there are good prospects for progress. Certain aspects of polymer use can be beneficial in this work.

Polymers are organic materials that are usually manufactured from petroleum feedstocks using processes that are environmentally benign or that can be made more environmentally compatible without crippling economic consequences. The polymer industry has successfully adopted many environmentally favorable processes, providing advantages over competing materials as described in the vignette "Paper or Plastic?," which also touches on some of the complicated issues involved in environmental decision making.

Similar complexities are evident in comparisons of polymers with other materials, such as metals and glass. Metal smelting plumes affect the atmosphere for hundreds of miles downstream, and land damage and the disposal of tailings from mining and refining operations are serious problems. Metal refining and glass making require large amounts of energy. Thus, from an environmental standpoint, comparisons of production processes may lead to a preference for using polymers rather than metals or glass. In addition, products fabricated from polymers often weigh less than those made from competing materials. Energy savings favor plastic for bottles over glass, when the energy requirements for production, transportation, and recycling are considered. Substitution of polymers for metals in aircraft and in automobiles results in weight reductions that translate to fuel efficiencies over the life of the vehicle. These efficiencies afford important operating economies and contribute to efforts aimed at decreasing U.S. dependence on petroleum.

Natural materials are not always better than synthetic materials from an environmental point of view. A comparison of fiber production is instructive. The natural fibers cotton and wool make heavy demands on agricultural resources, including land use, fertilizer (from petroleum), and fuel for transportation. Maintenance of clothing made from synthetic fibers requires less hot water. The trade-offs are complicated, but synthetic fibers offer many advantages.

A challenge to the use of all materials is posed by their disposal after use. National concern about the use of landfills has resulted in increased emphasis on recycling programs and a reluctance to use "once-through" products that must be sent to landfills. On a volume basis, polymer waste makes up about 20 percent of current landfill input (by weight, the percentage is lower), and methods must be devised to cope with this large and growing problem. Polymers degrade very slowly in landfills, but under typical landfill conditions even paper does not degrade rapidly enough to match the rate at which it enters the landfill. Although paper and other biodegradable materials degrade much more rapidly under composting conditions, this approach is not generally feasible. Polymers can be made that are degradable at a more rapid, controlled rate, but these materials are not competitive in cost or in other properties, such as durability. Recycling of materials is environmentally attractive but in many cases has not proved to be economically viable. Frequently, products can be made with less expense from



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