Identification of potential urinary exposure markers for the toxicant diisononyl phthalate in rubber worker urine specimens by high-resolution mass spectrometry-based metabolomics

Diisononyl phthalate (DiNP) is commonly used as a plasticizer in polyvinyl chloride (PVC) products. However, DiNP can interfere with the human endocrine system and is listed as a chemical with reproductive toxicity. It has a short half-life and can be metabolized into water-soluble substances that are excreted in the urine, and thus, DiNP exposure markers can be identified in urine, a noninvasive and easily accessible specimen. In a previous study, we established an isotope tracing strategy involving an in-house computational signal mining algorithm with isotope tracing (SMAIT) to filter probable metabolite signals from complex LC-MS data. In this study, we used SMAIT to filter the probable metabolite signals, which were verified as potential DiNP exposure markers by analyzing human urine specimens from rubber workers who had occupational exposure to DiNP. We filtered 16 probable metabolite signals out of approximately 1400 signals by SMAIT. Fourteen of the 16 probable metabolite signals were confirmed as DiNP structure-related metabolites according to the fragment ion at m/z 121.029, which is a benzoate ion (C₆H₅CO₂), identified in D₀-MMOP mass spectra by ultra-high-performance liquid chromatography-high-resolution tandem mass spectrometry (UHPLC-HRMS/MS) in the full-scan mode. The 14 structure-related metabolite signals were further verified as potential DiNP exposure markers by analyzing rubber worker urine specimens. Three DiNP structure-related metabolite signals at m/z 305.139 (MOINP), 307.155 (MHINP), and 375.142 (derivatives of MHINP) were identified as potential exposure markers of DiNP. We need more research to validate whether these metabolites could be used as specific biomarkers for human exposure to DiNP. The 3 structure-related metabolite signals could provide the basis for future exposure and risk assessment for DiNP.