Identification of candidate exposure biomarkers for acetyl tributyl citrate and acetyl triethyl citrate using suspect screening in human liver microsomes.

Acetyl tributyl citrate (ATBC) and acetyl triethyl citrate (ATEC) are increasingly used as alternatives to phthalates in various products, including food packaging, medical devices, and personal care items, raising concerns about their potential health impacts. This study aimed to investigate the in vitro human metabolism of ATBC and ATEC and identify potential exposure biomarkers applicable in human biomonitoring. Pooled human liver microsomes were utilized to conduct in vitro metabolism assays of deuterium labeled ATBC (ATBC-d) and ATEC, and ultra performance liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (UPLC-qToF/MS) was employed for analysis. Suspect screening workflow and confidence level assignment were applied for metabolite identification. Time-course analysis revealed rapid metabolism of both compounds, with estimated apparent half-lives of approximately 5 min for ATBC-d and less than 15 min for ATEC. Eleven metabolites were identified for ATBC-d and six for ATEC. The predominant chemical reactions observed were carboxylic ester hydrolysis, deacetylation, and hydroxylation. Based on their abundance and specificity, MB1 (hydroxylated) and MB11 (hydrolyzed and hydroxylated) were proposed as candidate exposure biomarkers for ATBC, and ME1 (hydrolyzed and deacetylated) for ATEC. The identified metabolites and proposed sequences of kinetic process enhance our understanding of the fate of these compounds in the human body, potentially informing future toxicological assessments and guiding the development of more comprehensive human biomonitoring strategies.