Contamination status of paralytic shellfish toxins in shellfish from Southeastern China in 2017–2021

Harmful algal blooms is a widespread problem in aquatic ecosystems, in particular dinoflagellates that produce PSTs which are harmful to animal and human health. To explore the contamination status of PSTs in shellfish in the Southeastern China, a total of 2355 shellfish samples were analyzed by ultra high-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) to study the toxin profiles of the 10 PSTs collected from the southeast coast of China from 2017 to 2021. From 2355 shellfish samples, 257 were detected (10.91%), with the highest value in samples of Perna viridis. Among the six source areas in China, the samples from Fujian recorded the highest detected rate (15.28%). PSTs were found in Fuzhou, Ningde, Quanzhou, Putian, Zhangzhou, and Xiamen, with Quanzhou and Fuzhou having the highest and lowest detection rates of 15.28% and 4.23%, respectively. Saxitoxin (STX), neosaxitoxin (neoSTX), gonyautoxin (GTX1, GTX2, GTX3, GTX4), N-sulfocarbamoyl toxin (GTX5), and decarbamoyl toxin (dcSTX, dcGTX2, dcGTX3) were detected, and GTX5 and dcGTX2 were dominant. In addition, the samples containing PSTs were mostly concentrated in May to August. The study confirms the risks of PSTs to shellfish consumers in the region. It will offer a great foundation for future monitoring of marine toxins and protecting the health of seafood consumers in China. This is the first detailed evaluation of PSTs occurrences and their profiles in shellfish from the Southeastern China over a period of multiple years. 2355 mussels from China were analyzed by UPLC-MS/MS for PSTs in 2017–2021. The predominant PSTs were GTX5, neoSTX and dcGTX2. Arca granosa and Crassostyea gigas exhibited higher levels than other shellfish. Shellfish containing PSTs were mostly concentrated in May to August. Maximum detected level in shellfish was 2137.10 ug STXeq/kg.


Introduction
The widespread occurrence of harmful algal blooms producing paralytic shellfish toxins (PSTs) are a global concern for fisheries, aquaculture, and human health (WHO 2020; Chorus and Welker 2021;Shahmohamadloo et al. 2023). PSTs are naturally produced in marine systems by the neurotoxic alkaloids of dinoflagellates including the genera of Alexandrium species, Gymnodinium, and Gonuaulax spp. (Li and Persson 2021). Saxitoxins (STXs), a group of potent neurotoxins with several analogues, are produced by these cyanobacterial species. STX toxicity is initiated by blocking the voltage-gated sodium channels in excitable cells, suppressing ion permeation (Smith et al. 2019), and resulting in a series of poisoning symptoms including limb muscle paralysis, headache, salivation, and even asphyxiation and death (Woo and Bahna 2011). This group of toxins comprises a family of more than 50 analogues. According to the chemical structure differences, the most common PSTs include three groups, namely carbamate, gonyautoxins, and dicarbamoyl. Carbamate comprise saxitoxin (STX), neosaxitoxin (NEO), and gonyautoxins (GTX1, GTX2, GTX3, and GTX4). Decarbamoyls include decarbamoyl-STX (dcSTX and dcNEO) and decarbamoyl- GTX (dcGTX1,dcGTX2,dcGTX3,and dcGTX4), and N-sulfocarbamoyls consist of GTX5, GTX6, and C toxins (C1, C2, C3, and C4) groups (Walker et al. 2019) (Fig. 1). Currently, regulatory testing for the presence of PSTs is a requirement in many nations, with a regulatory limit (RL) of 800 µg STXeq/kg of shellfish tissues (Dean et al. 2020).
Global incidents of PSTs mainly occur in coastal areas, especially in countries near the coastlines of the Atlantic and Pacific oceans (Arjen et al. 2010). Outbreaks of PSTs have also been reported following the consumption of toxic bivalves in coastal areas in China. Bivalves, which are filter feeding organisms, may accumulate and biotransform those compounds in their tissues during toxic algal blooms, not only causing serious harm to human health but also hindering the local economic development. Shellfish cultivation is an important industry in southeast coast of Fujian, China. Contamination by PSTs poses a potential threat to shellfish food safety in the region. However, no routine monitoring of PSTs in shellfish has been conducted so far in Fujian, southeast China. Investigation of PSTs is still quite limited and lacks a continuous and systematic monitoring. Zhou et al. (2022) monitored bivalves with high levels of PSTs in Shenzhen, China, in March and April 2019. Contamination of PSTs was monitored by Leng et al. (2014) in bivalves collected from coastal areas of Guangdong, China, in May and September. In monitoring Portuguese waters, Botelho et al. (2019) showed that levels of PSTs peaked in autumn and winter, and occasionally in summer. In June of 2017, 164 people were poisoned by consuming bivalve shellfish contaminated with PSTs in Fujian Province, southeast coast of China (Chen et al. 2018). Therefore, we hypothesized that seasonal and spatial variations would affect the levels of PSTs in bivalves in Fujian Province. To elucidate this hypothesis, the levels and composition of PSTs in shellfish samples collected from six areas along the Fujian coast were investigated, and their seasonal and spatial variation were studied.
Many approaches, involving mouse bioassay (MBA) (Long et al. 2021) and high-performance liquid chromatography with fluorescence detection (HPLC-FLD) (Keyon et al. 2014), have been developed to analyze PSTs in shellfish. The use of MBA testing has been criticized across the years for its unethical animal suffering, lack of sensitivity (may not detect all toxins at the levels required for protection of public health), and lack of specificity leading to procedural artefacts. Also, MBA cannot determine the structure and components of the toxins. HPLC-FLD requires derivatization for toxins, which are prone to introduce impurities or interferences during the derivatization process, and the operation process is also complicated. Recently, ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) has been widely and routinely applied to the monitoring of PSTs in mussels due to its high sensitivity and rapid identification of different toxin components (Huang et al. 2020;Turner et al. 2015).
This study aims to conduct UPLC-MS/MS analysis on 2355 shellfish samples comprising of six species of bivalve mollusks harvested from the waters of Fujian from 2017 to 2021 to elucidate the contamination status of the PST analogues typically seen in bivalves. Samples were analyzed using solid-phase extraction mass spectrometry to determine the individual PSTs concentrations and obtain the total PSTs content. The acquired data can facilitate the examination of the potential relationships to species type Fig. 1 The structure of PSTs and the geographical and temporal variabilities throughout the coastal waters of Fujian, China. The prevalence of 10 different PSTs (STX, neoSTX, dcSTX, dcGTX2, dcGTX3, GTX1, GTX2, GTX3, GTX4, GTX5) along the Southeastern Chinese coast was studied. For the first time in Southeast China, the toxin profiles, timing and geographical distribution of PSTs in such a large number of shellfish, have been analyzed for multiple years.

Sample collection
Representative and typical seafood markets in six cities of Fuzhou, Ningde, Quanzhou, Putian, Zhangzhou, and Xiamen in the south coastal areas were selected (Fig. 2). From 2017 to 2021, 2355 bivalve shellfish samples of six species were collected according to the seafood wholesale markets, including 630 samples of mussels (Perna viridis), 115 samples of razor clams (Sinonovaculla constricta), 133 samples of clams (Ruditapes philippinarum), 843 samples of oysters (Crassostyea gigas), 347 samples of scallops (Chlamys farreri), and 287 samples of mud clams (Arca granosa). The collected shellfish samples were placed in a cooler at − 20 °C, transported to the laboratory, and frozen before analysis and extraction.
Shellfish samples were cleaned with clean water, removing the meat from their shells, and rinsed again with Milli-Q water to remove silt from the flesh. Shellfish tissues, with meat and viscera (200 g of each batch), were removed and homogenized, placed in a kitchen blender, and then frozen at − 18 °C until extraction. To collect the entire soft tissue and digestive glands, the shell body was not cut, water was spread on the sieve for 5 min, and the shell meat was mixed. The edible part of the scallop sample was detected.

Toxin extraction and clean up
Toxins were extracted from the shellfish following the standardized operating methods according to China's national food safety risk monitoring manual: 2 g of homogenized specimen was vortex-mixed in a 10-mL centrifuge tube, and the tissues and the solvents were vortexed for 90 s before adding the capped tubes to a boiling water bath for 5 min. The samples were subsequently cooled in cold running water for a minimum of 5 min. After cooling, the tubes were centrifuged at 4500 r/min for 5 min prior to decanting the supernatant into a 15-mL tube.
Then, 1 mL of the above extract was added into a centrifuge tube of 2 mL, added 5 μL of NH 4 OH, and mixed well. An activate Supelco ENVI-Carb solid-phase extraction column was adopted to clean and enrich the toxins of shellfish with 3 mL of 20% acetonitrile aqueous solution (containing 0.8% acetic acid) and 3 mL of 0.1% ammonia solution in turn, and 0.25 mL of extraction solution was added. The cartridge was washed then with 700 μL of water, dried under vacuum for approximately 5 s, and finally eluted with 2 mL of 20% acetonitrile aqueous solution (containing 0.8% acetic acid). The eluent was collected in a 5-mL centrifuge tube and filtered through a 0.22-μm syringe membrane. Ultimately, the eluent was stored in a sample injection vial at 4 °C for analysis by UPLC-MS/MS.

UPLC-MS/MS analysis
Mass spectrometry detection uses a Waters Xevo TQ-XS triple quadrupole mass spectrometry detector (Waters Corporation, Milford, MA, USA) equipped with an electrostatic ionization source (ESI). Mass spectrometry was operated in both positive and negative electrostatic ionization modes for multiple reactions monitoring (MRM). The ESI conditions were optimized as follows: capillary voltage of 3.0 kV (positive), 3.0 kV (negative), offset of ion source of 30 V, desolvation temperature of 500 °C, gas flow rate of 1000 L/h, conical gas flow rate of 150 L/h, and atomizer of 7 bar. The MS/MS parameters are presented in Table 1. The MassLynx software (V4.2 Waters Corporation, Milford, MA, USA) was used for data acquisition and processing. The Acquity UPLC system (Waters Corporation, Milford, MA, USA) was used for the chromatographic separation of PSTs with a TSK-Gel Amide-80 column (2.0 mm × 150 mm, 5 μm) at 40 °C. The mobile phase was composed of (A) an aqueous solution containing 2 mmol/L of ammonium formate and 50 mmol/L of formic acid and (B) an acetonitrile solution containing 2 mmol/L of ammonium formate and 50 mmol/L of formic acid. The gradient program was set with an injection volume of 5 μL and a flow rate of 0.4 uL/ min, which starts at 20% A.

Statistical analysis
The acquired toxin content, toxin profiles of the marine organism samples were processed using Microsoft Excel  Table 2 presents the concentration data set from all the PSTs quantified in both species across the six sites. The samples collected from the Fujian coast in China were found to contain a range of PSTs analogues, including GTX1, GTX2, GTX3, GTX4, GTX5, dcSTX, STX, neoSTX, dcGTX2, and dcGTX3. The profiles were dominated by GTX5 (detection rate 4.46%), followed by neoSTX (3.48%) and dcGTX2 (2.93%). The remaining analogues were present at relatively low levels, with a detection rate of approximately 1.10-2.08%. In total, four of the 2355 samples had toxin levels above the European Food Safety Authority (EFSA) legal limit (0.17%) (Chain 2009). The 2137.10 μg STXeq/ kg was the strongest content, with a mean concentration from 9.59 to 16.24 μg/kg, while the maximum content was 45.90-4080 μg/kg. The shellfish species with a high detection rate were A. granosa, C. farreri, P. viridis, and C. gigas at 14.63%, 13.54%, 11.75%, and 10.79%, respectively. The highest concentrations were quantified in P. viridis and C. gigas from Quanzhou and Zhangzhou, with values over 800 μg STXeq/kg in both sites, with a maximum concentration of 2137.10 µg STXeq/kg in the P. viridis collected in June 2017 from Zhangzhou. Significantly lower total PSTs concentrations were obtained in the C. gigas collected from Quanzhou and Zhangzhou, with the highest concentrations of 1469.46 and 1983.89 µg STXeq/kg, respectively. At the A. granosa and C. farreri sites, lower (< 800 µg STXeq/ kg) levels than those of the P. viridis and C. gigas of PSTs were found between May 2017 and December 2021. Figure 3 shows the highest levels of PSTs in 2017, followed by 2018 and 2019, while almost no PSTs were detected in 2020 and 2021. The dominance of GTX5 was observed in 2017 (21.77%), followed by the detection rate of dcSTX (8.06%). The highest toxin level in 2018 was also the GTX5 (10.21%), followed by dcGTX2 (4.08%). The detection rate between 2019 and 2020 was less than 5%, and PSTs were not detected in 2021. According to monitoring data from Fujian Provincial Bureau of Ocean and Fisheries, dinoflagellate Gymnodinium catenatum that produce PSTs was detected in Fujian nearshore seawater for June 2017 and June 2018, with maximum cell densities of 5.6 × 10 4 cells/L and 4.10 × 10 6 cells/L, respectively. No PSTs-producing dinoflagellates were detected in the water of this region during 2019-2021, but the non-toxic Skeletonema costatum were predominant. This corresponds to the high detection rate of PSTs in shellfish samples collected in the area in 2017 and 2018.

Temporal variation
The distribution of toxins for each month in 2018 and 2019 is shown in Fig. 4. PSTs occurs mainly in the periods from May to July and November to December. GTX5 was present in almost every month, dcGTX2 was mainly present from May to August, while neoSTX showed high levels in November, December, and January. The recent work of Wang et al. (2017) showed evidence of PSTs in the area of Shenzhen through the radial basis function difference model and concluded that the accumulation time of PSTs was from January to June (Wang et al. 2017). Yao et al. (2019) studied seven elements in China and found that it was rarely detected in spring (April to May) and detected in summer (June to August). This may be related to temperature; warm climate is conducive to the reproduction and secretion of toxins by poisonous phytoplankton (Onofrio et al. 2021). The monthly mean temperature of coastal seawater in Fujian for 2019 were high from June to September (25.5-28 °C), with the highest temperature reaching 28 °C in July and August, as shown by data from the China Ocean Climate Monitoring (Fig. 5). Correspondingly, the maximum toxin content of shellfish collected in Fujian in 2019 was also high in June to August (108.6-696.7 μg STXeq/kg), with a maximum of 696.7 μg STXeq/kg in July.

Interspecific variation
PSTs undergo transformation from one form to another through different processes. Such processes include reduction, epimerization, oxidation, and desulfation, all of which  granosa samples throughout the observation period, with GTX5 observed every month in the C. gigas samples. The highest detection rate of 14.63% was found in the A. granosa samples, followed by the C. gigas, C. farreri, and P. viridis samples, with detection rates of 10.79%, 13.54%, and 11.75%, respectively, whereas the R. philippinarum samples exhibited only 2.26%. Moreover, differences among species were observed in the toxins content in this research. The PSTs content exceeding 800 µg STXeq/kg was recorded in 2 out of the 6 marine organism species from 6 sites, including the C. gigas and P. viridis mollusks samples. The mean concentration of all the detected PSTs in bivalve whole soft tissues collected in 5 years in the study area was obtained. Figure 6 illustrates that mean concentration of GTX5 in S. constricta (12.39 µg/kg) and neoSTX, dcSTX, dcGTX2&3, and GTX1-4 have the same mean concentration (10 µg/kg). The detected samples in other shellfish A. granosa, C. gigas, C. farreri, and P. viridis were higher than that of R. philippinarum. Two toxin analogues (STX, GTX2) were rich in A. granosa, whereas the profile observed in six cockle samples appeared to have a lower mean concentration of GTX5 than that found on average in the C. gigas data set. The C. gigas samples exhibited the dominance of the GTX5 toxin (22.25 µg/kg), followed by dcGTX2 (mean concentration 14.01%). GTX5 was the highest mean concentration (14.04 µg/kg), followed by dcGTX2&3 and GTX1 (mean concentration 10.54, 10.51, and 10.83 µg/kg, respectively); however, the remainder were lower levels (9 ~ 10 µg/kg) in C. farreri. Also, mean concentration of GTX5 (13.04 µg/kg) present in the Perna viridis was dominant toxin, followed by dcSTX and dcGTX2&3. S. constricta could not be compared because of the values below the detection limit. The PST components detected in shellfish toxins are mainly carbamates, and the toxic components of shellfish are related to the species that feed on poisonous algae, which are usually similar to the PST components contained in shellfish and the toxic components of poisonous algae. However, due to the metabolism and transformation of the toxins in shellfish, the proportion and components of the toxins in shellfish will change.

Spatial variation
Significant variation in PSTs was quantified between different geographical regions within Fujian province. Figures 7  and 8 illustrate the total PSTs quantified in the sampled areas of Fuzhou Ningde, Putian, Quanzhou, Xiamen, and Zhangzhou, each progressively exhibiting increased variation. More than half of the study samples were harvested from the most Ningde region of Fujian Province (21.61%). From these, the highest concentration was 403.26 µg STXeq/kg, with no samples above the RL (800 µg STXeq/kg). The highest toxicities were observed in the sampled areas of Quanzhou and Zhangzhou, with the latter of the three containing the samples showing the highest concentrations out of all the samples studied  (toxic equivalent = 2137.10, 1835.25, and 1983.89 µg STXeq/ kg respectively), with 0.17% of the total samples above the RL. Although shellfish products in every city were contaminated with at least some of paralytic marine toxins, the toxins concentration and composition varied widely among the various cities.
The four cities (Fuzhou, Quanzhou, Xiamen, and Zhangzhou) showed a similar trend of paralytic marine biotoxin contamination, and GTX5 is the most ubiquitous toxin. Most of the paralytic marine biotoxins, except for GTX4, were present in many specimens from Ningde and Xiamen. The detection rate of Fuzhou was 4.23%, and the maximum concentration was 344 µg/ kg, but STX, neoSTX, dcSTX, and GTX3 were not found in the area. neoSTX was the most detected in Ningde, accounting for 71.74% of the total toxins, and the maximum concentration was 330 µg/kg. Furthermore, dcGTX3 was not discovered in Putian, STX, neoSTX, and GTX4 were not recognized in Quanzhou. GTX5 was the most prevalent toxins, accounting for 41.33% of the total toxins in this area. The result suggests that the detection rate of Ningde and Quanzhou is high, and the difference in detection rate is insignificant, while the detection rate of Fuzhou is much lower than that in the other areas. Figure 9 summarizes the proportion of toxin analogues quantified in terms of STX equivalents in the bivalve mollusks harvested across each of the six regional areas along the Southeastern China coast. The figure shows that most of the toxin analogues were detected in May to August. PSTs from Xiamen and Putian were detected mainly in May to June, accounting for 33 to 67% of all detected samples, followed by Quanzhou and Fuzhou with 10 to 20%. The mollusks from Ningde exhibited low relative proportions in January to November, displaying the highest relative proportion (42%).

Seasonal and spatial variation
Temporal variations indicated that PST in bivalves from Fujian Province occurred mainly from May to August and from November to December. In particular, high levels This result confirms the hypothesis that the levels of PSTs in bivalves were correlated with seasonal variations. The temperature, the quantity of toxic algae, the tidal current and wind direction of the water, the species, and the rate of cyst formation affect the seasonal distribution of PSTs. The maximum level of PSTs in 2019 occurred in July, reaching 696.7 μg STXeq/kg in this study. Correspondingly, the highest average seawater temperature in 2019 was also in July, reaching 28 °C. PSTs are also related to the production of toxic dinoflagellates, PSTs-producing dinoflagellate Gymnodinium catenatum was detected in Fujian nearshore seawater from May to August in both 2017 and 2018. According to previous reports, PSTs-producing dinoflagellate grows well at appropriate temperature and has strong cytotoxicity at low temperatures (Garcés et al. 2004;Giacobbe et al. 1996), which seem to favor the growth of dinoflagellate. Meanwhile, during this period, nutrient loadings increased significantly in the bay (Wang et al. 2009), facilitating the rapid growth of phytoplankton. The cysts of dinoflagellate appear in most seasons of the year, and the cyst formation rate is the highest in winter. The investigation of PSTs in the inshore waters of the East China Sea and the South China Sea by Du et al. (2013) shows that the high exposure level of shellfish in winter may be related to the upwelling and wind direction. In addition, during the cyst germination in spring, poisonous algae exist mainly in vegetative cells in water, and the high level of shellfish poisoning in spring may be related to the large amount of toxic algae in the water. The monitoring results also confirmed that the levels of PSTs in bivalves in Fujian Province were correlated with regional variations. A comparison of the toxin levels between regionally studied areas was conducted, noting the differences in the detection rate between the six geographical zones from north to south: Fuzhou (4.23%), Ningde (13.36%), Putian (9.18%), Quanzhou (15.28%), Xiamen (12.15%), and Zhangzhou (10.13%). The spatial variability indicates that the highest risks from high PSTs originate from the sampled districts of Quanzhou and Zhangzhou, given the maximum concentrations of 1469.46 and 2137.10 µg STXeq/kg in those two regions. The concentration was still highly evident outside these two regions, with occasional samples exhibiting toxin levels well above the RL, and the mean values determined were notably low. Previous reports showed that the mean PSTs concentration ranged from 10.85-134.06 μg STXeq/kg, with maximum values ranging from 715.60 to 796.00 μg STXeq/ kg in Southeastern China (Zhou et al. 2022). GTX1-4 were detected in a few portions, which contain PSTs in Putian, and only trace amounts of neoSTX were detected with a mean proportion of 32.15%. The PSTs profiles in Quanzhou extracts were rich in GTX5 (mean 54.38% of the total) and dominated by dcSTX (mean 17.54% of the total), dcGTX2 (mean 24.56% of the total), and dcGTX2 (mean 26.31% of the total). In addition to these components, a trace amount of GTX5 (meaning 50% of the total) was detected in Xiamen. Similarly, large amounts of GTX5 were detected in Zhangzhou around 47.5% of the total, and GTX3 (mean 2.5% of the total) was the least proportion and the maximum toxin content in the samples collected was 3388.9ug/kg. GTX5 was the main toxin component in Zhangzhou, Quanzhou, Xiamen, and Fuzhou, while neoSTX was the main toxin component in Ningde and Putian. The detection rate in Quanzhou and Ningde was relatively high. There is little difference among the other three regions (Xiamen, Zhangzhou, and Putian).

High PSTs risk species and their toxin profile
Significant differences in toxin profiles were confirmed between sampling bivalves. STX and GTX2 constituted the largest proportion of mean concentration in the A. granosa samples, whereas STX, dcGTX3, and GTX5 presented relatively low proportions in the P. viridis samples. Furthermore, differences were also observed in the mean concentration determined for each individual shellfish species; the toxins of PST were mostly detected in P. viridis between the different species, followed by A. granosa and C. gigas. The calculation of toxin profiles in terms of detection rate revealed relatively high proportions of dcGTX2 and GTX1&2&3, most notably in R. philippinarum, where they represented a 0.75% detection rate. This figure is comparable with that reported by Moroo et al. (2003) and Nielsen et al. (2016) who found that oysters, scallops, and mussels may accumulate large amounts of marine toxins, which may be related to the high feeding rate of phytoplankton due to the large size of scallops and mussels (Moroo et al., 2003;Nielsen et al. 2016 Eight species of PSTs were detected in 35 species of shellfish, including Meretrixmeretrix, mussels, and Crassostrea spp, and 11 species of PSTs were detected in 24 species of shellfish in the South China Sea, including Nassarius spp, reflecting the interspecific differences in the accumulation of PSTs (Wu et al. 2008).
Most of the toxins were detected in C. farreri and A. granosa, with maximum amounts of 365.34 and 373.52 μg STXeq/kg collected in Southeastern China. The toxins in other tissues, such as R. philippinarum and S. constricta, were very low to undetectable, except for six samples collected, with a maximum level of 246.7 μg STXeq/kg. The results show that the PSTs from both C. gigas and P. viridis are unsafe for human consumption during the summer months. The toxin levels from P. viridis (maximum value of 2137.10 μg STXeq/kg) were significantly higher than those from other species. The sharp increase in concentrations of PSTs in January was coincident with the occurrence of the Alexandrium population (both vegetative cells and cysts). This phenomenon may be partly due to the influence of the aquaculture water environment. In fact, the accumulation of shellfish toxins is also related to the number and type of toxic algal cells in the water, the neurosensitivity of individual shellfish and the different metabolism. Thus, because the shellfish samples are not entirely from the same aquaculture area, farmers directly move the shellfish products from different waters to another water area to continue the temporary culture. If the oyster is relatively clean before migration, the culture time is short after migration, the cell concentration of the toxic algae in the culture water after migration is low, or does not encounter toxic algae, then the concentration of PSTs in shellfish may be relatively low or undetected.

Conclusion
PSTs were monitored for 5 years using the UPLC-MS/MS method based on liquid chromatography-mass spectrometry method using graphitized carbon solid-phase extraction. This approach enabled the generation of data describing the total PSTs proportion together with the mean concentrations of specific PSTs congeners. Ten detected toxins were STX, dcSTX, neoSTX, dcGTX1&2, and GTX1-5, with a detection rate of 10.91% (257/2355); among which, four samples exceeded the standard limit of 800 µg STXeq/kg, with the highest content of 2137.10 µg STXeq/kg. Highly variable numbers of detected samples were recorded annually, together with noticeable differences in the maximum levels of PSTs reached. PSTs have obvious seasonal characteristics, and the peaks occurred in May to August and November to December. The regions where toxin events were detected were also found to vary considerably, with some areas showing high levels of PSTs above the RL. The samples that exhibited a total STXeq above the regulatory action limit were predominantly P. viridis and C. gigas. The marine biological samples were affected by the geographical distribution, seasonal changes, and differences among