In Paul's most recent podcast, he and Bill are lamenting the herbicides that have been sprayed on Bill's property. Paul offered a few options for remediating the problem -- but most involved tilling to UV-degrade the chemicals, or adding additional soil in the form of sheet mulch in order to dilute the chemicals.
A third option is advocated by Paul Stemets -- using mushroom-inoculated mulch as a source of enzymes which digest the long-chain organic molecules which make up the herbicides.
This is not totally insane. In fact, in Mycelium running, Paul relates anecdotally some studies which were carried out feeding diesel-soaked dirt to oyster mushrooms to clean up an old parking lot. Other more recent examples of mushrooms eating organic molecules are here:
There have actually been extensive studies carried out in the scientific literature on mushroom's (usually oyster) ability to break down environmental toxins. One example, using atrazine, is discussed here:
Paul Stamets's strategy is simple: spread 1 inch of fresh wood chips over the site of the contamination. Wet well. Spread grain spawn, sawdust spawn, or myceliated straw or cardboard over the chips. Then cover with 3 inches of further wood chips. Don't go too deep, because the mycelium need oxygen.
Over the next 2-4 years, the mushrooms will grow through the wood chips, digesting them, and sweating digestive enzymes from their hyphae, which will then wash into the soil, where they will attack the organic molecules of the herbicide.
Be careful not to seat the mushrooms from these contaminated areas, since they will take up the herbicide into their tissue before they digest it. Also, double-check whatever mushroom species you use to see if it accumulates heavy metals, since fields with lead, selenium, or other minerals can be concentrated in the mushroom fruits.
Mycelium Running is an amazing book to get started with, and has a huge number of potentially awesome ideas for permies.