Incorporating Transformation Products for an Integrated Assessment of Antibiotic Pollution and Risks in Surface Water

The
widespread presence of antibiotics in aquatic ecosystems is
a global challenge, yet the occurrence and risks associated with their
transformation products (TPs) remain poorly understood. This study
investigated the occurrence and potential risks of antibiotics and
their TPs in water along the Chaobai River in Beijing. We used high-resolution
mass spectrometry and an integrated target, suspect, and nontarget
screening approach to identify 21 parent antibiotics and 78 TPs among
90 water samples, with the majority from macrolides and sulfonamides.
Notably, target quantification and machine-learning-assisted semiquantification
revealed that the cumulative concentrations of TPs were higher than
the cumulative concentrations of parent compounds, with average contributions
of TPs ranging between 50.7 and 63.7%. Most downstream water samples
were largely influenced by domestic sewage, as indicated by the significantly
higher concentrations and proportions of TPs, as well as the greater
diversity in their composition profiles compared to upstream and reservoir
samples. Moreover, of the 78 TPs, 26.9, 67.9, and 6.4% exhibited greater
persistence, mobility, or toxicity than their parent antibiotics,
respectively. Sixteen macrolide TPs presented both greater ecological
risks to aquatic organisms and higher resistance selection risks than
their parent antibiotics. TPs contributed substantially to the overall
antibiotic-related risks by an average of between 31.2 and 54.1%.
This study highlights the occurrence of antibiotic TPs in river water,
underscoring the need to consider TPs in comprehensive risk assessments
of antibiotics.