|Industrial Metabolism: Restructuring for Sustainable Development (UNU, 1994, 376 pages)|
|Part 2: Case-studies|
|11. Consumptive uses and losses of toxic heavy metals in the United States, 1880-1980|
The term "emission coefficient," as used in this context, means the fraction of the material in question that is released in mobile form (to the air or water) within a certain period (a decade, more or less). We exclude wastes that are recycled or disposed of in landfills or in sludge dumped offshore. We exclude toxic metals immobilized in clayey soil. In a few cases we also include production-related losses that were not included in the previous sections (e.g. process wastes in the plating, tanning, and chemical industries). These assumptions are obviously quite conservative, at least in the sense that a case could be made for significantly higher estimates of emissions.
It is unfortunate (and curious) that there are almost no published data on emissions coefficients consumption activities. Obviously, most analysts so far have not considered such activities to be "sources" of pollutants. In the absence of an existing body of literature (and of time to undertake more intensive research on this topic ourselves) we are led to a rather ad hoc choice of emissions coefficients. These are displayed in table 8. Each coefficient represents the fraction of total consumption in that category that is typically unrecoverable in principle.
It should be emphasized that these estimates are rather rough. In some cases, they are little better than "guestimates." The results presented here, therefore, are illustrative rather than authoritative. A task for the future is to improve the approach, and particularly to make it more relevant to major new policy initiatives.
In the case of tetra-ethyl lead (TEL) emissions from gasoline consumption, it is probably not necessary to compute emissions from an emission coefficient. Instead, on the assumption that all lead in gasoline is eventually emitted, input data on lead use as a gasoline additive should suffice. Such data are available from the Bureau of Mines. To compute strictly atmospheric emissions, however, the total lead used as a gasoline additive should be multiplied by a factor of 0.75 to reflect the fact that at least 25 per cent of the lead is trapped in the oil, oil filters, or exhaust system of the cars and not emitted directly to the atmosphere (Hirschler et al., 1957; Hirschler and Gilbert, 1964).
It must be pointed out that, while the numerical estimates in many cases are rather uncertain - sometimes even by a factor of two or three there are only a few important routes which clearly dominate the rest for each metal.