Hair as an alternative matrix to monitor human exposure to plasticizers - Development of a liquid chromatography - tandem mass spectrometry method.

The application and production of alternative plasticizers (APs) has been increasing in the last decade in replacement of conventional phthalates due to their toxicity. This calls for the development of non-invasive monitoring approaches to assess human exposure to APs. A method for the simultaneous measurement of exposure biomarkers of di(2‑propylheptyl) phthalate (DPHP), di(isononyl)cyclohexane‑1,2‑dicarboxylate (DINCH), di(2‑ethylhexyl) terephthalate (DEHTP) and di‑2‑ethylhexyl adipate (DEHA) in hair samples was developed and validated in this study. Prior to the analysis, the hair samples were washed in acetone and ultrapure water and pulverized to powder. Further, a solid-liquid and solid-phase extraction, followed by quantification using liquid chromatography - tandem mass spectrometry (LC-MS/MS) was performed. The method was validated in terms of recovery, matrix effects, carry-over, linearity, limits of quantification, within- and between-run precision and trueness. Satisfying results were obtained for all targeted compounds, except for mono(2‑ethylhexyl) adipate (MEHA), which was monitored only qualitatively. The optimized method was implemented in a pilot biomonitoring study with hair samples from 9 healthy volunteers. Detection frequencies of seven metabolites ranged from 11% to 100%. Mono(2‑ethylhexyl) terephthalate (MEHTP) and mono(2‑ethyl‑5‑oxohexyl) adipate (oxo-MEHA) were found in all hair samples. More hydrophobic monoester metabolites were found to be incorporated in hair to a greater extent compared to their oxidized counterparts. Obtained results show that the developed method can detect AP metabolites in hair, supporting the use of this alternative matrix in human biomonitoring.