Effects of polystyrene micro/nanoplastics on the feeding behavior, oxidative stress, and accumulation of diarrhetic shellfish toxins in the mussel Mytilus unguiculatus.

Polystyrene micro/nanoplastics (PS-MNPs) and microalgal toxins are widely distributed in marine environments. However, the impact of MNPs exposure on the accumulation of dissolved microalgal toxins in cultivated shellfish remains poorly understood. This study investigated the effects of PS-MNPs on the physiological status and diarrhetic shellfish toxins (DSTs) accumulation in the filter-feeding bivalve Mytilus unguiculatus. Results demonstrated that exposure to PS-MNPs significantly altered the grazing rates, condition index, and oxidative stress responses of mussels. Specifically, MNPs at a concentration of 10 mg L⁻1 or a particle size of 1.0 µm initially promoted feeding activity, which then gradually returned to control levels. In contrast, a high concentration of smaller MNPs (0.1 µm particle size at 50 mg L⁻1) caused prolonged suppression of feeding activity. Exposure to MNPs also induced mild oxidative stress characterized by transient increases in reactive oxygen species (ROS) levels in muscle tissue, while ROS concentrations in the digestive gland remained largely unchanged. Furthermore, MNPs significantly affected the accumulation of DSTs, including okadaic acid (OA) and dinophysistoxin-1 (DTX1), particularly enhancing DTX1 accumulation under high MNPs loads. These changes in toxin accumulation highlight the potential for MNPs to affect both ecosystem health and seafood safety. Although the direct threat posed by MNPs at current environmental concentrations appears limited, their capacity to alter toxin accumulation and interact with other stressors, necessitates a more nuanced risk assessment framework. Future efforts should aim to understand these complex interactions and develop effective monitoring and mitigation strategies to protect marine ecosystems and ensure food safety.