First observation of domoic acid and its isomers in shellfish samples from Shandong Province,China

A total of 133 shellfish samples were collected in seven cities of Shandong Province,China,from May to October,2019.The domoic acid(DA)concentrations were determined by liquid chromatographytandem mass spectrometry(LC-MS/MS),and their distribution characteristics were investigated.DA concentration was detected high in over 1/3(36.1%)of the samples of four kinds of shellfish in all three seasons in range from 0 to 102μg/kg.The highest DA concentrations were 102,101,36.7,and 10.2μg/kg in Crassostrea gigas,Chlamys farreri,Mactra veneriformis,and Mytilus edulis,respectively.Geographically,Yantai(22.0μg/kg)and Weihai(16.9μg/kg)showed relatively high concentrations of DA,whereas Rizhao and Dongying presented only 0.85-and 1.76-μg/kg DA,respectively.DA concentrations in the shellfish samples were strongly related to seasonal changes,being significantly higher in autumn and summer than that in spring.The DA risk exposure assessments indicate that dietary seafood consumption did not pose a health threat to general human population.In addition,three isomers(isoA,isoD,isoE)and 5′-epimer DA were detected in 3.00%-15.80%of the shellfish samples.This study is the first to observe DA and its isomers in shellfish samples of Shandong Province.The results demonstrate that DA contamination is very common and should be continuously monitored.

Phytoplankton community dynamics during Alexandrium blooms in 2019 off the Qinhuangdao coast,Bohai Sea,China

Alexandrium blooms in the northwest area of the Bohai Sea(Qinhuangdao coastal area),China,produce large amounts of toxins that could be enriched in shellfish and consequently harm human bodies.To understand the succession of the phytoplankton community structure during Alexandrium bloom events in the northwest area of the Bohai Sea off Qinhuangdao from April 2 to May 7,2019,microscopy observations and high-performance chromatography(HPLC)-pigment analysis were performed.Sixty species of phytoplankton were identified,mainly diatoms and dinofl agellates.The abundance of Alexandrium reached the maximum on April 16(3.3×10^(3) cells/L).HPLC-pigment CHEMTAX analysis showed that the phytoplankton community was composed mainly of diatoms,dinofl agellates,prasinophytes,and cryptophytes.Diatoms were the main contributor to the total Chl-a pool.There was a downward trend for the proportion of diatom biomass to the total Chl-a pool,followed by an upward trend.The proportion of dinoflagellate biomass showed the opposite trend,whereas that of the prasinophyte biomass presented an obvious increasing trend.Temperature,nutrients,and nutrient structures were the main factors on the distribution of different phytoplankton groups in the study area as shown in the redundancy analysis.This work illustrates the succession of phytoplankton community structures during Alexandrium blooms and provided a theoretical basis for studies on the mechanism underlying the outbreak of harmful algal blooms in sea areas.