Inadequate data and spatial dependence in the observations during geochemical studies are among the disturbing conditions when estimating environmental factors contributing to the local variability in the pollutants of interest. Usually, spatial dependence occurs due to the researcher 's imperfection on the natural scale of occurrence which affects the sampling strategy. As a consequence, observations on the study variable are significantly correlated in space. In this study, the machine learning approach was developed and used to study the environmental factors controlling the local variability in fluoride concentrations in drinking water sources of northern Tanzania within the East African Rift Valley. The approach constituted the use of geographical information systems (GIS) technology, exploratory spatial data analysis (ESDA) methods, and spatial regression modeling at a local level. The environmental variables used to study the local variation in fluoride concentration include topography, tectonic processes, water exchanges between hydrogeological layers during lateral movement, mineralization processes (EC), and water pH. The study was based on 20 local spatial regimes determined using GIS based on water sources density in the four hydrogeological environments. Specifically, the nonparametric (one-way Kruskal-Wallis sum ranks test and Multiple Comparisons Dunn Test), spatial statistics (Global Moran 's I statistic), ordinary least squares (OLS) regression, and spatial lag models were used to quantify the effects of topography, tectonic processes, water exchange between hydrogeological environments and water physiochemical parameters (pH and EC) on the spatial variability of fluoride concentrations in drinking water sources at a local scale. In order of significance, the local spatial variation in fluoride concentration is influenced by the EC, topography, tectonic processes, pH, and water exchange between hydrogeological layers during water movement. The results presented in this paper are crucial for safe water access planning in naturally contaminated aquifer systems.

Fluoride is essential for the human body and a global groundwater contaminant (the recommended WHO limit is 1.5mg/L). The mobilization and genesis of fluoride depend on fluoride-bearing rocks (e.g., fluorite, fluor-apatite, biotite, etc.) that are a part of the natural geogenic process, which later contaminate the groundwater. More specifically, the dissolution process (via infiltration), lateral water flow, ion exchange, climatic factors, and chemical weathering of “rocks and minerals” are highly responsible for the release of elevated concentrations of fluoride in groundwater. The intake of fluoride-contaminated groundwater and anthropogenically produced daily usable products (e.g., dental products, foods, etc.) causes physiological and metabolic disturbances in animals and humans. However, this fluoride can be removed effectively from water by technology-enhanced processes (e.g., reverse osmosis, nano-filtration, coagulation, adsorption, electrochemical, membrane distillation, ion exchange, and precipitation). This, in turn, means that climate-dependent contamination, mobilization mechanism, and bioaccumulation will be essential for selecting efficient, cost-effective green technologies. Adequate information should be provided to overcome people’s wrong perceptions concerning fluoride-related issues, especially in lower socioeconomic groups. Policy interventions are required to improve the quality of life in the developing world, where there is a lack of awareness about health issues. Extensive research in this field can identify fluoride “hot spots” (through regular monitoring) and removal technique(s) utilizing public-private sector collaboration.

Fluoride (F^-) concentration in drinking water is one of the water quality parameters in countries with high concentrations in groundwater sources. Natural minerals have shown considerable effectiveness in F^- removal. In this study, the performance of the locally available natural minerals, such as bauxite, magnesites, and gypsum, have been investigated at the laboratory scales and through modelling for F^- removal from drinking groundwater sources in Tanzania. Batch experiments were carried out to examine the optimum conditions for F^- removal by the calcined bauxite, magnesite, and gypsum. X-ray fluorescence spectroscopy (XRF) characterization showed that Al₂O₃, MgO, and SO₃ were the major oxides in bauxite, magnesite, and gypsum, respectively. The experimental data for the three treated adsorbents fitted well with the Freundlich adsorption isotherm and the pseudo-second-order kinetics. The values of ∆G° and ∆H° indicate that the F^- adsorption on bauxite and magnesite surfaces was spontaneous and endothermic. The randomness described by ∆S° at the solid–liquid interface was increased during the adsorption processes. While for gypsum, the reaction was spontaneous and exothermic, where the randomness at the solid–liquid interface decreased during the adsorption processes. At optimum conditions, calcined bauxite (400 °C), magnesite (650 °C), and gypsum (350 °C) lowered the F^- concentration from 8.27 mg/L to 1.02, 0.233 and 1.99 mg/L, respectively. Bauxite and gypsum lowered the pH of water from 9.38 to 6.74 and 7.41, respectively. Magnesite raised the pH from 9.38 to 10.12, which is above the World Health Organization (WHO) (6.5 - 8.5) and Tanzania Bureau of Standards (TBS) (6.5 – 9.2) drinking water standard; therefore, pH adjustments are needed before water can be used for drinking. The Bed Depth Service Time (BDST) plot showed that the service times for F^- adsorption on the calcined bauxite and magnesite surface increased with bed depth. The critical bed depths (Zo) for bauxite and magnesite obtained were 7.21 and 8.28 cm, respectively. The lower value of the kinetic rate parameter (Kα) for bauxite (1.43E-5 L/mg s) and magnesite (1.50E-5 L/mg s) highlighted that the breakthrough occurs in short beds; therefore, deeper beds are required to avoid breakthroughs. The experimental results and model predictions have helped to compare the adsorption processes as well as contrast their performance and sustainability for F^- removal using the bauxite, magnesite, and gypsum in the drinking water resources in Tanzania. The adsorption results and the overall cost analysis show that the cost of calcined bauxite and magnesite is low compared to other available adsorbents; therefore, they can be used in F^- removal from water.

Förhöjda koncentrationer av fluorid (F^-) i grundvattnet är en av vattenkvalitetsparametrarna som utgör en betydande utmaning för säker dricksvattenförsörjning i flera länder globalt. Naturliga mineraler har visat avsevärd effektivitet för att avlägsna fluor. I denna studie har prestandan hos de lokalt tillgängliga naturliga mineralerna, såsom bauxit, magnesit och gips, undersökts i laboratorieskala genom modellering av fluoridavlägsnande från grundvattenkällor i Tanzania. Batchförsök utfördes för att undersöka de optimala förhållandena för F^- borttagning av den kalcinerade bauxiten, magnesiten och gipsen. Röntgenfluorescens (XRF) spektroskopisk karakterisering visade att Al₂O₃, MgO och SO₃ var de viktigaste oxiderna i bauxit, magnesit respektive gips. Experimentell data för de tre behandlade adsorbenterna följde väl med Freundlich-adsorptionsisotermen och pseudo-andra ordningens kinetik. Värdena för ∆G^o och ∆H^o indikerar att F^- adsorptionen på bauxit- och magnesitytor var spontan och endoterm. Slumpmässigheten, som beskrivs av ∆S^o vid gränsytan mellan fasta fasen och vätskan, ökade under adsorptionsprocesserna. Medan för gips var reaktionen spontan och exoterm, där slumpmässigheten vid gränsytan mellan fasta fasen och vätskan minskade under adsorptionsprocesserna. Vid optimala förhållanden, sänkte kalcinerad bauxit (400 °C), magnesit (650 °C) och gips (350 °C) F^- koncentrationen från 8,27 mg/L till 1,02, 0,233 respektive 1,99 mg/L. Bauxit och gips sänkte vattnets pH från 9,38 till 6,74 respektive 7,41. Magnesit höjde pH-värdet från 9,38 till 10,12 vilket är över pH-intervallet mellan 6,5 - 8,5 och 6,5 - 9,2 som rekommenderats av Världshälsoorganisationens (WHO) riktlinjer för dricksvatten och Tanzania Bureau of Standards (TBS). Därför justering av pH behövs innan det behandlade vattnet kan användas för dricks ändamål. Designmodellen för bädd djupsservicetid (BDST) användes för att karakterisera genombrottsprocesserna. De kritiska bädddjupen (Zo) för erhållna bauxit och magnesit var 7,21 respektive 8,28 cm. Bädddjupsservicetid (BDST)-plotten visade att servicetiderna för F^- adsorption på den kalcinerade bauxit- och magnesitytan ökade med bädddjupet. Det lägre värdet på kinetisk hastighetsparameter (Kα) för bauxit (1,43E-5 L/mg s) och magnesit (1,50E-5 L/mg s) visade att genombrottet sker i korta bäddar; därför krävs djupare bäddar för att undvika genombrott. De experimentella resultaten och prediktionsmodellena har hjälpt till att jämföra adsorptionsprocesserna samt kontrastera deras prestanda och hållbarhet för avlägsnande av fluor med hjälp av bauxit, magnesit och gips i dricksvattenresurserna i Tanzania. Adsorptionsresultaten och den övergripande kostnadsanalysen visar att kostnaden för kalcinerad bauxit och magnesit är låg jämfört med andra tillgängliga adsorbenter; därför kan de användas vid F^- borttagning från grundvatten.

Mkusanyiko wa floridi (F^-) katika maji ya kunywa ni mojawapo ya vigezo vya ubora wa maji katika nchi zilizo na ukolezi mkubwa wa F^- katika vyanzo vya maji. Madini ya asili yameonyesha ufanisi mkubwa kwa kuondolewa kwa F-. Katika utafiti huu, utendaji wa madini asilia yanayopatikana humu nchini kama vile bauxite, magnesite na jasi umechunguzwa katika mizani ya maabara na kutoa mfano wa kuondolewa kwa F^- kutoka vyanzo vya maji ya chini ya ardhi nchini Tanzania. Majaribio ya kundi yalifanywa ili kuchunguza hali bora za uondoaji wa F^- kwa bauxite iliyokatwa, magnesite na jasi. Tabia ya uchunguzi wa uchunguzi wa X-ray fluorescence (XRF) ilionyesha kuwa Al₂O₃, MgO na SO₃ zilikuwa oksidi kuu katika bauxite, magnesite na jasi, kwa mtiririko huo. Data ya majaribio ya adsorbenti tatu zilizotibiwa ililingana vyema na isotherm ya Freundlich ya adsorption na kinetiki ya mpangilio wa pili wa uwongo. Thamani za ∆Gº, ∆Hº zinaonyesha utepetevu wa F^- kwenye uso wa bauxite na magnesite ulikuwa wa pekee na wa mwisho wa joto. Nasibu iliyoelezewa na ∆Sº kwenye kiolesura kigumu-kioevu iliongezwa wakati wa michakato ya utangazaji. Ilhali kwa jasi majibu yalikuwa ya hiari na ya kupita kiasi ambapo unasihi kwenye kiolesura kigumu-kioevu ulipungua wakati wa michakato ya utangazaji. Katika hali bora zaidi, bauxite iliyokaushwa (400 °C), magnesite (650 °C), na jasi (350 °C) ilipunguza mkusanyiko wa F^- kutoka 8.27 mg/L hadi 1.02, 0.233 na 1.99 mg/L, kwa mtiririko huo. Bauxite na jasi zilipunguza pH ya maji kutoka 9.38 hadi 6.74 na 7.41, kwa mtiririko huo. Magnesite ilipandisha pH kutoka 9.38 hadi 10.12 ambayo ni juu ya Shirika la Afya Duniani (WHO) (6.5 - 8.5) na Shirika la Viwango Tanzania (TBS) (6.5 – 9.2) kiwango cha maji ya kunywa, kwa hiyo marekebisho ya pH yanahitajika kabla ya maji kuongezwa. kutumika kwa kunywa. Mpango wa Muda wa Huduma ya Kina cha Kitanda (BDST) ulionyesha kuwa nyakati za huduma za F- adsorption kwenye uso wa bauxite iliyokaushwa na magnesite ziliongezeka kwa kina cha vitanda. Kina muhimu cha kitanda   kwa bauxite na magnesite zilizopatikana zilikuwa 7.21 na 8.28 cm, kwa mtiririko huo. Thamani ya chini ya kiwango cha mmenyuko mara kwa mara (Kα) kwa bauxite (1.43E-5 L/mg s) na magnesite (1.50E-5 L/mg s) iliyoangazia mafanikio yatatokea katika vitanda vifupi; kwa hiyo, vitanda vya kina vinahitajika ili kuepuka mafanikio. Matokeo ya majaribio na utabiri wa modeli umesaidia kulinganisha michakato ya utangazaji pamoja na utofauti wa utendaji na uendelevu wa kuondolewa kwa F^- kwa kutumia bauxite, magnesite na jasi katika rasilimali za maji ya kunywa nchini Tanzania. Bauxite iliyokaushwa na magnesite iliboresha uondoaji wa F^-.

Geogenic contamination of groundwater due to elevated fluoride (F-) concentrations is a significant issue worldwide (including in Tanzania). The present study focussed to assess the adsorption capacity of thermally treated (calcined) bauxite to remove the F- from contaminated water. Characterization of bauxite by X-ray fluorescence spectroscopy (XRF) revealed Al2O3, Fe2O3, and SiO2 as the major oxides in both raw and calcined bauxite. The major mineral phase in the raw bauxite was gibbsite, which disappeared after calcination. The optimum calcination temperature, dosage and contact time for F- removal by calcined bauxite were 400 degrees C, 40 g/L and 8 min, respectively. The experimental data revealed Freundlich isotherm as the best model to fit the F -adsorption process with kF and 1/n being 0.1537 mg/g and 0.8607, respectively. The pseudo-second-order ki-netic and intra-particle diffusion models explained well the F- adsorption process with the rate constants of 115.43 g/mg min and 0.0025 mg/g min0.5, respectively. The values of Delta G, Delta H and Delta S indicate the F- adsorption on bauxite surface indicated that the adsorption process was spontaneous, endothermic and structural changes occurred during the adsorption process. The F- adsorption under optimum conditions lowered the pH and F -concentration to WHO and Tanzania Bureau of Standards (TBS) standards.

Geogenic contamination of groundwater is frequently associated with gold mining activities and related to drinking water quality problems worldwide. In Tanzania, elevated levels of trace elements (TEs) have been reported in drinking water sources within the Lake Victoria Basin, posing a serious health risk to communities. The present study aims to assess the groundwater quality with a focus on the concentration levels of geogenic contaminants in groundwater around the Lake Victoria goldfields in Geita and Mara districts. The water samples were collected from community drinking water sources and were analysed for physiochemical parameters (pH, EC, Eh), major ions, and trace elements. The analysed major ions included Na+, K+, Ca2+, Mg2+, SO42-, HCO3- and Cl- whereas the trace elements were As, Al, Li, Ba, B, Ti, V, U, Zr, Sr, Si, Mn Mo, Fe, Ni, Zn, Cr, Pb, Cd, and V. The present study revealed that the concentration levels of the major ions were mostly within the World Health Organization (WHO) drinking water standards in the following order of their relative abundance; for cations, Ca2+-Na+ >Mg2+ >K+ and for anions was HCO3- > SO42- > NO3-, Cl- > PO43-. Statistical and geochemical modelling software such as 31 Studio', IBM SPSS, geochemical workbench, visual MINTEQ were used to understand the groundwater chemistry and evaluate its suitability for drinking purpose. The concentration of As in groundwater sources varies between below detection limit (bdl) and 300 mu g/L, with highest levels in streams followed by shallow wells and boreholes. In approximately 48% of the analysed samples, As concentration exceeded the WHO drinking water guideline and Tanzania Bureau of Standards (TBS) guideline for drinking water value of 10 mu g/L. The concentration of the analyzed TEs and mean values of physicochemical parameters were below the guideline limits based on WHO and TBS standards. The Canadian Council of Ministries of the Environment Water Quality Index (CCME WQI) shows that the overall water quality is acceptable with minimum threats of deviation from natural conditions. We recommend further geochemical exploration and the periodic risk assessment of groundwater in mining areas where high levels of As were recorded.

Over the years, groundwater has been used as a means of adaptation to the seasonal and perennial scarcity of surface water. Groundwater provides water for households, livestock, and irrigation in semi-arid areas of Tanzania. It is acknowledged that groundwater is sus-ceptible to chemical and other mineral contamination which not only poses a threat to the health of human beings and livestock but also agriculture. However, the potential of groundwater in terms of its viability and quality has not received adequate scrutiny from scholars. This paper provides a review of water quality and highlights the geogenic con-tamination of groundwater resources in Tanzania. The literature reviewed focused on the water resource sector in the major drainage basins of Tanzania, the information about drinking water quality with respect to geogenic contamination were sought. This paper has established that fluoride is the main and well-known groundwater contaminant. This is attributed to the existence of fluoride-rich minerals such as fluorite (CaF2), fluorapatite (Ca-5(PO4)(3)F), cryolite (Na3AlF6), sellaite (MgF2), villiaumite (NaF), and topaz ((Al-2(SiO4)F-2), bastnaesite ((Ca, La, Nd)CO3F), and their ash deposits peeling from the granite and alka -line volcanic rocks, dominant in the region. The presence of fluoride in water sources in northern Tanzannia, part of the EARV contributes to the serious health effects on humans such as dental, skeletal, and crippling fluorosis. In addition, some literature indicated ar-senic as a serious drinking water geogenic pollutant in the north-west parts of Tanzania. They pointed out that oxidation of arsenopyrite minerals is responsible for the dissolution and release of arsenic into groundwater. From this review we conclude that information on geochemistry/hydro-geochemistry of fluoride and arsenic in the aquifers is far inadequate and recommends that more research and development (R&D) effort s from scholars, researchers, and government institutions should be invested for further investigations and solutions. The focus should be creating awareness about the danger of using arsenic and fluoride contaminated water and development of affordable and environmental friendly water purification technologies.

Occurrence of elevated concentrations of fluoride in the drinking water supply in many regions of the world has caused widespread dental and skeletal fluorosis. In this paper the studies available on the routes of fluoride exposure, regions with excess fluoride in water sources and various defluoridation techniques has been reviewed. It is evident from the literature survey that no single technique fits for diverse technical and socioeconomic situations and there is a pressing need to develop suitable defluoridation techniques for household and community level water supply system in order to prevent fluorosis.

Fluoride (F^-) is one of the key water quality parameters of concern due to its impact on human health. High F^- intake has resulted in the development of dental and skeletal fluorosis in several countries, and removal of F^- from drinking water sources is important for securing the drinking water sources. The batch experiment was performed to determine the optimum parameters for F^- removal using calcined gypsum and magnesite. The optimum heating temperature, dosage, and contact time were found to be 350 °C, 100 g/L, and 40 min, respectively, for gypsum, and 650 °C, 20 g/L, and 36 min, respectively, for magnesite. The adsorption process on the surface of calcined gypsum and magnesite was well explained with the pseudo-second-order kinetic. The experimental data fitted well to the Freundlich isotherm model in both adsorbents with   values of 0.0303 mg/g for gypsum and 1.3505 mg/g for magnesite. The values of Gibbs free energy ( ΔG^o) and enthalpy ( ΔH^o) indicated that the F^- adsorption on the gypsum surface was spontaneous and exothermic, while that on the magnesite surface was spontaneous and endothermic. The concentration of F^- in water treated by gypsum was 1.99 mg/L, slightly above the World Health Organization (WHO) but within Tanzania Bureau of Standards (TBS) guidelines. Water treated by magnesite has F^- concentration below WHO standards and a pH above the WHO and TBS guidelines, so the pH needs to be adjusted before water can be used for drinking.

Fluoride (F^-) in the groundwater reported globally causes health problems due to prolonged consumption in higher concentrations, including dental and skeletal fluorosis. This paper investigates the ability of calcined bauxite, gypsum, and magnesite for fluoride removal using column experiments. The bed depth service time (BDST) design model showed that the service times for F^- adsorption on the surface of calcined bauxite and magnesite increased with beds depth. The higher doses have higher F^- removal efficiency and breakthrough times. The critical bed depths (Z_o ) for bauxite and magnesite obtained were 7.21 and 8.28 cm, respectively. The lower value of kinetic rate parameter (Kα) for bauxite (1.43E-5 L/mg s) and magnesite (1.50E-5 L/mg s) highlighted the breakthrough will occur in short beds; therefore, deeper beds are required to avoid breakthrough. Global cooperation and knowledge sharing is required for the development of more effective techniques using the low-cost affordable adsorbents for the removal of fluoride and other geogenic contaminants from drinking water sources in Tanzania.

Inadequate data and spatial dependence in the observations during geochemical studies are among the disturbing conditions when estimating environmental factors contributing to the local variability in the pollutants of interest. Usually, spatial dependence occurs due to the researcher’s imperfection on the natural scale of occurrence which affects the sampling strategy. As a consequence, observations on the study variable are significantly correlated in space. In this study, the machine learning approach was developed and used to study the environmental factors controlling the local variability in fluoride concentration in drinking water sources of northern Tanzania within the East African Rift Valley. The approach constituted use of the geographical information systems (GIS) technology, exploratory spatial data analysis methods, and spatial modeling at a local level. The environmental variables used to study the local variation in fluoride concentration include topography, tectonic processes, water exchanges between hydrogeological layers during lateral movement, the mineralization processes (EC), and pH. The study was based on 20 local spatial regimes determined using GIS based on water sources density in the four hydrogeological environments. The non-parametric (one-way Kruskal-Wallis sum ranks test and Multiple Comparisons Dunn Test), spatial statistics (Global Moran's I statistic), ordinary least squares (OLS) regression and spatial lag models were used to quantify the effects of topography, tectonic processes, water exchange between hydrogeological environments and waterphysiochemical parameters (pH and EC) on the spatial variability of fluoride concentrations in drinking water sources at a local scale. In the order of significance, the local spatial variation in fluoride concentration is influenced by the EC, topography, tectonic processes, pH and water exchange between hydrogeological layers during water movement. The results presented in this paper are crucial for safe water access planning in the naturally contaminated aquifers.