I have just come into a beautiful property with mature oaks and poplars. The location is a leafy suburb in Cape Town.
I am worried about the mature trees having accumulated heavy metals and/or other pollutants and the possibility of these unhealthy substances ending up in the mushrooms.
There is lots of shade on the property so if mushrooms work it could be a real boon!
I don't know much about this topic, but there is a book called "Mycelium Running" by Paul Stamets that has a chapter entitled "Mycoremediation". The chart on page 102 is a general guide to the bioacumulation coefficients of about 36 species of fungi and six toxic metals. There is also scientific literature cited in this book for further study. I hope this helps!
"In a fruit forest everyone is happy"- Sepp Holzer
While I am no mushroom expert my thought would be first to get a soil test as the soil around the tree is likely to have present any substances the tree would have taken in.
Is there any particular local history either the site itself or nearby that would make you believe a high level of toxic material present?
If you are worried about toxins from being near a roadside, you could avoid using those trees that were closer to the roadway and the ones farther away will likely have a much lower toxicity level.
Mycelium will break down many toxins into lesser toxic constituents including hydrocarbons, however heavy metals which are usually of an elemental nature will not break down. From what I can remember it appears that the heavy metals are concentrated by the fungi in the fruiting bodies. If one were to remove the fruiting bodies and dispose of them elsewhere, by burning or quarantine? The area would then have at least a lower concentration of toxic material present. Perhaps if you do discover the presence of heavy metals this would be a strategy to employ.
Hope this helps, maybe someone else who is more of an expert will verify this. Also M.K's suggestion was right on Mycelium Running by Paul Stamets would be the book that you probably want to go to.
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!
Florian Kogseder wrote: Finnaly testing the mushrooms will give you the best data about the safety of your product.
That's the only way you can be sure about what you have. That said, I would think that wood grown in a city would not be a problem, unless that city has a clear history of heavy metal contamination -- like there was a coal ash heap or drainage from a hard rock mine that was a source. A leafy suburb far away from any extractive industry? Probably going to test out pretty clean.
The big issue from a city, like the others said, is from a history of a coal plant/superfund site, etc. The other thing to think about is if you have a freeway with thousands of cars passing each day within 400 meters, but it doesn't sound like you have that.