Effects of Sorbate Speciation on Sorption of Selected Sulfonamides in Three Loamy Soils

Document Type

Article

Journal/Book Title/Conference

Journal of Agriculture and Food Chemistry

Volume

55

Issue

4

Publisher

American Chemical Society

Publication Date

2-21-2007

First Page

1370

Last Page

1376

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.Kurwadkar, S., Adams, C., Meyer, M., Kolpin, D. (2007) “Effects of Sorbate Speciation on Sorption of Selected Sulfonamides in Three Loamy Soils,” J. Agriculture and Food Chemistry, 55, 1370-1376.

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