Source Analysis Of Paralytic Shellfish Poisoning In Mussels And Preliminary Study On Its Formation Mechanism

Paralytic shellfish poisoning?PSP?is the main reasons for the current quality and safety accidents of shellfish food in China,and is also the focus and hotspots in the field of marine environment and shellfish product quality and safety research.According to statistics,almost 2000 people worldwide were poisoned by eating shellfish every year.Poisoning incidents caused by shellfish contaminated by PSP toxins occur frequently in China.In 2017?2019,there were multiple food poisoning incidents caused by the consumption of PSP-contaminated mussels in Zhangzhou,Fujian and Qinhuangdao,Hebei,which caused many deaths.Thus,the Chinese government attaches great importance on it and conducts PSP monitoring every year.However,due to the lack of understanding of the basic research on the source,production and elimination of PSP toxins,it is difficult to carry out targeted and comprehensive monitoring of PSP toxins,and the safety warning effect cannot be fully achieved.Therefore,carrying out research on the formation of PSP toxins in marine environment,and timely grasping the occurrence rules of PSP toxins,is a scientific problem that needs to be solved urgently in order to effectively improve the safety warning of shellfish in China.On the basis of previous studies,the risk of the enrichment of PSP toxins in mussels and the correlation to the abundance of toxic algae were studied by selecting the major shellfish breeding area in the East China Sea.The toxic dinoflagellate Alexandrium tamarense,which is a typical PSP-producing alga,was selected,then the toxin production capacity of A.tamarense and the accumulation,distribution and elimination of PSP toxins in mussels researched by artificially simulating the marine environment.The research results will provide a factual basis for the risk monitoring of PSP toxins.The main research contents and results are as follows:?1?Field investigation and source analysis of PSP in musselsTo investigate the risk of enrichment of paralytic shellfish poisoning?PSP?in mussels and the correlation with toxic algal abundance in typical shellfish culture areas,water samples and mussels were collected periodically from May 2017 to April 2018 at four sampling points that set up in the main aquaculture area of shellfish in Dongshan Bay,Fujian Province.The species and abundance of toxic algae in water body were monitored,the content of PSP toxin and its annual distribution in mussels was analyzed,then the risk of PSP toxin enrichment was evaluated.The results showed that the annual content of PSP in mussels were at 42.8?220.1?g·kg^-1,and only GTX5,GTX4 and GTX1were detected.Seven species of toxic algae were detected in the water body of Dongshan Bay throughout the year,among two species?A.tamarense and Gymnodinium catenatum?could produce PSP,and the cell abundance(2.00?8.74 cells·L^-1)was much lower than the safety limit of shellfish safety warning(200 cells·L^-1)for the whole year.There was a significant relationship between the accumulation of PSP toxins in mussels and the abundance of toxic algae and their size.The greater the abundance of toxic algae and the bigger the size,the more enrichment ability of mussels to PSP toxins and the stronger the risk of eating mussels.?2?Study on the capacity of PSP production of A.tamarenseTo explore the capacity of PSP production in A.tamarense,the strain was cultivated in different space volume,salinity and nutrient concentration,and the toxin content and profiles were analyzed.The results showed that A.tamarense contained at least 13 PSP components,of which the main components are GTX1&4,GTX5,and C1&2,accounting for 97.2%of the total toxins.There was a significant difference in the minimum number of algal cells required for the quantitative detection of each component.When the number of algal cells was less than 4×10³,none of the 13 components could be detected.All these13 components could be quantified only when the number of algae cells was higher than5.9×10⁶.It showed stronger capacity of PSP production when A.tamarense was cultivated in the flask of 1L,at the salinity range between 25‰to 35‰and 1/4 times of the f/2medium concentration.?3?Metabolic rules of PSP derived from A.tamarense in musselsTo explore the rules of the accumulation,distribution and elimination of PSP toxins in mussels,in this section,two dose groups of 1×10⁷ cells·L^-1 and 5×10⁶ cells·L^-1 were used to carry out metabolic experiments in mussels after high-density cultivation of A.tamarense.The metabolic experiment temperature was set at 25?and 30?,which divided in two stages of enrichment and purification.The entire cycle was 17 days,of which the enrichment phase was 3 days and the purification phase was 14 days.The results showed that mussels were more likely to accumulate PSP toxins at 25?than 30?under the same environmental conditions,and the accumulation of PSP toxins was closely related to the abundance of toxic algae under the same temperature.In the 25?×high dose(1×10⁷ cells·L^-1)group,mussels had the strongest capacity to accumulate PSP toxins.On the third day of the enrichment phase,the toxin content in the hepatopancreas exceeded the national safety limit of 800?g·kg^-1 under four conditions,with the highest was 3162.4?g·kg^-1 STX eq,while the content of PSP toxins in gills,mantle,gonads and muscles were less than 130?g·kg^-1.The hepatopancreas have the most abundant toxin spectrum,among them,10 kinds of PSP toxin components were detected,while only 5kinds of toxin components were found in other tissues.The main toxin components in each tissue were all GTX1&4,GTX5 and C1&2,which are basically similar to A.tamarense.In the 30?×low dose group,mussels had the highest toxin elimination rate,with a mean elimination rate of 0.180 d^-1,while the toxin elimination rate was the lowest in the 25?×high dose group,with an average elimination rate of 0.145 d^-1.