Trimethoprim and Clarithromycin transport in agricultural soils

The transport of solutes in the soil is crucial for both the soil-plant system and the processes within it. However, it can also be harmful because it can favour the transport of certain substances that can become pollutants, such as antibiotics, which reach the environment through the application of wastewater and sludge, such as irrigation water and soil amendments, which come from wastewater treatment plants. Once in the soil, these pollutants can be transported to different water compartments, favouring the propagation of resistant bacteria and genes. This study aims to determine the transport capacity of eight agricultural soils for two antibiotics belonging to the most widely used families. The experiments were carried out with Clarithromycin, a macrolide, and Trimethoprim, a diaminopyrimidine, in column experiments, finding that Clarithromycin can be more easily transported than Trimethoprim. There is no evident gradient of the eight soils according to the different soil properties they present. The results for both antibiotics were modelled with the means of temporal moment analysis and obtained retardation values ranging from 1.65 to 4.95 for Clarithromycin and between 3.31 and 13.37 for Trimethoprim. In addition, for the mean concentration breakthrough time, the values obtained were from 10.04 to 32.55 pore volume (PV) and between 23.24 and 66.06 PV, respectively. The fact that there is some transport of both antibiotics could suggest a risk of leaching into groundwater, implying a human and ecological risk. • Clarithromycin (CLA) is more mobile than Trimethoprim (TRI). • CLA retained up to 30 % and TRI 67 % in agricultural soil through column experiments. • Retardation and mean concentration breakthrough of antibiotic are higher for TRI.