Characterizing occurrence of emerging organic contaminants in Dinaric karst catchment of Jadro and Žrnovnica springs, Croatia

The occurrence of emerging organic contaminants (EOCs) was investigated in vulnerable Dinaric karst catchment of Jadro and Žrnovnica springs in Croatia, under varying flow conditions and across three different water resource types (groundwater, springs, and surface water). The maximal EOCs concentration in both springs were observed following autumn recharge events, while during peak discharge no detection above the limits of detection (LOD) was recorded due to dilution process. Contrarily to springs, groundwater from deep borehole exhibited highest total EOCs concentration under low flow conditions, underscoring the considerable karst aquifer vulnerability and its oligotrophic nature. The peak EOCs concentration in karstic Cetina River coincided with the river's lowest discharge. The highest mass flux of 1013 g/day was determined for very mobile pharmaceutical metformin detected in Cetina. The presence of potentially persistent to very persistent compounds, like DEET and 1H-benzotriazole, which exhibited highest detection frequencies across all sampling sites, was observed in association with varying hydrological conditions. Hypotheses regarding the occurrence of identified EOCs include surface contamination infiltrating directly through ponors and highly karstified areas, potential persistence in the epikarst and aquifer matrix, and site-specific contamination sources for compounds such as 1H-benzotriazole, gabapentin, and ketoprofen found in groundwater. To evaluate the risk of inadvertent human exposure to EOCs across various age groups, we utilized measured spring concentrations and calculated drinking water equivalent levels (DWEL), which ranged from 1.4 μg/L for cotinine to 503 mg/L for sucralose, both detected in Jadro spring. Although EOCs concentrations in ng/L are unlikely to pose a significant risk to healthy population, long-term exposure to EOCs mixture remains unknown. Given scarcity of research on EOCs in karst environments on both global and national levels, our study enhances comprehension of their occurrence and behaviour across different karst water resources that hold crucial importance for drinking water supply in regions like Dinarides.