Domoic acid, a powerful marine toxin produced by Pseudo-nitzschia species, is remarkably pervasive in North American coastal waters. This toxin is a threat to public health and some marine life, and has resulted in severe economic losses in the shellfish and crustacean harvesting industry. Originally discovered as the causative agent in an episode of fatal human poisoning in eastern Canada in 1987, domoic acid has subsequently been linked to other epizootics, particularly on the western coast of North America where it has resulted in the death of seabirds and mammals. Despite the significance of domoic acid to the biogeochemistry of marine systems, virtually nothing is known about the fate of that fraction of the toxin not transferred through the food chain - arguably the vast majority of toxic material produced during harmful algal blooms.
In this project, researchers at the University of North Carolina at Wilmington will determine the processes that control the biogeochemical cycling of domoic acid once it is released into the water column. This is significant because preliminary evidence indicates water column concentrations of domoic acid can reach as high as 100 nM during a bloom event. The research team will address the role of light (photochemically-mediated) and dark (microbial and/or chemical degradation) processes and trace metal complexation on the biogeochemical cycling and fate of this powerful toxin in natural waters. They hypothesize that photochemical reactions are particularly important because preliminary data indicates domoic acid is rapidly converted to a series of geometric isomers and decarboxylated derivatives when exposed to short-term irradiations using simulated sunlight. Photochemical degradation of domoic acid is extremely significant because it reduces the lifetime of this powerful toxin in surface seawater where it is produced, but at the same time may also produce more toxic photo-produced byproducts. A second hypothesis, based on recent evidence showing strong complexes are formed by domoic acid with Fe(III) and Cu(II), is that trace metals play an important role in the fate of the toxin once it is released into natural waters. Complexation of domoic acid by these redox-active trace metals is important because the complexes will have different photochemical reactivities than uncomplexed domoic acid (or its photo-isomers) and may therefore have very different residence times and fates in the environment. The experimental approach will be to irradiate domoic acid in seawater to its three geometric isomers and decarboxylated derivatives under a variety of conditions to quantify rates of photochemical degradation and identify the byproducts produced. Similar experiments using dark controls will provide information on kinetics of microbial and chemical degradation in coastal waters. A series of metal- binding studies with the same suite of compounds will determine the degree of metal complexation and the strength of the complexes formed.
The proposed research is expected to provide significant new information regarding the chemical and physical factors influencing the residence time and fate of domoic acid and its byproducts in natural waters. This proposal directly addresses fundamental ecological and oceanographic questions related to domoic acid, a powerful and pervasive toxin present in frequent Pseudo-nitzschia blooms in North American coastal waters. A major part of the requested funding will be used to support a post-doctoral researcher, a masters-level graduate student, and four undergraduate students per year. The involvement of undergraduates will be an integral part of the investigators research program. Young students are attracted to this type of study because they perform environmental research of international interest. The proposed research will continue this pattern by allowing undergraduates at a coastal university to become involved in a high profile research question associated with toxic algal blooms.
