Photochemistry of brevetoxin, PbTx-2, produced by the dinoflagellate, Karenia brevis

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Jaclyn Pitt (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Robert Kieber

Abstract: The predominant brevetoxin produced by Karenia Brevis, PbTx-2 was added to 0.2 µmfiltered Wrightsville Beach, North Carolina seawater (WBSW) and irradiated under simulated sunlight for six hours to determine its photolability. The average first order rate constant of PbTx-2 degradation was 0.20 ± 0.05 h-1 at 25 ºC. When PbTx-2 was added to UV-irradiated WBSW, the average rate constant decreased significantly to 0.08 ± 0.03 h-1 at 25 ºC relative to that of untreated WBSW suggesting dissolved organics are involved in the photodegradation of PbTx-2 in seawater. UV-irradiated WBSW treated with Chelex-100 resin to remove trace metals caused no degradation of PbTx-2 upon exposure to sunlight suggesting that trace metals, in addition to organics, are involved in the photodegradation of PbTx-2. Irradiation of PbTx-2 in deoxygenated filtered WBSW caused the toxin to degrade almost immediately upon exposure to simulated sunlight. The effect of deoxygenation on the photodegradation of other brevetoxins including PbTx-1, 3, 6 agreed with the rate of PbTx-2. PbTx-9 and the naturally-produced compound, brevenal, degraded considerably in deoxygenated WBSW but not as rapidly. These results demonstrate that photosensitizers are involved in the degradation mechanism, suggesting that PbTx-2 degrades by secondary photochemical pathway. The mechanism suggested here is that PbTx-2 degrades in the presence of the excited chromophoric dissolved organic matter (CDOM)* and trace metal complex. Furthermore, the removal of oxygen from seawater causes the rate of degradation to increase rapidly because (CDOM)* no longer scavenges oxygen thereby scavenging solely PbTx-2. A model is also proposed which suggests that 75% of PbTx-2 in coastal seawater can be removed in 6 hours by exposure to sunlight. This represents a significant impact on the residence time of the toxin in bloom indicating photodegradation is an important and perhaps the dominant sink of the toxin in coastal seawater.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Keywords
Dinoflagellates--Toxicology, Toxic marine algae, Photochemistry
Subjects
Dinoflagellates -- Toxicology
Photochemistry
Toxic marine algae