Sorption and desorption of sulfadimethoxine, sulfaquinoxaline and sulfamethazine antimicrobials in Brazilian soils

• The sorption of three sulfonamides was studied in four Brazilian soil–water systems.
• KF values indicate that the sulfonamides weakly adsorbed on the evaluated soils.
• There is high potential for surface and groundwater contamination.
• The adsorption is directly related to the lipophilicity of the sulfonamide.

Adsorption and desorption are important processes that influence the transport, transformation and bioavailability of antimicrobials in soils. The adsorption–desorption characteristics of sulfadimethoxine, sulfaquinoxaline and sulfamethazine in Brazilian soils (sandy, sandy-clay and clay) were evaluated using the batch equilibrium method. The sulfonamides were quantified in the soil solutions by a previously in house validated HPLC-PAD method. The adsorption/desorption data for the sulfonamides in soils fit the Freundlich isotherms well in the logarithmic form. The Freundlich adsorption coefficients ranged from 1.4 to 19.0 μg1 − 1 / n(cm3)1 / n g− 1, suggesting that all of the sulfonamides weakly adsorbed on the evaluated soils. The Freundlich desorption coefficients ranged from 0.85 to 24.8 μg1 − 1 / n(cm3)1 / n g− 1, indicating that the sulfonamides tend to be leached from soils with high sand and low organic carbon contents, suggesting that there is high potential for surface and groundwater contamination.