Geochemical and Isotopic Composition of Natural Waters in the Central Main Ethiopian Rift: emphasis on the study of source and genesis of fluoride

In the Main Ethiopian Rift (MER), the supply of drinking water principally relies on groundwater wells, springs (including some hot springs), and rivers, and is characterized by a significant problem of fluoride (F¯) contamination. New analyses reveal that the F− geochemical anomaly is sometimes associated with hazardous content of other potentially toxic elements such as As, B, Mo, U, Al, Fe, and Mn. The F¯ content exceeds the permissible limit for drinking prescribed by the World Health Organization (WHO; 1.5 mg/L) in many important wells (up to 20 mg/L), with even more extreme F concentration in hot springs and alkaline lakes (up to 97 mg/L and 384 mg/L respectively) and is causing prevalent endemic fluorosis disease in the region. 87 % of the groundwater wells, 38 % of rivers and 100 % of hot springs and lakes show F¯ content above 1.5 mg/L. The groundwater and surface water from the highlands, typically characterized by low Total Dissolved Solids (TDS) and Ca2+ (Mg2+)-HCO3¯ hydrochemical facies, do not show high F¯ content. The subsequent interaction of these waters with the various rocks of the rift valley induces a general increase of the TDS and a variation of the chemical signature towards Na+-HCO3¯ compositions, with a parallel enrichment of F¯. The interacting matrixes are mainly rhyolites consisting of volcanic glass and only rare F-bearing accessory minerals (such as alkali amphibole). Comparing the abundance and the composition of the glassy groundmass with other mineral phases, it appears that the former stores most of the total F¯ budget. This glassy material is extremely reactive, and its weathering products (i.e. fluvio/volcano-lacustrine sediments) further concentrate the fluoride. The interaction of these “weathered/reworked” volcanic products with water and carbon dioxide at high pH causes the release of fluoride into the interacting water. This mainly occurs by a process of baseexchange softening with the neo-formed clay minerals (i.e. Ca-Mg uptake by the aquifer matrix, with release of Na+ into the groundwater). This is plausibly the main enrichment mechanism that explains the high F¯ content of the local groundwater, as evidenced by positive correlation between F¯, pH, and Na+, and inverse correlation between F¯ and Ca2+ (Mg2+). Saturation indices (SI) were calculated (using PHREEQC-2) for the different water groups, highlighting that the studied waters are undersaturated in fluorite. In these conditions, fluoride can not precipitate as CaF2, and so F¯ mobilizes freely without forming other complexes. On the other hand, 35 % of the 23 investigated groundwater wells and 70 % of the 12 hot springs (and deep geothermal wells) show Arsenic concentration above the recommended limit of 10μg/L (WHO 2006). The average concentration of Arsenic is 0.9μg/L in rivers, 39μg/L in hot springs, 236μg/L in deep geothermal wells, 21.4μg/L in groundwater wells, 77μg/L in lakes, whereas maximum concentrations reach up to 3μg/L, 156μg/L, 278μg/L, 157μg/L and 405 μg/L respectively. Arsenic in groundwater wells shows positive correlations with Na+ (R2=0.63) and HCO3 − (R2=0.70) as well as with other trace elements such as Mo (R2=0.79), U (R2=0.70), V (R2=0.68) whereas no correlations are observed with Fe and Mn. PHREEQC speciation modelling indicates that Fe and Al oxides and hydroxides are stable in the water systems, suggesting that Fe and Al mineral phases are potential adsorbents and thus influence the mobility of As. The oxidizing, high pH condition combined with Na+- HCO3¯ hydrochemical facies (competing effect of HCO3 − for adsorption sites) of the MER waters play an important role in the mobilization of arsenic. Chemical analyses of leachates from MER rhyolitic rocks and their weathered and reworked fluviolacustrine sediments were performed in order to evaluate their contribution as a source of the mentioned geochemical anomalies. The leachates were obtained from a one-year leaching experiment on powdered rocks and sediments mixed with distilled water (10g:50ml). The sediment leachates contain as much as 7.6 mg/L of F¯, 220 μg/L of As, 181 μg/L of Mo, 64 μg/L of U and 254 μg/L of V suggesting that the local sediments represent the main source and reservoir of toxic elements. Laboratory column experiment was also conducted in volcanic ash sample using synthetic rain water flushing, and the result showed that significant amount of F¯ were leached out over the duration of the experiments. This showed that these elements were originally present in the glassy portion of the MER rhyolitic rocks, were progressively concentrated in weathered and redeposited products. It further confirms that the pyroclastic materials are the major source and reservoir of many of the chemical elements (e.g. F¯, As). Therefore, together with the renowned F¯ problem, the possible presence of geochemical anomalies in As, B, Mo, V, U, Al, Fe, and Mn have to be taken into consideration in water quality issues and future works has to investigate their possible health impact on the population of MER and other sectors of the east African rift. The stable δ18O, δD and radiogenic (87Sr/86Sr) isotopic composition of waters and representative volcanic rocks (Ignimbrite and basalt) were carried out during this study. Different ranges of isotopic values were recorded for different water groups: 10 hot spring samples show δ18O value with in the range of (-3.36‰ – 3.69‰) and δD (-0.95‰ – 24.23‰) (VSMOW), 12 groundwater wells δ18O (- 3.99‰ – 5.14‰) and δD (-19.69‰ – 32.27‰) in contrast to the 5 Lakes δ18O (3.98‰ – 7.92‰) and δD (26.19‰ – 45.71‰). The 2 deep geothermal wells and 1 of the 2 river samples are depleted in stable isotopic values. 87Sr/86Sr values range from 0.7045 to 0.7076 in the hot springs, and the two deep geothermal wells have 0.7043 and 0.7054 values. These signatures are typical of water interacted with mantle derived materials (with a minor crustal contamination), similar to the rocks widely covering the study area. The Sr isotope values of the basalt and ignimbrite samples are 0.7063 and 0.7071 respectively. Generally, the result shows that there exists a complex surface water and groundwater interactions that is reflected on a diversity of the stable and Sr isotopic signature in waters. The preliminary results of the study has showed that there is a need for future extended works on the geochemistry of solid samples (rocks, sediments and soils) as well as in waters that investigate all the spectrum of chemical elements that are potentially detrimental to human health and environment. Furthermore, from water resource point of view, the following works must focus on a comprehensive study of various isotopes and geochemical data to constrain groundwater age dating, water-rock interaction and flow path and thus help to model and systematize the hydrologic cycles in the basin

Nephrotoxic Contaminants in Drinking Water and Urine, and Chronic Kidney Disease in Rural Sri Lanka

Chronic kidney disease of unknown (“u”) cause (CKDu) is a growing public health concern in Sri Lanka. Prior research has hypothesized a link with drinking water quality, but rigorous studies are lacking. This study assesses the relationship between nephrotoxic elements (namely arsenic (As), cadmium (Cd), lead (Pb), and uranium (U)) in drinking water, and urine samples collected from individuals with and/or without CKDu in endemic areas, and from individuals without CKDu in nonendemic areas. All water samples—from a variety of source types (i.e., shallow and deep wells, springs, piped, and surface water)—contained extremely low concentrations of nephrotoxic elements, and all were well below drinking water guideline values. Concentrations in individual urine samples were higher than, and uncorrelated with, those measured in drinking water, suggesting potential exposure from other sources. Mean urinary concentrations of these elements for individuals with clinically diagnosed CKDu were consistently lower than individuals without CKDu both in endemic and nonendemic areas. This likely stems from the inability of the kidney to excrete these toxic elements via urine in CKDu patients. Urinary concentrations of individuals were also found to be within the range of reference values measured in urine of healthy unexposed individuals from international biomonitoring studies, though these reference levels may not be safe for the Sri Lankan population. The results suggest that CKDu cannot be clearly linked with the presence of these contaminants in drinking water. There remains a need to investigate potential interactions of low doses of these elements (particularly Cd and As) with other risk factors that appear linked to CKDu prior to developing public health strategies to address this illness

Nephrotoxic Contaminants in Drinking Water and Urine, and Chronic Kidney Disease in Rural Sri Lanka

Chronic kidney disease of unknown (“u”) cause (CKDu) is a growing public health concern in Sri Lanka. Prior research has hypothesized a link with drinking water quality, but rigorous studies are lacking. This study assesses the relationship between nephrotoxic elements (namely arsenic (As), cadmium (Cd), lead (Pb), and uranium (U)) in drinking water, and urine samples collected from individuals with and/or without CKDu in endemic areas, and from individuals without CKDu in nonendemic areas. All water samples—from a variety of source types (i.e., shallow and deep wells, springs, piped, and surface water)—contained extremely low concentrations of nephrotoxic elements, and all were well below drinking water guideline values. Concentrations in individual urine samples were higher than, and uncorrelated with, those measured in drinking water, suggesting potential exposure from other sources. Mean urinary concentrations of these elements for individuals with clinically diagnosed CKDu were consistently lower than individuals without CKDu both in endemic and nonendemic areas. This likely stems from the inability of the kidney to excrete these toxic elements via urine in CKDu patients. Urinary concentrations of individuals were also found to be within the range of reference values measured in urine of healthy unexposed individuals from international biomonitoring studies, though these reference levels may not be safe for the Sri Lankan population. The results suggest that CKDu cannot be clearly linked with the presence of these contaminants in drinking water. There remains a need to investigate potential interactions of low doses of these elements (particularly Cd and As) with other risk factors that appear linked to CKDu prior to developing public health strategies to address this illness

Groundwater Quality and Its Health Impact: An Assessment of Dental Fluorosis in Rural Inhabitants of the Main Ethiopian Rift

This study aims to assess the link between fluoride content in groundwater and its impact on dental health in rural communities of the Ethiopian Rift. A total of 148 water samples were collected from two drainage basins within the Main Ethiopian Rift (MER). In the Ziway-Shala basin in particular, wells had high fluoride levels (mean: 9.4 ± 10.5 mg/L; range: 1.1 to 68 mg/L), with 48 of 50 exceeding the WHO drinking water guideline limit of 1.5 mg/L. Total average daily intake of fluoride from drinking groundwater (calculated per weight unit) was also found to be six times higher than the No-Observed-Adverse-Effects-Level (NOAEL) value of 0.06 mg/kg/day. The highest fluoride levels were found in highly alkaline (pH of 7 to 8.9) groundwater characterized by high salinity; high concentrations of sodium (Na+), bicarbonate (HCO3−), and silica (SiO2); and low concentrations of calcium (Ca2+). A progressive Ca2+ decrease along the groundwater flow path is associated with an increase of fluoride in the groundwater. The groundwater quality problem is also coupled with the presence of other toxic elements, such as arsenic (As) and uranium (U). The health impact of fluoride was evaluated based on clinical examination of dental fluorosis (DF) among local residents using the Thylstrup and Fejerskov index (TFI). In total, 200 rural inhabitants between the ages of 7 and 40 years old using water from 12 wells of fluoride range of 7.8–18 mg/L were examined. Signs of DF (TF score of ≥ 1) were observed in all individuals. Most of the teeth (52%) recorded TF scores of 5 and 6, followed by TF scores of 3 and 4 (30%), and 8.4% had TF scores of 7 or higher. Sixty percent of the teeth exhibited loss of the outermost enamel. Within the range of fluoride contents, we did not find any correlation between fluoride content and DF. Finally, preliminary data suggest that milk intake has contributed to reducing the severity of DF. The study highlights the apparent positive role of milk on DF and emphasizes the importance of nutrition in management efforts to mitigate DF in the MER and other parts of the world

Fluoride Exposure from Groundwater as Reflected by Urinary Fluoride and Children’s Dental Fluorosis in the Main Ethiopian Rift Valley

This cross-sectional study explores the relationships between children’s F− exposure from drinking groundwater and urinary F− concentrations, combined with dental fluorosis (DF) in the Main Ethiopian Rift (MER) Valley. We examined the DF prevalence and severity among 491 children (10 to 15 This cross-sectional study explores the relationships between children’s F− exposure from drinking groundwater and urinary F− concentrations, combined with dental fluorosis (DF) in the Main Ethiopian Rift (MER) Valley. We examined the DF prevalence and severity among 491 children (10 to 15 years old) who are lifelong residents of 33 rural communities in which groundwater concentrations of F− cover a wide range. A subset of 156 children was selected for urinary F− measurements. Our results showed that the mean F− concentrations in groundwater were 8.5 ± 4.1 mg/L (range: 1.1–18 mg/L), while those in urine were 12.1 ± 7.3 mg/L (range: 1.1–39.8 mg/L). The prevalence of mild, moderate, and severe DF in children’s teeth was 17%, 29%, and 45%, respectively, and the majority (90%; n = 140) of the children had urinary F− concentrations above 3 mg/L. Below this level most of the teeth showed mild forms of DF. The exposure-response relationship between F− and DF was positive and nonlinear, with DF severity tending to level off above a F− threshold of ~6 mg/L, most likely due to the fact that at ~6 mg/L the enamel is damaged as much as it can be clinically observed in most children. We also observed differential prevalence (and severity) of DF and urinary concentration across children exposed to similar F− concentrations in water, which highlights the importance of individual-specific factors in addition to the F− levels in drinking water. Finally, we investigated urinary F− in children from communities where defluoridation remediation was taking place. The lower F− concentration measured in urine of this population demonstrates the capacity of the urinary F−method as an effective monitoring and evaluation tool for assessing the outcome of successful F− mitigation strategy in a relatively short time (months) in areas affected with severe fluorosis

The Effect of Non-fluoride Factors on Risk of Dental Fluorosis: Evidence from Rural Populations of the Main Ethiopian Rift

Elevated level of fluoride (F−) in drinking water is a well-recognized risk factor of dental fluorosis (DF). While considering optimization of region-specific standards for F−, it is reasonable, however, to consider how local diet, water sourcing practices, and non-F− elements in water may be related to health outcomes. In this study, we hypothesized that non-F− elements in groundwater and lifestyle and demographic characteristics may be independent predictors or modifiers of the effects of F− on teeth. Dental examinations were conducted among 1094 inhabitants from 399 randomly selected households of 20 rural communities of the Ziway-Shala lake basin of the Main Ethiopian Rift. DF severity was evaluated using the Thylstrup-Fejerskov Index (TFI). Household surveys were performed and water samples were collected from community water sources. To consider interrelations between the teeth within individual (in terms of DF severity) and between F− and non-F− elements in groundwater, the statistical methods of regression analysis, mixed models, and principal component analysis were used. About 90% of study participants consumed water from wells with F− levels above the WHO recommended standard of 1.5 mg/l. More than 62% of the study population had DF. F− levels were a major factor associated with DF. Age, sex, and milk consumption (both cow’s and breastfed) were also statistically significantly (p \u3c 0.05) associated with DF severity; these associations appear both independently and as modifiers of those identified between F− concentration and DF severity. Among 35 examined elements in groundwater, Ca, Al, Cu, and Rb were found to be significantly correlated with dental health outcomes among the residents exposed to water with excessive F− concentrations. Quantitative estimates obtained in our study can be used to explore new water treatment strategies, water safety and quality regulations, and lifestyle recommendations which may be more appropriate for this highly populated region

Geochemistry and water quality assessment of central Main Ethiopian Rift natural waters with emphasis on source and occurrence of fluoride and arsenic

Drinking water supply for the Main Ethiopian Rift (MER) area principally relies on groundwater wells and springs and is characterized by natural source of elevated fluoride concentration. New analyses reveal that the F geochemical anomaly is associated with other potentially toxic elements such as As, U, Mo and B. Particularly, 35% of the 23 investigated groundwater wells and 70% of the 14 hot springs (and geothermal wells) show arsenic concentrations above the recommended limit of 10 lg/L (WHO, 2006). Arsenic in groundwater wells has a positive correlation with Na+ (R2 = 0.63) and alkalinity (HCO 3 ; R2 = 0.70) as well as with trace elements such as U (R2 = 0.70), Mo (R2 = 0.79) and V (R2 = 0.68). PHREEQC speciation modelling indicates that Fe oxides and hydroxides are stable in water systems, suggesting their role as potential adsorbents that could influence the mobility of arsenic. Chemical analyses of leachates from MER rhyolitic rocks and their weathered and re-worked fluviolacustrine sediments were performed to evaluate their contribution as a source of the mentioned geochemical anomalies. These leachates were obtained from a 1-year leaching experiment on powdered rocks and sediments mixed with distilled water (10 g:50 ml). They contain as much as 220 lg/L of As, 7.6 mg/L of F, 181 lg/L of Mo, 64 lg/L of U and 254 lg/L of V suggesting that the local sediments represent the main source and reservoir of toxic elements. These elements, originally present in the glassy portion of the MER rhyolitic rocks were progressively concentrated in weathered and re-deposited products. Therefore, together with the renowned F problem, the possible presence of further geochemical anomalies have to be considered in water quality issues and future work has to investigate their possible health impact on the population of MER and other sectors of the East African Rift

Groundwater Quality and Its Health Impact: An Assessment of Dental Fluorosis in Rural Inhabitants of the Main Ethiopian Rift

This study aims to assess the link between fluoride content in groundwater and its impact on dental health in rural communities of the Ethiopian Rift. A total of 148 water samples were collected from two drainage basins within the Main Ethiopian Rift (MER). In the Ziway-Shala basin in particular, wells had high fluoride levels (mean: 9.4 ± 10.5 mg/L; range: 1.1 to 68 mg/L), with 48 of 50 exceeding the WHO drinking water guideline limit of 1.5 mg/L. Total average daily intake of fluoride from drinking groundwater (calculated per weight unit) was also found to be six times higher than the No-Observed-Adverse-Effects-Level (NOAEL) value of 0.06 mg/kg/day. The highest fluoride levels were found in highly alkaline (pH of 7 to 8.9) groundwater characterized by high salinity; high concentrations of sodium (Na+), bicarbonate (HCO3−), and silica (SiO2); and low concentrations of calcium (Ca2+). A progressive Ca2+ decrease along the groundwater flow path is associated with an increase of fluoride in the groundwater. The groundwater quality problem is also coupled with the presence of other toxic elements, such as arsenic (As) and uranium (U). The health impact of fluoride was evaluated based on clinical examination of dental fluorosis (DF) among local residents using the Thylstrup and Fejerskov index (TFI). In total, 200 rural inhabitants between the ages of 7 and 40 years old using water from 12 wells of fluoride range of 7.8–18 mg/L were examined. Signs of DF (TF score of ≥ 1) were observed in all individuals. Most of the teeth (52%) recorded TF scores of 5 and 6, followed by TF scores of 3 and 4 (30%), and 8.4% had TF scores of 7 or higher. Sixty percent of the teeth exhibited loss of the outermost enamel. Within the range of fluoride contents, we did not find any correlation between fluoride content and DF. Finally, preliminary data suggest that milk intake has contributed to reducing the severity of DF. The study highlights the apparent positive role of milk on DF and emphasizes the importance of nutrition in management efforts to mitigate DF in the MER and other parts of the world

Hydrogeochemical study in the Main Ethiopian Rift: new insights to the source and enrichment mechanism of fluoride

The central Main Ethiopian Rift suffers a severe water quality problem, characterized by an anomalously high fluoride (F) content that causes an endemic fluorosis disease. The current study, conducted in the Ziway–Shala lakes basin, indicates that the F content exceeds the permissible limit for drinking prescribed by the World Health Organization (WHO; 1.5 mg/l) in many important wells (up to 20 mg/l), with even more extreme F concentration in hot springs and alkaline lakes (up to 97 and 384 mg/l respectively). The groundwater and surface water from the highlands, typically characterized by low total dissolved solids (TDS) and Ca (Mg)–HCO3 hydrochemical facies, do not show high F content. The subsequent interaction of these waters with the various rocks of the rift valley induces a general increase of the TDS, and a variation of the chemical signature towards Na–HCO3 compositions, with a parallel enrichment of F. The interacting matrixes are mainly rhyolites consisting of volcanic glass and only rare F-bearing accessory minerals (such as alkali amphibole). Comparing the abundance and the composition of the glassy groundmass with other mineral phases, it appears that the former stores most of the total F budget. This glassy material is extremely reactive, and its weathering products (i.e. fluvio/volcano-lacustrine sediments) further concentrate the fluoride. The interaction of these ‘‘weathered/reworked’’ volcanic products with water and carbon dioxide at high pH causes the release of fluoride into the interacting water. This mainly occurs by a process of base-exchange softening with the neo-formed clay minerals (i.e. Ca–Mg uptake by the aquifer matrix, with release of Na into the groundwater). This is plausibly the main enrichment mechanism that explains the high F content of the local groundwater, as evidenced by positive correlation between F, pH, and Na, and inverse correlation between F and Ca (Mg). Saturation indices (SI) have been calculated (using PHREEQC-2) for the different water groups, highlighting that the studied waters are undersaturated in fluorite. In these conditions, fluoride cannot precipitate as CaF2, and so mobilizes freely without forming other complexes. These results have important implications for the development of new exploitation strategies and accurate planning of new drilling sites