Systematic suspect screening and identification of sulfonamide antibiotic transformation products in the aquatic environment

The formation of environmental sulfonamide transformation products (TPs) has only been investigated for very selected compounds, and their transformation pathways are incompletely elucidated. Given their homologous series, it is likely that similar transformation reactions occur for all sulfonamides. It has recently been demonstrated for sulfamethoxazole (SMX) that its derivative TPs retain antibiotic activity. Unfortunately, TP reference standards are often not available and a number of TPs are still unknown. Therefore, in the present study, a generic scheme was developed to predict 29 potential TPs of sulfonamide antibiotics via identification of the major transformation and breakdown reactions. Mass shifts were calculated for each transformation allowing for a suspect screening using LC/QTOF. Based on the structural elucidation of the parent sulfonamide product ion spectra, five characteristic product ions could be predicted for each of 15 derivative TPs. The predictions were confirmed with reference standards of SMX TPs as well as with data of TPs of further sulfonamides reported in literature. In a final step, samples of activated sludge biotransformation experiments were screened for suspect TPs of two sulfonamides. In total, 13 ecotoxicologically relevant TPs could be tentatively identified by use of the product ion predictions and LC/QTOF.