Abstract
Over the years, groundwater has been the primary source of potable water reserves in most of the 2 regions within Northern Ghana. This is largely attributable to the limited availability of treated 3 surface water sources. Despite its purity, groundwater remains susceptible to contamination or 4 pollution from both natural and human activities, whether direct or indirect. These can increase 5 the normal concentrations of groundwater potential harmful elements (PHEs), making water 6 unsafe for consumption. High concentrations of certain PHEs, like fluorine (F), can affect 7 groundwater quality. 8
The presence of F- in groundwater can impact its suitability for household use, particularly for 9 drinking, and thus poses a health risk to consumers. Therefore, this study focused on investigating 10 the occurrence, potential sources, and underlying mechanisms contributing to the high F- content 11 in groundwater within the central regions of the White Volta River Basin, Northern Ghana. 12 Furthermore, the research assessed the potential health risks to humans associated with consuming 13 elevated F- levels in groundwater by employing the human health risk assessment framework 14 developed by the United States Environmental Protection Agency (USEPA, 1989). 15
The area sampled is predominantly underlain by the Oti/Pendjari group. This group represents two 16 main formations; the Kodjari and Pendjari, which were deposited between 660 and 610 million 17 years ago during the Neoproterozoic era. The Kodjari Formation is composed of an unknown basal 18 tillite overlain by dolostone and limestone and the Pendjari Formation includes mudstone, 19 quartzites, shales, siltstone, and conglomerates. The major groundwater sources within the basin 20 are boreholes and hand-dug wells. 21
A total of thirty-six (36) groundwater samples were subjected to hydrogeochemical analysis to 22 investigate the underlying processes governing their chemical variability. The Trilinear Piper 23 diagram, Gibbs plots, thermodynamic calculations, and multivariate statistical analysis, e.g., 24 Spearman correlation matrix, and factor analysis, were conducted to identify the primary 25 mechanisms controlling the elevated fluoride levels in the groundwater. 26
The groundwater samples exhibited a wide range of F- levels, varying from 0.2 to 19.5 mgL-1 with 27 an average of 4.3 mgL-1. A significant majority of samples (84%, n=30) exceeded the World Health 28 Organization's (WHO, 2017) recommended limit of 1.5 mgL-1 (WHO, 2017). However, a small 29
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percentage (8%, n=3) contained F- levels below the WHO's recommended minimum of 0.5 mgL-30 1, considered essential for optimal dental and skeletal health. The remaining 8% of samples 31 showed concentrations within the acceptable range of 0.5-1.5 mgL-1 (WHO, 2017). The 32 predominant cation and anion in the studied samples were K+ and HCO3-, respectively and the 33 dominant hydrochemical facies were K–HCO3 (33%); Mg – K – HCO3 (25%); K– Mg – HCO3 34 (11.1%), with additional mixed water types. The Gibbs diagram and ionic bivariate plots indicated 35 that water-rock interactions and ion exchange processes were the primary factors influencing the 36 chemistry of the groundwater in the study area. Furthermore, the R-mode factor analysis revealed 37 seven distinct factors with eigenvalues greater than 1, accounting for 82.86% of the overall 38 variability. These PCs confirmed the dominance of mineral dissolution and ion exchange, in 39 controlling the chemistry of groundwater. The geospatial map of F- revealed higher levels in the 40 northeastern portion of the study location, while the lowest concentrations were observed in the 41 western fringe. 42
The study found high exposure to health risks among various populations resulting from the high 43 fluoride intake in most communities. The hazard quotient (HQ) values ranged from 1.06 to 27.63 44 exceeding the safe limit of 1.00 suggested by the USEPA (1989) to prevent health risks associated 45 with F-. However, Children were identified as the most susceptible population to F- toxicity in the 46 area, exhibiting the highest HQ values ranging from 1.56 to 27.63. This indicates a significant 47 impact of dental fluorosis among the local population, particularly children. Therefore, preventive 48 measures such as defluoridation techniques are suggested to be applied to curtail the high F- in the 49 groundwater to make it safe for drinking.