Materials matter in phosphorus sustainability
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MATERIAL MATTERS
Materials matter in phosphorus sustainability OPINION
By Jacob L. Jones, Yaroslava G. Yingling, Ian M. Reaney, and Paul Westerhoff
T
his year marks the 350th anniversary of the discovery of phosphorus by German alchemist Hennig Brandt.1 As element 15 in the periodic table, phosphorus is known to researchers for its luminescent and reactive characteristics in elemental form, as a dopant in semiconductors, as a key constituent in nerve agents and industrial detergents,2 and, most recently, in its two-dimensional (2D) form, phosphorene (a black phosphorus allotrope). However, its role in biology and agriculture has more foundational implications for society.3 It is part of the backbone of DNA. Because of its central role in biological energy transfer processes, phosphorus is also an essential component in fertilizers underpinning the productivity of global food systems, enabling society to sustain Earth’s growing population. Unfortunately, myriad cross-disciplinary challenges pervade the life cycle of phosphorus, from its sources and availability to its application and disposal or reuse.4,5 The challenges around the phosphorus life cycle are so complex that they have been termed a “wicked problem”;6,7 the problems are intractable, contested, and plagued by a high degree of uncertainty. These can be more deeply appreciated by noting that challenges in the phosphorus life cycle span 17 orders of magnitude in length scale—from the atomic scale of elemental phosphorus and the orthophosphate ion to farms and farmers, phosphate mines, and lakes to global economics and public policy (see Figure 1).8,9 These length scales involve diverse stakeholders with sometimes competing priorities.
The phosphorus life cycle
The challenges for phosphorus start at the cradle. Presently, phosphorus is a
nonrenewable resource extracted dominantly from phosphate mines (Figure 1j). The quantity of phosphorus mined and produced is large: In 2018, 270 million tonnes (Mt) of phosphate rock (mostly apatites [i.e., Ca5(PO4)3(F,Cl,OH,Br)] were used in global production, providing 66 Mt of P2O5 (used in fertilizers).10 By comparison, the global mining production of aluminum and copper were most recently reported to be 46 Mt and 16 Mt per year, respectively.11 Although China produces more than 50% of the world’s current supply of phosphorus, the world’s reserves of phosphate rock are concentrated, with 70% in Morocco and the Western Sahara.10 At current rates of use, the United States and the EU are expected to run out of their domestic phosphorus supplies within the next generation, significantly increasing their dependence on imports. The concentration of supplies and reserves can result in price fluctuations because of economic uncertainty or political unrest, as evidenced in 2008 when the price of phosphate rock spiked approximately 800%, from USD$50/ tonne to USD$430/tonne.12 Thus, phosphorus is a low-cost yet large-volume critical resource with an uncertain future supply. Approximately 90% of mined phosphate is used for f
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