Adsorption of domoic acid to marine sediments and clays

Abstract

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 (R² = 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.