Characterization of Emerging Organic Contaminants in the Awash River Basin
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Date
2025-04
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Addis Ababa University
Abstract
Emerging Organic Contaminants (EOCs) affecting freshwater quality have become a rising concern with adverse effects on human health and the environment. In this research, we characterized EOCs in the water supply sources (boreholes, surface water reservoirs, and river) and tap water in upper and middle Awash River sub-basins. Awash River basin is a rapidly growing and highly utilized and industrialized river basin in central Ethiopia where both surface and groundwater are used to supply major settlements and industries. Characterization of the EOCs was supplemented by hydro-chemical analysis (major anions, cations, and heavy metals). Environmental isotopes (2H, 18O, and 222Rn) were applied to further investigate the exchange of contaminants between surface and groundwater supply sources and groundwater recharge source. Environmental tracers and EC also used as a tool for backtracking the water source, estimating pipe water residence time and monitoring the instability of water quality in the water pipe network. Characterization of groundwater flow system using vertical profiling of EC and temperature data is used to identify the recharge sources of the shallow and deep groundwater system with respect to fate of contaminants along the depth of the aquifer system and along the Awash River flow direction. More than 100 EOCs are identified in all water supply sources and tap water. The EOCs are sourced from agricultural applications (Pesticides, herbicides, veterinary drugs, and plant growth regulators), urban (artificial sweeteners, pharmaceuticals, personal care products), and industries (surfactants, flame retardants, plasticizers, and volatile solvents). Based on the analysis of hydro-chemical and environmental tracers, the deep groundwater system is relatively safer from contamination caused by human activities than the river and the shallow groundwater system. Due to connectivity and the recharge source, the shallow wells are noticeably affected by urban, industrial, and agricultural pollutants discharged into the Awash River. Attributed to the different contaminant sources, distinct variations in terms of compound types were observed at different locations. Upstream water supply sources are dominated by urban and industrial contaminants while compounds from agricultural applications dominate downstream. Artificial infrastructures (i.e. Aba Samuel Lake, Koka Dam) seem to serve as attenuation points for urban and industrial compounds sourced from upstream. Characterization of EOCs showed new contaminant loads in the water supply sources, which haven’t been tested before. The new contaminant loads in the supply sources, with potential impact on human health, necessitate the need to revisit the customary water quality test and monitoring practices. Moreover, Electrical conductivity and temperature data shows that the local recharges zones are located in highly urbanized and industrialized areas; therefore attention should be given to protect groundwater resources from anthropogenic contamination.
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Keywords
Emerging Organic Contaminants, Groundwater Flow, Isotopes, Electrical Conductivity, Awash River Basin