In many countries, estimations of annual emissions of chemicals from point sources are now being regularly presented for the nation as a whole. For Sweden, the figures show that the emissions have been decreasing since the mid-1970s. This is, of course, encouraging with regard to environmental protection objectives. Unfortunately, however, these figures do not present a complete picture. Nor do they provide sufficient information to evaluate human impact on the environment systematically, especially in a long-term perspective. There are two major shortcomings of the standard estimates:
1. Lack of a spatial dimension; a nationwide scale is hardly satisfactory to assess impacts (or the value) of reduced industrial emissions.
The development of industry in Sweden has led to an increased use of chemicals and other materials. In this study we want to approach the environmental problems of tomorrow that will arise from the use of various materials, from a historical standpoint. This type of study could be used as an argument for what has recently been called the precautionary principle of environmental management (see O'Riordan, chapter 12 of this volume). The purpose is to develop methods to reconstruct the flows of materials and estimate the emissions over time. This is done through studies of the development of production, technology, trade, and the longevity of products in society. This last part in the chain will form the "consumption emissions."
The concept of industrial metabolism suggests that we should seek to estimate the total load of toxic substances in soils and sediments, i.e. to describe and assess the development of a new "immission landscape." In this chapter industrial metabolism is illustrated in terms of the total flow and accumulation of chromium (1920-1980) and lead (18801980) in Sweden (Anderberg et al., 1989, 1990; Bergbäck et al., 1989, 1992).
The method of analysis is based on a simplified flow scheme: Various substances enter the economy either through imports or domestic production. Production of goods and extraction of primary materials result in "production emissions." The main part of these emissions is found in the products themselves, and is accumulating in the "anthroposphere." Depending on the type of product, large amounts may remain for a long time. Some parts are recycled after use. However, a significant quantity is sooner or later spread to the environment through consumption emissions, dissipative losses (see Ayres, chapter 1 of this volume), consumer-related emissions, or emissions from diffuse sources.
This materials' balance approach method (inspired by Ayres and Kneese, 1969; Ayres, 1978; Ayres and Rod, 1986; Tarr and Ayres, 1990) consists, in somewhat simplified form, of the following steps:
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