Origin of Fluoride and Arsenic in the Main Ethiopian Rift Waters

Gianluca Bianchini,Tewodros Rango Godebo,Claudio Natali,Alessandro Rasini,Gian Marco Salani,Chiara Marchina,Valentina Brombin

doi:10.3390/min10050453

Gianluca Bianchini, Tewodros Rango Godebo + Show 5 more

Open Access

https://doi.org/10.3390/min10050453

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Abstract

In the Main Ethiopian Rift (MER) area, rural populations often use water that exceeds the World Health Organization thresholds for fluoride (F–) and arsenic (As), two elements that are hazardous for human health. In this study, twenty-nine water samples were collected from lakes and hot and cold springs in southern MER to investigate source(s) and health-risk of the F– and As contamination. According to major ion and trace element analyses, only cold spring water is safe for consumption, whereas hot spring water is the most contaminated. Leaching tests performed with the MER rhyolitic volcanic rocks and their weathered products (fluvio-lacustrine sediments) demonstrate that the main cause of the F– and As release is geogenic, i.e., not related to anthropogenic activities. The weathering of volcanic glass and minerals (apatites, clays, hydro-oxides) by CO2-bearing alkaline water induces the mobilisation of F– and As from solid to liquid phase. This process is particularly fast, when fluvio-lacustrine sediments are involved, and can be further enhanced by hot groundwater leaching. This study, investigating the distribution, sources, and mechanisms of F– and As release in MER water, could be of interest also for other sectors of the East African Rift and other similar volcano-tectonic settings.

Highlights

Groundwater is the major source of drinking water for over half of the global population [1]; its quality can be compromised by natural geogenic contaminants such as fluoride (F– )and arsenic (As)
The analyses presented in this work were performed in the same analytical session as other river water samples in which the As concentration was below the detection limit [45], indicating that the significant concentration of As measured in the Main Ethiopian Rift (MER) water was not related to systematic analytical interference
Lake water samples exhibited medium temperatures, alkaline pH values, and medium salinity levels (ECAwasa L. : 810 μS/cm; ECAbaya L. : 970 μS/cm; TDSAwasa L. : mg/L; TDSAbaya L. : 799 mg/L), with the exception of Chamo Lake water, which had the highest level of salinity (EC: 1640 μS/cm; total dissolved solids (TDS): 1225 mg/L)

Summary

Introduction

Groundwater is the major source of drinking water for over half of the global population [1]; its quality can be compromised by natural geogenic contaminants such as fluoride (F– )and arsenic (As). Groundwater is the major source of drinking water for over half of the global population [1]; its quality can be compromised by natural geogenic contaminants such as fluoride (F– ). Groundwater interacts with F– and As-enriched host aquifers, which releases these elements in levels that are hazardous for the human health [2]. The guideline values established by the World Health Organization (WHO) for F– and As in drinking water are. F– and As contamination represents a serious health issue, especially in rural communities that receive water from groundwater wells without testing for the presence of toxic contaminants (e.g., Bangladesh and India [5,6,7]).

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