METABOLIC ANDROGENIZATION OF FEMALE DAPHNIA-MAGNA BY THE XENOESTROGEN4-NONYLPHENOL

Vertebrates and invertebrates metabolize testosterone to a variety of less-polar derivatives that elicit varying degrees of androgenicity as well as polar elimination products. We have developed a model, using the cladoceran Daphnia magna, with which the ability of xenobiotics to alter steroid hormone metabolism can be assessed and possible physiol ogic consequences evaluated during a 3-week assay. This model was used to assess the effects of the xenoestrogen 4-nonylphenol on steroid-me tabolic processes. Exposure of daphnids to 100 mu g/L 4-nonylphenol fo r 48 h caused a significant increase in the accumulation of radioactiv ity derived from [C-14]testosterone provided to the exposure media. Mo re definitive analyses demonstrated that both 25 and 100 mu g/L 4-nony lphenol disrupted components of the testosterone metabolic pathway tha t would lead to a decrease in the metabolic elimination of testosteron e and an increase in the accumulation of androgenic derivatives. Expos ure of daphnids to 100 mu g/L 4-nonylphenol significantly decreased fe cundity of the organisms while having no effect on survival of the par ental organisms. Comparison of metabolic and reproductive effects of L C-nonylphenol revealed that 71 mu g/L, the reproductive chronic value, would reduce the metabolic elimination of testosterone by approximate ly 50%. This relationship is consistent with that which we have report ed for other toxicants and identifies a mechanism, in addition to estr ogenicity, that may contribute to the reproductive toxicity of this co mpound.