In this article, the author analyzes the relation between migration and the environment within the context of Wallonia, the former mining region of Belgium. By applying the eco-marxist concept of metabolism, the article examines long-time relations between coal and Belgian society and its ties with migration and circulation processes. Beginning from the aftermath of World War Two, the author focuses on the so-called “men in exchange for coal” agreement between Italy and Belgium signed in 1946. By adopting a transdisciplinary approach typical of environmental humanities, the article contributes to the rising field of the environmental history of migration, also touching upon occupational health, biopolitics, miners' bodies, and labor history. In its conclusion, the article reflects on the historiographical implications of the toxic heritage produced by the metabolism of coal as well as by progressive historical narratives.