Fluoride contamination in groundwater: A global review of the status, processes, challenges, and remedial measures

Groundwater pollution by fluoride is one of the prime concerns of the world population due to its toxicity, which results in adverse health impacts. In this paper, we review the current scenario of the fluoride contamination of groundwater in various countries across the globe and its impact on human health. During the last decade, several newly affected regions have been reported all over the world, with more than 100 countries affected by fluoride contamination in groundwater (concentration exceeding the acceptable limit of 1.5 mg/L defined by the World Health Organization). Fluoride poisoning is mainly due to the unsupervised ingestion of products for dental and oral hygiene and over-fluoridated drinking water. It is estimated that more than 200 million people from different countries are affected by fluoride-related groundwater issues and health problems. The highest among these are from the countries in Africa (38), Asia (28), and Europe (24), followed by countries like South America (5), North America (3), and Australia (2). The source of fluoride in drinking water is primarily geogenic, together with forage, grasses and grains, tea, and anthropogenic sources. These countries affected were correlated with climatic zones and geological factors to gain insights into geospatial relations. Our analyses show that most of the fluoride pollution-prone zones are located in high-grade metamorphic terranes with granitoid or alkaline intrusions, geothermal hot springs, and volcanic regions with arid or semi-arid climatic conditions. This study also finds that children across the globe are more vulnerable than adults to fluoride contamination. The review finds that, although there are efficient fluoride removal techniques, including filters with next-generation nanomaterials, to date, there has not been a single technique developed that can claim to be a practically robust solution for fluoride removal from drinking water. Therefore, we suggest developing next-generation filters that can retain essential minerals in water and remove only harmful ones and selecting purification technologies according to need, climate, geology, and geographic location. The findings from our review would help policymakers take effective and sustainable measures for safe water supply in the affected areas. Within the framework of the Sustainable Development Goals (SDGs), particularly SDG 3 (Good Health and Well-being) and SDG 6 (Clean Water and Sanitation), this study emphasizes the critical role of fluoride as a key indicator. It underscores the imperative of addressing elevated fluoride levels in drinking water, particularly in African and Asian countries, to achieve the overarching objective of universal and equitable access to safe, affordable, and uncontaminated drinking water for global society by the targeted year of 2030.