Photochemical treatment strategies for okadaic acid degradation: Effects of salinity, oxidants, and UV sources

Abstract

This study evaluates the degradation and detoxification of okadaic acid (OA), a marine biotoxin, through UV-assisted photochemical processes using environmentally relevant OA concentrations. Experiments were conducted in distilled water (DW) and artificial seawater (ASW), applying two UV sources: UV-LED (λmax = 275 nm) and low-pressure mercury lamp (LP-Hg; λ = 254 nm), combined with hydrogen peroxide (HP), sodium peroxydisulfate (PDS), and potassium peroxymonosulfate (PMS). Photolysis alone was ineffective, and kinetic rate constants (kobs; min−1) followed the trend UV/PMS > UV/PDS > UV/HP for both UV sources. While all treatments showed high OA removal (>79 %) in DW, degradation was significantly reduced for HP (72.8 %–89.9 %) and PDS (67.8 %–76.6 %) in ASW. In contrast, UV/PMS efficacy improved in saline media, achieving rapid and effective degradation of OA, and reaching 99 % detoxification (PP2A activity) within 15 min. The main transformation product, norokadanone (m/z 757.453), formed via decarboxylation, showed significantly reduced toxicity compared to OA. These results confirm the suitability of sulfate radical-based processes (particularly UV/PMS) for OA mitigation in marine environments. In addition, this work highlights the critical role of water matrix composition in marine toxin treatment and supports the development of scalable, mercury-free strategies for effectively mitigating hazardous compounds in coastal environments.