Effects of environmental variables on phycotoxin degradation and preliminary identification of transformation...

Phycotoxins are released from phytoplankton into the water column during rapid cell division or during bloom termination. These processes introduce pulses of dissolved phycotoxins into coastal systems that can deleteriously impact animal, environmental, and human health. Despite evidence that they can persist months beyond their extracellular release, environmental factors controlling phycotoxin fate and persistence within aquatic environments have not been thoroughly studied. As such, we investigated the stability of four phycotoxins (pectenotoxin-2, yessotoxin, azaspiracid-2, and okadaic acid) under select UV (ultraviolet) light, salinity, and temperature conditions that represent estuarine waters, and winter to summer surface temperatures for the mid-latitudes. Pectenotoxin-2 and okadaic acid were stable (minimal to no degradation) in the dark over the entire 5-d experimental period, independent of salinity and temperature conditions. Both phycotoxins exhibited photodegradation, with okadaic acid degrading slower than pectenotoxin-2 under UV. Azaspiracid-2 and yessotoxin degraded in water under both dark and light conditions. Azaspiracid-2 and yessotoxin demonstrated temperature dependence, but were not influenced by salinity in the range of 5 - 30. There was significantly less degradation of azaspiracid-2 and yessotoxin after five days at the lowest temperature, 15 °C, when compared to the two higher temperatures, 25 and 35 °C. Non-targeted analysis identified photodegradation products, i.e., isomeric rearrangements, for pectenotoxin-2 under UV, and transformation products for pectenotoxin-2 and yessotoxin. Novel transformation products were identified for azaspiracid-2 under dark conditions. Our results suggest that okadaic acid may persist in the environment longer than pectenotoxin-2, yessotoxin, and azaspiracid-2 due to lower UV susceptibility. In humic-rich or turbid environments with greater light attenuation, okadaic acid and pectenotoxin will be more stable than yessotoxin, with azaspiracid-2 being the fastest to degrade in the water column. Regarding UV, temperature, and salinity, azaspiracid-2 and yessotoxin would degrade within a period of days to weeks, while pectenotoxin-2 and okadaic acid may persist for weeks to months. The consistent detection of these phycotoxins year-round suggests other factors, such as sorption to particulates or burial in sediment may play a role in long-term stability of these phycotoxins. Research focused on the persistence, distribution, and fate of dissolved phycotoxins in the environment is needed to inform those who study harmful algal blooms and their impacts. Elucidation of possible removal mechanisms is also critical to desalination and aquaculture facilities that must manage contaminants in their respective systems.