Suspect screening candidate exposure biomarkers of acetyl tributyl citrate and acetyl triethyl citrate after human oral administration

Acetyl tributyl citrate (ATBC) and acetyl triethyl citrate (ATEC) are widely used as plasticizers, but their metabolites as exposure biomarkers for biomonitoring, as well as approximate human metabolic pathways, are not well understood. This study addresses this knowledge gap by conducting suspect screening to propose specific metabolites in human urine as potential biomarkers of exposure and explore their kinetic profiles. Ten volunteers were administered deuterium labeled ATBC (ATBC-d₃) and seven received ATEC or deuterium labeled ATEC (ATEC-d₃), with urine samples collected over 48 h post-administration. Employing ultra-performance liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (UPLC-qTOF/MS), six metabolites of ATBC were consistently detected, including (OH)₃-ATBC-d₃, ADBC-d₃, OH-ADBC-d₃, DBC, OH-DBC, and OH-DBA. For ATEC, four metabolites were identified: ADEC-d₃, AMEC-d₃, OH-ADEC-d₃, and DEC. Based on their high detection frequency, relative response, and specificity to their parent compounds, ADBC-d₃ and OH-ADBC-d₃ were identified as promising candidate biomarkers for ATBC exposure, while ADEC-d₃ emerged as a suitable biomarker for ATEC. Estimated urinary elimination half-lives ranged from 1.0 to 9.9 h for ATBC metabolites and 1.6 to 3.0 h for ATEC metabolites. One-compartment kinetic modeling provided preliminary insights into metabolite kinetics. This research advances the understanding of ATBC and ATEC metabolism in humans, providing a foundation for future exposure assessments and toxicological studies. The identified biomarkers and preliminary metabolic profiles offer valuable starting points for biomonitoring and risk assessment of these alternative plasticizers.