Should the soil coarse fraction be considered a key element in the functioning of highly anthropized soils, especially regarding risk associated to contaminants? Soil quality diagnosis systematically dismiss it as inert for not contributing to the soil's nutritional potential or contaminants in the short term. However, in forest context, it can contribute significantly to the assimilation of essential nutrients by plants. Yet, insufficient research has been done to understand its influence in terms of physicochemical fertility and contribution to toxicity in the context of highly anthropized soils. In these contexts, coarse materials are found in various quantities and natures and can constitute in some cases the main source of pedogenetic evolution of these systems. This raises the questions of the evolution of the properties of the soil coarse fraction constituents as a function of their size, and the intensity of their contribution to the fertility and toxicity of highly anthropized soils. In an original approach, the nature, the typology, and the reactivity of a brownfield soil coarse constituents are determined, and their fertile and toxic properties qualified. The results of this study confirm the high level of reactivity of the soil fine fraction and highlight the contribution of the coarse fraction to the provision of fertile and toxic elements. The coarse fraction loses its inert nature to the benefit of a reactivity, admittedly not intense, but still present that should be taken into account for risk assessment purposes.