Cumulative Effects of In Utero Administration of Mixtures of Antiandrogens on Male Rat Reproductive Development

Although risk assessments are typically conducted on a chemical-by-chemical basis the 1996 Food Quality Protection Act (FQPA) required the Environmental Protection Agency (EPA) to consider cumulative risk of chemicals that act via a common mechanism of toxicity. To this end, U we are conducting studies with mixtures to provide a framework for assessing the cumulative effects of antiandrogenic chemicals. Rats were dosed during pregnancy with antiandrogens singly or in pairs at dosage levels equivalent to about one half of the ED50 for hypospadias or epididymal agenesis. The pairs include: AR antagonists (vinclozolin plus procymidone), phthalate esters (DBP plus and DEHP plus DBP), a phthalate ester plus an AR antagonist (DBP plus procymidone) and linuron plus BBP. We predicted that each chemical by itself would induce few malformations; however by mixing any two chemicals together, about 50% of the males would be malformed. All binary combinations produced cumulative, dose-additive effects on the androgen-dependent tissues. We also conducted a mixture study combining seven antiandrogens together. These chemicals elicit antiandrogenic effects at two different sites in the androgen signaling pathway (i.e., AR antagonist or inhibition of androgen synthesis). In this study, the complex mixture behaved in a dose-additive manner. Our results indicate that compounds that act by disparate mechanisms of toxicity display cumulative, dose-additive effects when present in combination.