Toxicokinetic relationship between di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate in rats

The toxicokinetic relationship between di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate (MEHP), a major metabolite of DEHP, was investigated in Sprague-Dawley rats orally treated with a single dose of 14C-DEHP. Urinary excretion of total 14C-DEHP and of its metabolites was followed by liquid scintillation counting (LSC). Concentrations of DEHP and MEHP were determined 6, 24, and 48 h after treatment in rat serum and 6, 12, 24, and 48 h after treatment in urine by high-performance liquid chromatography (HPLC). After 24 h, peak concentrations of MEHP in both urine and serum were observed in animals treated with 40, 200, or 1000 mg DEHP/kg. HPLC showed that general toxicokinetic parameters, such as Tmax (h), Cmax (microg/ml), Ke (1/h), and AUC (microg-h/ml/) were greater for MEHP than DEHP in both urine and serum. In contrast, the half-lives (t1/2 h]) of DEHP were greater than those of MEHP. The AUC ratios between DEHP and MEHP were relatively smaller in serum than in urine, suggesting the important role of urinary DEHP data for exposure assessment of DEHP. The toxicokinetic relationship between DEHP and MEHP in rats suggests that DEHP exposure assessment should be based on DEHP and MEHP in urine and serum for risk assessment applications.