Balancing Environmental Safety and Economic Feasibility: A Review of Soil Fluorine Management Strategies in South Korea

Abstract

Soil naturally contains fluorine, but concerns arise when its levels or bioavailability are increased by human activities or specific compounds. South Korea faces challenges in regulating soil fluorine pollution despite implementing stricter total fluorine standards (e.g., 400 mg/kg for residential areas) than many developed countries (e.g., 4000 mg/kg for all land uses in Japan). Moreover, a recent national soil survey in Korea revealed widespread exceedance (15.2% of samples) of the Soil Worrisome Level, even in areas with naturally low background levels of fluoride. This highlights the limitations of regulations based solely on total fluorine content. This review explores the global landscape of soil fluorine management strategies and examines potential solutions that reconcile environmental protection with economic concerns. We recommend a shift towards regulating specific and hazardous fluorine compounds rather than total content and prioritizing remediation efforts based on assessments of bioavailable fluorine. This approach may help Korea establish a more effective and sustainable strategy for managing soil fluorine pollution.

1. Introduction

Fluorine is the 13th most abundant element in the Earth’s crust and exhibits high reactivity and electronegativity [1,2]. Fluorine-containing minerals include fluorite (CaF₂), cryolite (Na₃ALF₆), apatite (Ca₅(PO₄)₃(OH,F,Cl)), topaz (AL₂(SO₄)F₂), amphibole species, and mica species. Griceite, an extremely rare mineral, contains 73% fluorine [3].

Natural fluorine in minerals is mostly insoluble in water, very stable with minimal chemical reactivity, and has virtually no effect on the human body or ecosystems. Fluorine in soil can enter the atmosphere or water bodies through natural pathways, such as weathering, volcanic activity, marine aerosol emissions, and anthropogenic pathways, including the production and application of phosphate fertilizers, brickmaking, coal combustion, and aluminum smelting [4].

In trace amounts, fluorine plays a crucial role in maintaining oral health. It strengthens tooth enamel by incorporating into its structure, making it more resistant to acid attacks from bacteria and dietary sugars. This helps prevent tooth dissolution, a process that leads to cavities [5]. Additionally, fluoride inhibits the growth of harmful bacteria in the oral cavity, reducing the risk of periodontal diseases, which affect the gums and supporting structures of the teeth. Furthermore, fluoride promotes the remineralization of early-stage tooth decay by facilitating the deposition of minerals like calcium and phosphate back into the enamel [6].

While trace amounts of fluorine are essential for dental health, excessive exposure can have detrimental effects on both human and environmental health. In humans, chronic ingestion of high levels of fluoride, often through contaminated drinking water, can lead to dental and skeletal fluorosis, causing discoloration, weakening, and deformation of teeth and bones [7]. The maximum permissible limit for fluoride in drinking water for human consumption is 1.5 ppm [8]; therefore, fluorine levels must be checked before using groundwater for drinking purposes.

In the environment, the consequences of elevated fluoride concentrations can be far-reaching. Plants, serving as the foundation of many ecosystems, can experience stunted growth, reduced yields, and even visible damage due to fluoride toxicity [9]. This disruption cascades through the food chain, affecting herbivores, and subsequently, their predators. Furthermore, fluoride readily leaches into groundwater, contaminating this vital resource and posing a threat to both terrestrial and aquatic organisms that depend on it for survival. The accumulation of fluoride in aquatic systems can impair the health of fish and other aquatic life, further destabilizing delicate ecosystems [10].

In September 2023, the Korean government proposed to the Ministry of Environment amending soil fluorine management standards. The goal was to align these standards with international practices while also protecting public health and ecosystems. This amendment could potentially lead to harsher regulations compared to some developed countries. However, South Korea faces unique challenges in managing soil fluorine contamination. Despite having an average natural background level of fluorine in the soil of 204.5 mg/kg [11], which is below the global average of 321 mg/kg [12], a nationwide soil survey revealed that 15.2% of the sampling points across Korea exceeded the Soil Worrisome Level (SWL) [13]. This widespread exceedance, which indicates significant areas of concern, highlights the discrepancies between natural fluorine levels and regulatory thresholds, thereby complicating efforts to safeguard environmental and public health. We discuss this issue in greater detail later in Section 3. The Korean Ministry of Environment, in collaboration with the Korean National Institute of Environmental Research, is currently conducting research to identify the need to adjust soil fluorine remediation standards and address any potential inconsistencies. However, this proposal has sparked debate among academics and soil remediation companies, raising concerns about relaxing regulations in the absence of a comprehensive scientific awareness of the specific hazards posed by naturally occurring, less bioavailable forms of fluoride in Korea. The basis of this study is their query—“Is easing soil fluorine contamination standards truly in the best interests of the Korean people?”.

To address this question, we first reviewed the current literature to explore the sources and behavior of fluorine in the soil. Subsequently, we examined the soil fluorine content regulation strategies adopted by various countries. Next, we summarized the current challenges in managing soil fluorine in Korea. Based on this comprehensive study, we offer perspectives on soil fluorine management strategies in Korea (Figure 1).

2. Origin and Sources of Fluorine

2.1. Natural Sources

Although fluorine is present in some rock-forming minerals, such as fluorite and apatite, it is more abundant within the Earth’s lithosphere in hydroxysilicate minerals. In these minerals, fluorine substitutes for hydroxyl (OH) sites within the crystal lattice structure [4]. Fluorine is naturally derived from rock-forming minerals through weathering processes, wind-blown dust, marine-derived components, natural biomass burning, and volcanic activity.

2.1.1. Weathering

Weathering, a complex process involving adsorption–desorption and dissolution–precipitation, is a primary natural pathway for fluorine release into soil profiles [14,15]. The breakdown of granite massifs, for instance, initially releases fluorine, but its concentration can increase in the uppermost weathered layer. While the fluorine in apatite remains stable, mica’s fluorine readily leaches [16]. Fluorite, if present, dissolves slowly with water movement. Soil profiles generally show decreasing fluorine content away from the source rock [17,18], with micaceous components in clastic sedimentary rocks being major fluorine reservoirs [4,19].

Fluorine-to-OH exchange in clay minerals depends on various factors like fluorine concentration, water pH, and clay type [20]. For example, dioctahedral and trioctahedral illite can adsorb fluorine by replacing OH. Acidic environments favor fluorine adsorption, while alkaline ones promote desorption [20]. Rock weathering releases fluorine, some of which is adsorbed by clay in the surrounding water [21,22]. The overall soil fluorine content varies according to the composition and fluorine levels of the parent rocks, with an average fluorine content in the range of 90–980 mg/kg [23]. Recent studies have reported a fluorine content of 321 mg/kg in soils worldwide and 557 mg/kg in the continental crust [12,18].

Organic matter decomposition also releases fluorine, especially in warm- and humid-climate soils [24]. Fluorine can easily leach away in acidic soils, whereas it accumulates in organic matter, which hinders leaching. Similarly, in permafrost regions, decomposing plants release fluorine into the water, exhibiting comparable behavior. Climate further influences fluorine mobility: arid regions’ high calcium restricts movement, while semi-arid areas see seasonal changes. Dry seasons limit movement due to high calcium and low dissolved solids, whereas post-monsoon conditions, with lower calcium and higher ionic strength, enhance mobility [25,26].

2.1.2. Volcanic Activity

Volcanic activity, primarily through degassing rather than eruptions, releases substantial fluorine into the environment, mainly as hydrogen fluoride (HF) gas [18,27]. Volcanic ash further disperses fluorine, impacting areas beyond the eruption zone [28]. The dissolution of fluorine from ash into water and soil can lead to contamination exceeding permissible limits, posing risks to human and animal health [29,30]. Grazing animals on contaminated vegetation can lead to chronic fluorosis, affecting bones and teeth [31,32]. The 1783–1784 Laki eruption in Iceland, with massive HF release, exemplifies the devastating impact on livestock and crops [33]. Volcanic fluorine enrichment in surface and groundwater near volcanoes has also been linked to dental fluorosis in human populations [34,35,36].

While volcanoes were once considered the primary source of atmospheric fluorine, recent studies suggest these estimates may be overstated [2]. Although volcanic emissions are significant, their contribution might be lower than previously thought. Moreover, despite concerns about potential eruptions around Mount Baekdu in the near future [37], the Korean Peninsula has experienced minimal volcanic activity in the last millennium.

2.1.3. Marine-Derived Components

Marine aerosol and spray contributions to atmospheric fluorine and its geochemical cycle have been debated. Friend [35] hypothesized a significant marine flow of fluorine to the atmosphere, estimated at 0.4 to 1 Mt annually and second only to volcanic emissions. Taverner and Clark [2] offered estimates between 1 and 2 Mt, while other authors predicted a smaller flux of 20,000 t. The average seawater fluorine level is 1.3 mg/L; thus, marine-derived fluorine is considered crucial in the hydrogeochemical fluorine cycle. Seawater is a major source of fluorine in global precipitation [18,38,39]. Fluorine emissions from seawater include gaseous HF, with F/Cl ratios in precipitation being 10–1000 times higher than those in seawater [38,40,41]. However, some studies found no evidence of preferential fluorine enrichment in marine aerosols, and ascribed elevated fluorine levels to dust content [42,43]. The absence of a marked difference in fluorine content between coastal and inland rainfall suggests the influence of anthropogenic sources in rainwater [44,45]. Similarly, studies on ice and precipitation samples have reported minimal marine-derived fluorine, further supporting the limited contribution from marine sources [46,47,48].

In contrast, Linder and Frysinger [49] and Lewandowska et al. [50] hypothesized that coastal rainfall and marine-derived aerosols are enriched in fluorine, which correlates with the Na content. Some areas—such as mid-Wales and coastal soils in Victoria, Australia—show fluorine enrichment, which might be attributed to marine sources [51]. Overall, despite contradictory evidence, marine-derived fluorine contributions to the atmosphere seem to be minimal when compared to volcanic and anthropogenic sources. Although seawater fluorine may influence coastal rainfall, runoff, and soil chemistry, its impact is likely limited to regions 10–20 km inland.

2.1.4. Other Minor Sources

Fluorine release into the atmosphere is not solely attributed to major natural sources, such as volcanic eruptions and marine-derived components; other sources also play a significant role. Weinstein [3] has suggested that wind-blown soil contributes substantially to the atmospheric fluorine content. Approximately 6000 tons of fluorine are added to the atmosphere annually in the USA owing to the wind-induced removal of ~30 million tons of soil. Analytical data from ice cores in Greenland [46] and the Alps [52] indicate that wind-blown dust originating from soil was the primary source of atmospherically deposited fluorine before 1930. Despite anthropogenic activities dominating fluorine sources from the 1930s to 1980, wind-blown dust still accounted for 18 ± 2% of the fluorine in ice cores from the Alps between 1980 and 2000.

Biomass burning, both from natural processes and human activities such as agricultural practices and accidental fires, also contributes to atmospheric fluorine release. Although the majority of biomass fires are anthropogenic, natural fires—although less frequent—can destroy large areas of vegetation. De Angelis and Legrand [46] found elevated fluorine concentrations from biomass burning at high latitudes such as the Greenland ice caps, whereas Lewandowska et al. [50] identified biomass burning as a fluorine source in PM10 aerosols in the Baltic Sea area of Poland. Jayarathne et al. [53] investigated the fluorine emissions from biomass burning and found considerable amounts of fine particulates (PM2.5) containing fluorine; however, the degree of fluorine release varied with plant type and geographic distribution. Additionally, these authors estimated an annual release of 76,000 tons of fluorine from biomass burning, which is comparable to that from coal combustion. These minor sources, although individually smaller than major sources, collectively contribute substantially to atmospheric fluorine levels, highlighting the diverse nature of fluorine emission sources and their environmental impacts.

2.2. Anthropogenic Sources

Fluorine is also derived from anthropogenic sources. Emissions from industries—such as semiconductor manufacturing, steel production, aluminum smelting, and the production of glass, bricks, phosphate fertilizers, and items through electroplating processes—are important anthropogenic contributors to soil fluorine contamination [54].

2.2.1. Coal Combustion

Coal combustion is a major anthropogenic source of fluorine emissions [3], with fluorine recognized as one of the most hazardous substances released during this process [55]. Globally, coal has an average fluorine content of 88 mg/kg [56], a significant portion of which is emitted into the atmosphere during combustion. Research by Chen et al. [57] indicates that about 80% of fluorine in coal is released at temperatures around 800 °C, with complete release occurring at 1100–1200 °C [58].

The environmental impacts of fluorine emissions from coal combustion are well documented, including air pollution, plant damage, and fluorosis in animals and humans. For example, coal-fired power stations in Australia are the largest source of atmospheric fluorine, causing damage to vegetation [59]. Similar effects have been observed in grazing animals near coal plants in the United Kingdom [60] and in sheep near the Yatağan power station in Turkey [61]. In Europe, particularly in the northwest Czech Republic, coal emissions have been linked to fluorosis in wildlife [62,63].

China, a leading coal producer and consumer, faces severe challenges from fluorine emissions. Chinese coal has an average fluorine content of 130 mg/kg [64], with some regions, like Guizhou Province, showing even higher levels [64,65]. Fluorosis, both dental and skeletal, has been reported across several Chinese provinces, affecting millions due to indoor coal combustion [66,67,68]. The exposure stems from practices like burning coal in open stoves for food preservation and direct inhalation [64,66].

Coal waste also contributes significantly to environmental fluorine contamination. Gao et al. [69] found elevated fluorine levels in soils near coal waste sites in China, with spontaneous combustion of coal spoil heaps further contributing to atmospheric fluorine pollution [69]. While most fluorine is released during combustion, some remains in fly ash, which, despite its relatively low fluorine content, poses a potential risk for groundwater contamination when disposed of in lagoons [70].

Coal combustion is thus a major source of atmospheric fluorine, with significant environmental and health implications. Despite mitigation efforts, the scale of fluorine emissions highlights the need for ongoing research and stricter regulations. In South Korea, 58 coal-fired power plants contribute significantly to electricity generation, but there is a lack of studies on fluorine release from coal combustion in the country [71].

2.2.2. Brick and Ceramic Manufacturing

The production of bricks and ceramics, which involves roasting clays and clay-rich rocks at high temperatures [72], releases a significant amount of fluorine into the atmosphere, primarily as HF and silicon tetrafluoride (SiF₄) [3,73]. The fluorine originates from minerals like micas naturally present in the clay [74,75]. This poses a particular concern in developing countries with rapid urbanization and often inadequately regulated brickmaking practices [76,77]. These kilns, often located near urban areas, contribute significantly to air pollution [78,79] The resulting fluorine emissions have been linked to damage in fruit trees and reduced crop yields [80].

The global impact of these emissions is substantial. Based on industry estimates and average fluorine content in clay, brick production alone could release an estimated 1.8 million tons of fluorine annually, rivaling emissions from coal combustion [19,72]. The ceramics industry, with its similar high-temperature processes, also contributes to fluorine emissions, although the full extent remains understudied due to limited data on various ceramic products [76].

The evidence suggests that brick and ceramics manufacturing, especially in developing regions, poses a significant risk of fluorine air pollution, impacting vegetation and crop yields [78]. The adoption of cleaner technologies in these industries is crucial for mitigating these environmental effects and protecting public health.

2.2.3. Fluorine Emissions from Aluminum Smelting

Aluminum production is based on the Hall–Héroult process, which releases fluorine into the atmosphere. Despite significant success in reducing fluorine emissions, ongoing monitoring and technological advancements are crucial for minimizing environmental and ecological impacts. These challenges and advancements in the management of fluorine emissions from the aluminum smelting industry have been extensively investigated [81,82,83,84].

During the electrolytic process that produces aluminum from aluminum oxide, fluorine is released in both gaseous (mainly HF) and particulate forms [84]. In the mid-20th century, the rapid growth in aluminum production led to severe fluorine pollution near smelters, resulting in ecological damage and health issues for livestock and wildlife [85,86,87]. The industry has responded by adopting cleaner technologies, particularly wet scrubbing systems, which have significantly reduced emissions [88,89]. Estimates suggest that modern smelters emit as little as 15–30 kg of fluorine per ton of aluminum produced, with scrubbing further reducing this to <300 g per ton [81].

Despite these advances, fluorine emissions from aluminum smelters can still impact surrounding ecosystems. Rodriguez et al. [90] and Talovskaya et al. [91] documented elevated fluorine concentrations in vegetation and snowmelt water near smelters, highlighting the potential for long-distance transport. Hufschmidt et al. [92] and Kierdorf et al. [93] identified skeletal and dental fluorosis in kangaroos near an Australian smelter, indicating the potential health risks to wildlife. Global aluminum production is expected to reach 70.6 million tons by 2023 [84], and assuming most smelters limit fluorine emissions to 0.5–0.6 kg/ton of aluminum [81], an estimated annual release of 35,300–42,400 tons of fluorine is expected. However, data from World Aluminum [84] suggests slightly higher emission levels, potentially leading to an annual release of >45,000 tons [64].

2.2.4. Agricultural Sources

Agricultural practices—such as fertilizer application, sewage sludge disposal, and the use of certain agrochemicals—contribute to environmental fluoride contamination. Plants generally do not absorb fluoride from fertilizers, but it can potentially pose a threat to grazing animals and contaminate groundwater. Stricter regulations and monitoring of fluoride levels in agricultural inputs and practices are crucial for minimizing environmental fluoride contamination and safeguarding animal and human health.

Fluoride Release during Phosphate Fertilizer Production

The production of phosphoric acid, a key component in fertilizers, involves processes that release fluoride into the environment. This production is mainly carried out using wet and thermal processes that extract phosphoric acid from phosphate rock, a mineral rich in apatite [3,94]. The wet process, responsible for about 90% of global fertilizer production, uses sulfuric acid to process the rock, resulting in emissions of gaseous HF and SiF₄ [95,96]. While modern scrubbing systems in plants capture over 99% of these emissions, a small percentage still escapes into the atmosphere [96]. Studies on fertilizer plants in Brazil and Tunisia have emphasized this concern, with elevated fluoride concentrations reported in rainwater, groundwater, and nearby vegetation [97,98].

Additionally, the phosphogypsum byproduct, containing high fluoride levels, is stored in large ponds. These ponds are sources of environmental fluoride, either through leaks or when particles are dispersed by wind, leading to fluoride accumulation in nearby soil and water bodies [94,95,96]. Investigations in regions like Turkey have shown elevated soil fluoride levels near fertilizer production facilities, largely attributed to such phosphogypsum storage [99].

Globally, the demand for phosphate rock was approximately 263 million tons in 2017, with phosphate fertilizers expected to release between 0.694 and 1.04 million tons of fluoride annually through volatilization during processing [100]. This estimate considers both the gaseous emissions during the acidification phase and the additional contributions from particulate matter and phosphogypsum storage, highlighting a significant source of global fluoride emissions. Despite improvements in emission controls, the environmental impact of these processes necessitates ongoing research and stricter regulatory oversight to ensure sustainable practices in the fertilizer industry.

Fluoride Release during Phosphate Fertilizer Application

When applied to the soil, clay minerals and oxides strongly bind the fluoride from fertilizers, and thus, limit its uptake by plants. However, long-term application of phosphate fertilizers can result in fluoride accumulation in soil, raising concerns about the potential fluoride intake by grazing animals through the ingestion of contaminated soil [54,101,102]. Considering the large amounts of phosphate rock used for fertilizer production and the range of fluoride content in fertilizers (0.14–3.8 wt%), estimates suggest an annual addition of at least 2.3 million tons of fluoride to agricultural soils globally. Although fertilizer-derived fluoride is largely unavailable for plant uptake, soil ingestion poses a potential threat to grazing animals.

In some cases, fluoride from fertilizers can migrate from soil into groundwater, particularly under alkaline conditions [103]. Studies in India and Pakistan have reported elevated fluoride levels in groundwater from areas with extensive use of phosphate fertilizers [104,105].

Other Agricultural Fluoride Sources

Sewage sludge applied to agricultural land is another fluoride source. Sewage sludge can contain fluoride from various sources, including industrial wastewater, fluoridated drinking water, toothpaste, and medications [12]. Regulations typically limit the fluoride content of sludge applied to land (e.g., 200 mg/kg in the UK), but fluoride from sludge is likely to be more bioavailable than that from fertilizers [106].

Organofluorine-based agrochemicals, including insecticides, fungicides, and herbicides, are widely used in agriculture [107]. These compounds are persistent and resistant to degradation, raising concerns regarding their potential accumulation in soil and water resources [108]. Irrigation with fluorine-rich groundwater can also contribute to fluoride accumulation in plants, particularly via foliar uptake during overhead irrigation [109]. Botha et al. [110] suggested that fluoride-rich irrigation water may be partly responsible for livestock fluorosis in South Africa.

2.2.5. Fluoride Contamination by Various Industrial Sources

Mining and Waste Management

Past and present fluorite mining activities pose a considerable threat in terms of fluoride contamination. In the UK, studies have documented extremely high soil and vegetation fluoride levels near abandoned fluorite mines and waste piles. Fuge and Andrews [111] reported soil fluoride concentrations >2% near mines in northern England and Wales. High fluoride accumulation is found in the vegetation at these sites, and concentrations up to 1% in plants from the Peak District of England were reported by Cooke et al. [112]. Researchers have linked elevated fluoride levels to dental fluorosis in grazing animals [113]. Similar environmental concerns exist around china clay extraction sites in Cornwall, where fluoride-rich tailings contaminate nearby soils, plants, and waterways [111].

Fluoride in Steel Production

Fluorite is used as a flux in steelmaking, which releases fluoride as HF and SiF₄ gases [114]. Although a large portion of fluoride remains trapped in the slag byproduct [115], historical accounts mention instances of fluoride-related environmental problems near steel plants, including animal fluorosis [116]. However, the implementation of pollution control technologies in modern steelmaking plants is likely to result in minimal atmospheric fluoride emissions [3].

Glass and Other Industries

While the glass and enamel industries have historically contributed to environmental fluoride contamination through HF emissions during production, the implementation of efficient scrubbing systems in developed countries has notably reduced this [3]. Additionally, the relatively small amount of fluorite used in these industries—compared to steelmaking—minimizes the overall impact [117].

Fluorocarbons and Emerging Sources

Hydrofluoric acid is used in various industries, including the production of fluorocarbons and semiconductors. Weinstein and Davidson [3] estimated that the semiconductor industry in the USA released ~32 tons of hydrofluoric acid annually during the 1990s. Furthermore, the petroleum industry uses it as a catalyst, and Lewandowska et al. [50] suggested that vehicle exhaust fumes may emit fluoride due to its presence in fuels.

2.2.6. Urban Fluoride Emissions and Concerns

Many industrial activities that emit fluoride can considerably affect nearby urban areas. For example, artisanal brick production in Southeast Asia and aluminum smelting in Siberia are major sources of urban air pollution [77]. Coal and fuel combustion for domestic heating can also contribute to elevated fluoride levels in urban areas [50]. Vehicle emissions, possibly from fluoride-containing fuels and components, can also contribute [50]. The incineration of municipal solid waste releases considerable amounts of fluoride, primarily as HF. Although modern incinerators have emission control systems, the uncontrolled burning of waste can be a substantial source of HF and other fluoride-containing compounds in urban environments [3,118].

Airborne fluoride emissions from industry settle onto soil surfaces (dry deposition) or form acidic rain (wet deposition), and can impact the heath or nearby urban soils [119]. Plants play a further role in the transfer of fluoride to the soil by absorbing gaseous fluoride through their stomata (pores) or by taking it up from contaminated soil water [120]. While perfluorinated compounds (PFCs) and chlorofluorocarbons (CFCs) are persistent environmental pollutants with a long history of industrial use, their potential contribution to soil fluoride levels in urban environments remains unclear and requires further investigation [121].

2.2.7. Ubiquity and Persistence of Fluorinated Organic Compounds

The environment contains many fluorinated organic compounds, the majority of which are not naturally occurring [3]. These compounds are used in various applications, including agriculture, pharmaceuticals, and manufacturing. However, a major concern is the presence of perfluorinated compounds (PFCs), particularly those with long carbon chains. PFCs are resistant to degradation and can accumulate in the environment and biosphere [122]. Studies have shown their presence in humans and wildlife, with potential bioaccumulation and biomagnification effects [123]. PFC exposure has been related to a variety of health issues in humans, including cancer, thyroid disorders, and immune system dysfunction [124,125]. Some long-chain PFCs are classified as persistent organic pollutants due to their environmental persistence and adverse consequences.

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a class of PFCs that are of major concern because of their potential toxicity [126,127]. While data are limited, estimates suggest that their environmental impact on overall fluoride levels may be negligible compared to that of natural sources [126,128]. This is likely because the strong carbon–fluorine bonds in PFAS make them resistant to degradation. However, their presence in the environment and potential health consequences warrant continued research and regulation.

Chlorofluorocarbons and Their Replacements

Once widely used in refrigeration, air conditioning, fire extinguishers, and aerosol propellants, chlorofluorocarbons (CFCs) have been discovered to be a major cause of ozone depletion [129,130]. Their production was phased out and replaced with hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), which do not harm the ozone layer [3]. While HFCs, HCFCs, and other fluorinated gases contribute significantly to greenhouse gas emissions [131,132], their potential breakdown products or atmospheric interactions might influence soil fluorine levels. Further research is needed to explore this connection.

Trifluoroacetic Acid: A Persistent Byproduct

The degradation of certain fluoride-containing compounds, including HFCs and HCFCs, generates trifluoroacetic acid (TFA). TFA is also released from industrial production processes, the burning of fluoropolymers, and household waste incineration [3,129,133]. TFA is highly stable in the environment and readily forms salts. Although low in remote areas, TFA concentrations are elevated in urban and industrial areas [3,133]. TFA is weakly bound to soil and has the potential to migrate into groundwater [134]. TFA accumulates in water bodies, such as salt lakes and oceans due to evaporation; however, its presence in seawater at quantities greater than predicted from recent sources implies a natural source, possibly from hydrothermal vents [134].

2.2.8. Fluoride in Petroleum

Fluoride can occur in petroleum products because of its natural presence in crude oil or additives introduced during refining. This section explores the two main pathways for fluoride mobilization from petroleum sources—combustion and produced water [18]. Only the natural fluoride content of crude oil contributes to the additional anthropogenic mobilization of fluoride, as that added during refining originates from phosphate rock or mined fluoride and is already accounted for in environmental budgets. These estimates suggest that the average fluoride content of crude oil is very low (0.01 mg/kg) [135]. Considering global oil consumption data, the annual release of fluorine from petroleum combustion is estimated to be 0.000058 Tg [136]. Therefore, petroleum combustion appears to have minimal impact on the overall environmental fluoride budget.

Oil and gas production often involves the extraction of large volumes of water and hydrocarbons. These “produced waters” can contain large amounts of fluoride, with concentrations ranging from undetectable levels to over 190 mg/L [137,138]. Global oil production has increased steadily, leading to a corresponding increase in the amount of wastewater produced, with estimates suggesting that the water-to-oil ratio is ~3:1 globally [139]. Based on this ratio and the average fluoride concentration of 4 mg/L in produced water, these calculations indicate a small but increasing flux of fluoride associated with oil production. Estimates indicate that this flux increased from 0.04 Tg/yr in the early 1980s to 0.07 Tg/yr in 2018 [140]. While both petroleum combustion and produced water contribute to fluoride mobilization, their combined impact appears to be relatively less compared to that of natural sources. However, proper management and treatment of produced water is crucial to minimize potential environmental contamination from this source of fluoride.

Figure 2 provides a comprehensive overview of the global fluorine (F) cycle, effectively summarizing the key points discussed thus far. This cycle encompasses both natural and anthropogenic processes that influence the movement of fluorine between various reservoirs within the Earth’s system. The figure vividly illustrates the intricate interplay between these processes, shedding light on how they collectively govern the distribution and cycling of fluorine in the environment. Notably, it underscores the substantial impact of human activities on the fluorine cycle, particularly through industrial and agricultural practices. Given the absence of comprehensive studies on the fluorine cycle in Korea, this figure serves as a valuable tool for approximately quantifying the biogeochemical cycling of fluorine among different reservoirs within the Korean context.

Table 1. Industrial consumption of HF in Korea (Kim et al., [141], with the permission of authors).

No.	Industry Sector	HF Consumption (Unit: tons)
1	Manufacture of chemicals and chemical products except pharmaceuticals and medicinal chemicals	60,265 (37%)
2	Manufacture of electronic components, computers, and audiovisual communication equipment	38,679 (24%)
3	Manufacture of other non-metallic mineral products	31,547 (20%)
4	Manufacture of fabricated metal products except machinery and furniture	8765 (5%)
5	Others	21,867 (14%)
Total	-	161,123 (100%)

presents the consumption of hydrogen fluoride (HF) in tons across various industrial sectors in Korea in 2014 [141]. The sectors are categorized according to the Korean Standard Industrial Classification. The table shows that the chemical industry sector consumed the largest amount of HF (60,265 tons, 37%), followed by the electronics sector (38,679 tons, 24%), the non-metallic mineral products sector (31,547 tons, 20%), and the fabricated metal product sector (8765 tons, 5%). The remaining sectors consumed a total of 21,867 tons (14%) of HF. Although Table 1 is limited to 2014 and the industry sectors are somewhat different from those discussed in Section 2.2 above, it provides insight into the major industries contributing fluoride to soil and the environment.

3. Soil Fluorine Management Strategies

3.1. Global Variations in Soil Fluorine Regulations

Table 2 summarizes soil quality guidelines for fluorine management from various sources. Before directly comparing Korean soil fluorine contamination standards with those of other countries, it is essential to recognize the significant variations in climatic conditions and geological characteristics across different regions. Our findings indicate that only a limited number of countries (at least 12) in North America, Europe, and Asia currently regulate soil fluorine as a potential contaminant (Table 2). These countries have established diverse soil fluorine management standards based on criteria such as climate, geology, and intended land use.

Soil quality guidelines for fluorine show wide variations, with values ranging from a minimum of 45 mg/kg for special areas with high biological value in Belgium to a maximum of 4690 mg/kg for industrial areas in the same country (Table 2). This vast discrepancy highlights the significance of land use criteria when establishing soil fluorine management standards. Areas with potentially higher human exposure, such as residential or high-value ecological areas, often implement stricter limits.

Canada, which has a land area approximately 100 times that of South Korea, enforces a stricter limit (200 mg/kg) for agricultural land compared to Korea’s current regulations [13,142]. However, Canada demonstrates flexibility by allowing a higher limit (2000 mg/kg) for industrial and commercial lands. Similarly, Japan has a seemingly lenient standard of 4000 mg/kg for soil fluorine [13]. However, it is important to consider that Japan enforces a stricter regulation (0.8 mg/L) for fluoride in drinking water than that recommended by the World Health Organization (1.5 mg/L) [143]. This example emphasizes how countries might prioritize regulations based on their specific environmental conditions and potential exposure pathways. Water-soluble fluoride content, in addition to the total amount of soil fluoride, is the key factor influencing its mobility, plant uptake, potential toxicity, and risk of groundwater contamination [8]. The bioavailable fraction of soil fluorine is a more accurate predictor of potential environmental and human health risks.

The global trend in soil fluorine management indicates a move towards regulating specific fluoride compounds that pose clearly defined risks. This approach prioritizes the management of synthetic or naturally occurring fluoride compounds that directly impact human health or ecosystems. The focus is on regulating these specific compounds rather than the total soil fluorine content. The United States exemplifies this trend, where each of the climatically and geologically diverse 50 states has established independent soil pollution standards. However, a common thread across these standards is regulating the content of specific fluorine compounds, such as PFAS, which are detrimental to human health and ecosystems even at very low concentrations (Section 2.2.8) [144]. Regulatory action is then taken through risk assessments when the concentrations of these specific compounds exceed established thresholds.

To summarize, soil fluorine management standards vary considerably across different countries due to diverse climatic conditions, geological makeup, and land use considerations. While some countries have lenient total soil fluorine limits, they might compensate with stricter regulations for specific bioavailable fractions, water quality, or individual high-risk fluoride compounds. Understanding these nuances, as well as the global shift towards regulating specific high-risk fluoride compounds, is critical for establishing effective soil fluorine management strategies in South Korea.

3.2. Balancing Soil Fluorine Standards in Korea

The Soil Environment Conservation Act of 1995 serves as the cornerstone legislation governing the management of soil pollution in Korea [145]. Recognizing the importance of a healthy soil environment, the act identifies 24 soil pollutant types. Fluoride was included in 2002 alongside organic pollutants like trichloroethylene, tetrachloroethylene, and inorganic nickel [140]. This inclusion reflected growing concerns about potential negative impacts of elevated soil fluorine levels. To establish these standards, the Korean Ministry of Environment developed a framework called Soil Worrisome Levels (SWLs). This framework acknowledges that soil contamination often arises from secondary sources like air pollution, contaminated water, or various waste materials [140].

Table 2. Global soil quality guidelines.

No.	Country	Soil Quality Guidelines		Reference
		Land Use	Concentration (mg/kg)
1	Canada	Agriculture	200	CCME [142]
		Agriculture/residential (Alberta)	200
		Residential/parkland	400
		Commercial/industrial	2000
2	Australia	Industrial waste (Victoria)	450	EPA, Victoria [146]
3	Switzerland	All regions	400	Slooff et al. [147]
4	The Netherlands	Regions with high clay content (>25%)	500
		Regions with very little or no clay content	175
5	Austria	Agricultural/residential (trigger value)	200	Carlon et al. [148]
		Agricultural/residential (intervention value)	1000
6	Belgium	Special areas with high biological value	45
		Residential	3950
		Industrial	4690
7	The Czech Republic	Agricultural	500
8	Italy	Residential/public	100
		Agricultural	2000
9	Lithuania	Residential/recreational/agricultural	200
10	Slovakia	Maximum allowable limits	1000
		Value for decontamination measures	2000
11	The United States (US)	Residential	469	USEPA [149]
12	Japan	All regions except agricultural	4000	Noh [13]

Table 2. Global soil quality guidelines.

No.	Country	Soil Quality Guidelines		Reference
		Land Use	Concentration (mg/kg)
1	Canada	Agriculture	200	CCME [142]
		Agriculture/residential (Alberta)	200
		Residential/parkland	400
		Commercial/industrial	2000
2	Australia	Industrial waste (Victoria)	450	EPA, Victoria [146]
3	Switzerland	All regions	400	Slooff et al. [147]
4	The Netherlands	Regions with high clay content (>25%)	500
		Regions with very little or no clay content	175
5	Austria	Agricultural/residential (trigger value)	200	Carlon et al. [148]
		Agricultural/residential (intervention value)	1000
6	Belgium	Special areas with high biological value	45
		Residential	3950
		Industrial	4690
7	The Czech Republic	Agricultural	500
8	Italy	Residential/public	100
		Agricultural	2000
9	Lithuania	Residential/recreational/agricultural	200
10	Slovakia	Maximum allowable limits	1000
		Value for decontamination measures	2000
11	The United States (US)	Residential	469	USEPA [149]
12	Japan	All regions except agricultural	4000	Noh [13]

The current SWLs for fluorine in South Korea are differentiated based on land use: 400 mg/kg for region I (croplands, rice paddies, residential areas, and schools) and region II (forests and playgrounds), and 800 mg/kg for region III (factories, gas stations, and roads) (

Table 3. Soil Worrisome Levels for fluorine in South Korea (unit: mg/kg).

Region	Fluorine Content	Land Uses
I	400	Croplands, rice paddies, orchards, residential areas, and schools
II	400	Forests, salt farms, playgrounds, and religious sites
III	800	Factories, gas stations, roads, and military sites

). This tiered system reflects the potential health risks associated with varying exposure levels in different land use categories. However, implementing these standards presents significant challenges.

One major hurdle lies in the natural geological makeup of Korea. A large portion of the bedrock consists of granite [150], an igneous rock naturally rich in fluorine-containing minerals like feldspar and mica. This geology leads to widespread natural occurrence of fluoride in Korean soils. A study by Lim et al. [11] supports this observation. Their evaluation of soil samples across 82 locations in Korea revealed an average fluoride concentration of 204.5 mg/kg (ranging from 15.3 to 504.8 mg/kg). This falls below the global average of 321 mg/kg. Notably, the average concentrations showed regional variations, with regions I, II, and III having averages of 229.6, 195.7, and 273.4 mg/kg, respectively. A nationwide soil survey conducted by the Korea Environment Corporation between 2012 and 2021 highlighted another challenge: widespread exceedance of the SWLs even in areas with naturally occurring fluoride. The survey revealed that 1337 (15.2%) of the 8768 sampling points across Korea exceeded the SWL for region I (400 mg/kg). This widespread exceedance, even in areas with natural sources, raises concerns about the practicality of the current regulations.

Furthermore, the high soil remediation costs associated with fluoride pose a major financial burden, particularly for housing development projects. The cost for fluoride-related soil purification from 2018 to 2022 amounted to KRW 585.3 billion (approximately USD 427 million) in the metropolitan area of the capital Seoul alone [151]. Nationwide estimates are likely to be even higher. These substantial costs raise concerns about the economic feasibility of the current regulations.

While some experts claim that the current SWL (400 mg/kg) for sensitive areas such as croplands and residential areas is crucial for protecting public health and ecosystems by citing potential health risks associated with fluoride exposure, others advocate for a more nuanced approach. Proponents of a more nuanced approach emphasize that under natural conditions, the majority of fluorine in soil minerals is insoluble and very stable. Research directly linking health problems to stabilized soil-based fluorine compounds is limited. Although the presence of fluorine can help identify its source in the soil, the total amount of fluorine does not necessarily reflect its bioavailability [152]. However, research on the hazards of fluoride in air and water is well documented [111,153,154], raising the question of whether it is appropriate to relax the SWLs for fluorine. Examining other countries’ strategies to manage soil fluorine contamination can provide valuable insights for establishing effective and practical regulations in Korea. This may entail amending current SWLs or implementing targeted remediation strategies based on factors such as bioavailability and land use.

3.3. Advantages, Disadvantages, and Challenges of Soil Fluorine Management Strategies: Navigating the Complexities

3.3.1. Proposed Soil Fluorine Management Strategies for Korea

Based on the comprehensive review of the global fluorine cycle, international trends in soil fluorine management, and the current challenges faced in Korea, we propose a paradigm shift in soil fluorine management strategies. The focus should move away from solely regulating total fluorine content towards a more nuanced approach that targets specific hazardous fluorine compounds and prioritizes remediation efforts based on bioavailability assessments.

Shifting the Focus from Total Fluorine to Specific Compounds

The current Korean soil fluorine standards, based on total fluorine content, face significant challenges due to the naturally high background levels of fluorine in many regions [13]. This approach often leads to unnecessary remediation efforts and economic burdens in areas where the fluorine is predominantly in stable, non-bioavailable forms [151]. Therefore, we advocate for a transition towards regulating specific fluorine compounds that pose well-documented risks to human health and the environment. This approach aligns with the global trend observed in countries like the United States [144], where regulations target specific hazardous compounds like PFASs, even at very low concentrations.

Adjusting SWLs

In light of the above considerations, we propose a reevaluation of the current SWLs for fluorine in Korea. The existing standards (Table 2), based solely on total fluorine content, may be overly stringent in areas with naturally high background levels. By incorporating bioavailability assessments and focusing on specific hazardous compounds, the SWLs can be adjusted to reflect the actual risk posed by fluorine contamination, ensuring a more balanced and effective approach to soil fluorine management.

Prioritizing Remediation Based on Bioavailability Assessments

The bioavailability of fluorine in soil is a critical factor in determining its potential impact [155]. While total fluorine content provides a general indication of contamination, it does not accurately reflect the actual risk posed by the fluorine present. Therefore, we recommend incorporating bioavailability assessments into soil fluorine management strategies. This would enable prioritizing remediation efforts in areas where fluorine is readily available for uptake by plants or leaching into groundwater, thus posing a greater threat to human and environmental health.

3.3.2. Advantages—Benefits of Effective Soil Fluorine Management

The implementation of well-designed soil fluorine management strategies can yield a multitude of benefits that extend beyond mere regulatory compliance. These benefits encompass safeguarding public health, preserving environmental integrity, and fostering sustainable development.

Safeguarding public health: The foremost advantage of effective soil fluorine management lies in its potential to mitigate health risks associated with excessive fluoride exposure [156,157]. By regulating and controlling fluorine levels in soil, particularly in residential areas and agricultural lands, the incidence of dental and skeletal fluorosis can be significantly reduced [158]. This ensures a safer and healthier living environment for communities, especially vulnerable populations like children and the elderly. The focus on bioavailability assessments further enhances this benefit by targeting remediation efforts towards areas where fluorine poses the greatest risk of entering the food chain or contaminating drinking water sources [157].

Preserving environmental integrity: Fluorine contamination can disrupt delicate ecological balances, impacting plant and animal life [159]. Effective soil fluorine management helps protect ecosystems from the detrimental effects of fluorine toxicity. By regulating industrial emissions, promoting sustainable agricultural practices, and implementing targeted remediation measures, the integrity of natural habitats can be preserved, ensuring the continued provision of ecosystem services essential for human well-being.

Fostering sustainable development: The adoption of stringent fluorine management practices aligns with international environmental protection standards, demonstrating a commitment to responsible resource management and sustainable development. This can enhance a country’s global image, attract foreign investment, and facilitate international cooperation on environmental issues. Moreover, by balancing environmental protection with economic considerations, sustainable soil fluorine management can support economic growth while minimizing adverse impacts on human health and the environment.

3.3.3. Disadvantages—Limitations and Considerations

While the benefits of effective soil fluorine management are undeniable, it is crucial to acknowledge the potential disadvantages and trade-offs that may arise during implementation. These primarily revolve around the economic implications and potential disruptions to industrial activities.

High costs: The financial burden associated with soil fluorine management can be substantial. Remediation technologies, particularly for large-scale contamination or complex geological settings, can be expensive. The ongoing monitoring and assessment of fluorine levels in soil and water resources also require significant investments in infrastructure and personnel. These costs can strain public budgets and pose challenges for industries, especially small and medium-sized enterprises, potentially hindering their growth and competitiveness. The high cost of remediation is particularly relevant in the Korean context, where naturally high background levels of fluorine necessitate extensive soil treatment in many areas, even if the bioavailability is low.

Economic constraints: Stringent soil fluorine regulations can impose constraints on various industrial sectors, including agriculture, manufacturing, and construction. Compliance with these regulations may necessitate changes in production processes, adoption of cleaner technologies, or restrictions on land use. These adjustments can lead to increased operational costs, reduced productivity, and potential job losses, particularly in industries heavily reliant on fluorine-containing materials or processes. The balance between environmental protection and economic development is delicate, and overly stringent regulations can stifle economic growth and innovation.

3.3.4. Challenges—Key Considerations for Implementation

The effective management of soil fluorine contamination presents a multifaceted challenge that requires addressing various scientific, technological, regulatory, and societal hurdles. These challenges necessitate a comprehensive and adaptive approach to ensure the successful implementation of sustainable soil fluorine management strategies.

Natural background levels: The geological characteristics of Korea, with its abundance of granite bedrock, contribute to naturally elevated fluorine levels in many soils. This inherent variability poses a significant challenge in establishing and enforcing a universal soil fluorine standard that is both protective of human and environmental health and economically feasible. The discrepancy between natural background levels and regulatory thresholds can lead to conflicts in policy enforcement and potential over-regulation in areas with low bioavailability of fluorine.

Technological limitations: Accurately measuring and remediating fluorine contamination, particularly its bioavailable forms, remains a technological challenge. Current analytical methods may not fully capture the complex interactions between fluorine and soil components, leading to uncertainties in risk assessments. Furthermore, remediation technologies often face limitations in terms of cost-effectiveness, scalability, and long-term efficacy, particularly in addressing diffuse contamination or naturally occurring fluorine.

Policy and regulation: Striking a balance between environmental protection and economic development is a perpetual challenge in soil fluorine management. Overly stringent regulations can stifle industrial activities and impose significant economic burdens, while lax regulations can jeopardize public health and environmental integrity. The dynamic nature of fluorine contamination, coupled with evolving scientific understanding, necessitates adaptive and flexible regulatory frameworks that can respond to emerging challenges and technological advancements.

Public awareness and cooperation: Fostering public awareness and understanding of soil fluorine contamination and its associated risks is crucial for successful management. However, communicating complex scientific information in an accessible and engaging manner can be challenging. Moreover, gaining public support for regulations and remediation efforts, especially when they involve potential economic trade-offs, requires transparent communication and active engagement with stakeholders. The lack of public awareness and cooperation can hinder compliance with regulations and impede the implementation of effective management strategies.

4. Conclusions

In this study, we explored the sources, behavior, and management challenges associated with soil fluoride in Korea. We reviewed the current literature to understand the various sources of soil fluoride, including natural sources (weathering, volcanic activity, marine deposits, etc.) and anthropogenic sources (coal combustions, brick and ceramic manufacturing industries, aluminum smelting, agriculture, etc.). We also discussed the potential hazards of excessive fluoride intake, such as dental fluorosis and skeletal fluorosis. An analysis of Korea’s soil fluorine regulations highlights the complexities of balancing environmental protection with economic considerations. While some experts advocate for maintaining strict standards for total soil fluorine content, international practices and geological reality suggest the need for a more nuanced approach. First, global trends in soil fluorine management emphasize the regulation of specific fluorine compounds with proven risks. These typically include synthetic compounds or those exhibiting high bioavailability—such as PFASs—which have detrimental health and ecosystem effects even at low concentrations. Second, in Korea, the naturally high background levels of fluorine in soil owing to the abundance of granite make adherence to stringent total content standards economically impractical. The considerable financial burden associated with remediating soil that exceeds these standards, even if naturally occurring, impedes development initiatives and raises concerns about the overall feasibility of these regulations.

Considering the complexities of soil fluorine management in Korea, we advocate for a paradigm shift in regulatory strategies. The current focus on total fluorine content should be refined to prioritize the regulation of specific, well-defined fluorine compounds with documented environmental and health risks, similar to the approach adopted in the United States for PFASs. This targeted approach would ensure that resources are allocated efficiently to address the most pressing concerns. Furthermore, the incorporation of bioavailability assessments into soil management practices would enable the prioritization of remediation efforts in areas where fluorine poses the greatest risk of environmental contamination and adverse health effects. Additionally, the current Soil Worrisome Levels (SWLs) should be reevaluated to reflect the actual risk posed by fluorine contamination, considering both the specific compounds present and their bioavailability.

These approaches would enable South Korea to manage soil fluorine contamination more effectively, balancing the requirement to safeguard public health and the environment from an economic perspective. This would prioritize resources to address the most pressing concerns while minimizing excessive economic costs associated with naturally occurring, stable forms of fluorine in the soil.