Why is the use of aluminum or teflon coated cookware not recommended? Is there any scientific studies which I can look up that show a decrease of stopping the effectiveness of the tea?Why isn't microwaving it allowed? Do microwaves change the chemical composition of Essiac? Or is it because it's harder to monitor its temperature when re-heating the tea?

Here is some info I have gotten from the Google search and there is a LOT out there, so it is by no means definitive.  

Perfluorooctanoic Acid (PFOA) is the offending component in Teflon.  Studies in humans have found that people with workplace exposure to PFOA have higher risks of bladder and kidney cancers.  Here is the link to the source of this info:  http://www.cancer.org/cancer/cancercauses/othercarcinogens/athome/teflon-and-perfluorooctanoic-acid--pfoa I haven't used Teflon in a long time because it is gross how it starts flaking off and I think it is best to use something that won't do that.

 As far as aluminum pots, Rene Caisse used an aluminum pot for years, but changed to enamel in her later years as aluminum began to get bad press.  I found this: 

ALUMINUM Very soft metal. Extreme chemical reaction between food and pan. "All Vegetables cooked in Aluminum produce hydroxide poison which neutralizes digestive juices, producing stomach and gastrointestinal trouble, such as stomach ulcers and colitis." Dr. A. McGuigan's Report on Findings for the Federal Trade Comm. In Docet Case No. 540 Washington, D.C. Note: The sale of aluminum cookware is prohibited in Germany, France, Belgium, Gr. Britain Switzerland, Hungary and Brazil. 

The newer aluminum pots appear to be safer because it is hardened aluminum.  I avoid aluminum because of the sum of incoming aluminum from all sources in our environment, which is mounting due to its use in other applications besides cookware, which clearly is not the biggest offender. I just think there are better choices for making Essiac.  But practically speaking, it makes sense to use what you have as opposed to investing a lot of money in replacing aluminum cookware if that is what you use and like.  

 The admonition is more about the associated possible health risks of Teflon and aluminum than any specific knowledge about how these might interact with the Essiac herbs.  This would be a good subject to further research in the lab.

 Re:  microwave ovens.  First off, they emit radiation, which is an increasingly pervasive form of pollution, from all of our electronic devices.  It depends on who wrote the article as to whether or not microwaves emit a dangerous level or not, but there is no question that they do emit some radiation, but that it's better than in the earlier days!  Then there is the matter of what the microwave does to the integrity of the molecules it blasts, and the question of over-heating.  However, as long as one doesn't heat the decoction itself, it is probably ok to microwave the water, if one must.  Info here.

 Masaru Emoto has written much on how water is affected by very subtle things, let alone microwave radiation..best to avoid it.