Di(2-ethylhexyl) phthalate (DEHP) is a ubiquitous environmental contaminant. Epidemiological studies suggest that DEHP decreases masculinization of male fetuses. Numerous rat studies report DEHP reduces fetal testosterone production at doses greatly exceeding human exposure. We fed pregnant CD-1 mice 0.5-500,000 μg/kg/day DEHP from gestation day (GD) 9-18 and examined mothers and male fetuses on GD 18. We assessed non-monotonic dose-response by adding a quadratic term to a simple linear regression model. Except at the 500,000 μg/kg/day dose, DEHP stimulated an increase in maternal and fetal serum testosterone and increased anogenital distance (AGD). Non-monotonic dose-response curves were noted for AGD and maternal, and testis testosterone (P values 0.013-0.021). Because data from our highest dose (500,000 μg/kg/day) did not differ significantly from controls, this dose could have been incorrectly assumed to be the NOAEL had we only tested very high doses, as is typical in studies for regulatory agencies.
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