Urinary metabolite excretion after oral dosage of bis(2-propylheptyl) phthalate (DPHP) to five male volunteers--characterization of suitable biomarkers for human biomonitoring

Abstract

Di(2-propylheptyl) phthalate (DPHP), a high molecular weight phthalate, is primarily used as a plasticizer in polyvinyl chloride and vinyl chloride copolymers for technical applications, as a substitute for other phthalates currently being scrutinized because of endocrine disrupting effects. We determined urinary excretion fractions of three specific DPHP metabolites (mono-2-(propyl-6-hydroxy-heptyl)-phthalate (OH-MPHP), mono-2-(propyl-6-oxoheptyl)-phthalate (oxo-MPHP) and mono-2-(propyl-6-carboxy-hexyl)-phthalate (cx-MPHxP)) after oral dosing of five volunteers with 50mg labelled DPHP-d4 and subsequent urine sampling for 48 h. These excretion fractions are used to back calculate external intakes from metabolite measurements in spot urine analysis. Following enzymatic hydrolysis to cleave possible conjugates, we determined these urinary metabolites by HPLC-NESI-MS/MS with limits of quantification (LOQ) between 0.3 and 0.5 μg/l. Maximum urinary concentrations were reached within 3-4h post dose for all three metabolites; elimination half-lives were between 6 and 8h. We identified oxo-MPHP as the major oxidized metabolite in urine representing 13.5±4.0% of the DPHP dose as the mean of the five volunteers within 48 h post dose. 10.7±3.6% of the dose was excreted as OH-DPHP and only 0.48±0.13% as cx-MPHxP. Thus, within 48 h, 24.7±7.6% of the DPHP dose was excreted as these three specific oxidized DPHP metabolites, with the bulk excreted within 24h post dose (22.9±7.3%). These secondary, oxidized metabolites are suitable and specific biomarkers to determine DPHP exposure. In population studies, however, chromatographic separation of these metabolites from other isomeric di-isodecyl phthalate (DIDP) metabolites is warranted (preferably by GC-MS) in order to distinguish DPHP from general DIDP exposure. Palatinol(®), Hexamoll(®) and DINCH(®) are registered trademarks of BASF SE, Germany.

Keywords: Biomonitoring; DPHP metabolites; Di(2-propylheptyl)phthalate; HPLC–NESI–MS/MS; Human volunteer study; Urinary excretion.