Date of Award

6-1-2015

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences/Environmental, Earth & Ocean Sciences

First Advisor

Robert E. Bowen

Second Advisor

David G. Terkla

Third Advisor

Helen C. Poynton

Abstract

Domoic acid is a neurotoxin produced by the marine diatom genus Pseudo-nitzschia and causes cell death primarily in the area of the brain responsible for long-term memory. The resulting severe illness has been termed amnesic shellfish poisoning. Domoic acid accumulates in shellfish and planktivorous fish that consume Pseudo-nitzschia, resulting in exposure to humans through consumption of planktivorous seafood. A regulatory standard in seafood was developed shortly after its discovery in 1987 to protect against acute effects. This regulatory standard has not been revised despite significant recent data in the scientific literature.

This dissertation is divided into four sections: (1) an identification of anthropogenic and natural drivers of nutrient dynamics as well as social dynamics that can contribute to current and future exposure to domoic acid; (2) a review of the weight of evidence for revisiting the current regulatory standard based on recent low level chronic effects data in the toxicological literature, sensitive subpopulation information and long term seafood consumption data; (3) an analysis of monitoring data on the presence of Pseudo-nitzschia in ocean waters and domoic acid in seafood to examine spatial and temporal trends in human exposure; and (4) evaluation of the regulatory framework for natural toxins in seafood with domoic acid as an example.

Nutrient and social dynamics have the potential to drive exposure in humans. Recent toxicological data are not reflected in the current standard as it is based on data for acute toxicity and protects against gross observable neurotoxicity rather than chronic effects. The recent literature has shown that exposure to domoic acid can result in more subtle physical and behavioral brain impacts that have been observed in limited human data as well as extensive data on laboratory animals and marine mammals. Toxicological studies have demonstrated that certain groups such as the young, and the elderly are much more sensitive to domoic acid exposure. This is of particular concern because monitoring data for domoic acid in seafood are limited and may not ensure protection of the public. Pseudo-nitzschia is ubiquitous both temporally and spatially. This dissertation concludes that the regulatory approach warrants revisiting.

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