There is the well known of synegistic effects from pollutant combinations....

In metals and chemicals that we find in the air in products in our
teeth as how they mixed metals together..

All though there is much information out there on all of this..

The Department of Biology & Biochemistry..
Joint Action Of Pollution Combinations...

The synergistic effect...

http://www.bath.ac.uk/internal/bio-sci/bbsafe/lab2_1.htm

Look up the Journel Of Environment Engineering materials..
Industrial waste materials approve for road construction..

And I've allways wondered the many ways one could dispose
of industrial waste if they needed a cheaper way of disposal..

http://scitation.aip.org/getabs/ser...01&idtype=cvips&gifs=yes

The synergistic effect.... Evidence

http://www.generationrescue.org/quotes9.html

Or how about the toxicity of metal mixtures to chicken embryos ?

You can find that study as well...