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 °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 °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 °C (40–50%) was much lower than that at 25 °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.