Bioaccumulation, microbiome composition and immunity, and epigenetic signatures associated with exposure to spherical, fibrous, and fragmented microplastics in the mussel Mytilus galloprovincialis

Abstract

Microplastic (MP) pollution has become a major global concern due to the widespread use and discharge of plastics into the environment. However, very few studies have assessed the potential variations in the toxicity of MPs according to their shape and size. Therefore, our study sought to identify the biotoxic effects of spherical, fiber-shaped, and fragment-shaped polyethylene terephthalate MPs of different sizes at different concentrations on the Mediterranean mussel Mytilus galloprovincialis. The survival rate after exposure to small-sized MPs was lower than that observed for the larger type MPs. Bioaccumulation of MPs was different depending on the exposure periods and MP shapes. Interestingly, the fiber-shaped MPs underwent morphological modifications in the mussel body upon uptake. MP exposure also increased the global DNA methylation levels (i.e., an epigenetic signature), expression of the microbiota immunity-related toll-like receptor gene, and alteration of the gut microbial composition in the mussel. These findings indicated that MPs of different shapes and sizes at different concentrations can alter the bioaccumulation sensitivity of mussels according to the exposure periods, and the balance of gut immunity and epigenetic process. Furthermore, our results demonstrated that MPs of different shapes, particularly fiber types, can undergo morphological modification in mussel tissues, thus posing a hazardous threat. Plastic wastes are globally recognized as the fastest-growing source of pollution worldwide and are therefore an environmental concern of high priority. Microplastics (MPs) in aquatic environments occur in various sizes and exhibit different surface physicochemical characteristics and shapes. In addition, MP ingestion can have severe effects in marine biota. In the study, biotoxic effects of MPs with different shapes, sizes, and concentrations were revealed in the survival, MP bioaccumulation, DNA methylation levels, and gut microbiota and immunity of the M. galloprovincialis mussel. We propose the hazardous threats of fiber type MPs with morphological modification and a high epigenetic signature.

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