Industrial ecology includes thinking about ways to manage wastes and effluents; to prevent the use of materials that are toxic¹ or otherwise dangerous or difficult to use and handle, so that they are not released into the environment; and to use wastes and effluents products themselves. It envisions an economic system whose processes and products lead to outputs that are reusable and recyclable. Waste is waste. Having purchased material at the front end of a plant, only to throw part of it away at the back end suggests that efficiency of material use might be improved; having a product that embodies the energy and effort needed to produce it go out of the plant door forever suggests that reusing the material and embodied energy at the end of the useful life of the product might be more efficient than disposing of the product.

We do not "consume" materials; we use energy to transform materials, to create materials from other materials. Many of our materials, particularly metals, are neither changed nor consumed in use, but merely stored (e.g., copper wire in walls and iron in automobile engine blocks). Even the contents of landfills, particularly if they were so designed, could be considered to be materials-inventory sites.

Material products generally and many wastes and effluents specifically embody energy and effort that make them potentially less expensive to use to make new products than starting from dispersed virgin raw materials. But systems must be appropriately designed. We must include in the economics the energy and effort that would be required to dispose of otherwise-discarded wastes, effluents, and products in an environmentally benign and acceptable manner.

A further dimension of new possibilities is a re-examination of what is really being provided to customers as the product. Is the customer interested in cleaning