Role of Fe(III), phosphate, dissolved organic matter, and nitrate during the photodegradation of domoic acid in the marine environment

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)](0) 0-4 mu; [NO3-](0) 0-35 mu M; [PO43-](0) 0-4 mu M; [DOM](0) 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/m(2) and initial domoic acid concentration of 0.96 mu M, domoic acid half-lives range over 12-36 h, with half-life a function of [Fe(Ill)], [PO43-], and dissolved organic matter loadings. An NMR based technique for measuring domoic acid-Fe(III) binding (1.72 x 10(11)) is reported.