Unveiling the inhibition of chlortetracycline photodegradation and the increase of toxicity when coexisting with silver nanoparticles

Abstract

Silver nanoparticles (AgNPs) and antibiotics inevitably co-exist in water environment. Nonetheless, little is known regarding the interactions between AgNPs and antibiotics or the effects of AgNPs on environmental behavior of antibiotics, particularly on sunlight-driven transformation. In the present work, we found that AgNPs obviously inhibit the photochemical decay of chlortetracycline (CTC), and CTC boosts the dissolution of AgNPs. With the help of electron paramagnetic resonance (EPR) and quenching experiment, we ascertained that these results originated from the competition between AgNPs against CTC for capturing ¹O₂ generated from CTC photosensitization. ¹O₂ reacting with CTC contributed mostly to CTC photodegradation, while ¹O₂ as well reacting with AgNPs leads to release of Ag⁺. When compared to reaction of ¹O₂ with CTC, ¹O₂ is prone to react with AgNPs, based on lower Gibbs free energy of AgNPs reacting with ¹O₂. Therefore, upon CTC co-existing with AgNPs, the release of Ag⁺ was accelerated and the photodegradation of CTC was inhibited obviously. Furthermore, the accelerated release of Ag⁺ significantly increased their toxicity toward E. coli cells under simulate sunlight irradiation. Overall, the findings demonstrate how AgNPs interact with CTC and how these interactions affect the environmental behaviors of CTC or AgNPs, allowing more accurate assessments of the risk to ecosystems posed by AgNPs coexisting with antibiotics.

Keywords: (1)O(2); Chlortetracycline; Photodegradation; Silver nanoparticles.