New metabolites of di(2-ethylhexyl)phthalate (DEHP) in human urine and serum after single oral doses of deuterium-labelled DEHP

Abstract

The metabolism of di(2-ethylhexyl)phthalate (DEHP) in humans was studied after three doses of 0.35 mg (4.7 microg/kg), 2.15 mg (28.7 microg/kg) and 48.5 mg (650 microg/kg) of D4-ring-labelled DEHP were administered orally to a male volunteer. Two new metabolites, mono(2-ethyl-5-carboxypentyl)phthalate (5cx-MEPP) and mono[2-(carboxymethyl)hexyl]phthalate (2cx-MMHP) were monitored for 44 h in urine and for 8 h in serum for the high-dose case, in addition to the three metabolites previously analysed: mono(2-ethyl-5-hydroxyhexyl)phthalate (5OH-MEHP), mono(2-ethyl-5-oxohexyl)phthalate (5oxo-MEHP) and mono(2-ethylhexyl)phthalate (MEHP). For the medium- and low-dose cases, 24 h urine samples were analysed. Up to 12 h after the dose, 5OH-MEHP was the major urinary metabolite, after 12 h it was 5cx-MEPP, and after 24 h it was 2cx-MMHP. The elimination half-lives of 5cx-MEHP and 2cx-MMHP were between 15 and 24 h. After 24 h 67.0% (range: 65.8-70.5%) of the DEHP dose was excreted in urine, comprising 5OH-MEHP (23.3%), 5cx-MEPP (18.5%), 5oxo-MEHP (15.0%), MEHP (5.9%) and 2cx-MMHP (4.2%). An additional 3.8% of the DEHP dose was excreted on the second day, comprising 2cx-MMHP (1.6%), 5cx-MEPP (1.2%), 5OH-MEHP (0.6%) and 5oxo-MEHP (0.4%). In total about 75% of the administered DEHP dose was excreted in urine after two days. Therefore, in contrast to previous studies, most of the orally administered DEHP is systemically absorbed and excreted in urine. No dose dependency in metabolism and excretion was observed. The secondary metabolites of DEHP are superior biomonitoring markers compared to any other parameters, such as MEHP in urine or blood. 5OH-MEHP and 5oxo-MEHP in urine reflect short-term and 5cx-MEHP and 2cx-MMHP long-term exposure. All secondary metabolites are unsusceptible to contamination. Furthermore, there are strong hints that the secondary oxidised DEHP metabolites-not DEHP or MEHP-are the ultimate developmental toxicants.

Estimated daily intake of phthalates in occupationally exposed groups

“…Our workers were most likely exposed to phthalates by inhalation or dermal contact. Koch et al (2005a) found no dose dependency in DEHP metabolism and excretion (dose range: 4.7 to 650 mg/kg). Although one of our workers had a DEHP daily intake estimate 4800 mg/kg/day, 95% of our workers had DEHP estimates that were o70 mg/kg/day.…”

“…Nonetheless, with 9-25 workers per sector, some of this temporal variability was likely averaged across workers. Temporal variability in metabolite concentrations is further heightened by the metabolites' relatively short half-lives and rapid elimination in the urine (Anderson et al, 2001;Api, 2001;Koch et al, 2005aKoch et al, , 2004. Within-person variability in urinary phthalate metabolite concentrations has been shown to depend on the population, phthalate metabolite, and time frame of interest (Hoppin et al, 2002;Hauser et al, 2004;Fromme et al, 2007;Teitelbaum et al, 2008).…”

“…DEHP daily intake was estimated using three or four DEHP metabolites combined and F UE values based on human data ( (Koch et al, 2005a). We converted creatinine-adjusted metabolite concentrations to moles per gram before summing.…”

A critical evaluation of the creatinine correction approach: Can it underestimate intakes of phthalates? A case study with di-2-ethylhexyl phthalate

“…The elimination half-life of MEHP has been reported as 5 h in a human metabolism experiment (Koch et al, 2005b), so that 24 h after exposure, five halflives have passed, and only about 3% of the total mass of MEHP that was formed by the exposure remains to be eliminated. It is easy to see that a day following an exposure to DEHP, the concentration of MEHP could be very low or fall below a detection limit.…”

“…Meanwhile, secondary metabolites could be still forming if their rate of formation and excretion is slower than that of MEHP. Koch et al (2005b) measured four additional metabolites of DEHP in the experiment, and found that these secondary metabolites of DEHP have elimination half-lives in the range of 10-15 h. This implies that MEHP might be a poor candidate as an indication of exposure to DEHP. Indeed, Barr et al (2003) advocated the urinary analysis of secondary metabolites of phthalates as perhaps better indicators of exposure, compared with the monoester primary phthalate metabolites, for just this reason.…”