Keep in mind, that different species of plant and fungy take up pollutants quite differently.
I would take soil samples for testing (especially for toxic materials and heavy metals from industry), but also wood samples from trees you expect the highes exposure to airborne pollutants. Finnaly testing the mushrooms will give you the best data about the safety of your product.
Where I live, the only relevant pollutant when it comes to mushrooms is caesium from the nuclear accident in Tschernobyl, and I know that there is a huge difference in caesium levels in different wild mushroom species.
The most common edibles are frequently tested around here. The highest level of caesium is found in Boletus badius.
Chanterelles have about 30%, king boletes around 15% and Macrolepiota procera only 0.15% the caesium concentration found in bay boletes!
Data was taken from this link, but it's in German
http://bmg.gv.at/home/Schwerpunkte/VerbraucherInnengesundheit/Lebensmittel/Radioaktivitaet_in_heimischen_Wildpilzen