UV-B radiation reduced the susceptibility of Brachionus plicatilis to microplastics by decreasing their toxic effects and bioaccumulation

Microplastics (MPs) have been proved to threaten zooplankton by direct damage or bioaccumulation. Due to living in the upper mixed layer of ocean, marine zooplankton frequently expose to ultraviolet (UV) radiation stress, while how UV radiation change the effects of MPs on marine zooplankton is lack of study. In this study, we targeted on the floating MPs-polymethyl methacrylate (PMMA) MPs and the model marine zooplankton Brachionus plicatilis, comprehensively investigated the joint effects of PMMA MPs (1 μm) and UV-B radiation (at natural intensity) on B. plicatilis, referring to toxicities and transfer along the Chlorella sp.-B. plicatilis food chain. An antagonistic effect between PMMA MPs and UV-B radiation was observed in B. plicatilis. Further physiological-biochemical and transcriptomic analysis indicated that the antagonistic effect was attributed to the prolonged lifespan, decreased filtering and feeding rates, enhanced antioxidant abilities and activated apoptotic processes caused by UV-B radiation. Additionally, B. plicatilis could bioaccumulate PMMA MPs both from the water phase and food chain transfer. UV-B radiation exposure inhibited the bioaccumulation of PMMA MPs by B. plicatilis, especially for those from water phase, accompanied with the decreased bioconcentration factor (BCF) and biomagnification factor (BMF) values. This study elucidated the joint effects and mechanisms of PMMA MPs and UV-B radiation on B. plicatilis, enhancing the understanding of how MPs affect the planktonic food web in the complex natural environment, with significant ecological implications.