Sorption/desorption behavior of oxytetracycline and sulfachloropyridazine in the soil water surfactant system

Sorption/desorption of antibiotics, oxytetracycline (OTC), and sulfachloropyridazine (SCP) was investigated in the presence of a nonionic surfactant Brij35. Batch sorption experiments indicated that Freundlich equation fits sorption isotherms well for OTC. The sorption coefficients, K (F), values were computed as 23.55 mL g(-1) in the absence of Brij35 and 25.46 mL g(-1) in the presence of Brij35 in the monomer form (below critical micelle concentration CMC, of 74 mg L-1). However, the K (F) values reduced to 12.76 mL g(-1) in the presence of Brij35 at 2.5 g L-1. Therefore, irrigation with surfactant-rich water may increase the leaching potential of OTC. In the case of SCP, the K (F) value, in the absence of Brij35, was 19.95 mL g(-1). As a result of increasing the concentration of Brij35 to 0.25 g L-1 (about 2.5 CMC), K (F) values first increased and reached a maximum value of 95.49 mL g(-1) and then reduced to 66.06 mL g(-1), at surfactant concentration of 5 g L-1. Unlike OTC, the presence of surfactant in irrigation water is likely to decrease SCP leaching. In the case of OTC, hysteresis was found at Brij35 concentrations below CMC. However, OTC desorbed readily from soil (no hysteresis) at Brij35 concentrations above CMC. In the case of SCP, no hysteresis was found in the presence of the surfactant, both below and above CMC. Further, the obtained values of the efficiency coefficient (E), reveals that Brij35 had the potential to release more OTC from the soil (E > 1) as compared to SCP (E < 1). From these results, it can be concluded that regular use of manure on agricultural soils, especially in regions where poor quality irrigation water is used, can increase OTC contamination of water resources.