Unveiling the transformation products and toxicity of paralytic shellfish toxins under photodegradation and peroxymonosulfate oxidation

Biotoxins produced by harmful algal blooms (HABs) are a substantial threat to ecosystems and human health. Significantly, paralytic shellfish toxins (PSTs), are prevalent globally and cause significant environmental and economic losses. However, their transformation products (TPs), reaction pathways, and potential risks during photodegradation and oxidative treatment are poorly understood. In this study, the TPs of three typical PSTs subjected to photodegradation and peroxymonosulfate (PMS) oxidation were analyzed by liquid chromatography-high resolution mass spectrometry (LCHRMS). For saxitoxin (STX), gonyautoxin 2&3 (GTX2&3), and gonyautoxin 1&4 (GTX1&4), seven, nine, and nine TPs were identified under photodegradation and five, four, and six TPs were identified under PMS oxidation. Most TPs underwent structural modifications and mass reductions. Substitution, ring-opening, and nucleophilic reactions are proposed as the main photodegradation pathways. PMS oxidation involves carbamate removal and substitution. In silico prediction demonstrated that photodegradation formed TPs with human toxicity. Conversely, PMS oxidative degradation effectively inhibited highly toxic products formation, reducing the ecological risks to environments. Meanwhile, the growth of Escherichia coli as toxicity test validated low toxicity of the PMS oxidation. Compared with photodegradation, oxidation markedly mitigated the environmental risks associated with PSTs after degradation, offering a novel approach for managing PSTs-related ecological and health risk.