In Paris the mayor programme “Main Verte” gathers most of the participative urban agriculture projects. It explicitly not recommends to grow vegetable in the city soil which is heavily polluted.  Instead city farmers could use soil transported from arable land in the region into “off-ground” tanks or roof tops.

Nevertheless if city farming plan to scale up, soil decontamination would become a major issue in the coming years.

Natural decontamination methods are tested. World renowned mycologist Paul Stamets shows in a TED video how the mycelium can absorb the pollution. This decontamination techniques using living organism is call bioremediation and could be very efficient (see also Mycoremediation in the case of mushrooms based method).

A french starts up called Polypop is currently participating in a pilot project to experiment fungy-based decontamination techniques.

In 25 days the following effects are observed:

47% of heavy hydrocarbons and 35% of aromatic hydrocarbons are destroyed.
55% of cadmium and 40% of lead are removed.

Fungi are more and more proven to be a very cheap, effective and environmentally sound way for helping to remove a wide array of toxins from damaged environments which could be used to prepare city soil for city farming.