Suspect and Nontarget Screening Reveal the Underestimated Risks of Antibiotic Transformation Products in Wastewater Treatment Plant Effluents

Antibiotics are anthropogenic contaminants with a global
presence
and of deep concern in aquatic environments, while less is known about
the occurrence and risks of their transformation products (TPs). Herein,
we developed a comprehensive suspect and nontarget screening workflow
based on high-resolution mass spectrometry to identify unknown antibiotic
TPs in wastewater treatment plant effluents. We identified 211 compounds
(35 parent antibiotics and 176 TPs) at confidence levels of ≥3
and 107 TPs originated from macrolides. TPs were quantified by 17
TPs standards and semiquantified by the predicted response factors
and accounted for 55.6–95.1% (76.7% on average) of the total
concentrations of parents and TPs. 22.2%, 63.1%, and 18.8% of the
identified TPs were estimated to be more persistent, mobile, and toxic
than their parent antibiotics, respectively. Further ecological risk
assessment based on concentrations and toxicity to aquatic organisms
revealed that the cumulative risks of TPs were generally higher than
those of parents. Despite the newly formed N-oxide TPs, the tertiary
treatment process (mainly ozonation) could decrease the averaged 20.3%
of concentrations and 36.2% of the risks of antibiotic-related compounds.
This study highlights the necessity to include antibiotic TPs in environmental
scrutiny and risk assessment of antibiotics in different aquatic environments.