Adsorption of domoic acid to marine sediments and clays

Conditional solid-water distribution coefficients ( K-d) for the adsorption of domoic acid ( DA) to a series of complex sediments and clays were determined in artificial seawater. K-d ranged from 5.11 L g(-1) to 0.97 L g(-1), with a corresponding ranking of: kaolinite > Gulf of Mexico sediment > Santa Barbara Basin sediment > Bread and Butter Creek sediment > poorly crystallized kaolin > Ca-montmorillonite > Na-montmorillonite > well crystallized kaolin > diatomaceous earth. Adsorption correlated with the anion exchange capacity of the clays tested ( R-2 = 0.98), but not the more structurally complex sediments. The effect of added transition metals ( Fe( III), Cu( II), Al( III)) and terrestrially derived dissolved organic matter ( Suwannee River DOM, SRDOM) on DA adsorption to Na-montmorillonite, well crystallized kaolin, and Gulf of Mexico sediment, was also tested. The addition of transition metals led to increased adsorption to all surfaces by a factor of 2-7, presumably by enabling the adsorption of DA-metal complexes. SRDOM enhanced DA adsorption by a factor of approximately 2.5. The release of adsorbed DA from sediments was also examined. Under our conditions, adsorbed DA equilibrated with the overlying aqueous phase within minutes with approximately 50% release.