Fluoride Action Network


The health of millions of people worldwide is negatively impacted by chronic exposure to elevated concentrations of geogenic fluoride in groundwater. Due to health effects including dental mottling and skeletal fluorosis, the World Health Organization maintains a maximum guideline of 1.5?mg/L in drinking water. As groundwater quality is not regularly tested in many areas, it is often unknown if the water in a given well or spring contains harmful levels of fluoride. Here we present a state-of-the-art global fluoride hazard map based on machine learning and over 400,000 fluoride measurements (10% of which >1.5?mg/L), which is then used to estimate the human population at risk. Hotspots indicated by the groundwater fluoride hazard map include parts of central Australia, western North America, eastern Brazil and many areas of Africa and Asia. Of the approximately 180 million people potentially affected worldwide, most reside in Asia (51-59% of total) and Africa (37-46% of total), with the latter representing 6.5% of the continent’s population. Africa also contains 14 of the top 20 affected countries in terms of population at risk. We also illuminate and discuss the key globally relevant hydrochemical and environmental factors related to fluoride accumulation.

*Original full-text full-text article  at https://doi.org/10.1038/s41467-022-31940-x


Table 1. Top 20 countries in population potentially affected by fluoride concentrations in groundwater greater than 1.5 mg/L.

Rank Country Population at risk (range) Rank Country Population at risk (range)
(million) (million)
1 India 49 (26–89) 11 Malawi 4.0 (3.5–4.8)
2 China 22 (1–50) 12 Zambia 3.4 (1.4–3.6)
3 Dem. Rep. Congo 15 (2–16) 13 Mozambique 2.6 (1.7–3.4)
4 Ethiopia 9.6 (4.0–13.8) 14 Angola 2.2 (0.7–2.4)
5 Pakistan 7.6 (2.3–14.5) 15 Afghanistan 1.7 (0.5–4.8)
6 Kenya 7.5 (4.2–8.3) 16 Cameroon 1.6 (0.3–2.5)
7 Nigeria 7.4 (1–17) 17 Madagascar 1.4 (0.7–2.3)
8 Tanzania 6.9 (3.7–7.9) 18 Chad 1.2 (0.1–2.2)
9 Uganda 4.8 (0.9–8) 19 Niger 1.2 (0.2–2.6)
10 Yemen 4.3 (2.6–4.4) 20 Myanmar 1.1 (0.07–3.3)

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Fig. 1: Fluoride in groundwater.
figure 1

a Probability of naturally occurring fluoride in groundwater exceeding the WHO drinking water guideline of 1.5 mg/L. The map was developed by applying the final random forest model to the 12 most statistically important predictor variables. Panel b shows the fluoride data points (n = 402,452) used in analysis and modeling. Closer views of the global map are given for the western U.S. and Mexico (c), eastern South America (d), the southern half of Africa (e), and western South Asia (f). The data sources are listed in Supplementary Table 1 and a large-scale map of the fluoride points is shown in Supplementary Fig. 1 along with large-scale versions of the prediction map focused on each continent in Supplementary Figs. 38.

Two regions with large potentially affected populations for which only relatively few direct measurements of groundwater quality were available to constrain the model are China and Central Africa (Fig. 1b and Supplementary Fig. 1). The model also indicates a particularly elevated fluoride risk across much or most of Angola, Cameroon, Chad, Democratic Republic of the Congo (DRC), Ethiopia, Eritrea, Kenya, Madagascar, Malawi, Mozambique, Nigeria, Somalia, Tanzania, Zambia, and Zimbabwe as well as Yemen (Table 1). The at-risk population figures provide only a rough estimate of the actual number of people affected, which can only be verified by epidemiological studies on the ground. Nevertheless, Fig. 4 provides a meaningful broad-scale indication of where such investigations are most needed.

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This study was funded by:

Federal Department of Foreign Affairs | Direktion für Entwicklung und Zusammenarbeit (Swiss Agency for Development and Cooperation)
and the Swiss National Science Foundation


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