Suspected Microplastics in Blue Crab (Callinectes sapidus) from the Po Delta Coastal Lagoons (Northern Adriatic Sea, Italy): A First Assessment of Occurrence in Edible and Non-Edible Tissues

The blue crab (Callinectes sapidus) is an invasive alien species of growing ecological and economic concern in the Mediterranean Sea, including the Po Delta (Northern Adriatic, Italy), where it has caused significant damage to bivalve aquaculture since 2023. As a benthic omnivore, it is particularly exposed to microplastic (MP) pollution, and has been proposed as a sentinel species for coastal contamination monitoring. This study investigated the occurrence and distribution of suspected microplastics (MPs) in three tissues—digestive tract, gills, and muscle—of 96 C. sapidus specimens collected from Sacca degli Scardovari lagoon in August 2023. Microplastic isolation was performed via hydrogen peroxide oxidative digestion, vacuum filtration, and optical microscopy. Strict contamination controls were applied throughout. Suspected MPs were detected in the digestive tract of 11.5% of specimens and in the gills of 3.1%; all detected particles were fibrous (MFs). No suspected MPs were detected in any muscle tissue sample. All values are prevalence figures obtained by presence/absence screening and represent conservative minimum estimates, given the 8 µm lower size boundary of the filtration step and the absence of spectroscopic confirmation. Blue fibres were the predominant particle type across all positive samples. No statistically significant associations were found between the occurrence of suspected MPs and sex or weight class. These findings provide baseline data for MP monitoring in the Northern Adriatic and suggest the potential utility of C. sapidus as a sentinel species for coastal plastic pollution, a role that requires validation across sites and seasons.