Untangling transformation products in a semi-closed sea by nontarget and suspect screening analysis.

Although transformation products are important parts of chemical contaminants in the environment, their occurrence and risks remain largely unclear. In this study, MS2-initiated nontarget analysis and MS1-initiated suspect screening analysis strategy were performed to identify transformation products. The integration of these two approaches provided a complementary strategy to broaden transformation product identification, by covering diverse structural modifications during transformation processes and fragmentation behaviors in mass spectrometry. A total of 47 transformation products originating from 29 parent compounds were identified in the Bohai Sea and the surrounding estuarine waters. The identified transformation products were widespread across the Bohai Sea, with 38 detected in over 80 % of the sites. Transformation products constituted a significant proportion of xenobiotic compounds present in the Bohai Sea, cumulatively accounting for over 50 % of the total instrumental response of their parent compounds. Transformation processes under field conditions played a key role in shaping the composition of transformation products. Moreover, transformation products was a substantial contributor to the ecological risk posed to aquatic organisms, owning to both toxicity and abundance. The results emphasize the necessity of including transformation products when profiling composition and evaluating ecological risks of xenobiotic compounds.