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.

The study evaluates the performance of bauxite for arsenic (As) elucidation from water. The raw, calcined, and alkaline ferric-bauxite composite was applied in batch experiments to evaluate the influence of dosage, initial As concentrations, contact time, and pH. The X-ray diffraction studies revealed significant content of gibbsite (Al(OH)3 in the bauxite. Visual MINTEQ simulation indicated As removal increases with an increase in dosage, the pH range between acidic and near neutral favors maximum removal. The 100 g/L calcined bauxite at pH 7.4 removed 99.9% As to below 0.001 mg/L after 20 minutes from an initial concentration of 1 mg/L. The raw 100 g/L bauxite at pH 6 removed 99.86% As to below 0.003 mg/L after 1 hour from an initial As concentration of 1 mg/L. The alkaline ferric-bauxite composite used for treatment of 2 mg/L As raised pH from pH 4 to 12, and removal efficiency declined to 31% after 4 hours. Aluminium (Al) was sensitive to pH, and about 435 mg/L was released in water at pH 12. Despite the decrease in specific surface area during calcination at 500 °C, the As removal was more improved for the calcined bauxite. The removal capacity was high, up to 6 mg/g, when less dosage of 0.5 g/L bauxite was used. The kinetic reaction process using 5 g/L reaction obeys pseudo-secondorder with R2 of 0.99 while its removal isotherm obeys Langmuir with R2 of 0.98 and is confirmed favorable.

This study evaluates gypsum behavior for arsenic (As) reduction from water. The parameters, such as initial As concentration, contact time, gypsum dosage, and pH, were evaluated in batch experimentsfor natural water and As solution. VisualMINTEQ simulations reveal that the removal of As increases with the increase in pH and dosage.Application of calcined gypsum at pH 10 adsorbed Asto below 10 µg/L after 3 hours from initial As concentration of 1 mg/L. Application of calcined gypsum for treatment of natural water shows As(V) reduction to 0.019mg/L (84% removal) and As(III) to below 0.1 µg/L (98% removal). Theexperimental data fitted pseudo-second-order with a correlation coefficient R2 of 0.99. The Freundlich isotherm explained the experimental result better with R20.99 and 1/n of 0.73. Intraparticle diffusion was better explained with the dosage of 50 g/L calcined gypsum applied to removeAs concentration of 5.3 mg/L.The linear regression modelshows pH as a significant parameter for As removal when100 g/L calcined gypsum was applied. Gypsum is a locally available resource in Tanzania that stabilizes As contamination below 1 mg/L from drinking water sources around gold mining areas.

The occurrence of arsenic (As), fluoride (F-), and other trace elements (TEs) with potential toxicity in groundwater is a global environmental concern. According to the National water resource mapping database, about 76 % of the drinking water supply in Tanzania is abstracted from groundwater sources. In northern Tanzania groundwater accounts for more than 80 % of the drinking water supply. Albeit the importance of groundwater in northern Tanzania, its quality concerning geogenic contaminants is not optimally understood. The present study focused on estimating the groundwater quality using analytical, geochemical modeling, statistical, and GIS techniques which were carried out to better understand the chemical quality of groundwater in the framework of safe drinking water supply in Tanzania. Fluoride was established as the principal geogenic groundwater contaminant in northern Tanzania, particularly in the Pangani and internal drainage basins, parts of the East Africa Rift Valley (EARV) system. About 8 % and 57.6 % of the water samples collected from Geita and Sanya alluvial plain have indicated F- concentration above the WHO guidelines value (1.5 mg/L) for drinking water. The high F- concentration in groundwater originates from F- rich minerals and ash deposits from the granitic and alkaline volcanic parent rocks. The consumption of elevated concentrations of F- in groundwater has been responsible for dental, skeletal, and crippling fluorosis. In the Lake Victoria basin (LVB) goldfields, As was reported to be the main geogenic contaminant of health concern. The concentration of As in 50 % and 82 % of the groundwater samples from Tarime and Geita respectively exceeded the WHO guidelines (10 µg/L). The high concentration of As in groundwater from the LVB was highly associated with natural geochemical processes as well as gold mining activities. Results from geochemical modeling revealed that As mobilization was influenced by oxidative and/or reductive dissolution of As-containing sulfide and iron minerals, respectively from the parent rocks. The concentrations of other TEs (aluminum, chromium, cobalt, copper, iron, manganese, nickel, and zinc) were observed below the WHO drinking water guideline. The spatial variability of As and F- concentration from drinking groundwater sources was associated with the different groundwater levels, screened depths, and contact time of groundwater interaction with the As and F-- containing rock minerals in the aquifers. Furthermore, irrigation water sourced from the F- contaminated boreholes poses risks of contaminating the shallow aquifers that are easily accessible for human and domestic animals’ consumption. The current WHO recommended guidelines of 10 µg As/L and 1.5 mg F-/L intake for humans are open to further epidemiological scrutiny, especially considering chronic/long-term exposure in the region. The present study highlights the need for large-scale hydrogeochemical and human health risk investigations concerning geogenic contaminants in the region. The findings contribute to the local, regional, and global initiatives toward sustainable exploitation of groundwater resources in conformity with the Sustainable Development Goal (SDG) 6 for universal access to safe water and sanitation for all.

Förekomsten av arsenik (As), fluorid (F-) och andra spårämnen (TE) med potentiell toxicitet i grundvattnet är ett globalt miljöproblem. Enligt den nationella kartläggningsdatabasen för vattenresurser kommer omkring 76 % av dricksvattenförsörjningen i Tanzania från grundvattenkällor. I norra Tanzania står grundvattnet för mer än 80 % av dricksvattenförsörjningen. Även om grundvattnets stora betydelse i norra Tanzania, grundvattenkvalitet med avseende på geogena föroreningar är inte optimalt förstått. Denna studie fokuserade på att uppskatta grundvattenkvaliteten med hjälp av analytiska, geokemiska modellerings-, statistiska och GIS-teknik som utfördes för att belysa grundvattnets kemiska kvalitet för att säkerställa dricksvattenförsörjning i Tanzania. Fluor etablerades som den främsta geogena grundvattenföroreningen i norra Tanzania, särskilt i avrinningsområden Pangani och Internal Drainage Basin, delar av Östafrikanska gravsänkesystemet (East Africa Rift Valley-system, EARV). Cirka 8 % och 57.6 % av vattenproverna från Geita och Sanya alluvial slätt har visat F- koncentration över WHO:s riktlinjer (1.5 mg/L) för dricksvatten. Den höga F- koncentrationen i grundvattnet härrör från F-rika mineraler och askavlagringar från de granitiska och alkaliska vulkaniska moderbergarterna. Konsumtionen av förhöjda koncentrationer av F- i grundvatten har orsakat omfattande tand-, skelett- och förlamande fluoros bland lokala befolkning. I guldfälten i Lake Victoria Basin (LVB) rapporterades As som den främsta forekommande geogena föroreningen med konsekvent hälsoproblem bland befolkning i området. Arsenik koncentrationen i 50 % och 82 % av grundvattenproverna från Tarime respektiv Geita översteg WHO:s riktlinjer (10 µg/L). Den höga koncentrationen av As i grundvattnet från LVB var starkt förknippad med naturliga geokemiska processer såväl som guldbrytningsaktiviteter. Resultat från geokemisk modellering visade att As-mobilisering påverkades av oxidativ och/eller reduktiv upplösning av As-innehållande sulfidmineraler respektive As-innehållande järnmineraler från moderbergarterna. Koncentration av andra spårämnen så som aluminium, krom, kobolt, koppar, järn, mangan, nickel och zink var under WHO:s riktlinjer för dricksvatten. Den rumsliga variationen av As och F- koncentrationen från dricksvattentäkter var relaterade till de olika grundvattennivåerna, djupet till brunnskärm och kontakttid för grundvattnets interaktion med de As och F-innehållande mineralerna i berg under grundvattenflödet. Dessutom bevattningsvatten från de F- förorenade grundvatten som används från borrade brunnar utgör risker för att förorena de grunda akvifererna som är lättillgängliga för konsumtion av människor och husdjur. De nuvarande WHO rekommenderade riktlinjerna för 10 µg As/L och 1.5 mg F-/L intag för människor är öppna för ytterligare epidemiologisk granskning, särskilt med tanke på kronisk/långvarig exponering i regionen. Den föreliggande studien belyser behovet av storskaliga utredningar för hydrogeokemiska och mänskliga hälsorisker när det gäller geogena föroreningar i regionen. Resultaten bidrar till de lokala, regionala och globala initiativen mot hållbart utnyttjande av grundvattenresurser i enlighet med Sustainable Development Goal (SDG) 6 för universell tillgång till rent vatten och sanitet för alla.

Utokeaji wa aseniki (As), floride (F- ), na elementi nyingine (TEs) zenye sumukwenye maji yaliyopo ardhini ni suala mtambuka la kimazingira duniani. Kwamujibu wa kanzidata ya taifa ya upatikanaji wa rasilimali maji, takribani 76% yamaji ya kunywa yanayosambazwa nchini Tanzania hupatikana kwenye vyanzovya maji yaliyopo ardhini. Katika upande wa kaskazini mwa Tanzania majiyaliyopo ardhini hutumika kwa zaidi ya 80% kwa ajili ya kunywa. Licha yaumuhimu wa maji hayo kaskazini mwa Tanzania, ubora wake kuhusiana nauchafu wa kijiojeniki bado haujafahamika vizuri. Utafiti huu ulijikita kukadiriaubora wa maji yaliyopo ardhini kwa kutumia uchambuzi, modeli ya jiokemikali,kitakwimu, na Mifumo ya Taarifa za Kijiografia (GIS) ili kuelewa zaidi ubora wakikemikali wa maji yaliyopo ardhini katika kiunzi cha usambazaji wa maji yakunywa nchini Tanzania. Floridi iliripotiwa kama kichafuzi kikuu cha kijiojenikicha maji yaliyopo ardhini kaskazini mwa Tanzania hususani katika bonde laPangani, ambayo ni sehemu ya ukanda wa bonde la ufa la Afrika Mashariki.Takribani 8% na 57.6% ya sampuli za maji yaliyokusanywa Geita na kwenyeuwanda wa aluvia ya Sanya yameonesha ukolezi wa F- , zaidi ya kipimo chamwongozo wa shirika la afya duniani, (WHO) ambacho ni 1.5mg/L kwa maji yakunywa. Ukolezi mkubwa wa F- katika maji yaliyopo ardhini huanzia kwenyemadini yenye F- nyingi na tope la umajivu kutoka kwenye miamba mikuu yakivolkano ya graniti na alikali. Matumizi ya maji yaliyopo ardhini yenye kiwangokikubwa cha F- yamechangia udhoofu wa meno na mifupa. Katika migodi yadhahabu kwenye Bonde la Ziwa Victoria (LVB), As iliripotiwa kama kichafuzikikuu cha kijiojeniki cha masuala ya kiafya. Ukolezi wa As kwa 50% na 82%katika sampuli za maji yaliyopo ardhini kutoka Tarime na Geita mtawalia zilizid imwongozo wa WHO (10 μg/L). Kiwango kikubwa cha As kwenye maji yaliyopoardhini kutoka LVB kilihusishwa sana na michakato asilia ya kijiokemikalipamoja na shughuli za uchimbaji wa dhahabu. Matokeo ya modeli ya jiokemikaliyamebainisha kuwa ujitokezaji wa As ulichochewa na uoksidishaji na/auuyeyukaji wa taratibu wa madini ya salfidi na chuma mtawalia yenye As kutokakwenye miamba mikuu. Elementi nyingine (alminiamu, kromiamu, kobalti,shaba, chuma, manganizi, nikeli na zinki zilionekana kuwa chini ya kiwangokilichopendekezwa katika muongozo wa maji ya kunywa uliotolewa na WHO.Ubadilikajibadilikaji wa kimazingira wa ukolezi wa As na F- kutoka kwenyevyanzo vya maji ya kunywa kutoka ardhini ilihusianishwa na ngazi mbalimbali zamaji yaliyopo ardhini, vina na muda wa kuchanganya maji yaliyopo ardhini namiamba ya madini ya As na F- kwenye vyanzo vya maji. Aidha, umwagiliaji wamaji yaliyotoka kwenye visima vilivyochafuliwa na F- huweka uwezekano wakuvichafua vyanzo vya maji vyenye vina vifupi ambavyo hufikiwa kirahisikwenye shughuli za kibinadamu na matumizi ya nyumbani. Mapendekezo ya sasaya mwongozo wa WHO ya 10 μg As/L na 1.5 mg F- /L kwa ajili ya matumizi yabinadamu yanahitaji tafiti za kitabibu zaidi, hasa kwa kuzingatia matumizi yamuda mrefu ya maji ya kunywa. Utafiti huu unadokeza mahitaji makubwa yakuchunguza madhara ya haidrojiokemikali pamoja na afya za binadamu kuhusuuchafu wa kijiojeniki katika eneo husika. Matokeo ya utafiti huu yanachangiakwenye jitihada za kitaifa, kikanda na kidunia kuhusu matumizi sahihi yarasilimali maji yaliyopo ardhini kwa kuzingatia Lengo namba 6 la MaendeleoEndelevu (SDG 6) kwa ajili ya upatikanaji wa maji safi na salama kwa watu wote.

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.

Arsenic (As) removal studies were carried out through batch experiments to investigate the performance of the locally available calcined magnesite mineral rocks from Tanzania. Natural water from a stream source in Tanzania and the prepared synthetic water at the laboratory were used for the studies. Parameters such as initial As concentration, calcined magnesite dosage, contact time and pH were evaluated for As removal using an overhead rea×2 shaker. Arsenic concentration was reduced from 5.3 to 1.1 mg/L As(V) at 180 min when 0.5 g/L calcined magnesite was applied to a synthetic water sample, whereas the concentration of 117 μg/L As(V) and 5.2 μg/L As(III) was reduced to below 0.1 μg/L in natural water. An increase in calcined magnesite dosage resulted in increased As removal up to below 0.01 mg/L. The calcined magnesite raised the pH of the water sample from 6.8 to 10 when the applied dosage increased between 0.002 g/L and 0.05 g/L. The pH was constant at around 10 even when the amount of 0.05 g/L was added 2000 times. Despite the high pH, the amount of magnesium released in water was low. The calcination of magnesite at 500 ◦C increased surface area by 4 times as compared to the natural magnesite and X-ray diffraction showed presence of MgCO3 phase as the dominant phase at this temperature. The reaction kinetics of As removal on 0.5 g/L calcined magnesite fitted with the pseudo-second-order (R2 = 0.96). Reaction isotherm was strongly fitted with Freundlich isotherm (R2 = 0.98). Linear regression and artificial intelligence neural network showed the As removal was influenced by both contact time and pH. Arsenic can be removed from As water using calcined magnesite and will be suitable for water treatment around gold mining areas. 

In the past two decades, several studies on arsenic (As) occurrence in the environment, particularly in surface and groundwater systems have reported high levels of As in some African countries. Arsenic concentrations up to 10,000 mu g/L have been reported in surface water systems, caused by human activities such as mining, industrial effluents, and municipal solid waste disposals. Similarly, concentrations up to 1760 mu g/L have been reported in many groundwater systems which account for approximately 60% of drinking water demand in rural Africa. Naturally, As is mobilized in groundwater systems through weathering processes and dissolution of As bearing minerals such as sulfides (pyrite, arsenopyrite, and chalcopyrite), iron oxides, other mineralized granitic and gneissic rocks, and climate change factors triggering As release in groundwater. Recently, public health studies in some African countries such as Tanzania and Ethiopia have reported high levels of As in human tissues such as toenails as well as in urine among pregnant women exposed to As contaminated groundwater, respectively. In urine, concentrations up to 150 mu g/L were reported among pregnant women depending on As contaminated drinking water within Geita gold mining areas in the north-western part of Tanzania. However, the studies on As occurrence, and mobilization in African water systems, as well as related health effects are limited, due to the lack of awareness. The current study aims to gather information on the occurrence of As in different environmental compartments, its spatial variability, public health problems and the potential remediation options of As in water sources. The study also aims at creating awareness of As contamination in Africa and its removal using locally available materials.

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.

Groundwater contamination from geogenic sources paces challenges to many countries, especially in the developing world. In Tanzania, the elevated fluoride (F-) concentration and related chronic fluorosis associated with drinking F- rich water arc common in the Fast African Rift Valley regions. In these regions, F- concentration is space dependence which poses much uncertainty when targeting safe source for drinking water. To account for the spatial effects, integrated exploratory spatial data analysis, regression analysis, and geographical information systems tools were used to associate the distribution of F- in groundwater with spatial variability in terrain slopes, volcanic deposits, recharge water/vadose materials contact time, groundwater resource development for irrigated agriculture in the Sanya alluvial plain (SAP) of northern Tanzania. The F- concentration increased with distance from steep slopes where the high scale of variation was recorded in the gentle sloping and flat grounds within the SAP. The areas covered with debris avalanche deposits in the gentle sloping and flat grounds correlated with the high spatial variability in F- concentration. Furthermore, the high spatial variability in F- correlated positively with depth to groundwater in the Sanya flood plain. In contrast, a negative correlation between F- and borehole depth was observed. The current irrigation practices in the Sanya alluvial plain contribute to the high spatial variability in F- concentration, particularly within the perched shallow aquifers in the volcanic river valleys. The findings of this study arc important to the overall chain of safe water supply process in historically fluorotic regions. They provide new insights into the well-known F- contamination through the use of modern geospatial methods and technologies. In Tanzania's context, the findings can improve the current process of drilling permits issuance by the authority and guide the local borehole drillers to be precise in siting safe source for drinking water.

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.