## 4 Results
### Risk Evaluation
#### 4.4.2 Human Health Risk Assessment  
74% (\(n=29\)) of sampled water points had HQ values \(>\)1 for children under the age of 6, indicating possible and increasing risk of dental fluorosis from exposure to fluoride in drinking water from those groundwater points (Table 3). 44% (\(n=17\)) of water points had HQ values \(>\)1 for children under the age of 12 and 28% (\(n=11\)) had HQ values \(>\) 1 for adults over 19 years old. The latter also included all children under 12 years old. 26% (\(n=10\)) had HQ values \(<\)1 for all age groups and appear safe for anyone to drink from. Water Point 13, which displayed the highest HQ value (4.11), also displayed the highest fluoride concentration in the study area (3.75 mg/L) (Table 3).  
Figure 9: Geological fluoride risk map showing lithologies with risk of groundwater fluoride concentrations \(>\)1.5 mg/L as graded zones. Blank zones (Grade 0) reflect areas where geological data are available but corresponding hydrochemical data are not. Sampled water points are shown with their corresponding sample numbers.  
Statistical analysis of HQ values with corresponding host lithology (Table 4) demonstrated that for all age groups, augen gneiss carries the most groundwater fluoride risk. For children under the age of 6: 94% of water points in this lithology displayed HQ values >1. Statistically, hornblende-biotite gneiss appeared to be highest risk lithology for that age group (100% of HQ values >1) but again, low sample numbers (\(n=3\)) prevents definitive conclusion. The lithology with least fluoride risk was charnockitic gneiss and granulite with only 55% of water points displaying HQ values >1. For children under the age of 12: water points within augen gneiss, again, were the most vulnerable with 69% displaying HQ values > 1. 67% of water points within hornblende-biotite gneiss have HQ values >1 and only 20% for charnockitic gneiss and granulite. The same trend was observed in adults over the age of 19 (Table 4).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Water Point Type** &
\begin{tabular}{c} **Fluoride** \\ **(mg/L)** \\ \end{tabular} & \multicolumn{2}{c}{**Hazard Quotient (HQ)**} \\ \hline  & & \multicolumn{2}{c}{**Adults**} & **Children** & **Children** \\  & & \multicolumn{2}{c}{**(>19 years old)**} & **(12 years old)** & **(6 years old)** \\ \hline
1 & Borehole & 1.84 & 0.86 & **1.28** & **2.00** \\
2 & Borehole & 2.02 & 0.95 & **1.42** & **2.22** \\
3 & Borehole & 1.78 & 0.86 & **1.28** & **2.00** \\
4 & Borehole & 1.45 & 0.67 & 0.99 & **1.56** \\
5 & Borehole & 2.31 & **1.10** & **1.63** & **2.56** \\
6 & Borehole & 2.08 & **1.00** & **1.49** & **2.33** \\
7 & Borehole & 3.04 & **1.43** & **2.13** & **3.33** \\
8 & Protected dug well & 1.41 & 0.67 & 0.99 & **1.56** \\
9 & Borehole & 2.80 & **1.33** & **1.98** & **3.11** \\
10 & Protected dug well & 0.89 & 0.43 & 0.64 & **1.00** \\  
*1.20** & **1.89** \\ \hline \hline \end{tabular}
\end{table}
Table 3: Calculated HQ values for each age group and each water point from the study area. HQ values >1 shown in bold.  
These results again support augen gneiss as the dominant source of groundwater fluoride, therefore posing the highest dental fluorosis risk.