title: Effects of sorbate speciation on sorption of selected sulfonamides in three loamy soils.
abstract: Sorption of sulfamethazine (SMN) and sulfathiazole (STZ) was investigated in three soils, a North Carolina loamy sand, an Iowa sandy loam, and a Missouri loam, under various pH conditions. A significant increase in the sorption coefficient (KD) was observed in all three soils, as the sulfonamides converted from an anionic form at higher pH to a neutral/cationic form at lower pH. Above pH 7.5, sulfonamides exist primarily in anionic form and have higher aqueous solubility and no cationic character, thereby consequently leading to lower sorption to soils. The effect of speciation on sorption is not the same for all sulfonamides; it is a function of the pH of the soil and the pKa of the sulfonamides. The results indicate that, for the soils under investigation, SMN has comparatively lower KD values than STZ. The pH-dependent sorption of sulfonamides was observed to be consistent in all three soils investigated. The KD values for each speciated form-cationic, neutral, and anionic-were calculated using an empirical model in which the species-specific sorption coefficients (KD0, KD1, and KD2) were weighted with their respective fractions present at any given pH.
authors.affiliation: Environmental Research Center for Emerging Contaminants, Department of Civil, Architectural and Environmental Engineering, Butler Carlton Hall, University of Missouri-Rolla, 1870 Miner Circle, Rolla, MO 65401, USA.
authors.forename: Sudarshan T
authors.initials: ST
authors.lastname: Kurwadkar
authors.forename: Craig D
authors.initials: CD
authors.lastname: Adams
authors.forename: Michael T
authors.initials: MT
authors.lastname: Meyer
authors.forename: Dana W
authors.initials: DW
authors.lastname: Kolpin
mesh_terms: D000327:Adsorption; D000890:Anti-Infective Agents / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006863:Hydrogen-Ion Concentration; D007484:Iowa; D008923:Missouri; D009657:North Carolina; D012987:Soil / Q000032:analysis*; D013011:Sorbic Acid / Q000737:chemistry*; D013449:Sulfonamides / Q000737:chemistry*
chemical_list: D000890:Anti-Infective Agents; D012987:Soil; D013449:Sulfonamides; D013011:Sorbic Acid