Interestingly, the use of metals from secondary sources, recycling, was in 1996 roughly equal to that from primary resources However, in the last several years this encouraging trend seems to be reversing. It should be noted that all metals do not necessarily exhibit the same trends as shown here. Industrial minerals rose rapidly during the first half of the century, but followed the population trend from about 1950 onward. Currently, there is some recycling of construction minerals, estimated to be about 100 million MT per year, of the order of 10 per cent of annual input, but the data are poor and no quantities are shown in the data presented here.
During the 20th century, the extensive per capita use of renewable organic material
(forest and agricultural resources) declined until after World War II, when it began to parallel the growth This overall trend resulted from dramatically different growth rates for wood and paper. (See Figure 22.5 - underlying data in Table 22A.3). Wood use declined during the early part of the century, and then leveled off after World War II. In contrast, the growth in the use of paper was steady throughout the century. Currently, the use of wood and paper is about equal, and recycled paper is approaching 50 per cent of use. During the last couple of decades, the per capita use of wood was fairly constant, while that for paper rose. The computer and electronic age does not appear to be decreasing the
use of paper. Physical goods obtained from agricultural and fishery resources rose slightly during the century, but were an order of magnitude less than that obtained from forest resources.
The use of non-renewable organic (NRO) material (Figure 22.6 - underlying data in Table 22A.4), derived mainly from petroleum and natural gas, displayed a dramatic growth during the century. Asphalt and road oil drove the growth during the early years of the century, but from 1940, until about 1970, the use of petrochemicals rose at a rate faster than any group of commodities. In 1996, the US annual use of petrochemicals was
about 67 million metric tons. Petrochemicals provide the feedstocks for plastic, synthetic fibers, medicinal chemicals and other materials which are now of major importance to the economy of the USA. They are also of increasing concern with respect to the impacts caused by their manufacture, use and disposal. Because of their dramatic growth and significance, plastics, derived from petrochemical material, have been portrayed separately in Figure 22.7 (underlying data in Table 22A.4). This illustrates the spectacular rise in plastic use from 1941 to the present from 0.1 to almost 40 million tons per year. The trend shows only slight signs of abating and, unfortunately, only a small amount of plastic is currently recycled.
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