Phosphorus Compounds

Fundamental understanding of phosphorus behavior is a key to solving environmental problems of plant, animal and microbe nutrition, eutrophication, corrosion, and geochemistry. Researchers of such problems nearly always assume that phosphorus in natural systems occurs exclusively in the +5 oxidation state as orthophosphate, polyphosphates, organophosphates, and paniculate phosphates. This assumption has never been explicitly proven.

Phosphorus is unique among the major nutrients (carbon, oxygen, nitrogen, phosphorus) in that it is often assumed to lack a gaseous species for atmospheric transport. However, the recent work of Glindeman et al. (1996a, 1996b, 1996c, 1999) and Han et al. (2000, 2003) unambiguously confirmed that volatile phosphine gas (i.e., hydrogen phosphide or PH3) can be detected in the earth’s atmosphere at trace levels. Several sources of phosphine have been also identified by these authors. Unfortunately, perhaps because of the erroneous assumption that phosphorus is nonvolatile, study of total transport through this mechanism has received minimal attention, and all atmospheric phosphorus transport is assumed to be via phosphate dust.

Atmospheric transport of phosphorus is significant. Pierrou (1979) estimated that atmospheric fallout of phosphorus is in the range of 3.6-9.2 Tg (1 Tg = 10^sup 12^ g) P/yr for terrestrial ecosystems (6.3-12.8 Tg P/yr for the earth), and Graham and Duce (1979) attempted to quantify P flux from land to the atmosphere and estimated to be 4.3 Tg P/yr. If this phosphorus was uniformly dissolved in the world average annual rainfall of about 400 χ 103 km^sup 3^, it would suggest an average phosphate concentration of about 10 ppb in rainwater. The potential importance of atmospheric phosphorus loading to oligotrophic lakes was seemingly confirmed by Lewis et al. (1985), who quantified soluble phosphate in rainwater to remote mountain lakes and determined it accounted for 25% of the total annual phosphate flux to the watershed. Interestingly, this phosphate was not associated with dust or pollen. Atmosphere input of soluble P to the coastal ocean was estimated to be 12 10^sup 10^ mol P yr^sup -1^ (Benitez-Nelson, 2000). This is about 10% of dissolved inorganic phosphate from rivers (Duce, 1986; Delaney, 1998). The issue of atmospheric phosphate is discussed in later sections in light of the results of Glindeman et al. (2003).

The phosphate industry directly and indirectly produces many reduced phosphorus compounds. The United States is the largest producer and consumer of phosphate rock in the world. In 1997, the marketable production of phosphate rock in the United States was 32% of the world total production (United States, 45.9 million metric tons; world total, 143 million metric tons). In 2001, the marketable production and sale of phosphate rock decreased worldwide due to decreased demand for fertilizer (USGS, 2001), and the U.S. share of production dropped to 25%.