Although growing vegetables in urban gardens has several benefits, some questions in relation with the safety of foods remain when the self-production is carried out on highly contaminated garden soils. To better assess the local population's exposure to Cd and Pb induced by the past activities of a lead smelter, a participatory program was initiated in 115 private kitchen gardens located in northern France to assist gardeners in understanding their soil environment. The challenge included contributing to the database of urban garden soils with the collection of a large number of samples: 1525 crops grouped into 12 types (leaf, fruiting, root, stem and bulbous vegetables, tubers, cabbages, leguminous plants, celeriac, fresh herbs, fruits, and berries), 708 topsoils, and 52 samples of self-produced compost. The main results were as follows: (i) topsoils were strongly contaminated by Cd and Pb compared to regional reference values; (ii) great variability in physicochemical parameters and metal concentrations in topsoils; (iii) the highest concentrations of Cd and Pb for celeriac and fresh herbs and the lowest for fruits and fruiting vegetables; (iv) a high percentage of vegetables that did not comply with the European foodstuff legislation; and (v) most self-produced compost samples were strongly contaminated. This study aimed to raise awareness and generate functional recommendations to reduce human exposure and to provide useful data that could be considered in other environmental contexts.