Impact of Humic and Fulvic Acids in Liquid Swine Manure on the Mobility of Sulfamethoxazole in Manured Soils

Abstract

Sulfamethoxazole (SMX) is widely used in the swine industry; hence, it is detected in manure and the environment. This study examined the impact of liquid swine manure dissolved organic carbon (SM-DOC) on SMX sorption onto bentonite clay. Humic acid (HA) and fulvic acid (FA) were extracted, characterized, and used in a batch sorption study, and then sorption mechanisms were described. Surface-oriented phenolic groups primarily induced the hydrophilicity of FA, whereas HA was rich in aliphatic amide and carboxylic groups. Surface-oriented unsubstituted aliphatic groups determined the hydrophobicity of FA, while it was unsubstituted aromatic groups for HA. Cuboidal-shaped FA formed unstable macrocolloids. Spherical-shaped HA fell within the submicroparticle to nanoparticle range, providing a larger surface area for sorption. SMX binds to FA through fluorophore-quencher mechanisms with surface phenols, while HA involves nonfluorophore quencher mechanisms with aliphatic carboxylic and amide groups. Organo-mineral complexation reorients the non-polar aromatic and aliphatic functional groups in FA and HA to facilitate hydrophobic interactions with SMX. Multivalent metal ions in the SM-DOC promote chemisorption of organic carbon on a 2:1 mineral surface; in the absence of metal ions, SM-DOC is physically stabilized.

Keywords: sulfamethoxazole, Swine manure, Humic acid, Fulvic acid, sorption