New biotransformation pathways from sulfamethoxazole and ciprofloxacin removal in sewage treatment along the spatial profile of an anaerobic fixed bed bioreactor

Rodrigo B. Carneiro^a, Carolina A. Sabatini^b, Guilherme M. Titato^a, Tanare C.R. Ferreira^a, Marcelo Zaiat ^b, Álvaro J. Santos-Neto^a

Laboratory of Chromatography (CROMA), Institute of Chemistry of São Carlos, University of São Paulo (USP), 400, Trabalhador São-Carlense Ave., São Carlos, São Paulo 13566-590, Brazil.

In this work, the biotransformation products (BTPs) from the removal of the antibiotics sulfamethoxazole (SMX) and ciprofloxacin (CIP) were assessed for the first time in an anaerobic packed bed biofilm reactor (APBBR) treating municipal sewage. Anaerobic batch assays at high concentrations of the antibiotics (5 mg·L−1) were performed to identify the BTPs generated during the SMX and CIP biodegradation. From the mass transitions of the identified BTPs, they were analyzed along the spatial profile of the APBBR fed with sewage (400 ngSMX·L−1 and 300 ngCIP·L−1). Three BTPs were identified: m/z 256 and m/z 270 from SMX, and m/z 316 from CIP. The molecular structures of the BTPs revealed that SMX biotransformation occurs in the isoxazole ring and a dehydroxylation in the CIP molecule. This study showed new biotransformation pathways of SMX and CIP during anaerobic digestion, contributing to the understanding of the fate of these pharmaceutical compounds in the environment.