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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 MgCO 3 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. [Display omitted] • Arsenic (As) from natural water was reduced from 117 μg/L As(V) to below 0.1 μg/L. • Visual MINTEQ simulation shows increased As removal percentage with increase in adsorbent dosage. • The arsenic removal depends on contact time, pH and an increase in adsorbent dosage. • High pH does not affect release of magnesium in water after treatment. • Adsorption isotherm fitted Freundlich with R2 of 0.98 [ABSTRACT FROM AUTHOR]

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+, SO 4 2−, HCO 3 − 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 HCO 3 − > SO 4 2− > NO 3 −, Cl− > PO 4 3−. Statistical and geochemical modelling software such as 'R 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 μg/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 μg/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. [Display omitted] • The occurrence of arsenic and other TEs was assessed in 40 groundwater samples. • Hydrogeochemistry and water quality evaluation were done by geochemical modelling and statistics. • 48% of water samples exceeded the WHO guideline value of 10 μg arsenic/L for drinking purposes. • Consumption of arsenic-polluted water poses health risks to the exposed communities in the study area. • Regular update of water quality monitoring programs is recommended. [ABSTRACT FROM AUTHOR]

Groundwater contamination from geogenic sources poses 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 are common in the East 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 are 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., Competing Interests: Declaration of competing interest No potential conflict of interest., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

The population of the semi-arid areas of the countries in the East African Rift Valley (EARV) is faced with serious problems associated with the availability and the quality of the drinking water. In these areas, the drinking water supply largely relies on groundwater characterised by elevated fluoride concentration (> 1.5 mg/L), resulting from interactions with the surrounding alkaline volcanic rocks. This geochemical anomaly is often associated with the presence of other naturally occurring potentially toxic elements (PTEs), such as As, Mo, U, V, which are known to cause adverse effects on human health. This study reports on the occurrence of such PTEs in the groundwater on the populated flanks of Mt. Meru, an active volcano situated in the EARV. Our results show that the majority of analysed PTEs (Al, As, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Se, Sr, Pb, and Zn) are within the acceptable limits for drinking purpose in samples collected from wells, springs and tap systems, suggesting that there is no immediate health risk associated with these PTEs. However, some of the samples were found to exceed the WHO tolerance limit for U (> 30 μg/L) and Mo (> 70 μg/L). The sample analysis also revealed that in some of the collected samples, the concentrations of total dissolved solids, Na +  and K +  exceed the permissible limits. The concerning levels of major parameters and PTEs were found to be associated with areas covered with debris avalanche deposits on the northeast flank, and volcanic ash and alluvial deposits on the southwest flanks of the volcano. The study highlights the need to extend the range of elements monitored in the regional groundwater and make a more routine measurement of PTEs to ensure drinking water safety and effective water management measures., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Safe drinking water supply systems in naturally contaminated hydrogeological environments require precise geoinformation on contamination hotspots. Spatial statistical methods and GIS were used to study fluoride occurrence in groundwater and identify significant spatial patterns using fluoride concentrations. The global and local Morans I indices were used. While the significant positive global Morans I index indicated spatial structure in fluoride occurrence, the significant spatial clusters were identified using local Morans I index and mapped at p-value of 0.05. The spatial clusters demonstrated patterns of drinking water sources with fluoride concentrations below or above WHO guideline and Tanzania standard for drinking water and were considered as 'regional fluoride cool spots' and 'regional fluoride contamination hotspots', respectively. Two regional fluoride contamination hotspots were identified and mapped around the Stratovolcano Mountains in the north-east and south-west of the study area; and along the Neogene Quaternary volcanic formations and Palaeo-Neoproterozoic East African Orogen (Mozambique Belt). The two largest regional fluoride cool spots dominated the major and minor rift escarpments in the west and east of the study area respectively while the small ones emerged around the volcanic mountains in the north and south. Furthermore, significant spatial outliers emerged at the boundary of regional fluoride hotspots and cool spots as an indication of the spatial processes controlling the mobilization of fluoride in groundwater. While all water sources in the cool spots had fluoride concentrations below 1.5 mg/L, some had extremely low concentrations below 0.5 mg/L which is not safe for human consumption. For hotspots, 96% of water sources had fluoride concentrations above 1.5 mg/L. The probability of having safe source of drinking water varied from one geological unit to another with sources in the Neogene Quaternary volcanic formations having least probabilities., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)