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.

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 recent years, high arsenic (As) levels of about 300 µg/L have been reported around the gold mining areas of Geita and Mara regions within the Lake Victoria basin (LVB) in Tanzania. During a sampling campaign at Geita and Mara, the groundwater and surface water samples revealed the presence of high As concentrations as well as Fe and sulfide. Several wells are abandoned because of odor due to high content of sulfide, as well as red color, due to high iron content. About 53% of the analyzed As water samples exceeded the WHO guideline for drinking water. The release of As is primarily attributed to the weathering of sulfide minerals like arsenopyrite related to gold mining activities. In some parts of the LVB, an increasing number of cancer cases are being reported, and clinical investigations are now on the national agenda to identify the possible causes. Water treatment using bauxite, gypsum, and magnesite shows promising results, especially bauxite and magnesite, which could lower As concentrations to below 0.1 µg/L. Both bauxite and magnesite worked efficiently on As removal even at higher concentrations above 5 mg/L, while gypsum is preferable for treatment of low As concentrations. Furthermore, magnesite has a unique chemical character of influencing other materials to have high efficiency of As removal; however, it raises the pH of the water up to 10. Addition of 5 g/L magnesite to water containing 5 mg/L As, could lower the As concentration to below 10 µg/L within 30 min. The As removal increased with dosage and contact time up to 98 % in 4 hours, which is in agreement with Visual MINTEQ simulation. The performance of calcined magnesite, and gypsum fitted well with Freundlich adsorption isotherm, which indicates the presence of chemical reaction as controlling factor for As removal, while bauxite fitted Langmuir isotherm indicates monolayer surface coverage. The kinetic reactions were observed to follow pseudo-second-order. The statistic obeys linear regression with R2 ranging between 0.7 and 0.9. The artificial neural network revealed pH as a most influencing parameter for As removal from water. The mini-scale column revealed that a flow rate of 0.5 – 1 mL/min for 30 min gave an adsorption capacity ranging between 0.07 and 0.14 µg/g, which follows Thomas linear model with rate constant of kTH of 29.48 to 211.25 mL/min µg. The release of elements from spent magnesite, gypsum, and bauxite, such as magnesium (Mg), aluminum (Al), iron (Fe), and calcium (Ca) were found to be below WHO standards after water treatment. However, the desorption process of As from spent magnesite and gypsum was a challenge, which means there was formation of strong bond between Mg-O-As and Ca-O-As. This study is based on 5 papers that provide significant insights to the scientific community, policymakers, and the community living around As contaminated areas to learn about the occurrences of As and simple remediation techniques evaluated in this study.

Under de senaste åren har höga halter av arsenik (As) på cirka 300 μg/L rapporterats runt guldgruveområdena i Geita- och Mara-regionerna i Victoriasjöns avrinningsområde (LVB) i Tanzania. Under provtagningskampanjen vid Geita och Mara visade grundvatten- och ytvattenproverna förekomst av höga As-koncentrationer samt Fe och sulfid. Flera brunnar överges på grund av lukt orsakad av högt innehåll av sulfid, liksom röd färg, på grund av hög järnhalt. Cirka 53 % av de analyserade vattenproverna överskred WHO:s riktlinjer för dricksvatten. Frisättningen av As tillskrivs främst vittring av sulfidmineraler som arsenopyrit i samband med guldbrytningen. I vissa delar av LVB rapporteras allt fler cancerfall och kliniska undersökningar står nu på den nationella agendan för att identifiera möjliga orsaker. Vattenrening med bauxit, gips och magnesit visar lovande resultat, särskilt bauxit och magnesit kan sänka As-koncentrationerna till under 0.1 μg/L. Både bauxit och magnesit fungerade effektivt för As-avlägsnande även vid högre koncentrationer över 5 mg/L, medan gips är att föredra för behandling av låga As-koncentrationer. Dessutom hade magnesit en unik kemisk karaktär för att påverka andra material att ha hög effektivitet vid As-borttagning; Det höjer dock vattnets pH upp till 10. Vid tillsats av 5 g/L magnesit i vatten med 5 mg/L As, kan As halten sänkas till under 10 μg/L inom 30 min. As-borttagningen ökade med dosering och kontakttid upp till 98 % efter 4 timmar, vilket är i överensstämmelse med Visual MINTEQ-simulering. Prestandan hos kalcinerad magnesit och gips passade väl med Freundlich-adsorptionsisoterm, som indikerar närvaron av kemisk reaktion som styrande faktor för As-avlägsnande medan bauxit stämde med Langmuir-isoterm, vilket indikerar yttäckning i ett lager. De kinetiska reaktionerna observerades följa pseudo andra ordningen. Statistiken följer linjär regression med R2 som sträcker sig mellan 0.7 och 0.9. Det artificiella neurala nätverket avslöjade pH som en av de mest inflytelserika parametrarna för avlägsnande av As från vatten. En kollonn i liten skala med en flödeshastighet på 0.5 – 1 mL/min under 30 minuter visade en adsoprtionskapacitet mellan 0.07 och 0.14 μg/g som följer Thomas linjära modell med hastighetskonstanten kTH på 29.48 till 211.25 mL/min μg. Frisättning av element från förbrukad magnesit, gips och bauxit såsom magnesium (Mg). aluminium (Al), järn (Fe), kalcium (Ca) visade sig ligga under WHO:s standarder efter vattenrening. Desorptionsprocessen av As från förbrukad magnesit och gips var dock en utmaning, vilket innebär att det bildades en stark bindning mellan Mg-O-As och Ca-O-As. Denna studie är baserad på 5 artiklar som ger betydande insikter till forskare, beslutsfattare och samhället runt As-förorenade platser för att lära sig om förekomsten av As och enkla saneringstekniker som utvärderas i denna studie.

Katika miaka ya hivi karibuni, viwango vya juu vya As vya 300 μg/L vinaripotiwa karibu na maeneo ya uchimbaji wa dhahabu ya mikoa ya Geita na Mara ndani ya bonde la Ziwa Victoria (LVB) nchini Tanzania. Wakati wa kampeni ya sampuli katika mikoa ya Geita na Mara, sampuli za maji ya ardhini na maji ya mito zilifichua uwepo wa viwango vya juu vya As pamoja na Fe na sulfide. Visima kadhaa vimeachwa kwa sababu ya harufu kutokana na sulfide iliyomo kwenye maji, pamoja na rangi nyekundu, kwa sababu ya chuma. Karibu 53% ya sampuli za maji zilizochambuliwa zilizidi mwongozo wa WHO wa maji ya kunywa. Kutolewa kwa As kimsingi kunahusishwa na hali ya hewa ya madini ya sulfide kama arsenopyrite inayohusiana na shughuli za madini ya dhahabu. Katika baadhi ya maeneo ya LVB, idadi kubwa ya kesi za saratani zinaripotiwa na uchunguzi wa kliniki sasa uko kwenye ajenda ya kitaifa ya kutambua sababu zinazowezekana. Matibabu ya maji kwa kutumia bauxite, gypsum na magnesite inaonyesha matokeo ya kuahidi, hasa bauxite na magnesite inaweza kupunguza viwango vya As mpaka chini ya 0.1 μg/L. Wote bauxite na magnesite walifanya kazi kwa ufanisi juu ya As kuondolewa hata katika viwango vya juu ya 5 mg/L wakati gypsum ni bora kwa matibabu ya viwango vya chini vya As kwenye maji. Zaidi ya hayo, magnesite alikuwa na tabia ya kipekee ya kemikali kushawishi nyenzo zingine kuwa na ufanisi mkubwa juu ya As kuondolewa; hata hivyo huinua pH ya maji hadi 10. Baada ya kuongeza 5 g/L magnesite katika 5 mg/L As, inaweza kupunguza As chini ya 10 μg/L ndani ya dakika 30. Kuondolewa kwa As iliongezeka hadi 98% kulingana na kipimo cha madini kuongezeka, pia na wakati wa maji kugusana katika masaa 4 ambayo inakubaliana na simulation ya Visual MINTEQ. Utendaji wa magnesite iliyochomwa, na gypsum ulioneshwa vizuri na Freundlich adsorption isotherm, ambayo inaonyesha uwepo wa majibu ya kemikali kama sababu ya kudhibiti kwa As kuondolewa wakati bauxite ilifaa vizuri kwenye Langmuir isotherm inayoonyesha chanjo ya uso wa monolayer. Mwitikio wa kinetic ulizingatiwa kufuata utaratibu wa pili wa pseudo. Takwimu hutii regression ya mstari na R2 kuanzia kati ya 0.7 na 0.9. Mtandao wa neva bandia ulifunua pH kama kigezo cha kushawishi zaidi kwa As kuondolewa kutoka kwa maji. Safu ndogo ilifunua kiwango cha mtiririko wa 0.5 - 1 mL/min kwa dakika 30 na uwezo wa mtiririko kati ya 0.07 na 0.14 μg/g ambayo inatii mfano wa Thomas linear na kiwango cha mara kwa mara cha kTH ya 29.48 hadi 211.25 mL/min μg. Kutolewa kwa vitu kutoka kwa magnesite iliyotumika, gypsum, na bauxite kama vile magnesiamu (Mg). alumini (Al), chuma (Fe), kalsiamu (Ca) ilipatikana kuwa chini ya viwango vya WHO baada ya matibabu ya maji. Hata hivyo, mchakato wa kuiachanisha As kutoka kwa magnesite iliyotumika na gypsum ilikuwa changamoto ambayo inamaanisha kulikuwa na muungano mgumu kati ya Mg-O-As na Ca-O-As. Utafiti huu unategemea machapisho 5 ambapo utachangia ufahamu muhimu kwa jamii ya kisayansi, watunga sera na jamii inayoishi karibu na maeneo yaliyochafuliwa, kujifunza kuhusu matukio ya uchafuzi wa vyanzo vya maji pamoja na mbinu rahisi za kuondoa As zilizotathminiwa katika utafiti huu.

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.

Spatial uncertainty caused by large-scale variation in fluoride (F-) occurrence remains a setback for water supply authorities in the F- belts of the world. It is estimated that approximately 80 million people in the East African Rift Valley (EARV) regions and volcanic areas exhibit a wide variety of fluorosis symptoms due to drinking water with F- concentrations higher than 1.5 mg/L (WHO guideline limit). In this study, we combined geostatistical techniques, spatial statistical methods, and geographical information systems (GIS) to (i) map the probable places with F- < 0.5 mg/L and F- > 1.5, 4.0 and 10.0 mg/L using probability kriging (PK) method, (ii) estimate the probable total population at high or low F- risk levels using univariate local Moran's I statistic, and (iii) map the spatial distribution of population at high and low F- risk levels in Manyara, Arusha and Kilimanjaro regions using GIS. It was predicted that places along the major and minor EARV mountain ranges and around the flanks of major stratovolcanoes were dominated by groundwater sources with extremely low F-(<<0.5 mg/L). In contrast, places within EARV graben were dominated by groundwater sources with F- > 1.5 mg/L. About 1 million people (similar to 20% of the total population) living around Mt. Kilimanjaro in Rombo, Moshi, and Mwanga districts are at high dental caries risk. Furthermore, it was estimated that about 2 million people (similar to 41% of the total population) in Siha, Hai, Arusha City, Hanang', Arusha, Simanjiro, and Meru districts are at high risk of dental, skeletal, and crippling fluorosis. Fluorosis, especially dental and crippling fluorosis, is an increasing disease burden at the community level due to prolonged consumption of F- contaminated water within EARV graben. The major findings of the present study are very crucial for authority to minimize the uncertainty caused by high spatial variability in geogenic F- occurrence.