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

Abstract

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 (<10–20μm) sediments exhibited photorelease of PbTx-2 after a six-hour full spectrum irradiation. The magnitude of photorelease of a size-fractionated sediment (250±20pmolg−1) was greater on a per gram basis compared to an analogous bulk sediment (1.66±0.89pmolg−1). Experiments conducted with photosynthetically active radiation (λ=400–700nm) 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.