Publication date: Dec 06, 2024

The COVID-19 pandemic has increased the co-occurrence of quaternary ammonium compounds (QACs) and antidepressants in aquatic environments. Microalgae are sustainable and cost-effective candidates for removing emerging pollutants. QACs have a robust ability to adsorb on cell surface and alter membrane permeability, but little is known about the influence of QACs on microalgal bioremediation of co-existing pollutants like antidepressants. In this study, the influence mechanisms of didecyldimethylammonium chloride (DDAC) on the removal of fluoxetine (FLX) by C. pyrenoidosa were explored. The results showed that C. pyrenoidosa exhibited high removal efficiency of single FLX (75. 23 %-88. 65 %) mainly through biodegradation (57. 12 %-67. 19 %). However, the coexisting medium and high concentrations of DDAC considerably decreased the biodegradation amount (10. 50 %-33. 30 %) and removal efficiency (29. 47 %-52. 89 %) of FLX by C. pyrenoidosa. In contrast, the presence of DDAC increased extracellular and intracellular FLX concentrations due to the enhanced extracellular polymeric substance content, cell surface hydrophobicity, and cell membrane permeability. Meanwhile, DDAC showed synergistic effects with FLX on microalgal growth through exacerbated oxidative damage and photosynthesis inhibition. Moreover, transcriptomics revealed that the dysregulations of key genes involved in the DNA replication and repair, ribosome biogenesis, photosynthesis-antenna proteins, peroxisomes, and glutathione metabolism pathways were important molecular mechanisms underlying the synergistic toxicity. Furthermore, the principal component analysis suggested that the enhancement of extracellular and intracellular FLX concentrations induced by the coexistence of DDAC increased the mixture’s toxicity, resulting in the decreased biodegradation amount and ultimately a reduction in the removal efficiency of FLX. Our results highlight the significance of recognizing the influence of QACs on microalgal remediation and ecological risks of antidepressants.

Semantics

Original Article