Photorelease and Phototransformations of Sedimentary Bound Brevetoxin (PbTx-2) Upon Resuspension

Bulk and size fractionated marine sediments impacted by Karenia brevis blooms were resuspended in Wrightsville Beach Seawater and irradiated with simulated solar radiation to examine the photochemical mobilization of sedimentary bound PbTx-2 and its photoproducts into the aqueous phase. All bulk sediments and size fractionated sediments exhibited a photorelease of PbTx-2 into the aqueous phase after a six hour full spectrum simulated solar irradiation. The magnitude of photorelease of size fractionated sediment was greater on a per gram basis compared to corresponding bulk sediments (1.66 ± 0.89 and 250 ± 20 pmol g^-1 respectively for size fractionated and bulk sediment for site North Florida 3). In experiments to determine the role of photosynthetically active radiation (λ=400-700 nm; PAR), one of three PAR irradiated sediment suspensions exhibited a statically significant photorelease of PbTx-2 into the aqueous phase. The photorelease magnitudes were 1.66 ± 0.89 and 1.51 ± 0.97 pmol g^-1 for six hours of full spectrum and PAR irradiation, respectively. Three sediments were autoclaved prior to irradiation with full spectrum simulated sunlight. One of the three autoclaved sediments exhibited a statistically significant photorelease into the aqueous phase. Using the photorelease data from the size fractionated sediment from site North Florida 3 the concentration of PbTx-2 during a sediment resuspension event was calculated using the measured total suspended solids common during wind driven sediment resuspension event. The calculated photoreleased PbTx-2 concentration was approximately 10 % of the extracellular brevetoxin concentration previously reported during a low level Karenia brevis bloom. Photochemical mobilization from resuspended sediments represents a potentially long-term source of PbTx-2 to overlying waters and ecosystems long after a Karenia brevis bloom has ended. This is important given the trophic transfer of the toxin up the food chain to higher life forms.