Fate Of Representative Fluoroquinolone, Macrolide, Sulfonamide And Tetracycline Antibiotics In Subsurface Environments

Background/Need:
The problem of antibiotics entering the environment from municipal and agricultural sources is well recognized and is a matter of growing concern. Several reports documenting the presence of antibiotics in groundwater, both in the U.S. and Europe, have been published within the last decade. Since soils are the recipients of various types of wastes and have the capability to serve as potential “sinks,” a better understanding of processes controlling the interaction of antibiotics with soils is required. Quantification of the extent of sorption and elucidation of underlying mechanisms of interaction with soil constituents is especially important,
because sorption determines the fraction of antibiotics that is available for transport to groundwater or is biologically active. Antibiotics possess molecular properties expected to favor their sorption to soil components. There is a paucity of information related to the fate and transformation of antibiotics in soil/water environments.
In a recent WI statewide survey of wastewater treatment plants funded by the GCC (Karthikeyan and Meyer, 2006), members of five antibiotic compound classes were detected in the following order of frequency: tetracyclines and trimethoprim > sulfonamides > macrolides > fluoroquinolones. These compounds were also detected in the first nationwide survey conducted by the USGS (Kolpin et al., 2002). In the WI survey, sulfamethoxazole (a sulfonamide) and tetracycline were also detected in groundwater monitoring wells adjacent to the treatment systems. Sorption of these antibiotics to soils can be expected to be controlled by the nature of their interactions with important soil components, such as clay minerals, hydrous metal oxides, and organic matter (both in dissolved and particle-bound forms).

Objectives:
The study objectives were to: (1) quantify the extent of sorption of selected antibiotics (one compound from each family of antibiotics detected in the WI survey: tetracyclines, sulfonamides, macrolides, fluoroquinolones) to humic substances (HS) associated with hydrous iron and aluminum oxides and smectitic clays; and (2) investigate antibiotic association with dissolved organic matter and how such association facilitates antibiotic transport under unsaturated flow conditions.