UV‐Irradiation of the Antibiotic Sulfathiazole Surprisingly Leads to Former Antituberculotic Promizole

Abstract

Pharmaceuticals are widely distributed in low concentrations in the water compartment. Conventional sewage treatment plants (STP) are not capable to remove pharmaceuticals to the full extent, so alternative methods such as ozonization or photooxidation are tested as additional stage. However, it has been shown that in many cases no complete mineralization is achieved during these processes and transformation products occur. Up to now only little is known about these transformation products in terms of their structure and toxicity. The antibiotic sulfathiazole (STZ) is used in veterinary medicine and it can be detected in different water matrices such as STP effluent or surface water. We tested the ability of photooxidation for degradation of STZ using a medium pressure mercury lamp. LC‐UV showed the formation of several minor compounds and one main transformation product which has been isolated subsequently. Using NMR and high resolution mass spectrometry techniques, we were able to reveal the structure of promizole, an antituberculotic, used in the 1950s. This compound showed a reduced microbial activity in Brilliant Black Reduction Maximum Residue Level test. Furthermore, there was no difference in the effects of promizole when compared to STZ on cell toxicity and cell proliferation in two murine cell lines.