Role of Fe(III), Phosphate, Dissolved Organic Matter, and Nitrate during the Photodegradation of Domoic Acid in the Marine Environment

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The photodegradation of domoic acid in model seawater containing varying amounts of total Fe(III) (expressed as Fe(III)), NO3-, total phosphate (expressed as PO43-), and dissolved organic matter (DOM) is reported. A multivariate, microscale, high-throughput experimental approach is described for evaluating how these components interact to control the removal of domoic acid from natural waters. Under the nominal conditions of the study ([Fe(III)]o 0−4 μM; [NO3-]o 0−35 μM; [PO43-]o 0−4 μM; [DOM]o 0−10 mg/L), it is apparent that Fe(III) and DOM are significant promoters of domoic acid photooxidation. In contrast, PO43- interacts with Fe(III) to inhibit the photooxidation of domoic acid, but PO43- alone does not act to slow or accelerate domoic acid photodegradation. No other variables (singly or interactively) have a statistically significant impact. At an incident light intensity of 765 W/m2 and initial domoic acid concentration of 0.96 μM, domoic acid half-lives range over 12−36 h, with half-life a function of [Fe(III)], [PO43-], and dissolved organic matter loadings. An NMR based technique for measuring domoic acid−Fe(III) binding (1.72 × 1011) is reported.