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

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 (Kd and Kf) 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 Kf and log Kfoc 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. [Display omitted] •Accurate soil sorption/desorption data is necessary for risk assessment of antibiotics.•Most sorption studies use high water to soil ratios that don't emulate soil conditions.•Using high water to soil ratios may underestimate sorption coefficients for antibiotics.•Ofloxacin and trimethoprim tightly bind soil particles and would be less mobile.•Sulfamethoxazole and lincomycin interact less with soil and would be more mobile.