Interactions between the co-contamination system of oxcarbazepine-polypropylene microplastics and Chlorella sp. FACHB-9: Toxic effects and biodegradation.

The co-contamination of microplastics and pharmaceutical pollutants has attracted increasing attention. However, studies on the joint toxicity of pollutants on organisms in aquatic ecosystems are still lacking. This study aimed to investigate the joint toxicity of oxcarbazepine (OXC, 30 mg/L) and polypropylene microplastics (PP-MPs, 500 mg/L and particle size of 180 μm) microplastics on microalgae (Chlorella sp. FACHB-9) and the biodegradation of OXC by strain FACHB-9. Compared to the single OXC exposure, the cell density of microalgae was decreased by 38.93% in OXC/PP-MPs co-contamination system, with enhanced oxidative stress and decreased photosynthetic efficiency. Transcriptomic analyses indicated that photosynthetic pathways and TCA cycle pathways were significantly inhibited, while DNA damage repair pathways were up regulated in microalgae co-exposed to OXC and PP-MPs. Moreover, strain FACHB-9 showed a remarkable degradation effect (91.61% and 86.27%) on OXC in single and mixture group, respectively. These findings significantly expanded the existing knowledge on the joint toxicity of pollutants on microalgae, indicating prospective promise of microalgae for the bioremediation of polluted aquatic environments.