title: Triazine adsorption by saponite and beidellite clay minerals.
abstract: We investigated the sorption of three triazine herbicides (atrazine, simazine, and metribuzin) by saponite and beidellite clay minerals saturated with K+, Cs+, Na+, and Ca2+. Saponite clay sorbed a larger fraction of each pesticide from aqueous solution than did beidellite clay. The lower cation-exchange capacity in saponite compared to that in beidellite presumably results in a less crowded interlayer, with more siloxane surface being available for adsorption. Generally, Cs-saturated clays sorbed more triazines than did clays saturated by K+, Na+, or Ca2+. We attribute this to the smaller hydrated radius of Cs+, which again increases the siloxane surface that is available for sorption. Furthermore, the relatively weak hydration of Cs+ reduces the swelling of clay interlayers, thus making sorption domains less hydrated and more receptive to hydrophobic molecules. The Cs-saponite manifested a sorption of more than 1% atrazine by weight above equilibrium concentrations of 6 mg/L, which to our knowledge is the largest sorption of neutral atrazine from water yet reported for an inorganic sorbent. Molecular dynamics simulations indicate that atrazine interacts both with clay basal planes and with multiple cations in the clay interlayer.
authors.affiliation: Department of Crop and Soil Sciences and Environmental Science and Policy Program, 283 Plant and Soil Sciences Building, Michigan State University, East Lansing, Michigan 48824-1325, USA.
authors.forename: Vaneet
authors.initials: V
authors.lastname: Aggarwal
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Teppen
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry; D001280:Atrazine / Q000737:chemistry*; D000077215:Clay; D004787:Environmental Pollution / Q000517:prevention & control; D006540:Herbicides / Q000737:chemistry*; D012839:Simazine / Q000737:chemistry*; D014227:Triazines / Q000737:chemistry*; D014867:Water
chemical_list: D000538:Aluminum Silicates; D006540:Herbicides; D014227:Triazines; D014867:Water; C010863:beidellite; C099453:saponite; D001280:Atrazine; C009235:metribuzin; D012839:Simazine; D000077215:Clay