Evaluating the Single and Combined Effects of BMDM and PS Microplastics on Chlorella sp.: Physiological and Transcriptomic Insights

In the environment, the coexistence of microplastics (MPs) with other pollutants may either enhance or reduce the toxicity of MPs themselves or the co-occurring pollutants toward microalgae. This phenomenon is particularly notable when MPs interact with emerging pollutants, such as ultraviolet absorbers. This study investigates the single and combined exposure effects of ultraviolet absorber (Butyl methoxydibenzoylmethane, BMDM, 50 μg/L) and MPs (Polystyrene, PS, 10 mg/L, d = 1 μm) on <i>Chlorella</i> sp. with a stress duration of 7 days. The results showed that cell density, chlorophyll a (Chla) concentration, and physical properties of cell surface integrity were higher in the combined stress group compared to the BMDM single stress group. Furthermore, transcriptome sequencing analysis revealed that the number of differentially expressed genes (DEGs) in the combined exposure group (885 DEGs) was lower than in the single exposure groups (BMDM: 1870 DEGs and PS: 9109 DEGs). Transcriptomic profiling indicated that individual stressors of BMDM and PS disrupted 113 and 123 pathways, respectively, predominantly associated with protein synthesis and energy metabolism. Conversely, combined exposure significantly enriched 86 pathways, including ribosome function and oxidative phosphorylation, thereby manifesting an antagonistic effect. This study provides new insights into the effects of BMDM and PS on <i>Chlorella</i> sp. and offers valuable information for the risk assessment of multiple pollutants.