The challenge of creating metabolic justice is to apply this understanding to today’s urban environment.  If cities are to function more like cyclical ecosystems, waste must be treated like a valuable resource that can be used to increase ecosystem health rather than a negative externality of industry.  Like the other “spheres” of the urban ecosystem, toxicity in the waste stream presents a significant barrier to achieving urban ecosystem justice.  The key to interrupting the unsustainable linear throughput model of urban metabolisms is to prevent the mixing of toxic materials into non-contaminated materials to begin with.  This is likely most important in the case of consumer products and building materials whose infusion with toxic substances prevents them from being safely composted or otherwise re-used.  The disposal of these toxic materials in landfills and incinerators results in the production of considerable toxic emissions and residue that affect the health of communities near and far.  In consideration of this, it is critically important to advance green chemistry technologies to replace toxic consumer products with materials that are ultimately non-toxic and compostable (Anastas, 2000).

While the discussion of all forms of urban waste is vast, multi-faceted, and critically important, for the purposes of this articles the analytical focus will be on the composting of urban organic wastes, and specifically food residues, as they have the greatest relevance to urban ecosystem justice. It is my belief that learning how to successfully transform food wastes into soil and in turn in to food is one of the most important skills that any urban resident can learn.