Deactivation and transformation products in biodegradability testing of ß-lactams amoxicillin and piperacillin

Antibiotics have increasingly been detected in effluents and the environment. However, information on the degree of deactivation and mineralization, and the nature of possible formed dead-end transformation products is scarce but desirable for proper risk assessment. An important group of antibiotics is the ß-lactams. We studied the transformation of the closely structurally related ß-lactams piperacillin and amoxicillin in two OECD biodegradability batch tests. None of the antibiotics was biodegraded in the closed bottle test (CBT). However, primary abiotic elimination as monitored by HPLC–UV–VIS was 20% and 100% in the CBT within 14 days, respectively. With HPLC–UV–VIS and ion trap LC–MS/MS primary elimination was shown to be more than 94% for both antibiotics within seven days in the Zahn-Wellens test (ZWT). Both compounds were deactivated by hydrolysis. For piperacillin, a dead-end transformation product resulted after hydrolysis of the ß-lactam ring. For amoxicillin full mineralization of the transformation products was observed.