Phosphate builds your bones, powers your cells and feeds the world's crops
Much of the energy a cell uses comes from snapping phosphate groups off molecules like ATP. The same simple ion, one phosphorus atom ringed by four oxygens, hardens bones and teeth and fertilises farmland. China mines the most, Morocco holds the largest reserves, and estimates of when supplies run short vary wildly.
Chemically, phosphate comes from phosphoric acid, H3PO4, by stripping away hydrogen ions one at a time. Lose one and you get dihydrogen phosphate, lose two and you have hydrogen phosphate, lose all three and you reach the bare phosphate ion, which weighs 94.97 grams per mole and has its four oxygens arranged in a tetrahedron. Which form dominates depends on acidity: near pH 4.7 almost everything is dihydrogen phosphate, near 9.8 it is hydrogen phosphate, and only above pH 13 does the fully stripped ion take over. Chemists exploit this to crystallise particular salts simply by setting the pH.
Inside the body the balance shifts from place to place. In the fluid of a cell, at neutral pH, about 62% is dihydrogen phosphate and 38% hydrogen phosphate, while in the slightly more alkaline fluid outside cells the ratio flips to roughly 20 to 80. Phosphate groups are stitched into DNA and RNA and into the energy carriers AMP, ADP and ATP, and adding or removing them is a central switch in metabolism. Bones and teeth are built largely of hydroxyapatite, a crystalline calcium phosphate, and the tough enamel of mammal teeth may contain fluoroapatite, where fluoride replaces some hydroxyl groups. High blood phosphate, most often caused by kidney failure in people, dogs and cats, is linked to higher death rates and to hardening of blood vessels.
Farming depends on phosphate fertiliser, but runoff can trigger runaway plant growth, and mining can release heavy metals. Major deposits lie in central Florida's Bone Valley, south-eastern Idaho and coastal North Carolina, while the Pacific islands of Nauru and Banaba, once rich in top-grade ore, were stripped by overmining.
How long reserves will last is contested. A 2007 estimate gave 345 years at current use, others predicted a peak within 30 years, and one researcher suggested depletion in 50 to 100 years. The US Geological Survey put world reserves at 71 billion tons in 2012, against 0.19 billion tons mined in 2011.
Source: Phosphate
