Sorption and desorption behavior of four antibiotics at concentrations simulating wastewater reuse in agricultural and forested soils

Abstract

Due to rises in antibiotic resistance, fate and transport of antibiotics in soil systems requires greater understanding to determine potential risks to human and animal health. Adsorption coefficients (K_d and K_f) are standard measures for determining sorption capacity and partitioning behavior of organic contaminants in solid matrices. Frequently, sorption studies use higher antibiotic concentrations (mg L^-1) and larger spiked water volume to mass of soil (>5:1), which may not reflect sorption behaviors of antibiotics at low concentrations (ng L^-1 - μg L^-1) in natural soils. The aim of this study was to determine sorption and desorption behaviors of four antibiotics commonly found in soils due to wastewater reuse using parameters replicating typical soil conditions. Concentrations (μg L^-1) of sulfamethoxazole (SMX), trimethoprim (TMP), lincomycin (LIN) and ofloxacin (OFL) were equilibrated with four soil types at a 2:1 ratio of spiked water volume to mass of soil, which better represents field conditions. Log K_f and log K_foc value ranges in this study were 1.88-1.95 and 3.2-4.7 for TMP, 0.43-1.4 and 2.7-3.2 for SMX, and 0.65-1.4 and 2.0-4.1 for LIN, respectively. Ofloxacin adsorbed tightly to soil particles, and adsorption coefficients could not be calculated. Sorption values were higher than previous studies that used similar soil types but had higher ratios of spiking solution to mass of soil (>5:1). Overall, OFL and TMP are expected to strongly interact with soil particles and be less mobile, while SMX and LIN are expected to be more mobile due to weaker sorption interactions.