Biogeochemical cycling of domoic acid and its isomers in the ocean

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

Abstract: Domoic acid, a non-protein amino acid, is a neurotoxin produced by species of the marine diatom Pseudo-nitzschia. Adsorption of dissolved domoic acid (DA) and its geometrical isomers (iso-DAs D, E, and F) was assessed in filtered seawater solutions containing various types of particles. Adsorption of DA occurred onto natural seawater particles and chromatographic silica. Slight DA adsorption occurred onto estuarine bottom sediment and humic acid. No DA losses were seen in the presence of illite, kaolinite, montmorillonite, or silica sand. Biological degradation accounted for DA losses in seawater without particles. Iso- DAs D, E, and F showed negligible adsorption onto particles, suggesting DA isomers are hydrophilic and not particle reactive. These results suggest that adsorption onto particles is not an important sink for DA or its photochemically produced isomers in natural waters. Another facet of domoic acid’s cycling is its interaction with metals present in natural waters. Results of competitive ligand equilibration/ adsorptive cathodic stripping voltammetric studies (CLE-ACSV) reveal that domoic acid forms a chelate with copper with a conditional stability constant: cond CuDA Cu K , 2+ = 6.7 x 1011 M-1. Speciation experiments were also performed to determine binding abilities of DA with 22 nM Zn, 0.5 nM Cd, 0.5 nM Co, and 20 nM Ni in the presence of 5 nM Cu. None of these metals were able to outcompete Cu for DA, suggesting in a natural water matrix Cu is the dominant of these metal chelators. A second set of experiments designed to determine the metal binding abilities of DA and two of its geometrical isomers, iso-DAs E and F utilized excitation-emission matrix (EEM) fluorescence spectroscopy. EEMs of 0.1 µM DA and 0.1 µM Fe, compared to EEMs of 0.1 µM DA alone, exhibited an increase in fluorescence resulting from the complexation of DA to Fe. Scans repeated with 0.1 µM added Cu also exhibited an increase in fluorescence consistent with the strong complexation of DA with Cu determined electrochemically. In contrast to DA, its geometrical isomers iso-DAs E and F showed significant quenching of fluorescence upon addition of both iron and copper, indicating that iso-DAs E and F also form complexes with iron and copper. Results of these studies have important ecological implications because they demonstrate that DA and iso-DAs E and F form complexes with both Cu and Fe. The formation of these complexes may affect the toxicity of Cu, the bioavailability of Fe, and the toxicity of DA and its geometrical isomers in natural waters where the blooms occur.

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
Algal toxins, Biogeochemical cycles, Coastal ecology, Diatoms, Domoic acid, Marine toxins
Subjects
Marine toxins
Coastal ecology
Diatoms
Biogeochemical cycles
Domoic acid
Algal toxins