Marine bivalves have a wide distribution and play vital roles regarding the ecosystem structure and functioning. Some of these species are highly appreciated by humans and have an important commercial value. To meet the ever-growing requirement for seafood resources, including marine bivalves, aquaculture production has expanded worldwide over the past few decades, and is now responsible for producing 92% of the total marine bivalves available for human consumption. In Portugal, marine bivalves are produced in aquacultures at several transitional waters systems, including the Ria de Aveiro coastal lagoon. Despite being ideal sites for bivalve production, these systems are highly impacted by a vast number of pollutants, including microplastics, that may be ingested or absorbed and cause negative impacts in the marine biota, influencing their growth, survival and biochemical composition. Regarding this major concern, it is crucial to understand if microplastics are in the tissues of marine bivalves that are being produced in aquacultures for human consumption, as well as in its surroundings, i.e. in the water and sediment surfaces. Therefore, this on-going study aims to address the occurrence and seasonal variation of microplastics in different tissues (muscle tissue, digestive gland, gills, and remaining visceral mass) of the marine commercial bivalve species Crassostrea gigas and Ruditapes philippinarum produced in a Portuguese aquaculture located in the Ria de Aveiro coastal lagoon and in the surrounding environmental matrices (water and sediment surfaces). The preliminary results reveal that the microplastics most abundant in the water surface of the aquaculture tanks are fibers, films and beads. It is expected, to find similar microplastics in the sediment surface of the aquaculture tanks, as well as in the tissues from the bivalves destined for human consumption.