evolved so that any available source of useful material or energy is used by some organism in the system. Animals and plants live on each other and on each other's waste matter. Materials and energy tend to circulate in a complex web of interactions: Animal wastes and dead plant material are metabolized by microorganisms and turned into forms that are useful nutrients for plants. The plants, in turn, may be consumed by animals or simply die, decay, and cycle again through the system as nutrients and components of other flora and fauna. These systems do, of course, leave some waste materials, or fossil fuels would not exist. On the whole, the system regulates itself and consumes what it produces.

Can industrial systems be more self-sufficient and closed with regard to the flow of materials so that interactions with the environment are more compatible? The lessons of the planned economies of the former Soviet Union suggest that planning and controlling the industrial system is not the solution. Rather, we need to experiment with changes in policy and industrial practices to see what actions will nudge the system in the desired direction. These nudges must be regarded as experimental, to be adjusted in the light of experience (Frosch, 1996; Frosch and Gallopoulos, 1989; Frosch and Gallopoulos, 1992).

USING MATERIALS EFFICIENTLY

One way for industry to be more self-sufficient and closed is to improve the efficiency of materials use. Surprisingly, this obvious idea has not been much attempted. If material is bought at one end of the system and thrown away at the other, it is probably wasteful in the ordinary sense, and materials are not being used as efficiently as practicable.

In addition to the waste materials from production, the products themselves (which industrial firms generally do not regard as part of their system once they are sold) eventually become part of the waste stream of society. When products wear out or are replaced by newer models, they are usually thrown away. They may be used as landfill or incinerated or they may litter the landscape. It seems worthwhile to examine both production processes and product designs to see if the use of materials (and energy) can be improved.

Regulatory pressures and shifting public opinion have spurred the industrial and engineering community to initiate efforts aimed at closing the materials loops more effectively and improving energy-use efficiencies (Allenby and Richards, 1994; National Academy of Sciences, 1992; Richards and Frosch, 1994; Schmidheiny and the Business Council for Sustainable Development, 1992; Smart, 1992). Automobile manufacturers such as BMW and Volkswagen have designed cars for easy disassembly and recycling (Simon and Woodell, this volume). Companies such as Hewlett-Packard, Canon, and Xerox have begun to take back their own used components, such as toner cartridges, and to manufacture new ones using refurbished components and recycled materials from the old ones. By considering



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