The objective of this study was to determine the concentrations of the metabolites of four selected phthalates, widely used industrial chemicals which possess endocrine-disrupting properties, in samples of amniotic fluid and maternal urine collected in the same day, in order to verify if the latter can be considered a measure of the fetal exposure. The quantitative determination of the metabolites was carried out by HPLC-MS/MS with isotopic dilution from 70 pregnant volunteers. Detectable concentrations of phthalates metabolites were found in amniotic fluids. As phthalate monoesters are excreted in the urine conjugated with glucuronic acid, an enzymatic hydrolysis is carried out before analysis. Amniotic fluids were tested with and without hydrolysis and only the free phthalate metabolites, not conjugated with glucuronic acid, were found. The concentration of metabolites after enzymatic hydrolysis in maternal urine is not correlated to those of amniotic fluids, but the free form concentrations are. These results suggest that only the free forms can cross the placenta. A significant number of mothers showed urine phthalate monoesters concentrations higher than non-pregnant women.
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