Abstract:From 1990 to 2020, red tides of Alexandrium tamarense—which produces paralytic shellfish toxins (PSTs)—were monitored in the waters of the Nanhuangcheng Island Sea area in Changdao County, China, with a cumulative affected area of 2.37 km2. PST-producing Gymnodinium spp. were also detected in the Yantai Sishili Bay and Weihai coastal waters, with a cumulative affected area of 48.88 km2. In 2020, lipophilic shellfish toxin (LST)-producing Dinophysis spp. were detected in the North Yellow Sea. In 2021, amnesic shellfish toxin (AST)-producing Pseudo-nitzschia was detected in small quantities in the typical Patinopecten yessoensis culture area of Zhangzi Island and Yantai Sishili Bay in the North Yellow Sea. PSTs, LSTs, ASTs, and their toxin-producing algae are widely found in the Yellow and Bohai seas. Shellfish and phytoplankton samples were collected from waters off Changdao Island from June to October 2023, and screened for 29 shellfish toxins, including 14 PSTs, 14 LSTs, and domoic acid (DA). PSTs and LSTs were detected throughout the survey period, whereas DA was not. The main detected components of PSTs were GTX1, GTX2/3, C1, and C2, while LSTs were detected less frequently and at low concentration, and PTX2 was detected only in the Chlamys farreri sample of June (2.46 μg PTX2eq./kg SM), which is much lower than the current EU safety limit of 160 μg PTX2eq./kg SM. As the risks of DA and LSTs in the sea area around Changdao Island were low in this study, we focused on analyzing the pollution characteristics and potential sources of PSTs. None of the PSTs detected in the shellfish samples from June to October exceeded the EFSA safety limits. The GTX2, GTX5, C1, and C2 of PST components were detected, with GTX2 being the highest detection rate of 53.3 %, and C1 being the maximum concentration of 179 μg/kg. Among the shellfish samples collected during the entire survey period, PSTs were not detected in Mytilus galloprovincialis and Crassostrea gigas in June and August, and in all shellfish samples collected in July. PSTs were detected in Chlamys farreri in September at 478 μg/kg, the highest concentration among all the months, followed by Chlamys farreri in October at 221 μg/kg. Among the phytoplankton samples, PSTs were detected at stations S2, S3, and S4 in September and at stations S1 and S2 in October, with relatively low concentrations of PSTs. PSTs were not detected in other months or stations. The highest level of PSTs in phytoplankton was 23.92 μg/L at station S2 in September, and the average level was 20.7 μg/L. The average PST level in October was 2.67 μg/L. In October, only two components were detected at stations S1 and S2—dcGTX3 and GTX4. In September, PSTs were more abundant, with seven components: GTX1/4, GTX2, dcGTX3, GTX5, and C1/2. High-throughput analysis of phytoplankton revealed the presence of eight Alexandrium spp. with the highest abundance of Alexandrium spp. in September. Alexandrium spp. cysts were found in the sediments in September, which suggests that the toxicity-producing algae of PSTs in the Changdao Island waters in the present study may be Alexandrium spp. Although PST concentrations in the samples off Changdao Island were relatively low compared to other regions in the Yellow Sea and Bohai Sea, there is still a potential risk of PST contamination. To guarantee the quality and safety of aquatic products, monitoring of shellfish toxins should be strengthened to provide basic data for the early warning of toxin contamination in aquaculture areas.
