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Microplastics (< 5 mm) are present all over the world, causing ecological and economic problems. Coastal and marine areas have gained the attention of researchers in recent years as they are the end point of most of these particles, their presence being evidenced in the most remote points of the ocean and also in hundreds of species that inhabit these ecosystems, which can cause serious physiological damage to the most different groups and also ecological risks, by the transfer of plastic particles through the food chain. In addition, microplastics can also reach human populations, since most groups of aquatic organisms are used as food around the world. Bivalves are a group of organisms widely studied in this type of research, mainly for three reasons: (1) their filtering and low mobility way of life; (2) ecological relevance, being an important link between primary producers and other levels of the food chain; and (3) high economic importance, representing a considerable part of global marine production. Thus, the present thesis aimed to verify the concentrations of microplastics in bivalve species of economic importance in the southeastern region of Brazil. First, studies that aimed to identify microplastics in bivalves collected in the environment were reviewed, in order to verify the main global trends. Next, for the characterization of microplastics in bivalves in the state of Espírito Santo, mussels were collected in natural and aquaculture sites, mussel, oyster and scallop species were purchased in markets and the amounts of particles retained by the Perna perna species in an experimental approach were analyzed. It was possible to identify that all bivalve’s species studied contained microplastics, regardless of whether they were collected in the environment or bought in markets. In addition, through the experiment it was possible to identify that the retention of particles may depend on the thickness of the microplastics, something unprecedented in this type of research. This thesis showed the importance of this type of evaluation and the need to continue studies that aim to identify the concentrations of microplastics in this group of organisms, due to their ecological importance and also because they are a source of particles for humans, thus causing damage to aquatic ecosystems and also to the health of populations that feed on these organisms.