycling and microbial populations. While the specific impacts of fluoride on soil microorganisms are not extensively discussed in the provided context, research on other chemical stressors suggests that soil invertebrate communities and microbial diversity can be significantly affected by contaminants e.g., fluorides (Pramanik et al., 2025). Alterations in soil microbial communities caused by fluoride pollution can disrupt essential ecosystem services and the natural mitigation of environmental pollution. The consequences of soil fluoride pollution extend beyond the immediate environment, posing risks to human health through the food chain. Fluoride can be taken up by plants grown in contaminated soil, potentially entering the food chain and causing health issues in humans. While lower concentrations of fluoride (<1.0 mg L–1) are beneficial for dental health, higher concentrations (>1.5 mg L–1) can lead to dental and skeletal fluorosis, and in extreme cases, even death (Biswas et al., 2017). In soils, fluoride solubility is pH dependent, and sorption decreases at lower pH due to the formation of soluble Al–fluoride species such as (AlF)2+ and (AlF2)+ complexes, while at high pH, pH-dependent negative charges on variably charged clay surfaces (oxides and hydroxides of Fe and Al) create an unfavorable electrostatic potential, reducing fluoride retention and increasing fluoride concentration in the soil solution (Fig. 1B).

The increase in fluoride concentration in the soil solution can be attributed to the displacement of adsorbed fluoride, which is prompted by an increased concentration of hydroxide ions (OH–) in the soil solution, especially at higher pH levels and by the isomorphous substitution of hydroxide ions (OH–) within clay minerals (Gitari and Mudzielwana, 2018). The adsorption capacity of different materials varies, and in bentonite, the Al(OH)3 precipitate exhibits a notable capacity for fluoride adsorption. Unlike exchanging with the OH– groups in the crystal lattices of clay minerals, fluoride adsorption primarily occurs through the exchange with OH– groups derived from Al(OH)3 and basic Al polymers that are adsorbed on the surfaces of minerals. In calcareous soils, the limited movement of fluoride is attributed to the formation of slightly soluble fluoride (CaF2) and fluoride complexes with Al, iron (Fe), and silicon. Conversely, in sodic soils, elevated levels of exchangeable sodium increase the solubility of fluoride (Yadav et al., 2018). Studies have also reported a linear correlation between the increase in water-soluble fluoride and the rise in exchangeable sodium percentage (ESP) (Barnwal et al., 2017).

Furthermore, soil health is impacted by fluoride in soil by disrupting soil pH, i.e., lowering pH, which enhances Al and Mn mobility and thereby their toxicity in soil (Muthu Prabhu et al., 2023). They also pose detrimental effects on symbiotic associations, e.g., arbuscular mycorrhizal fungi, impairing phosphorus and Zn uptake, forming complexes with Al, Fe, and Ca, and enhancing bioaccumulation of Cd and Pb in soil biota (Wang et al., 2022a, Zhao et al., 2025). Fluorides also inhibit enzyme activities, e.g., urease and phosphatase, thereby affecting SOM decomposition (Waugh, 2019). Moreover, they affect N-fixing and phosphate-solubilizing bacteria (PSB), thereby altering microbial diversity (Singh et al., 2023b). Furthermore, fluorides displace essential soil nutrients, e.g., Ca2+, Mg2+, and K+, damaging soil structure, reducing water infiltration and water-holding capacity (WHC), altering redox potential, and affecting Fe and Mn cycling and nutrient availability (Asgari et al., 2025b, Bhat et al., 2015) (Fig. 3).

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Fig. 3. Conceptual summary of fluoride-driven impacts on soil health, nutrient cycling, and biodiversity. The figure illustrates soil chemical and biological disruptions associated with elevated fluoride, including soil acidification with reduced N–P–K availability, increased availability of toxic metals, complexation with Al/Fe/Ca, and disrupted cation-exchange capacity (CEC) via competition with major anions and displacement of base cations (Ca2+, Mg2+, K+). Biological effects shown include reduced symbiosis (e.g., AMF), impaired P and Zn uptake, soil toxicity to soil biota, reduced SOM decomposition/humification with inhibition of key enzymes (e.g., urease, phosphatase, cellulase), and altered microbial communities (including impacts on N-fixing bacteria and PSB). Physical consequences depicted include aggregate loss/compaction, reduced infiltration, and reduced WHC, alongside altered redox potential affecting Fe/Mn cycling. AMF: arbuscular mycorrhizal fungi, WHC: water-holding capacity, PSB: phosphate-solubilizing bacteria, SOM: soil organic matter, CEC: cation-exchange capacity. Created in www.BioRender.com.

4.3. Fluorides uptake in plants and subsequent entry into food web

Fluoride content in plants/crops depends on the concentration of fluoride in the soil and the irrigated water. Therefore, fluoride content could vary from place to place, country to country, and region to region. All types of foodstuffs contain trace amounts of fluoride (Ghosh et al., 2013). The food items contain fluoride, which is up-taken from soil and irrigation water, as shown in Supplementary Table S2. Among cereals, boiled pasta has an average fluoride concentration of 0.07 mg kg–1, while rice has a concentration of 5.9 mg kg–1. In the case of nuts and oilseeds, mustard (Brassica juncea L.) seed has a fluoride concentration of 5.7 mg kg–1. Dry tea (Camellia sinensis L.) leaves have a fluoride concentration of about 400 mg kg–1, among the highest among beverages. Among animals, fish have a fluoride concentration of 6.5mg kg–1. In the case of fruits, Guava (Psidium guajava L.) has a fluoride concentration of 5.1 mg kg–1. Among all edible items, rock salt and tobacco (Nicotiana tabacum L.) have concentrations of 250 mg kg–1 and 38 mg kg–1, respectively. Tea consumption has also been identified as a potential source of fluoride exposure; a study evaluating fluoride concentrations in tea among and a study from Iran found that the hazard quotient (HQ) for women and children was within the safe zone (HQ<1), indicating no potential non-carcinogenic risk. However, in men, one case showed HQ> 1, suggesting a probable risk of fluorosis (Karami et al., 2019). In addition, fluoride contamination in food and water sources leads to fluorosis, affecting both humans and animals (Mukherjee and Singh, 2018b). The primary source of fluoride exposure is through groundwater contamination, which makes water unsuitable for drinking purposes (Saeed et al., 2020). The health effects of fluoride contamination range from mild impacts on teeth and bones to severe kidney problems, neurotoxicity, and even cancer. Children are particularly susceptible to fluoride toxicity, with studies suggesting that exposure to high fluoride levels during childhood can lower IQ scores. The mechanism behind fluoride’s neurotoxicity is not fully understood, but it is known to disrupt biochemical processes and alter normal brain function (Saeed et al., 2020).

Estimating fluoride intake in children is challenging due to significant variations. Various studies, e.g., De et al. (2021b), Mridha et al. (2021) and Rizzu et al. (2021) have reported that most of the fluoride intake in children occurs from its concentrations in contaminated water, contaminated food, and beverages, which should be monitored to limit the excessive fluoride intake among children. A study found that meat contains higher levels of fluoride than vegetables. The concentration of fluoride exceeded the limit in all samples, including plants and crops, but meat had higher levels (Barmao et al., 2019). Carbonated drinks are also among the prominent sources of fluoride, accounting for 59% of dietary fluoride intake (Zohouri et al., 2006). Excessive fluoride intake can cause dental and skeletal fluorosis, mottled teeth, bone deformities, and joint pain (Taher et al., 2024). High fluoride exposure also impairs cognitive development and thyroid function, and children are more vulnerable due to their lower body weight and developing organs (Rehman et al., 2022).

Although fluorides are present in water and soil in total fluorides form, upon entry into the soil environment, they partitioned into water soluble, exchangeable, bounded, and residual forms. Different soil properties, e.g., pH decides the fate of fluorides mobility and entry into the food chain. Fluorides movement i.e., bioavailability is higher in alkaline conditions in which fluorides move into plant and end up in their edible parts such as grains and tissues. For example, Asgari et al. (2025b) described a framework of fluorides movement and their entry into the edible plant food chain via irrigation water where total fluorides-loaded water is applied which cause their buildup in soil, making fluorides availability to edible parts and subsequent movement to food chain. They reported total fluoride concentrations up to 4.0 mg L–1 in irrigation water and upon repeated irrigations, soil total fluorides load went up to 110.5 mg kg–1, from which 2.38, 1.89, and 0.39 mg kg–1 of fluoride concentrations were detected in tomato, onion, and cucumber. Similar results were reported by Havale et al. (2022) that fluorides concentrations in red grams were recorded up to 4.26 mg kg–1 upon fluoride-contaminated water which increased soil fluoride concentration (1.23 mg kg–1), while Naik et al., 2017) reported up to 1.43 mg kg–1 fluorides in Jowar grains upon fluorides contaminated irrigation water (1.63 mg L–1), which increased soil fluorides concentration (2.63 mg kg–1),and end up in Jowar grains (Table 2).

5. Factors affecting fluoride entry into soil-plant system

The concentration of fluorides entering to water, soil, and the plant system are determined by the combination of soil properties and various environmental factors. The factors include geochemical characteristics of soil and clay minerals, pH and salinity of soil solutions, climate, grazing, and agricultural activities. Arid environments, high clay content, and saline-alkali soils are favorable for fluoride accumulation. In acidic soil, the solubility of fluoride is increased due to the formation of complexes (i.e., AlF2+, AlF2+, and AlF3) and the presence of salts, i.e., sodium, potassium, and zinc fluorides (NaF, KF, and ZnF2), respectively. Thus, fluoride is not available for prolonged periods in these soils (Harrison, 2005). On the other hand, in neutral or alkaline soil, fluorine-bearing minerals (e.g., CaF2, MgF2, and KMg3AlSi3O10F2) play a crucial role, especially in alkaline conditions, promoting fluoride enrichment in soil (Gago et al., 2012). In sodic soil, a higher exchangeable sodium content facilitates fluoride dissolution (Dehbandi et al., 2017b). Wang et al. (2022b) reported that rice planting in saline-alkali soil reduced the contents of water-soluble and exchangeable fluoride, while increasing the content of organic matter-bound fluoride, thereby decreasing the soil bioavailability of fluoride and the risk of groundwater fluoride migration.

The distribution characteristics of fluoride in the soil profile are affected by changes in pH and clay content (El-Said et al., 2016). According to studies, fluoride sorption in soil is maximum at pH 6.0 and drops rapidly (by a factor of 2.0) at pH values one unit higher or lower (Wehr et al., 2022). This phenomenon explained the natural fluorapatite’s solubility pattern at various pH values. According to Barrow and Ellis (2006), there should be little free fluoride ion in soil solution at low pH due to the formation of Al-fluoride complexes. An increasingly unfavorable electrostatic potential at high pH reduces fluoride ion retention in soil and increases their concentration in the soil solution. According to Larsen and Widdowson (2006), it is also caused by the increased concentration of OH– in the soil solution at higher pH, which displaces adsorbed fluoride ions. Soils with fine grains, particularly those with a significant clay component, are easier to retain fluoride than sandy soils (Pickering, 1985). The variation in fluoride content across different particle sizes of aggregates is due to the replacement of OH– groups with fluoride ions within clay particles, creating a favorable environment for fluoride accumulation (Nabbou et al., 2018).

The uptake of fluoride by plants depends upon the soil pH, organic matter, Ca, and P (Cronin et al., 2000). Studies on fluoride bioavailability in farmland ecosystems have primarily been conducted in tea-growing areas (Shu et al., 2003). Tea plants have absorbed fluoride from the soil, and it is mainly distributed in the leaves (Wang et al., 2021). Tea plants are known to be Al-hyperaccumulators, and the presence of Al remarkably increases fluoride absorption by tea plants (Peng et al., 2021), which can be regulated through membrane potential depolarization. The exogenous addition of Ca and other soil amendments (charcoal or bamboo charcoal) significantly decreases fluoride concentration in tea leaves by reducing the amount of available fluoride in soil, by retaining fluoride in the roots as F-Ca complexes, or by affecting the properties of the leaf cell wall and membrane permeability (Ruan et al., 2004). Mackowiak et al. (2003) reported that fluoride given to plants in solution culture as AlF3 resulted in root and new shoot fluoride concentrations being more strongly elevated than with NaF treatment. He et al. (2021) reported that the fluoride content of test vegetables in high-fluoride areas exceeded the national standard value (1.0 mg kg–1). The fluoride content in vegetables was positively correlated with the water-soluble fluoride content in soil (Dagnaw et al., 2017). Fluoride in soil is transported through paddy field drainage into surface water (Gago et al., 2012).

6. Impacts of fluoride pollution

Fluoride pollution has a wide-ranging effect. Aerial emissions from industries contribute to air pollution, while deposits of fluoride-containing minerals in groundwater further damage soil, plants, crops, vegetables, and freshwater bodies, among other parts of the environment.

6.1. Plants

Plants are mainly affected by fluoride concentration when supplied with contaminated irrigation groundwater. The distribution of fluoride in plant tissues is such that the leaf has lower fluoride concentrations than the stem and roots (Fig. 4). There is no evidence for the necessity of fluoride for plant growth; rather, it is toxic to plants, and excessive fluoride concentrations lead to physical disorders (Scholz et al., 2015). Increasing its concentration in irrigation water reduces plant biomass, indicating that fluoride contamination suppresses plant growth and yield via impairing seed germination and physiological and metabolic frameworks. Fluoride accumulation in chloroplasts inhibits Hill reaction and increase chlorophyllase concentration which degrades chlorophyll pigments, exacerbating this effect through stomatal closure and restricts glucose synthesis (Kaminski et al., 2024). In plant metabolism, fluoride acts as a competitive inhibitor of Mg-dependent enzymes, enolase and pyruvate kinase, thereby disrupting glycolysis and tricarboxylic acid cycle (Singh et al., 2023c). This energy deficit, combined with inhibited ATPases, halts nutrient translocation and protein synthesis (Wu et al., 2025). Consequently, reduced carbon skeletons and ATP availability lead to a decline in biomass, resulting in stunted growth and significantly lower crop yields (Mondal, 2017). Lower fluoride contamination did not affect plant growth, whereas higher concentrations inhibited it (Álvarez-Ayuso et al., 2011). The initial symptoms of fluoride injury in plants are marginal and tip necrosis. Mondal (2017) reported up to a 19% reduction in seed germination after application of 20 mg L–1 fluoride via irrigation water. Fina et al. (2016) reported a 57% and 73% decrease in root length and vigor index after application of 8.0 ppm fluoride. Similar results were reported by Bustingorri and Lavado (2014), who noted a reduction of up to 68% in soybean biomass and a 30% yield reduction. Banerjee and Roychoudhury (2021) reported a 14.4% yield reduction in rice due to fluoride contamination, indicating its adverse effects on crop productivity. Furthermore, fluoride contamination also reduces nutrient availability and causes imbalances by forming insoluble CaF2 and displacing PO43-, limiting Ca, Mg, and P uptake (Chen et al., 2024). Biochemically, it increases reactive oxygen species (e.g., H2O2 and O2–) and inhibits antioxidant enzymes, including superoxide dismutase, catalase, and peroxidase (Ghosh et al., 2013). It interferes with carbon and N metabolism. Ghiloufi et al. (2024) reported decreased soil pH (6%), a 54% reduction in total nitrogen (N), and a 35% reduction in Ca2+. Chahine et al. (2022) reported decreases in dehydrogenase, B-glucosidase, urease, and phosphomonoesterase activities, as well as 33.7% and 41.6% reductions in Ca2+ and Mg2+ concentrations. Furthermore, fluoride contamination cause shift in soil microbes through suppressing key enzyme functions such as urease, phosphatase and beneficial bacteria e.g., N-fixing bacteria (Szostek, 2015). This disrupts nutrient cycling, reducing the availability of essential nutrients e.g., N and P for crops and cause decline in plant growth, photosynthesis, and yields (Choubisa et al., 2023). This risk travels up the food chain when crops cultivated in such contaminated soils accumulate fluoride in their edible tissues (Rizzu et al., 2020). When humans and animals consume these crops or related products (e.g., grains, tissues) are exposed to elevated fluoride levels, leading to chronic health issues such as dental and skeletal fluorosis (Kabir et al., 2020).

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Fig. 4. Integrated plant responses to fluoride stress: physiological injury, oxidative stress, nutrient imbalance, and root growth constraints. Fluoride exposure is associated with reduced chlorophyll synthesis and photosynthesis, leading to chlorosis and oxidative stress (ROS accumulation), altered antioxidant defense activities (SOD, CAT, POD), and impacts on carbon metabolism. Soil–plant nutrient effects shown include the formation of relatively insoluble Ca/Mg–F complexes and reduced PO43- availability, both of which contribute to nutrient imbalance. Root-level outcomes include reduced nutrient uptake, suppressed mitotic activity, reduced primary root elongation, and constrained lateral root development. ROS, reactive oxygen species; SOD, superoxide dismutase; CAT, catalase; POD, peroxidase. Created in www.BioRender.com.

6.2. Human health

Fluoride contamination of soil, plants, and water bodies poses severe health risks to humans, plants, and animals. In humans, excessive fluoride intake leads to dental fluorosis, causing enamel discoloration and brittleness, while skeletal fluorosis results in joint pain, stiffness, and bone deformities (Wu et al., 2022). Neurological disorders, including cognitive decline and lower IQ, have also linked to fluoride exposure due to its neurotoxic effects (Miranda et al., 2021). Additionally, fluoride disrupts the endocrine system by interfering with thyroid function, leading to hypothyroidism and metabolic imbalances, while also impairing glucose metabolism and increasing the risk of diabetes mellitus. Prolonged exposure can cause kidney and liver damage, reducing organ efficiency and triggering oxidative stress (Tiwari et al., 2023). Cardiovascular issues such as hypertension, arterial stiffness, and atherosclerosis arise due to fluoride-induced vascular calcification. Reproductive health is also affected, with fluoride reducing sperm quality in men, disrupting ovarian function in women, and increasing the risk of miscarriage and lower birth weight (Su et al., 2021).

Although the benefits of applying fluoride-containing products to teeth have been recognized, there is currently insufficient evidence to establish any beneficial effects via systemic absorption (Duffin et al., 2022). Excessive fluoride concentrations can have a significant adverse impact on human health (Fig. 5). In terms of acute toxicity, fluoride is slightly less toxic than As and more toxic than Pb. Higher concentrations of fluoride can lead to serious poisoning incidents with death. It causes many diseases, including dental diseases and cancers. Fluoride concentrations exceeding 1.5 mg L-1 cause dental mottling associated with tooth damage due to softening of enamel, while concentrations exceeding 4.0 mg L–1 cause severe tooth damage (especially to the temporary and permanent teeth of infants), and softening of the enamel, especially with continuous use of contaminated water (Odiyo and Makungo, 2011). Skeletal fluorosis, characterized by fluoride accumulation in bones, leads to deformities, joint pain, and stiffness, with severity varying across affected individuals (Duvva et al., 2022). The symphony of toxic effects extends across diverse organ systems-liver, kidneys, heart, lungs painting a complex canvas of physiological repercussions (Dharmaratne, 2015, Shanmugam et al., 2016). Neurotoxic effects, muscle degeneration, and gastrointestinal and reproductive system issues are also associated with elevated fluoride levels, indicating systemic health consequences (Guth et al., 2020, Zwierello et al., 2023).

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Fig. 5. Major systemic outcomes associated with excessive fluoride exposure in humans (schematic overview). The figure summarizes key endpoints commonly reported in chronic high-fluoride exposure, including dental fluorosis, skeletal/crippling fluorosis, gastrointestinal toxicity, renal outcomes (kidney stones), reproductive toxicity, and neurotoxicity/neurodevelopmental concerns (illustrated by neuronal degeneration and lower IQ in children). Created in www.BioRender.com.

7. Prevention and remedial measures to cope with fluoride contamination in water–soil–plant system

There are numerous remediation strategies for fluoride removal from soil, including precipitation, ion exchange, membrane separation, electrocoagulation, adsorption, and bioremediation (Solanki et al., 2022). Different removal strategies and their removal efficiencies in soil systems are described in Table 3. The ultimate and core objective for the remediation of fluorides from environment solely concentrates on reducing the bioavailable form which can travel to food chain and affects human and plant health.

Table 3. Bioremediation approaches for the remediation of fluorides in the soil and water environment.

Area Technology Specie Removal efficacy Main mechanism References
Water environment
India Rhizofiltration Azolla, Pistia, and Eichhornia sp. 69.2% Release of citric and malic acid which aid in rhizofiltration (Banerjee and Roychoudhury, 2022)
India Phytoremediation Pistia stratiotes 38.89% Biosorption (Karmakar et al., 2018)
India Phytoremediation Vetiveria zizanioides 38.1% Contaminants accumulation in plant tissues (Thakur et al., 2021)
India hyperaccumulation Epipremnum aureum 18.07%/day Fluorides accumulation in plant tissues (Singh et al., 2019)
Mexico Hyperaccumulation Camellia, sugar cane sp. Sugarcane: 1000–1400 mg/kg
Camelia: 100–500 mg/kg		 Accumulation and adsorption (Camarena-Rangel et al., 2015)
Mexico Constructed wetland Canna hybrid, Alpinia purpurata, and Hedychium coronarium Canna hybrid: 42.5%
Alpinia purpurata: 36.8%
Hedychium coronarium: 30.7%		 Hyperaccumulation (Marín-Muñiz et al., 2024)
Soil environment
India Microbial Staphylococcus lentus 92% Sorption and immobilization (Mukherjee and Singh, 2018a)
China Cerium based metal organic framework (MOF) – 159.6 mg g–1 Electrostatic interaction, ion exchange, and surface coordination (Tang et al., 2023)
Iran Algal biochar + MOF Sargassum oligocystum for biochar 99% Adsorption (Foroutan et al., 2024)
Iran Magnetic chitosan aerogel + biochar + MOF 99.1% Heterogeneous surface interactions and chemical bonding (Foroutan et al., 2025)
China Microbial Cupriavidus sp. W12 91.93% Ion exchange, co-precipitation, and chemisorption (Yang et al., 2022)
China Microbial Aquabacterium sp. CZ3 87.50% Co-precipitation and adsorption (Zhang et al., 2022)
China Microbial + seed crystals Pseudomonas sp. WZ39 70.10% Chemisorption, ion exchange, and co-precipitation. (Wang et al., 2022c)
China Microbial Cupriavidus sp. W12 87.52% Bioprecipitation (Liu et al., 2022)
China Microbial Acinetobacter H12 96.33% Co-precipitation (Ali et al., 2021)
India Plants Canna indica, Epipremnum aureum, Cyperus alternifolius and Cyperus rotundus Up to 95% Hyperaccumulation (Khandare et al., 2021)
India Plants Nerium oleander, Portulaca oleracea, and Pogonatherum crinitum Up to 92% Hyperaccumulation (Khandare et al., 2017)
India Plant Vetiveria zizanioides 38.1% Hyperaccumulation (Thakur et al., 2021)
Brazil Plant Lactuca sativa L. 82.8% Hyperaccumulation (Almeida Rodrigues et al., 2022)
Mexico Plant Canna hybrid, Alpinia purpurata, and Hedychium coronarium 42.5% Evapotranspiration and rhizofiltration (Marín-Muñiz et al., 2024)
India Plant Epipremnum aureum 88% – (Rahul et al., 2023)

7.1. Physicochemical methods

Adsorption is a widely used method due to its simplicity and cost-effectiveness. It involves the adsorption of fluoride ions onto the surfaces of adsorbent materials such as biochar, activated carbon, graphene oxide, carbon nanotubes (CNTs), and nanostructured materials containing metals and metal oxides with higher surface area and reactivity (Tolkou et al., 2021). This process is governed by chemisorption, characterized by strong interactions between fluoride ions and adsorbent sites (Wei et al., 2022). Moirana et al. (2023) used hydroxyapatite-activated seaweed biochar for fluoride remediation and reported up to 79% efficacy through adsorption. Similarly, Yi et al. (2026a) used Ca-modified biochar for the same purpose and reported 48.6% remediation efficacy through adsorption, nutrient mobilization and modulation of microbial community. Similarly, fermented seaweed showed 85.3% fluoride immobilization efficacy via reducing fluoride bioavailability (Moirana et al., 2022). This was also accomplished through increasing soil pH and cation exchange capacity, potentially leading to fluoride immobilization through surface adsorption and precipitation mechanisms (Guo et al., 2020). In another study, nano-hydroxyapatite application reduced soil fluoride content by up to 87.8% due to the formation of CaF2 and ion exchange processes (Gan et al., 2021). Similarly, application of biochar at 50 g kg–1 to soil reduced fluoride uptake in safflower (Carthamus tinctorius L.) plants.

7.2. Bioremediation techniques

Bioremediation techniques involve the strategic use of microbes and plants for contaminant removal through phytoremediation, phytoextraction, phytostabilization, rhizofiltration, and mycorrhiza-assisted remediation (Fig. 6, Table 3). Bioremediation technologies work to reduce the bioavailability of fluorides to plant and humans. In plants, fluorides are accumulated in non-edible parts, mostly roots and leaves, thereby preventing their uptake and translocation in edible parts e.g., grains, and their subsequent transport to human bodies.

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Fig. 6. Bioremediation pathways for reducing fluoride mobility and bioavailability in contaminated systems. Schematic of biologically mediated mitigation showing (i) micro-remediation involving plant growth–promoting bacteria and phosphorus-solubilizing activity that facilitates biological precipitation and immobilization (e.g., CaF2 and Ca–phosphate–F mineral formation), (ii) phytoremediation processes operating in the rhizosphere/root zone to intercept and stabilize fluoride, and (iii) cellular bioaccumulation/sequestration via membrane channels and enzyme-mediated stabilization/biotransformation toward less toxic products. PGPR: plant growth promoting rhizobacteria, PSB: phosphate solubilizing bacteria, MOFs: metal organic frameworks.

7.2.1. Phytoremediation

Phytoremediation employs phytostabilization, phytoextraction, and rhizofiltration to remediate fluoride-contaminated soils. Phytoextraction involves the absorption of fluorides by plant roots and their transfer to other organs for harvesting, yielding super-enriched plants with high biomass and rapid growth, which are crucial for green remediation (Biswas et al., 2018). Specific plants, such as mesquite (Prosopis juliflora L.), tea (Camellia japonica L.), tobira (Pittosporum tobira L.) Thunb., and sugarcane (Saccharum officinarum L.), exhibit varying capacities to accumulate and remove fluoride through distinct gene expression mechanisms (Santos-Díaz and Zamora-Pedraza, 2010). Super-enriched plants, with bioconcentration, translocation, and enrichment factors greater than 1.0, play a pivotal role in this process (Gamalero and Glick, 2024). Vaz et al. (2023) reported that tropical duckweed (Eichhornia crassipes L.) was used for fluoride removal, achieving 60% efficacy in soil. Additionally, sorghum (Sorghum bicolor L.) crops display resistance to fluoride exposure, while Gossypium and Saccharum officinarum show resilience to fluoride toxicity, particularly in clay-rich black soils. Sugarcane employs a detoxification process involving Ca to remediate fluoride contamination (Weerasooriyagedara et al., 2020). Khandare et al. (2021) reported up to 95% fluorides removal from water through African arrowroot (Canna indica L.) due to the hyperaccumulation of fluoride in plant roots. Giri et al. (2024) also reported higher fluoride accumulation (1.23 mg gm–1) in its roots (Fig. 6).

7.2.2. Microbial remediation

Microbial remediation is another effective method for mitigating fluoride toxicity in soil using ecologically efficient microorganisms, including bacteria, fungi, and algal biomass. It degrades fluorides into simpler components for metabolic activities such as energy production and reproduction (Isingoma et al., 2025). The processes involved in microbial remediation include natural attenuation, biostimulation, and bioaugmentation (Periasamy and Gopi, 2023b). A diverse array of microorganisms can be used for fluoride removal from soils, e.g., Staphylococcus lentus can reduce fluoride concentrations up to 3.2 mg g–1 (Mukherjee and Singh, 2018a). Acinetobacter sp. H12 can reduce soil fluoride concentration by up to 75% (Wu et al., 2021). Importantly, these microbes prove effective without inducing toxic effects, particularly under fluoride exposure (Kumar et al., 2021). Banerjee and Roychoudhury (2023) used Acinetobacter indicus to remove up to 68% fluoride. Bacillus megaterium, known for its robust tolerance to elevated fluoride levels, can remove up to 70% of fluorides from soil (Pal et al., 2022). Similarly, various fungal species, including Trichoderma longibrachiatum, P. ostreatus, and Rhizopus arrhizus, exhibit diverse capacities for fluoride due to their alginate-based cell walls, which contain acidic functional groups (Kavisri et al., 2023). Notably, algal species such as Padina sp. exhibit substantial fluoride adsorption rates (up to 85.9%), highlighting their effectiveness in mitigating fluoride contamination (Mohamed et al., 2020), underscoring the efficacy of different microbial species use for fluorides remediation.

7.2.3. Biomaterials

Organic amendments, such as biochar, compost, vermicompost, and organic acids, have a high surface area and enhance the adsorption of fluoride ions (Sadhu et al., 2021). Compost enhances SOM and microbial activity, which aids fluoride adsorption through plant uptake and detoxifies fluoride, facilitating phytoremediation (Saghi et al., 2022). Organic acids, such as humic acid, chelate fluoride, affect its mobility and stabilization in soils. Similarly, vermicompost boosts microbial activity and enhances soil structure, increasing fluoride adsorption and converting fluoride into less harmful forms through microbial transformation. For example, vermicompost reduced soil fluoride levels by up to 16.4 mg kg–1 (Maitra et al., 2016).

7.2.4. Integrated approaches

The integration of physicochemical and biological techniques for fluoride remediation can yield more favorable, sustainable results in soil remediation. Makete et al. (2022) explored the efficacy of integrated phytoremediation and chemical treatment strategies in reducing soil fluoride contamination, presenting a notable improvement over a single treatment method. Uptake efficiency (67.7%) and biomass content (57.03%) in Prosopis juliflora were enhanced after treatment with P. fluorescens bacterium (Chaudhary et al., 2019). Brachiaria distachya plant demonstrated hyperaccumulator traits, accumulating 779.9 g kg–1 of fluoride, further improved by the presence of Bacillus cerus and P. vermicola microbes (Periasamy and Gopi, 2023b). Vermicompost and compost treatments were effective in removing organic and inorganic contaminants, enhancing soil fertility, and inhibiting fluoride transport to plants (Periasamy and Gopi, 2023a). Maitra et al. (2016) explored fluoride toxicity removal using combined vermicompost, compost, and bacterial consortia treatments. Recycling agricultural waste through organic mulching (Romar-Gasalla et al., 2017), and the application of biochar also proved effective in mitigating fluoride contamination (Yi et al., 2026b). However, concerns arise over the negative impact of excessive biochar addition on earthworms through physical damage, desiccation, oxidative stress, reproductive impairment, and increased mortality rates (Cui et al., 2023, Elliston and Oliver, 2020). Cover crop manure emerged as a cost-effective solution to counter fluoride pollution, promoting nutrient management and microbial activity in the soil, with leguminous green manure exhibiting higher effectiveness (Periasamy and Gopi, 2023b).

7.3. Critical evaluation of remediation strategies in the field context

While Table 3 documents a wide array of fluoride remediation techniques with impressive remediation efficiencies under controlled conditions, a critical gap exists between laboratory promise and field-scale reality. The true test of any remediation strategy lies not in its maximum adsorption capacity (mg g–¹) in a laboratory-based experiment, but in its performance, durability, and safety within the complex, dynamic environment of an agricultural field. A primary limitation across physicochemical methods is their lack of scalability and economic feasibility for large-scale soil remediation. Adsorption techniques using biochars, nanomaterials, or layered double hydroxides may be highly effective in soil and water treatment or small contaminated hotspots. However, the cost of synthesizing, transporting, and incorporating modified biochars or engineered nanomaterials at a farm scale (t/ha-1) is often prohibitive for routine agricultural use. Similarly, electrocoagulation and membrane filtration are energy-intensive and impractical for in-situ soil treatment, limiting their application to ex-situ setups or water purification. A second major concern is longevity and durability i.e., many studies report impressive removal percentages immediately after amendment application (e.g., nano-hydroxyapatite reducing soil fluoride by 87.8%). However, the critical question is whether this immobilization is permanent. Under field conditions, factors like fluctuating pH (e.g., from N-fertilization), changing redox potential (from flooding/drying cycles in paddy soils), and the presence of competing anions (phosphate, bicarbonate) can reverse the adsorption or precipitation of fluoride, leading to its re-release into soil solution over time. The durability of these amendments under multi-season cropping cycles remains severely under-evaluated. Moreover, the potential for unintended consequences on soil health is frequently overlooked. While a sorbent may effectively bind fluoride, its impact on non-target soil properties must be scrutinized. For example, the excessive application of certain biochars or chemical amendments could alter nutrient availability e.g., immobilization of fluoride via Ca-based amendments could inadvertently reduce P-availability due to the formation of insoluble calcium phosphates (Singh and Chaudhari, 2023). It can also disrupt soil biota e.g., earthworms and beneficial microbial communities, whose functions (nutrient cycling, organic matter decomposition) are essential for long-term fertility (Montagnolli et al., 2017). They can also introduce secondary contaminants i.e., some industrial by-products or unmodified nanomaterials may contain trace heavy metals that add a new pollution vector while solving another. Furthermore, biological approaches such as phytoremediation and microbial remediation face their own set of practical hurdles i.e., phytoremediation is slow, requiring multiple growing seasons to significantly reduce soil fluoride, which is impractical for farmers needing to use their land annually for food production (Tang, 2023). The safe disposal of fluoride-laden plant biomass also presents a logistical challenge. For microbial remediation, while fluoride-tolerant strains like Acinetobacter and Bacillus show promise in lab cultures, their survival, colonization efficiency, and sustained activity in a competitive and often hostile natural soil microbiome are highly uncertain (Malusà et al., 2021).

8. Recent approaches for fluoride remediation

Recent approaches for the remediation of fluorides from the soil environment include nanotechnology, biochars, genetic engineering of plants and microbes, layered double hydroxides, metal-organic frameworks, electrochemical methods, constructed wetlands, and algal biosorption. Nanotechnology-based remediation includes nanomaterials that have a higher surface area-to-volume ratio and enhanced reactivity, making them particularly effective for environmental remediation (Guerra et al., 2018), e.g., amino-functionalized carbon (NH2C) prepared via electrical discharge of nonequilibrium plasma exhibited a remarkable fluoride adsorption capacity of approximately 121.1 mg g–1, which is several times higher than previously reported values. The simultaneous carbonization and amination process introduced numerous amino groups into the carbon framework, significantly enhancing the adsorption efficiency (Tipplook et al., 2024). Biochar has also shown promising results in removing fluoride from soil. Their efficacy depends upon the various factors, including biochar preparation methods, pyrolysis temperature, and modifications.

Metal-organic frameworks (MOFs) are also used for the same purposes, but their application in soil remediation is less explored. Electrocoagulation uses aluminum or iron electrodes to generate coagulants in situ, which then remove fluoride via mechanisms such as adsorption and precipitation (Mousazadeh et al., 2021). Capacitive deionization (CDI) is also used for fluoride removal from soil. In addition, microbial and plant genetic engineering approaches offer promising solutions to soil fluoride pollution. These techniques enhance organisms’ natural capabilities to accumulate, transform, degrade, or volatilize fluoride, making bioremediation more efficient and effective. In microbial genetic engineering, researchers have focused on enhancing bacterial mechanisms of fluoride resistance. For instance, studies have explored modifying genes responsible for efflux pumps, intracellular sequestration, and fluoride riboswitches to improve bacterial tolerance and removal capacity (Singh et al., 2023a). While specific fluoride-removal efficacy data for genetically engineered microbes are not provided in this context, there is potential for significant improvements. Plant genetic engineering has also shown promise in fluoride bioremediation. Gene editing and manipulation techniques can enhance plant-microbe interactions for fluoride remediation (Katiyar et al., 2020, Singh et al., 2023a). These modifications could increase the bioaccumulation factor, enrichment factor, and translocation factor in plants, thereby improving their fluoride uptake and translocation capabilities. The combination of genetically engineered plants and microbes could lead to more effective strategies for fluoride removal. For example, enhancing the symbiotic relationship between plants and fluoride-resistant PGPR strains could improve overall remediation efficiency (Gupta et al., 2024, Singh et al., 2023a).

8.1. Research gaps and future strategies

Effective management of fluoride contamination in the water–soil–plant continuum requires a shift from descriptive monitoring toward mechanism-based, field-validated intervention. First, research and practice should adopt standardized, risk-relevant fluoride metrics. Reporting should move beyond total fluoride to include plant-up taken fluoride fractions as plant available fractions of fluorides are only moved to edible parts and cause toxicity to plant and humans. Such harmonization is critical for cross-site comparability, defensible risk assessment, and prediction of plant uptake. Second, surveillance should emphasize matched-compartment sampling (irrigation water, soil fractions, edible tissues) to identify dominant exposure pathways and separate root-mediated uptake from foliar deposition, particularly in settings influenced by industrial emissions. Third, mitigation should prioritize source control where feasible, including improved irrigation water management (blending, alternative sources, or on-farm defluoridation where appropriate) and reductions in anthropogenic inputs (fertilizer/by-product quality control and emission regulation). Fourth, remediation should be evaluated through multi-season field trials that explicitly quantify durability and trade-offs. Mechanism-based immobilization (e.g., Ca-bearing amendments and targeted sorbents) should be tested for longevity under alkaline and saline conditions, impacts on nutrient availability and soil biota, and effects on yield and product quality. For this, a concise evaluative framework for future field trials should contain core indicators (water-soluble fluoride, nutrient availability, microbial activity, crop fluoride content), evaluation over 3–5 cropping seasons, durability criteria (maintaining >70% efficacy under seasonal variability), and explicit assessment of agronomic (yield, grain quality) and ecological (soil biota, nutrient cycling) trade-offs. Biological approaches, microbial remediation, and phytoremediation are promising but require rigorous screening of fluoride-tolerant strains and crops, clear performance endpoints, and assessment of ecological safety. Fifth, translation will depend on agronomic–economic evaluation frameworks that quantify cost-effectiveness, co-benefits (soil fertility, yield stability), and unintended consequences, enabling adoption by farmers and stakeholders.

9. Conclusion

Fluoride risk in agroecosystems is governed not by total soil inventories but the fraction, which is up taken by plants, which are controlled by pH, alkalinity, and sorption dynamics. Yet, the field remains constrained by critical limitations i.e., most studies report only total fluoride, precluding cross-site comparability, obscuring dominant exposure pathways, and remediation evaluations are overwhelmingly short-term and laboratory-based, with scant attention to durability under field conditions or unintended consequences for soil fertility and microbiota. Translating knowledge into action demands a shift from descriptive monitoring to mechanism-based intervention. Priorities include adopting standardized fraction metrics, conducting multi-season field trials that assess both efficacy and agronomic trade-offs, and integrating source control with targeted immobilization strategies. Without such systemic, field-validated approaches, even robust laboratory findings will fail to deliver scalable, sustainable solutions for safeguarding soil health, crop productivity, and food security in fluoride-affected regions.

CRediT authorship contribution statement

Zia Ur Rahman Farooqi: Writing – original draft, Methodology, Formal analysis, Data curation, Conceptualization. Abdul Karim: Writing – review & editing, Visualization, Methodology, Investigation, Conceptualization. Ayesha Abdul Qadir: Writing – review & editing, Visualization, Software, Methodology, Formal analysis. Ayesha Sonia: Writing – review & editing, Visualization, Validation, Software, Investigation, Data curation. Waqas Mohy-Ud-Din: Writing – review & editing, Visualization, Validation, Methodology, Formal analysis. Enos Wamalwa Wambu: Writing – review & editing, Visualization, Validation, Software, Investigation, Formal analysis. Qasim Ali: Writing – review & editing, Visualization, Validation, Software, Methodology. Fasih Ullah Haider: Writing – review & editing, Visualization, Methodology, Investigation, Data curation. Mayank Anand Gururani: Writing – review & editing, Visualization, Validation, Investigation, Formal analysis. Usman Zulfiqar: Writing – review & editing, Visualization, Validation, Software, Methodology, Investigation.

Funding

This work was supported by the UAE University Grants UPAR [12S114] and AUA [12R172], awarded to Mayank Anand Gururani.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

All the authors want to acknowledge the facilities provided by Kunming University of Science and Technology, Kunming, China to review the literature for this manuscript. This work was supported by the UAE University Grants UPAR [12S114] and AUA [12R172], awarded to Mayank Anand Gururani.

Appendix A. Supplementary material

Data availability

All the data are available in the manuscript.

References