Fluoride Variations in Rivers on the Slopes of Mount Meru in Tanzania
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Hindawi Journal of Chemistry Volume 2018, Article ID 7140902, 18 pages https://doi.org/10.1155/2018/7140902 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; [email protected] 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 volcanic, granitic, and gneissic rocks [8]. Being the case in Tanzania, the problem occurs both in the rif valley zones Te understanding of fuoride distribution in Tanzanian in the northern and southwestern part of the country asso- rivers is of great importance since majority of the Tanzanian ciated with volcanic activity and in the crystalline basement population obtain their domestic freshwater from rivers, complex of the central plateau [9]. Enrichment of fuoride springs, and lakes. It is reported that 30% of these are water minerals in water occurs through evaporation, weathering sources with fuoride concentration exceeding 1.5 mg/l [1]. of volcanic rocks, and geothermal solutions in the rif valley Despite the fact that fuoride has health benefts, consump- system,aswellasdissolutionfromsalinerocksassociated tion above the optimal level is unhealthy. Te WHO and with fuoride [9, 10]. TBS recommend that the healthy intake of fuoride in water Fluorine is the most electronegative element with the should not exceed 1.5 mg/l and 4.0 mg/l, respectively [2, 3]. electronegativity value of 3.98 on the Pauling Scale; thus, it is Excessive consumption of fuoride has been shown to cause very reactive [11]. Terefore, this property makes the element crippling skeletal fuorosis due to the reaction of F and exist in diferent forms of mineral salts in the environment Ca in the bones; thus, it is extremely reactive in biological rather than in its pure form [12]. Te fuoride containing systems, thus afecting the enzymes and the whole organism minerals are grouped into fuorides, phosphates, silicates, as well [4, 5]. In Tanzania, fuorides are distributed in the and mica [13]. In Tanzania, fuorapatite, fuorite, topaz, regions of Arusha, Moshi, Singida, and Shinyanga, with a phlogopite, and lepidolite predominate. All these minerals severely afected area being on the foothills of Mount Meru are water-insoluble and hence their ability to release fuoride and Kilimanjaro [6, 7]. Fluoride-rich waters are associated ions in surface and groundwater depends on the conditions with sediments of marine origin in mountainous areas and which favor their solubility such as high temperature and 2 Journal of Chemistry pH. Terefore, fuorides enter surface water by leaching efectively dry, although occasional showers do occur during (being the main cause) and surface runof from fertilizers this period [23, 24]. Te four rivers contribute to the Pangani containing phosphates, industrial emissions, and efuents basin subcatchment feeding the Pangani River. Te study area [14]. Te average dissolved fuoride content in major rivers of was divided into three regions depending on the river and ∘ � �� the world is between 0.01 mg/l and 0.02 mg/l, whereas in lakes land development, namely, pristine (headwater) (3 15 00 Sto ∘ � �� ∘ � �� ∘ � �� it is below 0.5 mg/l [3], but in Tanzania the concentrations are 3 20 00 S), middle (3 20 00 Sto3 25 00 S), and food plain ∘ � �� ∘ � �� above the mentioned values in the vulnerable regions [14]. (3 25 00 Sto335 00 S). Te catchment area for the rivers Previous studies carried out to establish sources of high is considered as pristine (headwater) which is characterized fuoride concentrations and distribution in the environment by artifcial and natural forest conservation, the middle area on the slopes of Mount Meru have mostly put emphasis on of the river consists of mixed peasant agriculture and human groundwater. In surface water, studies reported the fuoride settlement, and the foodplain is the downstream area of the levels of 12-13 mg/l, 21–26 mg/l, 61–65 mg/l, and 690 mg/l for river characterized by bare land, intensive grazing, large-scale Maji ya Chai and Engare Nanyuki Rivers, pond water, and agriculture, and serious fooding in wet season. Lake Momela, respectively [9, 14–18]. Te contaminated areas have shown health implications to some children and adults living around the foot of Mount Meru [5, 15]. Further studies 2.2. Sampling. Te GPS predetermined sampling points were on fuoride levels were carried out in groundwaters within identifed based on confuence, accessibility, and preestab- thesameareaandfoundaconcentrationofupto68mg/l lished monitoring stations. Two-liter water samples were which was highly associated with the alkaline volcanism collected in each point downstream from the source of each andhighpH[19,20].Tevulnerabilityofalkalinesoil river (Figure 1). One-liter water sample was used for chemical for fuoride dissolution in soil has recently been associated − parameter measurement and the second liter for fuoride and with the presence of bicarbonate ions (HCO3 ), which nutrients measurement. Sampling was done thrice in one- accelerates the alkalinity and fuoride availability [21]. Since week interval during the wet season (mid-March to early surface/river water is a contribution of groundwater dis- April) and dry season (August) in 2015. In each season, 159 charge and precipitation, fuorides in water are mainly from leaching of rocks from groundwater and fuoride containing representative samples were collected for analysis. stuf. Despitetheabovefacts,thegeneraltrendsoffuorides 2.3. Chemicals. Analytical-grade reagents from Sigma- in rivers afer interaction with diferent environments of this Aldrich (Merck) for the preparation of TISAB II and TISAB studyareahavebeenlittlestudiedandmapped,thusraising IV were prepared from glacial acetic acid, NaCl, NaOH, HCl, the importance of this study. Tus, this work was conducted tris(hydroxymethyl) amino methane, and sodium tartrate to investigate the spatial distribution of fuorides in rivers dihydrate, respectively. Also, the analytical grade of Ion afer such interactions have occurred together with tracing Electrolyte Reference Filling Solution (P/N 51344750) was their point sources of contamination, if any. Studies in these rivers are of profound importance since water from these obtained from the same company. rivers is used in various domestic activities including cooking and drinking in Arusha City. 2.4. Extraction, Pretreatment, and Cleanup of Water Samples. Samples for major ions measurements were not pretreated with any chemical except for the samples with solids and 2. Materials and Methods other organic debris that were fltered using a 0.45 �mflter 18 2 before measurement. Samples for � Oand� Hanalysiswere 2.1. Description of the Study Area. Te study area involved ∘ kept cooled at 4 C before and on transport to the Stable four rivers, namely, Temi and Nduruma which lie within the Arusha City and Tengeru and Maji ya Chai which lie within IsotopelaboratoryatWaterlooUniversityinCanada. the Meru District. Te four rivers originate from a common subcatchment of foothills of Mount Meru lying from the 2.5. Detection Limit of the Instrument and Calibration. Te easternparttothesouthwestofthemountain(Figure1).Te calibrated detection limit of the instrument was reconfrmed rivers run downstream from the mountain to the southeast. by measuring in triplicate the serially diluted primary stan- Natural vegetation is typically tropical forest to savannah. Te topography of the study region is dominated by the dard solution with the lowest concentration of 0.02 mg/l, MountMeruvolcanicconeofPleistocenetorecentorigin. which was the calibrated minimum detection limit (MDL), Te local climate of the area