Effects of Emerging Pollutant Mixtures: Assessing the Impact of Caffeine and Ionic Liquid on Cyanobacteria and Diatom Species

Abstract

The presence of micropollutants poses significant environmental concerns due to their potential toxicity in aquatic ecosystems. However, the effects of micropollutant mixtures, particularly synergistic or antagonistic interactions, remain underexplored. The study employs nonstandard biomarkers to investigate the interaction effects of binary mixtures of caffeine, a prevalent anthropogenic contaminant, and the imidazolium-based ionic liquid IMI-8C(CN)₃, a representative of a new group of micropollutants, on two photosynthetic microorganisms: the marine diatom Phaeodactylum tricornutum and the freshwater/brackish cyanobacterium Microcystis aeruginosa, under chronic exposure conditions. Key findings reveal photoprotective responses in both microorganisms, including enhanced non-photochemical quenching (NPQ), activation of the xanthophyll cycle, and photosynthetic activity disruption as indicated by altered chlorophyll a fluorescence parameters. Environmentally relevant caffeine concentration (10 µg/l) significantly increased the DI₀/RC (dissipation of photochemical energy per reaction center) parameter, indicating heightened energy dissipation as a stress response. Mixture toxicity predictions using concentration addition (CA) and independent action (IA) models showed predominantly antagonistic interactions. These findings underscore the importance of investigating combined micropollutant effects to better understand their ecological impacts, particularly in understudied marine ecosystems. Further research is essential to inform regulatory policies and mitigate the risks posed by emerging pollutants.