Dissolved organic matter quality and emerging pollutants in coastal Baltic Sea waters: Insights into photodegradation

Coastal seas represent critical interfaces under intense anthropogenic pressure, at the center of the land-ocean continuum. These biogeochemically dynamic environments receive high loads of pollutants and natural organic matter. The fate of these pollutants is strongly impacted by photodegradation, a process potentially mediated by dissolved organic matter (DOM). In a laboratory-scale irradiation experiment, we examined pollutant degradation in coastal Baltic Sea water and in treatments amended with solid-phase-extracted organic matter from a marine and a terrestrial source with the potential to contribute to the study site, over 68 days. Investigated contaminants of emerging concern (CEC) included pharmaceuticals, estrogens, and a UV-filter. Their concentrations were monitored over time via LC-MS/MS. DOM dynamics and composition were assessed using absorbance and fluorescence measurements, with subsequent parallel factor analysis (PARAFAC). Our results corroborate the importance of both direct and indirect photochemical removal of CEC in coastal systems. Observed losses ranged from complete, DOM-source-independent removal of diclofenac within hours to minimal removal of the UV-filter and caffeine. All studied estrogens showed consistently slower degradation in the presence of terrestrial DOM, whereas no differences in marine and terrestrial matrices were observed for carbamazepine and sulfamethoxazole. The complex DOM composition-specific and pollutant-specific effects highlight the need for well-differentiated approaches to assess the potential fates and environmental implications of the thousands of CEC released into aquatic and marine environments.