Distinct effects of copper on the degradation of β-lactam antibiotics in fulvic acid solutions during light and dark cycle

This study revealed the dual roles of Cu(II) on the beta-lactam antibiotics degradation in Suwannee River fulvic acid (SRFA) solution during day and night cycle. Amoxicillin (AMX) and ampicillin (AMP) were selected as the representative beta-lactam antibiotics. Cu(II) played a key role in the dark degradation of AMX and AMP via catalytic hydrolysis and oxidation. However, Cu(II) mainly exhibited an inhibitory effect on SRFA-involved photochemical degradation of AMX and AMP. In the presence of 500 nM of Cu(II), the degradation rate of AMX and AMP in the light condition were around 5 times higher than that in the dark condition, suggesting the photodegradation of beta-lactam antibiotics was much more pronounced than catalyzed hydrolysis and oxidation. The triplet excited state of SRFA ((3)SRFA*) primarily contributed to AMX and AMP photodegradation. Hydroxyl radicals ((OH)-O-center dot) and singlet oxygen (O-1(2)) exhibited limit impacts. The redox cycle of Cu(II)/Cu(I) restricted the electron transfer pathway of (3)SRFA* with AMX and AMP. During the day and night cycles for 48 h, Cu(II) served as a stronger inhibitor rather than a promotor. These findings highlight the interactions between Cu(II) and SRFA are distinct under day and night conditions, which could further affect the fate of beta-lactam antibiotics in natural environments. (C) 2020 The Author(s). Published by Elsevier B.V. on behalf of Chinese Society for Environmental Sciences, Harbin Institute of Technology, Chinese Research Academy of Environmental Sciences.