Research Environmental Exposure Assessment of Fluoroquinolone Antibacterial Agents from Sewage to Soil EVA M. GOLET, † IRENE XIFRA, ‡ HANSRUEDI SIEGRIST, † ALFREDO C. ALDER,* ,† AND WALTER GIGER † Swiss Federal Institute for Environm ental Science and Technology (EAWAG), Swiss Federal Institute of Technology Zurich (ETH), CH-8600 Du ¨bendorf, Switzerland, and Universitat de Girona (UdG), E-17071 Girona, Spain The behavior of fluoroquinolone antibacterial agents (FQs) during mechanical -biological wastewater treatment was studied by mass flow analysis. In addition, the fate of FQs in agricultural soils after sludge application was investigated. Concentrations of FQs in filtered wastewater (raw sewage, primary, secondary, and tertiary effluents) were determined using solid-phase extraction with mixed phase cation exchange disk cartridges and reversed- phase liquid chromatography with fluorescence detection. FQs in suspended solids, sewage sludge (raw, excess, and anaerobically digested sludge), and sludge-treated soils were determined as described for the aqueous samples but preceded by accelerated solvent extraction. Wastewater treatment resulted in a reduction of the FQmass flow of 88- 92%, mainly due to sorption on sewage sludge. A sludge- wastewater partition coefficient (log K d ∼ 4) was calculated in the activated sludge reactors with a hydraulic residence time of about 8 h. No significant removal of FQs occurred under methanogenic conditions of the sludge digesters. These results suggest sewage sludge as the main reservoir of FQresidues and outline the importance of sludge management strategies to determine whether most of the human- excreted FQs enter the environment. Field experiments of sludge-application to agricultural land confirmed the long- term persistence of trace amounts of FQs in sludge-treated soils and indicated a limited mobility of FQs into the subsoil. Introduction Municipal wastewater treatment plants play an important role in the life cycle ofhuman-use pharmaceuticals because they act as point sources to the aquatic environment. If sorption to sewage sludge is the major removalpathwayfrom the wastewater stream, the application of sewage sludge as soilfertilizer representsan additionalentryroute for human- use pharmaceuticals into the environment. Hence, it is important to understand the behavior ofpharmaceuticals as they pass through wastewater treatment plants. Although it is well-known that the discharge of treated wastewater effluentsto surface water accountsasthe major entrypathway to the environment for most human-use pharmaceuticals (1-3), their behavior during wastewater treatment is still mostly unknown. Some studies have investigated the fate of pharmaceuticalsin laboratory-scale sewage treatment plants (4, 5)or have involved laboratorytestingon biodegradability (1, 4, 5).Some data are also available for full-scale wastewater treatment plants on the overall removal of some pharma- ceuticals from the aqueous phase (3, 6-8), but there is still a lackofdetailed studies on the efficiencyofsingle treatment processeson the elimination ofpharmaceuticals.Quantitative data on the occurrence ofpharmaceuticals in sewage sludge are also scarce. Fluoroquinolone antibacterial agents (FQs) are among the few pharmaceuticals that have been measured in both wastewater effluents (6) and in sewage sludges (9, 10). The most consumed FQs in Switzerland, ciprofloxacin (CIP) and norfloxacin (NOR),were determined at the ng/Llevelin Swiss wastewater effluents(6)and at the low mg/kglevelin sewage sludges (9, 10).Because FQs are excreted bythe human body in urine (CIP 45-62%, NOR 20-40%) and feces (CIP 15- 25%, NOR 28%) (11, 12), the analysis ofboth liquid and solid sewage matrices is necessary to determine the entry route of FQs to the environment. During wastewater treatment, FQs are substantially removed from the aqueous phase (6). Based on laboratory studies (13-15), sorption to sewage sludge appears to be the main removal process, yet confir- mation ofsuch predictionsfor full-scale wastewater treatment is needed. The sludge management strategyultimatelyimplemented willdetermine the finalfate ofFQ residues sorbed to sewage sludge.Although controversial(16),the application ofsewage sludge as fertilizer to agricultural land is still widely used in several countries. In Switzerland for instance, 42% of the sewage sludge produced in 1999 (about 88 000 tons) were applied to agricultural land (17). As protection against potential adverse effects of sewage sludge constituents, a revision of the European Union Directive 86/278/EEC is planned to limit the amount of organic micropollutants released to the environment by sewage sludge disposal (18). However,pharmaceuticalsare not included in the directives. A more rigorous decision has been taken in Switzerland, where the disposal of sewage sludge into agriculturally used areas is forbidden since May 2003. Nonetheless, as long as such a disposalpractice occurs elsewhere,better knowledge on the fate and effects of chemicals in sludge-treated soils is needed. FQs have already been identified as persistent pollutants in sludge treated soils (9) and sediments (19), so their behavior in the terrestrial environment is of special interest. The first part ofthis study reports on field measurements in which the analytical methods for the determination of FQs in aqueous (20) and solid (9) sewage matrices are jointly used to perform a mass balance of FQs in a municipal wastewater treatment plant. In the second part, a field investigation was conducted to gain insight on the fate of FQs in sludge-treated soils. Finally, the obtained field data are compared with the literature on FQs sorption and biodegradation to assessthe physicochemicaland biological processesthat mayaffect the environmentalbehaviorofFQs. Experimental Section Description ofthe WastewaterTreatment Plant. The largest municipal wastewater treatment plant (WWTP) in Switzer- *Corresponding author phone: + 41 1 823 5478; fax: + 41 1 823 5311; e-mail: alfredo.alder@eawag.ch. † Swiss Federal Institute for Environmental Science and Technol- ogy(EAWAG)and Swiss FederalInstitute ofTechnologyZurich (ETH). ‡ Universitat de Girona. 10.1021/es0264448 CCC: $25.00  2003 American Chemical Society VOL. 37, NO. 15, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 3243 Published on Web 06/28/2003