Sorption of Three Fluoroquinolone Antibiotics to a Wetland Soil.

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The presence of antibiotic pharmaceutical compounds in the aquatic environment is an area of growing concern. In Louisiana, many municipalities treat wastewater using lagoons, aeration basins and wetlands.  Many of these treatment plants discharge into natural wetlands for tertiary treatment of the wastewater, which can contain pharmaceuticals with a concentration range from low parts per-million to high parts per-trillion.  Therefore, it is important to understand removal mechanisms of these compounds in wetland systems. The European Union’s Organization for Economic Cooperation and Development (OECD) method 106, adsorption – desorption using a batch equilibrium method, was followed to determine sorption/desorption of ciprofloxacin, norfloxacin and ofloxacin to a wetland soil of Southeast Louisiana.  New analytical methods were developed using an HPLC with UV and fluorescence detection. Fifty percent of each compound sorbs within the first 20 hours of incubation and equilibrium (60-90% sorption) was reached between 2 and 3 days.  Only 5-12% of sorbed compounds were released from the soil (desorption) over a 3 day period.  These results indicate high loading onto the soil, but low release after binding.  Therefore, sorption to soil can be a major removal pathway for these compounds from water. We found that competition between individual compounds can decrease the sorption of other compounds to the soil. This could lead to a decrease in sorption rates of certain compounds and a greater release downstream in a wastewater treatment system that could contain hundreds of pharmaceutical compounds.