Seasonal and spatial dynamics of organic micropollutants in a Mediterranean river: implications for environmental risk assessment.

This work represents the first integrated assessment in the Litani River Basin, Lebanon's longest river, which flows into the Mediterranean Sea, combining multi-class organic micropollutant occurrence, specifically pharmaceuticals and aromatic hydrocarbons, in both surface water and sediment with a quantitative environmental risk assessment. Surface water and sediment samples were collected across consecutive dry (summer) and wet (winter) seasons from nine sites along the Upper Litani River Basin and analyzed using advanced analytical methods. Among the 27 tested pharmaceuticals, ibuprofen (4.7 µg/L), caffeine (23.6 µg/L), telmisartan (833.5 ng/L), carbamazepine (658.5 ng/L), gemfibrozil (71.0 ng/L), mefenamic acid (64.7 ng/L), and diphenhydramine (65.9 ng/L) were the most frequently detected, with some reaching notably high concentrations in the µg/L range in surface water. Sediments revealed ubiquitous contamination by ibuprofen, telmisartan, climbazole, diphenhydramine, and azithromycin. Spatial profiling identified pollution hotspots closely linked to the discharge of untreated municipal sewage, and hospital and industrial effluents. Environmental risk assessment results highlighted substantial ecological risks posed by telmisartan, ibuprofen, diclofenac, climbazole, and caffeine. Among the aromatic hydrocarbons, xylene, ethylbenzene, and benzene were frequently detected in the sediments at ecologically hazardous concentrations, while naphthalene and benzo[a]pyrene exhibited seasonal and spatial variability in occurrence and risk potential. The findings from this study contribute to the state of knowledge of pollution levels of emerging contaminants in a major Mediterranean river and permit to inform and guide future mitigation and management strategies. The environmental risk assessment applied in this study enabled the translation of measured concentrations into ecologically meaningful indicators allowing the identification of priority contaminants and high-risk locations.