Occurrence and transport of selected micropollutants in surface water and groundwater under varying dynamic condition : application on the Qachqouch karst catchment- Lebanon

Abstract

The occurrence of specific micropollutants (MPs), indicators of domestic and hospital wastewater, was investigated in this specific River based on two sampling campaigns under varying flow conditions. The MPs characterized by a high frequency of occurrence; Acesulfame-K (ACE-K), Ibuprofen (IBU), Gemfibrozil (GEM), Nonylphenol (NON), and Iohexol (IOX) were highly reflective of wastewater discharged in ephemeral streams and tributaries, as well as specific point sources such as farms and hospital effluents. A mixing model based on chloride mass fluxes allows the quantification of the percentage of untreated wastewater effluents in inflowing water from river tributaries, which varied between 0.7-99 percent and 5.0-10 percent in low flow and high flow respectively. The frequency of occurrence of MPs is related to the volume of wastewater input, extent of river dilution, persistence of the MPs, and type of point source contamination on the River. Relationships were established between MPs such as IBU and ACE-K, indicating their co-existence in highly consumed generic medicine and their suitability as wastewater co-tracers. Multiple artificial tracer experiments showed that Nahr El Kalb River is connected to the Qachqouch spring through a point source sinking stream. A detailed analysis of selected spring responses' chemograph and hydrograph following a multi precipitation event shows that three of the tracked MPs, especially ACE-K, and to the exception of IOX, can be used as specific indicators for point source domestic wastewater in karst systems. They have revealed to be persistent, source specific, conservative, and highly correlated with in-situ parameters easily measurable at the spring (chloride and turbidity). Even if the selected MPs are found in the system during low flow periods, they are mostly transported to the spring through fast flow pathways from flushed wastewater with surface water or flood rainwater. The highest mass inflow of ACE-K, IOX and GEM originated from a sinking stream, while SUC infiltrated exclusive