Effects of pH and Ionic Strength On Sulfamethoxazole and Ciprofloxacin Transport In Saturated Porous Media.

Effects of pH and Ionic Strength on Sulfamethoxazole and Ciprofloxacin Transport in Saturated Porous Media

Chen Hao¹, Bin Gao^2*, Hui Li³ and Lena Q Ma^1*

¹ Department of Soil and Water Science, University of Florida, Gainesville, FL 32611

² Department of Agricultural and Biological Engineering, University of Florida, Gainesville, FL 32611

³ Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824

* Corresponding author, lqma@ufl.edu, bg55@ufl.edu

 

Abstract

 

Many antibiotics regarded as emerging contaminants have been frequently detected in soils and groundwater; however, their transport behaviors in soils remain largely unknown. This study examined the transport of two antibiotics, sulfamethoxazole (SMZ) and ciprofloxacin (CIP), in saturated porous media. Laboratory columns packed with quartz sand was used to test the effects of solution pH and ionic strength (IS) on their retention and transport. The results showed that these two antibiotics behaved differently in the saturated-sand columns. In general, SMZ showed a much higher mobility than CIP for all experimental conditions tested. Almost all SMZ transported through the columns within one pore volume in deionized water (i.e., pH=5.6, IS=0), but no CIP was detected in the effluents under the same condition after extended column flushing. Perturbations in solution pH (5.6 and 9.5) and IS (0 and 0.1 M) showed no effects on SMZ transport in the saturated columns. When pH increased to 9.5, however, ~93% of CIP was found to elute from the sand columns. Increase of IS from 0 to 0.1 M also slightly enhanced the mobility of CIP within the sand column at pH 5.6, but still no CIP was found in the effluents. A mathematical model based on advection-dispersion equation coupled with equilibrium and kinetic reactions successfully simulated the transport of the antibiotics in water-saturated porous media with R²=0.99.