Quantification of phthalate and DINCH metabolites in human urine and maternal breast milk: Assessing maternal body burden and infant exposure

Based on toxicological evidence, human exposure to phthalates (PHs) and diisononylcyclohexane-1,2-dicarboxylate (DINCH) may contribute to adverse health effects, especially during vulnerable developmental stages. To support the exposure assessment for this group of endocrine disruptors, we developed and validated a method for the analysis of 14 PH and 3 DINCH metabolites in human urine and maternal milk, applied the method in a pilot study, and identified crucial obstacles in the path of establishing maternal milk as a routine matrix in human biomonitoring. Urine and milk samples were extracted with solid-phase extraction (SPE) and QuEChERS salts, respectively, and analysed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The method accuracy was confirmed for urine samples via a certified standard reference material and the G-EQUAS intercomparison programme. We identified a need for sampling protocols, reference materials, and external method verification schemes in order to establish maternal milk as a routine matrix. Finally, the method was tested for its applicability in a pilot biomonitoring study on 30 paired urine and milk samples from lactating mothers, with medians ranging from