Groundwater fluoride contamination in Ghana and the associated human health risks: Any sustainable mitigation measures to curtail the long term hazards?

Fluorine is a halogen that naturally exists in the form of fluoride (F^?) due to its high reactivity and electronegativity (Ganyaglo et al., 2019; Zhang et al., 2020; Murray et al., 2021). It constitutes about 0.06–0.09% of the earth’s crust, been the 13th most abundant element (Rusiniak et al., 2021).

Fluoride (F^?) occurs in waters in varied concentrations (Jacks et al., 2005; Brindha and Elango, 2011; Dar et al., 2011; Vithanage and Bhattacharya, 2015a, b). Its natural concentration in waters depends largely on the nature of the geologic formations; fluoride-bearing minerals, anion exchange capacity of aquifer materials (OH^? for F^?), pH, alkalinity, temperature and residence time of waters within a particular formation (Saxena and Ahmed, 2001; Sunkari et al., 2018; Sunkari et al., 2019; Zango et al., 2019). Some of the minerals that have the greatest impact on the hydrogeochemistry of fluoride are: fluorite, apatite, mica, amphiboles, some clay minerals (such as illite, montmorillinite and kaolinite) and villiamite (Dar et al., 2011; Sunkari et al., 2018). Fluoride is colourless, tasteless or scentless when dissolved in water thereby making it difficult to be determined through physical examination. Its concentrations in waters can only be determined by chemical analysis (Brindha and Elango, 2011).

Fluoride causes health problems in people all over the world. A concentration of at least 0.6 mg/L promotes growth of human teeth and bones (Narbutait? et al., 2007). Intake of groundwater with fluoride levels exceeding 1.5 mg/L will eventually lead to dental fluorosis (Sunkari et al., 2019; Kimambo et al., 2019; Aravinthasamy et al., 2020; Zango et al., 2021; Ijumulana et al., 2021). A further consumption of higher concentration will result in skeletal fluorosis (Brindha and Elango, 2011; Ijumulana et al., 2020, 2021). There are several ways of mitigating fluoride contamination in groundwater. These methods include: dilution of the groundwater contaminated with fluoride, adsorption, ion exchange, and precipitation among others. Preference of any of these methods depends on the: affordability, magnitude of the contamination of groundwater as well as the origin of the contaminants; whether it is natural or anthropogenic (Bannerman and Ayibotele, 1984; Apambire et al., 1997; Abugri and Pelig-Ba, 2011; Brindha and Elango, 2011; Kimambo et al., 2019).

Ghana is one of the fluorosis endemic countries in West Africa. The highly fluoridated parts of Ghana are mainly restricted to the northern fringes of the country, which are largely dominated by varying lithologies involving rocks belonging to the Birimian Supergroup and the Voltaian Supergroup (Fig. 1). These rocks are mainly volcanic and sedimentary rocks that are intruded by granitoids (Fig. 1). The fluorosis endemic parts of Ghana have been the focus of many researchers in the past decades (Apambire et al., 1997; Anku et al., 2009; Atipoka, 2009; Salifu et al., 2012; Yidana et al., 2012; Firempong et al., 2013; Alfredo et al., 2014; Craig et al., 2015, 2018; Anornu et al., 2017; Tay, 2017; Sunkari et al., 2018; Donzagla et al., 2019; Ganyaglo et al., 2019; Sunkari et al., 2019; Zango et al., 2019, 2021; Zakaria et al., 2021). Most of these studies are localized to specific communities, districts, municipalities and districts in northern Ghana. However, there is no comprehensive review on the fluoride menace to the groundwater resources in the entire country. This study aims at reviewing all studies previously conducted in Ghana, especially in the highly fluoridated parts of northern Ghana to elucidate the: groundwater fluoride levels, sources of fluoride enrichment in groundwater, extent and severity of fluorosis, and sustainable mitigation measures of high groundwater fluoride.