Prevalence of lipophilic phycotoxins with different forms in the benthic environments of a typical mariculture bay.

Lipophilic phycotoxins (LPTs) are toxic and lipophilic secondary metabolites produced by toxic microalgae, which pose a serious threat to marine shellfish culture industries. LPTs were systematically investigated in bottom seawater, suspended particulate matter (SPM), sediment, and sediment porewater of Laizhou Bay, a typical mariculture bay in China, to understand the chemical diversity and environment behaviors of LPTs in the benthic environments. Okadaic acid (OA), pectenotoxin-2 (PTX2), dinophysistoxin-1 (DTX1), azaspiracid-2 (AZA2), gymnodimine (GYM), pectenotoxin-2 seco acid (PTX2 SA), 7-epi- pectenotoxin-2 seco acid (7-epi-PTX2 SA), 13-desmethylspirolide C (SPX1), yessotoxin (YTX) and homo YTX (h-YTX) were detected in the benthic environment of Laizhou Bay in spring, indicating that LPTs are rich in chemical diversity. OA and PTX2 were dominant in bottom seawater and porewater; PTX2 and PTX2 SA were dominant in SPM; and PTX2 and AZA2 were dominant in sediments, but AZA2 was present in sediments only. At the bottom seawater-SPM interface, the average proportion of LPTs in the dissolved phase (DP) (84.35%) was significantly higher than in the particulate phase (PP) (15.65%), indicating that LPTs were mainly distributed to the DP in the bottom seawater. At the sediment-porewater interface, a considerable variation exists in the partitioning behavior of different groups of LPTs, with abundant PTX2 and OA in DP, while the AZA2 and YTX group of LPTs were present in PP. The concentration of total lipophilic phycotoxins (∑LPTs) in the bottom seawater ranged from 8.07 ng L to 37.11 ng L, with an average of 22.63 ng L, showing that the spatial distribution characteristics of ∑LPTs of the northern farshore are higher than in the southern nearshore. Concentrations of ∑LPTs in sediment and porewater ranged from 1.51 ng kg-32.67 ng kg (mean: 17.32 ng kg) and 17.32 ng L-226.54 ng L (mean: 88.72 ng L), respectively. Notably, the concentration of ∑LPTs in porewater is significantly higher than in bottom and surface seawater, indicating that the potential harm of LPTs to benthos needs more attention.