Stability of Colistin and Carbapenems in Water and Wastewater

This study identified the stability of two categories of last-resort antibiotics: colistin (colistins A and B) and carbapenems (meropenem, doripenem, biapenem, and ertapenem) in water and wastewater. Colistin and carbapenems at -20 degrees C showed a considerable degradation over 3 weeks, with the highest decay noted for ertapenem. Under an acidic pH, all carbapenems showed a comparable level of decay in both water and wastewater. However, under neutral pH, the degradation under wastewater (k(ww) = 0-0.0117 h(-1)) was higher than in water (k(w) = 0-0.0042 h(-1)). For colistin at pH 7, degradation observed in wastewater within 24 h was significantly higher than that in water, with an observed k(ww) of 0.44 h(-1) (pH 7, 25 degrees C) in comparison to a k(w) of 0.0128 h(-1). Temperature deteriorated the stability of colistin in wastewater at pH 7, as the degradation at 4 degrees C (40-50%) was much lower than that at 25 degrees C (80-90%). The stability of colistin A and B was identical in both water and wastewater under acidic conditions (pH 5) irrespective of the temperature, with an observed degradation of less than 10%. These results shed light on the environmental stability of last-resort antimicrobials for wastewater-based epidemiology and other related applications.