There is various aspect of the Urban Agriculture in Paris and around, some are social, others are to limit the supply chain and to participate in the urban metabolism. Majority of people interested by UA wants to grow their own food.
Parisian area had various types of industries during the 19th and 20th century, the ground might still contain marks of former use. French legislation is strict on this matter, before construction or rehabilitation, a diagnostic is needed (ground analyzes). Knowing that mercury and lead can generate various physiological issues (some are toxic for reproductive organ and lead to degenerative reproductive cells), is it not hazardous to let public use ground to cultivate?
Urban Agriculture Book Series; Chapter 1: Innovative Commercial Urban Agriculture in the Paris metropolitan area).