Paralytic Shellfish Toxins in Coastal Waters of Changdao Island (China): Toxin Profiles, Potential Producers, and Environmental Conditions.

In recent decades, there have been frequent occurrences of paralytic shellfish toxin (PST) contamination in the Yellow and Bohai Seas, China. The waters around Changdao Island, situated at the convergence of these two seas, have suffered harmful algal blooms of Alexandrium spp., indicating a potential risk of PST contamination in shellfish. However, a systematic investigation and assessment of PSTs in this area is still lacking. The presence of PSTs in plankton concentrates and shellfish in coastal areas of Changdao Island was monitored from April to October 2022, using liquid chromatography-tandem mass spectrometry. The potential toxin-producing microalgae were analyzed, as were the environmental conditions associated with their occurrence. The highest levels of PSTs in plankton concentrates and shellfish were both observed in September, reaching levels of 105.8 ng STXeq./L and 114.7 μg STXeq./kg, respectively. The main analogues were C1, C2, and GTX1-4. High-throughput analysis of the plankton concentrates identified eight species of Alexandrium, which are potential producers of PSTs. Sediment samples also revealed the presence of permanent cysts of Alexandrium. This research represents a significant advance in our understanding of the distribution and hypothetical sources of PSTs in the coastal waters of Changdao Island.