Positive mode APCI represents a significant improvement in detection and quantification of PbTx-2 by LC/MS allowing for smaller sample sizes compared to previous studies using (+) ESI. This in turn leads to higher throughput of samples during and after bloom events giving stakeholders detailed information on the fate of this potent marine toxin.

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.