Confounding Factors in the Risk Assessment of Mixtures of Estrogenic Chemicals.

It is well known that chemicals present in our rivers can act as hormones and hormone mimics, and by doing so disrupt reproduction in fish. In the more serious situations, all male fish have been 'feminized' to varying degrees. Many are intersex - part male, part female. These fish cannot breed as successfully as unaffected fish. Very recently, it has been demonstrated that these effects are not due to the fish being exposed to just one chemical, but to mixtures of chemicals, with each chemical contributing a little to the overall effect. The next step in protecting fish, and other aquatic wildlife, from these 'feminizing' chemicals is to find out if other characteristics of the aquatic environment influence how much these 'feminizing' chemicals feminize fish. We will determine how much changes in water temperature, oxygen level, and the simulataneous presence of other (non-hormonal) chemicals affect the response of fish to a mixture of 'feminizing' chemicals. Until we know this, we cannot adequately protect our fish from these 'feminizing' chemicals.