This study was carried out in Arumeru district, to provide the critically missing information that could aid in the improvement of water quality policies, management practices, and public health protection. The physico-chemical parameters and the fluoride concentration for springs, rivers, lakes, boreholes, and dug wells were determined on 101 samples while the arsenic, boron, and lead concentrations were determined on 90 samples. All data were subjected to cluster analysis and principal components analysis (PCA). Fluoride (F) was found to be high, above the recommendedstandard, in all the water sources with a median F value of 3 mg/L. The abundance pattern for F was similar to the total dissolved solids (TDS) pattern, of alkaline lakes>dug wells>boreholes>streams>fresh water lakes>springs. The lowest fluoride and TDS values were observed in springs (median F=1.3 mg/l, TDS=145 mg/L) and were attributed to a short water-rock interaction time and to the geology. Some lakes and dug wells were found to have low dissolved oxygen (DO) owing to high organic matter inputs and poor aeration. The highest median F value was found in leeward alkaline lakes (median=260 mg/L) and lowest in windward springs (median=1 mg/L). The fluoride and high TDS values in the water sources were found to be controlled by the geological materials, water-rock interaction time (short in mountainous areas due to a high hydraulic gradient in a slightly fractured formation), and the precipitation levels and evaporation rates which also control the formation and dissolution of salts. Arsenic and lead, which were present in water sources above the recommended standard in 14% of the analysed samples (As: median=0.3 mg/L, Pb: median=0.1 mg/L), were found to have a similar concentration profile. Boron was high and above the recommended standard in one sample only (1.65 mg/L in Lake Big Momella, 1% of the samples). The samples were clustered into 9 groups with the first four clusters characterized by high TDS and fluoride. PCA indicated that TDS, fluoride, boron, arsenic, lead, and pH were the major loading components accounting for 86.9% of the total variance. Spatially, fluoride and boron were associated with lahars, ash, and pyroclastic materials whereas arsenic and lead were associated with pyroclastics and nephelinitic to phonolitic lava. Communities in areas with high levels of these heavy metals are further exposed to health risks, in
addition to those of fluoride, when such water is used for drinking. This finding, which has not been previously reported, calls for a detailed assessment to be made of the heavy metals in water used for consumption. Due to the toxicity of arsenic and lead, water sources with a high concentration of these, beyond the recommended standards,
should either be treated, before being supplied as drinking water, or completely abandoned.
*Read full study online at http://fluoridealert.org/wp-content/uploads/malago-2020.pdf