Seasonal and regional variability of lipophilic marine phycotoxins in eutrophic coastal waters of the South China Sea

Lipophilic marine phycotoxins (LMTs), primarily produced by toxigenic dinoflagellates, pose significant risks to marine ecosystems and human health due to their toxicity and widespread distribution. This study investigates the spatial and temporal distribution of LMTs in the surface seawater from representative estuarine and bay areas of the South China Sea (SCS) during period from 2022‒2023. Using active solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry (Active-SPE-LC-MS/MS), the study revealed that significantly higher LMTs concentrations in semi-enclosed bays (13.15 ± 8.61 ng L⁻¹) compared to estuarine regions (8.55 ± 8.59 ng L⁻¹), with Daya Bay (DB) and Jian River Estuary (JRE) exhibiting the highest toxin levels. The most prevalent toxins were diarrhetic shellfish toxins (OA, DTX1) and pectenotoxin-2 (PTX2), with PTX2 being dominant in most regions. Seasonal variations were evident, with higher LMTs concentrations observed during the wet season, particularly in spring and summer. Principal component analysis (PCA) revealed distinct toxin profiles, with PTX2, GYM, and OA being prevalent in the Pearl River Estuary (PRE), while AZA2 and DTX1 were more abundant in Qinzhou Bay (QB). The study highlights the influence of local environmental conditions, such as seasonal and region variations on LMTs distribution. These findings provide critical insights into the ecological dynamics of LMTs in eutrophic coastal waters, emphasizing the need for continuous monitoring to mitigate risks to marine ecosystems and human health. This research contributes to a deeper understanding of LMTs distribution patterns in the SCS, supporting future risk assessments and management strategies.