A Canadian Study revealed the introduction of estrogen in a minnow population led to near extinction by interfering with reproduction. Pretty much the male fish underwent a sex change when exposed. This allows the level of insects in the environment to increase, a distortion in nature which could contribute to an increase in disease.
Our effect on natural ecological cycles is devastating simply from pharmaceuticals excreted in urine and feces that pass into the environment after sewage treatment.
Another study in the Puget Sound revealed traces of "Cocaine, Spices, Hormones Found in Drinking Water." Pretty much we are not doing nature any favors.