Photochemical release of sediment bound brevetoxin (PbTx-2) from resuspended sediments

Marine sediments from coastal Florida, USA impacted by Karenia brevis blooms were resuspended in seawater and irradiated in a solar simulator to determine if sedimentary bound PbTx-2 is photolytically released into the aqueous phase. All bulk and size-fractionated (< 10-20 μm) sediments exhibited photorelease of PbTx-2 after a six-hour full spectrum irradiation. The magnitude of photorelease of a size-fractionated sediment (250 ± 20 pmol g− 1) was greater on a per gram basis compared to an analogous bulk sediment (1.66 ± 0.89 pmol g− 1). Experiments conducted with photosynthetically active radiation (λ = 400-700 nm) indicated that these less energetic wavelengths are also capable of releasing toxin from sediments. Two of three sediments autoclaved prior to irradiation with full spectrum sunlight exhibited a statistically significant photorelease of PbTx-2 into the aqueous phase suggesting abiotic processes are important in photoproduction of the toxin. The importance of PbTx-2 production from exposure of resuspended sediments to sunlight was estimated using photorelease data from the current study and previously reported total suspended solid concentrations for this region. The PbTx-2 produced from this process could account for 0.5-13% of extracellular brevetoxin concentration previously reported during a low level Karenia brevis bloom. Results of this study have significant implications for water quality management because they suggest a potentially important vector of toxin to overlying waters and ecosystems even in the absence of a Karenia brevis bloom.