An approach to the development of quantitative models to assess the effects of exposure to environmentally relevant levels of endocrine disrupters on homeostasis in adults

The workshop "Characterizing the Effects of Endocrine Disrupters on Human Health at Environmental Exposure Levels" was held to provide a forum for discussions and recommendations of methods and data needed to improve risk assessments of endocrine disrupters. This article was produced by a working group charged with determining the basic mechanistic information that should be considered when designing models to quantitatively assess potential risks of environmental endocrine disrupters in adults. To reach this goal, we initially identified a set of potential organ system toxicities in males and females on the basis of known and/or suspected effects of endocrine disrupters on estrogen, androgen. and thryoid hormone systems. We used this integrated, systems-level approach because endocrine disrupters have the potential to exert toxicities at many levels and by many molecular mechanisms. Because a detailed analysis of all these untoward effects was beyond the scope of this workshop, we selected the specific end point of testicular function for a more detailed analysis. The goal was to identify the information required to develop a quantitative model(s) of the effects of endocrine disrupters on this system while focusing on spermatogenesis, sperm characteristics, and testicular steroidogenesis as specific markers. Testicular function was selected because it is a prototypical integrated end point that can be affected adversely by individual endocrine disruptors or chemical mixtures acting at one specific site or at multiple sites. Our specific objective was to gather the information needed to develop models in the adult organism containing functional homeostatic mechanisms, and for this reason we did not consider possible developmental toxicities. Homeostatic mechanisms have the potential to ameliorate or lessen the effects of endocrine disrupters, but these pathways are also potential target sites for the actions of these chemicals.