The adsorption of saxitoxin to clays and sediments in fresh and saline waters

The adsorption of saxitoxin to Na- and Ca-montmorillonite, kaolin (crystalline and amorphous), kaolinite, Bread and Butter Creek sediment (an estuarine tidal creek), Gulf of Mexico sediment, and Santa Barbara Basin sediment in deionized water and 32‰ salinity simulated seawater (Instant Ocean™) is reported. Adsorption was partially reversible for all cases and best described using a Freundlich isotherm. The corresponding Freundlich constants (KF) ranged from 8.83 × 103 μmol/kg to 6.76 × 104 μmol/kg for freshwater and 4.73 × 103 μmol/kg–1.11 × 104 μmol/kg for seawater. There is a positive linear correlation seen between the KF values and the cation-exchange capacity of the adsorbents. The release of saxitoxin from previously equilibrated adsorbents was determined in freshwater (0–18%) and seawater (4–53%).