Glucuronidation patterns of common urinary and serum monoester phthalate metabolites.
Level 4 - case-series / case-control
Cross-sectional biomonitoring study evaluating metabolite concentrations in human biospecimens.
PubMed 14574443 · doi:10.1007/s00204-003-0486-3
What was done
Researchers measured the proportion of free versus glucuronide-conjugated forms of four phthalate monoesters—monoethyl phthalate (mEP), monobutyl phthalate (mBP), monobenzyl phthalate (mBzP), and mono-2-ethylhexyl phthalate (mEHP)—in human urine (mEP n=262, mBP n=283, mBzP n=328, mEHP n=119) and serum (mEP n=93, mBP n=149, mEHP n=141) samples collected from the general US population.
What was found
For lipophilic monoesters (mBP, mBzP, and mEHP), the geometric mean of free monoester excretion in urine ranged from 6% to 16% (84% to 94% conjugated). Conversely, about 71% of the hydrophilic monoester mEP was excreted in urine as free monoester. Free-to-conjugated proportions were consistent between serum and urine for mEP, mBP, and mEHP. Serum mBzP was mostly below the limit of detection. Serum mEP and mBP concentrations were less than 3% and 47% of their urinary concentrations, respectively, while mEHP concentrations were similar in urine and serum.
Why it matters
Understanding phthalate glucuronidation patterns is critical for interpreting exposure biomonitoring data and quantifying circulating levels of the bioactive, unconjugated monoesters.
Limits
The abstract does not state the total number of unique participants or demographic characteristics. The study relied on cross-sectional biofluid samples without controlled exposure dosing or longitudinal clearance measurements, and serum mBzP was mostly undetectable.
Cited by
- supports Phthalates are water-soluble compounds whose metabolites are excreted and measurable in human urine.