Differential effects of polyvinyl chloride microplastics and kaolin particles on gut immunity of mussels at environmental concentrations

Both microplastics (MPs) and kaolin are marine suspended particles capable of influencing the physiology of bivalve mollusks. However, the current research on MPs lacks the analysis of their own physical and chemical toxicity, and the comparative study of the toxicity of microplastics and natural suspended particles (NSPs) in aquatic environment. In this work, three experiments are layered, with Experiment 1 directly comparing polyvinyl chloride MPs (PVC MPs) and kaolin and showing that MPs have greater deleterious effects on thick-shelled mussels than kaolin, with the exception of physical damage and effects on gut microorganisms. As the presence or absence of chemicals may be the main difference between MPs and kaolin, in Experiment 2 the toxicity drivers of PVC MPs itself were investigated, demonstrating that the chemicals in MPs are indeed toxic and that the harmful effects of MPs on mussels may be due to the superposition of their own physical and chemical toxicity. Finally, in Experiment 3 mussels were exposed to the chemicals in PVC MPs and kaolin in a composite and found that the toxicity of the composite exposure was greater than that of the single exposure to kaolin, suggesting that the chemicals may be the main factor contributing to the difference in toxicity between PVC MPs and kaolin. In conclusion, this work addresses the lack of a natural particle control group in current studies of MPs, confirms that the toxicity drivers of MPs are due to both physical and chemical factors, highlights the role of NSPs in the environment, and provides new insights for evaluating the toxic effects of MPs in the natural marine environment.