Research Article Fluoride Variations in Rivers on the Slopes of Mount Meru in Tanzania Aldo J. Kitalika , Revocatus L. Machunda, Hans C. Komakech, and Karoli N. Njau Department of Water and Environmental Science and Engineering, Nelson Mandela African Institute of Science and Technology, P.O. Box 447, Tengeru, Arusha, Tanzania Correspondence should be addressed to Aldo J. Kitalika; kitalikaa@nm-aist.ac.tz Received 17 August 2017; Revised 2 December 2017; Accepted 13 December 2017; Published 23 January 2018 Academic Editor: Maurizio Barbieri Copyright © 2018 Aldo J. Kitalika et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis study reports the variations of fuoride ions in rivers on the slopes of Mount Meru in the northern part of Tanzania. More than 318 water samples were collected from Temi, Nduruma, Tengeru, and Maji ya Chai Rivers in both wet (mid-March and April) and dry (August) seasons. Te samples were analyzed for fuoride levels using Ion Selective Electrode (ISE). Te minimum and maximum average fuoride levels in the wet season were 0.24 ± 0.03 mg/l and 65.20 ± 0.03 mg/l, respectively, whereas the average lowest and highest levels in the dry season were 1.02 ± 0.02 mg/l and 69.01 ± 0.03 mg/l, respectively. Tengeru River had the lowest fuoride levels in both seasons, whereas Maji ya Chai recorded the highest fuoride levels in both seasons. Te headwater of all rivers with the exception of Maji ya Chai met the World Health Organization’s (WHO) maximum acceptable fuoride levels of 1.50 mg/l and the downstream environment qualifed for Tanzania Bureau of Standards (TBS) maximum permissible fuoride concentration in drinking water of 4.00 mg/l. Also, the laboratory experiments showed that fuoride containing rocks exposed to pH above 7.6 display high leaching of F − in solution which gradually increased with the increase in pH, indicating that dissolution of fuoride in water is a function of pH. 1. Introduction Te understanding of fuoride distribution in Tanzanian rivers is of great importance since majority of the Tanzanian population obtain their domestic freshwater from rivers, springs, and lakes. It is reported that 30% of these are water sources with fuoride concentration exceeding 1.5 mg/l [1]. Despite the fact that fuoride has health benefts, consump- tion above the optimal level is unhealthy. Te WHO and TBS recommend that the healthy intake of fuoride in water should not exceed 1.5 mg/l and 4.0 mg/l, respectively [2, 3]. Excessive consumption of fuoride has been shown to cause crippling skeletal fuorosis due to the reaction of F and Ca in the bones; thus, it is extremely reactive in biological systems, thus afecting the enzymes and the whole organism as well [4, 5]. In Tanzania, fuorides are distributed in the regions of Arusha, Moshi, Singida, and Shinyanga, with a severely afected area being on the foothills of Mount Meru and Kilimanjaro [6, 7]. Fluoride-rich waters are associated with sediments of marine origin in mountainous areas and volcanic, granitic, and gneissic rocks [8]. Being the case in Tanzania, the problem occurs both in the rif valley zones in the northern and southwestern part of the country asso- ciated with volcanic activity and in the crystalline basement complex of the central plateau [9]. Enrichment of fuoride minerals in water occurs through evaporation, weathering of volcanic rocks, and geothermal solutions in the rif valley system, as well as dissolution from saline rocks associated with fuoride [9, 10]. Fluorine is the most electronegative element with the electronegativity value of 3.98 on the Pauling Scale; thus, it is very reactive [11]. Terefore, this property makes the element exist in diferent forms of mineral salts in the environment rather than in its pure form [12]. Te fuoride containing minerals are grouped into fuorides, phosphates, silicates, and mica [13]. In Tanzania, fuorapatite, fuorite, topaz, phlogopite, and lepidolite predominate. All these minerals are water-insoluble and hence their ability to release fuoride ions in surface and groundwater depends on the conditions which favor their solubility such as high temperature and Hindawi Journal of Chemistry Volume 2018, Article ID 7140902, 18 pages https://doi.org/10.1155/2018/7140902