Assessment of the anthropogenic fluoride export in Addis Ababa urban environment (Ethiopia)

Protection of natural waters against excess of fluoride is a priority in the Middle Ethiopian Rift where high concentrations of fluoride occur in groundwater, lakes and hot springs. In recent years, a growing attention has been paid to geogenic sources of fluoride, while anthropogenic sources have been completely disregarded. Ethiopian people are subject to high levels of fluoride intake via food or drinks, resulting in elevated concentrations of fluoride in urine and subsequently in the human slurry waste. In Addis Ababa, 3 millions of people live without a suitable sewage waste collection/treatment facility and the superficial water system of the city often receives untreated domestic and municipal effluents. In this study, the impact of fluoride-rich human slurry on surface waters quality in Addis Ababa was evaluated. Physical-chemical and bacteriological assessments of rivers and shallow groundwater samples were performed. Several samples displayed critical levels of fluoride and faecal coliforms bacteria in the north-western part of the city. When uncontaminated fresh water flowing from the highland travels through the city, it experiences a rapid deterioration because of the interaction with untreated sewage outlets. This was clearly inferred by the combined analysis of water stable isotopes, fluoride and faecal coliforms bacteria. The methodological results of this study could be used to distinguish anthropogenic from geogenic sources of fluoride in urban environments of developing countries, which are often affected by multiple sources of fluoride.