Pharmaceutical biodegradation under three anaerobic redox conditions evaluated by chemical and toxicological analyses

Biodegradation of pharmaceutically active compounds (PhACs) in the subsurface layer of constructed wetlands (CWs) under various anaerobic redox conditions is rarely studied. In this study, CW sediment microbial populations were enriched for PhAC biodegrading organisms. Biodegradation effectivity of a mixture of six PhACs (caffeine, CAF; naproxen, NAP; metoprolol, MET; propranolol, PRO; ibuprofen, IBP; carbamazepine, CBZ) and single compounds (CAF, NAP) was investigated under nitrate reducing, sulfate reducing, and methanogenic conditions using chemical and toxicological analyses. Biodegradation efficiencies varied strongly among the six PhACs and three redox conditions chosen. CAF and NAP were completely biodegraded under sulfate reducing and methanogenic conditions whereas biodegradation efficiencies of the other PhACs were much less (MET, PRO <20%; IBP, CBZ, negligible). CAF and NAP showed significantly lower biodegradation under nitrate reducing conditions than under the other two redox conditions. No difference was found in biodegradation efficiencies of CAF and NAP when present as single compound, or as a mixture with other PhACs. Different intermediates were observed, indicating different biodegradation pathways under different redox conditions and when the PhACs were present as single compound or in a mixture. From toxicological perspective, toxicity of PhACs and/or their intermediates to Vibrio fischeri was attenuated during the biodegradation process. Chemical and toxicological data showed positive correlations in principle component analysis, by which potentially toxic PhACs and intermediates are indicated for further ecotoxicological hazard assessment.