Progress in Fishery Sciences (Oct 2023)
Surveillance and Risk Assessment of Diarrhetic and Paralytic Shellfish Toxins in the Tangshan Shellfish Culture Areas of Bohai Sea, China
Abstract
Shellfish are filter feeders that can accumulate toxic algae and their related toxins, increasing risk when consumed. Shellfish toxins can directly affect the physiological activities of marine organisms and threaten the stability of marine ecosystems. Ultimately, these toxins pass through the food chain and can endanger human health and economic security. Globally, shellfish poisoning incidents have occurred in many countries. The Bohai Sea is a semi-enclosed inland sea, where severe eutrophication of the seawater has occurred in recent years, leading to harmful algal blooms. To date, no simultaneous surveillance of diarrhetic shellfish poisonings (DSP) and paralytic shellfish poisonings (PSP) have been reported in the Tangshan shellfish culture area.To better understand shellfish toxin pollution in the shellfish culture areas of Tangshan and the dietary and health risks to residents, Mactra veneriformis, Ruditapes philippinarum, Rapana venosa, Crassostrea gigas, Cyclina sinensis, Meretrix meretrix, Mercenaria mercenaria, and Azumapecten farreri were collected for toxin monitoring from the Tangshan shellfish culture areas in Bohai Sea from October 2019 to September 2020. A total of 34 samples were collected for each shellfish species. Each sample weighed approximately 3 kg. All samples were transported to the laboratory on ice. In the laboratory, samples were flushed with tap water to remove sand and silt and shucked to collect the soft tissue. The tissue was thoroughly homogenized with a household blender, and approximately 50 g of tissue from each sample was stored at –20 ℃ until required for analysis. Five DSP including okadaic acid (OA), dinophysistoxin 1 (DTX1), dinophysistoxin 2 (DTX2), yessotoxin (YTX), and azaspiracid 1 (AZA1), and 14 PSP including saxitoxin (STX), neosaxitoxin (NEO), gonyautoxin 1/4 (GTX1/4), gonyautoxin 2/3 (GTX2/3), decarbamoylsaxitoxin (dcSTX), decarbamoylneosaxitoxin (dcNEO), decarbamoylgonyautoxin 2/3 (dcGTX2/3), gonyautoxin 5 (GTX5), gonyautoxin 6 (GTX6), and N-sulfocarbamoyl toxin 1/2 (C1/2) were tested using high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The detection limit of the DSP method was 5 μg/kg, and the detection limit of the PSP method was 10–20 μg/kg.The DSP toxins were not detected in any of the samples. Several PSP toxins were detected, including saxitoxin (STX), gonyautoxin 1 (GTX1), gonyautoxin 2 (GTX2), and decarbamoylgonyautoxin 3 (dcGTX3). The GTX1 levels were the highest overall PSP toxin at 537.95 μg/kg in April. The results revealed positive rates of PSP for R. philippinarum, C. gigas, M. meretrix, and M. mercenaria, which were 11.76%, 47.06%, 5.90%, and 8.82%, respectively. Of the toxins tested, none were detected in the remaining samples. The highest PSP toxin levels in the positive samples from R. philippinarum, C. gigas, M. meretrix, and M. mercenaria were 414.26, 532.57, 452.77 and 195.46 μg STXeq/kg, respectively. We ranked the species in order of highest to lowest PSP toxin levels as: C. gigas > M. meretrix > R. philippinarum > M. mercenaria. In general, the toxin content of the shellfish in this area was lower than the EU limit of 800 μg STXeq/kg. The composition of shellfish toxins is related to many factors, including the sampling location and collection time. The toxin accumulation capacity by shellfish is also affected by many factors, including water pollution, salinity, light intensity, and most importantly, the species and density of the toxic algae in the surrounding waters.The ecological risk assessment methods used in this study were the risk quotient method (RQ) and the point assessment method. The RQ method is primarily used for semi-quantitative risk assessments to determine whether the pollutant concentrations have harmful effects. The point assessment model is a dietary exposure assessment tool. We applied risk quotient and point assessment methods to determine risk. There was no safety risk in the consumption of shellfish harvested from the Tangshan coastal study area during the study period. According to the point assessment method, at this specific time it was safe to consume the shellfish as the toxin levels were low. This analysis indicated that the safe single intake quantity of shellfish during months with high levels of shellfish-enriched toxins was reduced. As the toxin levels accumulating in different shellfish tissues can vary greatly, each sampled tissue was analyzed separately. The results indicate when there is a high accumulation of shellfish toxins present, consumers should restrict their consumption to a single serving rather than regularly consuming shellfish as part of their daily diet. The safety risk assessment results indicate that the seven shellfish species posed no food safety risk during the study period.This study provides a scientific basis for improving shellfish management practices to ensure shellfish are safe for consumption. This study analyzed the effects of toxin residues in shellfish species; different seasons and different locations vary in toxin content and components. We recommended consumers regulate their consumption to avoid potential poisoning events. This study provides social, economic, and ecological benefits in promoting green and healthy aquaculture of shellfish products, by ensuring the safety of shellfish products for consumer health. However, continuous long-term monitoring of both phytoplankton and biotoxins are recommended to ensure the development of the shellfish aquaculture industry and to support consumer health.
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