In groundwater, excessive fluoride concentration has been evidenced in more than 20 developing and developed countries, including India, wherein 19 states are confronting serious problems owing to fluorosis. Essential for skeletal and dental development in small quantities, excessive fluoride intake leads to fluorosis, a debilitating disease impacting approximately 200 million people globally. India faces a severe crisis with high fluoride intake, leading to dental and skeletal health issues.
The harmless fluoride concentration in drinking water is around 1.5 mg/l. Geological factors, such as granite gneisses and slate stones, contribute to fluoride ion concentration, with variations in rock types and mineral breakdown. Additionally, climate, contact time with aquifer minerals, and arid regions significantly influence fluoride levels. Human activities, including burning fossil fuels and the production of fly ash, contribute to elevated fluoride content, posing health risks worldwide.
<p>A recent paper ‘<a href="https://doi.org/10.1016/j.indic.2023.100305">Recent advancements in fluoride impact on human health: A critical review</a>’ in the journal Environmental and Sustainability Indicators delves into the complex landscape of fluoride exposure, offering insights into its intricate effects on human health, groundwater composition, and innovative removal techniques. With a focus on global implications, the study covers diverse aspects, from geological factors influencing fluoride concentrations to the intricacies of skeletal fluorosis and the broader spectrum of health impacts.</p>
Numerous scientists have reported that a small amount of fluoride is beneficial for strengthening the bone and preventing dental caries, instead, its high dose causes severe effects on human health such as skeletal fluorosis, dental fluorosis, increase in bone fracture, decrease in birth rates, impaired thyroid functions, increased rates of urolithiasis and lower intelligence quotient (IQ) in children. Fluoride exposure may lead to high frequency of chronic irritative respiratory disease, chronic bronchitis. Due to high intake of sodium fluoride pesticides and dental products, severe fluoride toxicity and death have also been witnessed.
Fluoride ion exhibits the lowest solubility within the pH range of 5.0–6.5 (Adriqno, 1986). At higher pH levels, ionic exchange between fluoride and hydroxyl ions (found in minerals like mica, illite, and amphiboles) occurs, leading to increased fluoride absorption in groundwater (Sunkari et al., 2022). The presence of elevated bicarbonate and sodium levels, coupled with higher pH, facilitates fluoride leaching from minerals into groundwater, enhancing the solubility of fluoride-containing minerals due to the alkaline nature of the water. In alkaline environments, fluoride ions are desorbed, contributing to the suspension of fluoride minerals.
Excessive fluoride in groundwater is often linked to higher concentrations of bicarbonate ions and, in certain locations, elevated nitrate ion levels (Handa, 1975). Higher Total Dissolved Solids (TDS) concentrations elevate ionic strength, further increasing the solubility of fluoride ions in groundwater (Perelman, 1967). Prominent fluoride-containing minerals include muscovite, lepidolite, biotite, fluorapatite, fluorite (fluospare), cryolite, and topaz. The dissolution of fluoride (CaF2) contributes significantly to high fluoride concentrations in groundwater globally, as reported by Smedley and Edmunds (2013).
Fluorine, with its high electronegativity, has a unique affinity for positively charged cations similar to calcium. Modest fluoride consumption has been associated with reduced dental fluorosis and strengthened bones under specific conditions (Rao, 2003; Kaminsky et al., 1990; Harrison, 2005; Heller et al., 1997; Doull et al., 2006). Free fluoride ions in the fluid phase also contribute to the growth of apatite minerals (Aoba and Fejerskova, 2002).
The recognition of fluoride's benefits dates back to the 1930s, when researchers aimed to determine an optimal fluoride content in drinking water to reduce dental deformities and promote bone development. Adequate fluoride intake has been linked to preventing osteoporosis, as demonstrated in studies conducted in North Dakota (Bernstein et al., 1996).
Several factors, including weathering of rocks, evaporation, climate, diet, anthropogenic activities, and population characteristics, determine fluoride content standards in drinking water. Fluoride deficiency in drinking water can lead to tooth decay, while controlled addition up to 1.0 ppm through water fluoridation helps prevent dental issues. However, excess fluoride causes tooth mottling and bone defects, prompting adherence to safe limits.
<p>Fluoride occurs naturally and through human activities, posing challenges in regulating total fluoride consumption within safe boundaries for individuals in specific regions. Public water supplies are prioritised for monitoring, leaving many private well owners unaware of their fluoride exposure. Despite numerous studies standardising fluoride intake, uncertainties and conflicting findings persist, with long-term excessive fluoride concentrations (above 2 mg/l) deemed harmful. Disagreements surround optimal fluoride levels; while fluoride supports strong bones and teeth, health issues have been reported at concentrations below 2 mg/l.</p>
Establishing drinking water standards for fluoride involves complex considerations such as climate, diet, and population characteristics. The U.S. Environmental Protection Agency (EPA) sets a maximum contaminant level (MCL) of 4 mg/l and a secondary MCL (SMCL) of 2 mg/l. The World Health Organisation (WHO) recommends less than 1.5 mg/l, while India and China adopt a 1 mg/l standard due to naturally higher fluoride levels. Groundwater quality studies, such as in Dausa district, Rajasthan, reveal varying fluoride concentrations, emphasising the need for tailored assessments in different regions (Wu et al., 2015; Chen et al., 2017; Tiwari et al., 2020).
Addressing elevated fluoride levels in water is crucial for ensuring safe drinking water. Various methods, categorised as in-situ and ex-situ treatments, aim to reduce fluoride concentrations.
In 2019, the Indian government launched the Jal Jeevan Mission to provide piped drinking water to every rural household by 2024, addressing water management and contamination issues. This initiative aligns with the broader goal of mitigating skeletal fluorosis and enhancing water quality across the country.
<p>The impact of fluoride ion exposure on human health is nuanced, with benefits observed at trace levels but adversities emerging at higher concentrations. While the safety and unsafe limits of fluoride ion doses remain unclear, this review emphasises that fluoride is health-beneficial in moderation. Yet, higher concentrations lead to acute and chronic health problems, some of which are incurable. Drinking water standards are challenging to set due to varying threshold levels among populations.</p>
Groundwater, a major source of fluoride accumulation, results from mineral decomposition, dissociation, and dissolution, particularly in areas with weathering rocks, volcanic activities, or fluoride-rich sedimentary formations. Anthropogenic sources, such as pesticide use and industrial runoff, contribute to elevated fluoride levels.
Various techniques, including reverse osmosis, distillation, adsorption with activated alumina, flocculation, and bone charcoal, offer solutions for removing fluoride from water. The global challenge involves addressing fluoride-related health problems in third-world countries due to insufficient access to clean water and knowledge gaps. Developed nations also grapple with health issues, often linked to dietary choices. Thus, establishing a clear link between fluoride intake and its impact on human health, coupled with increased awareness, is crucial for ensuring a healthier future.
<p>Fluoride research, integral to medicine, industry, and public health, is advancing in key areas. Ongoing studies examine fluoride's role in preventing dental caries, focusing on effective and safe delivery methods to teeth while assessing potential adverse effects. Research is broadening to comprehend fluoride's impact on overall health, encompassing bone health, brain development, and the endocrine system.</p>
Environmental ramifications of fluoride are under scrutiny, evaluating potential toxicity to wildlife and ecosystems. Researchers explore alternative fluoride sources beyond traditional toothpaste and water fluoridation, introducing new compounds and delivery methods.
In developing countries, studies assess the effectiveness of fluoride programs, aiming to enhance fluoride access and dental care. As technology and research methods progress, the landscape of fluoride research will likely expand, driven by growing concerns for health and the environment.
The full paper can be accessed here