in Figure 6. The most important inorganic chemicals other than the three noted above are ammonia, sulfur (sulfuric acid), and salt (chlorine and sodium hydroxide) (Figure 7). The major groupings are discussed in the following sections. Others are mostly derived from these. For example, nitric acid and urea are both made from ammonia.

Domestic production of ammonia in 1988 was 12.544 MMT (N content). Net imports (imports minus exports) plus stock changes increased apparent domestic consumption of ammonia to 14.745 MMT (N). In addition, there were significant imports and exports of nitrogen-containing chemicals. The major net import items were urea (0.483 MMT N) and ammonium nitrate (0.091 MMT N), while major net export items were ammonium phosphates (1.150 MMT N) and ammonium sulfate (0.155 MMT N). In all, fertilizers accounted for nearly 80 percent of the supply of fixed nitrogen (Figure 7).

The nitrogen content of monomers embodied in plastics and resins in 1988 added up to 0.669 MMT. Nitrate and nitro-explosives, excluding amines, accounted for about 0.777 MMT (N). Urea fed to animals accounted for 1.55 MMT (N); unspecified uses of nitric acid, including phosphate rock processing and steel pickling, accounted for 0.135 MMT (N). Other identifiable final uses, including dyes, rubber chemicals, herbicides and pesticides, and sodium cyanide used in the gold mining industry, added to 0.153 MMT (N). Process losses are probably at least 2 percent. (Nitrogen wastes are less than they might otherwise be, however, because ammonia-bearing waste streams are easily neutralized by sulfuric acid to produce a useful by-product, ammonium sulfate fertilizer.) We estimate that process losses altogether account for 0.3-0.35 MMT (N). There is some possibility of undercounting of the use of nitrogen in mixed fertilizers where published data seem to be spotty. However, lacking further information, we assume the remaining "missing" nitrogen (about 0.4 MMT) is allocated mostly to household cleaning agents and other consumer products. In summary, we can account for about 0.737 MMT of fixed nitrogen embodied in products of the synthetic organic chemicals sector and on the order of 0.16 MMT of nitrogenous losses associated with organic synthesis, for a total of 0.9 MMT.

In terms of environmental pollution, the 2 percent loss rate suggested above is insignificant compared with dissipative uses of nitrogenous chemicals. Apart from fertilizers and animal feeds, these include industrial explosives, pesticides and herbicides, dyes, surfactants, flotation agents, rubber accelerators, plasticizers, gas conditioning agents, and so on. In fact, except for plastics and resins (and plasticizers), it is safe to assume that virtually all nitrogenous chemicals are soon dissipated in normal use, but mainly by other sectors or final consumers. In the case of plastics and fibers, the dissipation is merely slower.

Sulfuric acid (37.7 MMT in 1988) is derived from elemental sulfur; 11.584 MMT of sulfur were produced in 1988, most of which (10.3 MMT) was used to produce sulfuric acid, which is the starting point for most sulfur-based chemicals (Figure 7). Elemental sulfur is also recovered from natural-gas processors and

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