Toxic effects on ciliates under nano-/micro-plastics coexist with silver nanoparticles

Owing to the degradation of plastics, microplastics (MPs) and nanoplastics (NPs) have remained the focus of global attention. Silver nanoparticles (AgNPs) could adversely affect marine organisms due to their broad application. So far, the combined effects of MPs/NPs (strong adsorbents) with AgNPs on marine organisms are scant. Thus, four sizes polystyrene beads (80 nm, 220 nm, 1.07 µm, and 2.14 µm) combined with AgNPs (30 nm) were assessed using ciliated protozoa Uronema marinum. Results showed that MPs/NPs dramatically decrease the abundance, biovolume, and carbon biomass of U. marinum. And, exposure could cause changes of antioxidant enzyme activity and antioxidant content on U. marinum. The combined toxicity of MPs/NPs with AgNPs to ciliates showed an enhanced effect compared to exposure alone. Additionally, the negative effects under exposure of NPs plus AgNPs were more significant than those of MPs plus AgNPs. Transcriptome sequencing showed that co-exposure could affect the energy metabolism and lipid metabolism of ciliates, even cause DNA and protein damage. Our study provided a novel insight and first-hand basic data for the understanding of combined toxicity of MPs /NPs with AgNPs on the basic trophic level ciliated protozoa in marine ecosystems. The continuous degradation of plastics has resulted in an increasing of micro-/nano-plastics in the environment. Meanwhile, in the natural environment where various pollutants coexist, micro-/nano- plastics becomes the carrier of other pollutants (e.g., heavy metals) due to the high specific surface area and hydrophobic properties, which cause more significant negative effects on marine organisms. This work will enhance our understanding of the combined toxicity of micro-/nano-plastics and silver nanoparticles (one of the metal nanoparticles widely commercialized) to marine organisms, and suggest that more attention should be paid to the studies of combined toxicity of micro-/nano-plastics and other pollutants.