Effects of microorganisms, temperature and irradiation on the stability of dissolved okadaic acid and dinophysistoxin-1 in seawater.

Diarrhetic shellfish toxins (DSTs) are widespread in marine environments, posing potential threats to marine ecosystems, shellfish aquaculture, and human health. Despite their prevalence, knowledge of the stability of dissolved DSTs in seawater is still limited. This study aimed to investigate the effects of bacteria, temperature, and irradiation on the stability of dissolved okadaic acid (OA) and dinophysistoxin-1 (DTX1) in seawater. Results indicated that bacteria did not contribute to the biodegradation of OA and DTX1, while their growth was inhibited by the toxins over the 7-day experiment. During a 28-day period without irradiation at 4 °C, 20 °C, and 37 °C, no degradation of OA was observed, whereas significant degradation of DTX1 occurred, with concentrations dropping to 58%-78% of the initial concentration at the end of the experiment. Under xenon lamp irradiation at 1000 W, the concentrations of DTX1 decreased by 15%-19% in seawater after 160 min, while the concentrations of OA showed minimal change. Conversely, both OA and DTX1 underwent significant degradation under mercury lamp irradiation with an irradiation intensity-dependent pattern. Additionally, the degradation rates of OA and DTX1 increased with higher concentrations of dissolved organic matter in the range of 1.2-15 mg C L⁻. This study enhances the understanding of DST stability in seawater under varying temperature and light conditions, highlighting the complexities involved in their degradation processes. The results of this study found that ultraviolet is an important driving environmental factor for OA and DTX1 degradation in the natural marine environment. In case of harmful algal blooms with associated phycotoxins, ultraviolet irradiation can be used as a removal method for OA and DTX1.