Scientists began to realize that some of these endocrine disruptors were able to interact with estrogen receptors.  The chemical structures for 3 drugs that target estrogen-sensitive tissues along with natural estradiol are shown here.  Though their structures are similar, they are not exactly the same.  What was once thought of as a specific lock and key, receptor to hormone system was not so specific.  Moreover the effects of endocrine disruptors like DES were not limited to pharmaceuticals but were showing their effects in pesticides, herbicides, fungicides, and industrial chemicals