Facing up to Phosphorus, continued

What remains a point of contention is exactly when such problems might arise. Cordell and others insist that this scenario could play out in a very few decades, as the quality of available phosphate begins to decline.

“Importantly, this means increasing energy and other resources (like sulfur) are therefore required to mine, process and extract the same nutrient value from phosphate rock while simultaneously generating more waste,” she says. “Further, the global trade of phosphate commodities to the farm gate currently relies on fossil fuel energy, yet in a carbon-constrained future, shipping millions of tons of phosphate rock and fertilizers around the globe may no longer be appropriate or possible.”

Opponents of this view harken back to doomsday forecasts framed decades ago by prominent analyses like The Limits to Growth or The Population Bomb. Economic and environmental disasters that should already have overwhelmed us by now have instead been postponed indefinitely, thanks to changes in our behavior, economic policy or technological capabilities. Discussion of those disasters undoubtedly prompted at least some of the necessary changes, and could do so again in the case of phosphorus.

This optimistic perspective benefited from a 2010 revision of estimates of the world’s phosphate reserves. New figures from the International Fertilizer Development Center raise the estimate from 16 billion metric tons to more than 60 billion metric tons. The author of that report, geologist Steven Van Kauwenbergh, insists that this finding should put an end to any immediate concerns about peak phosphorus.

“Based on this estimate,” he says, “at current rates of production, phosphate rock reserves to produce fertilizer will be available for 300 to 400 years.”

At the same time, Van Kauwenbergh cautions that the sources of information used for this estimate tends to be limited, provided primarily by industrial interests. “A collaborative effort by phosphate rock producers, government agencies, international organizations and academia will be required to make a more definitive estimate of world phosphate rock reserves and resources,” he concludes.

Brave New Sources

Even if phosphate is more abundant than previously thought, the distribution of reserves poses a big challenge.

Morocco alone appears to control no fewer than 51 billion of the estimated 60 billion metric tons of phosphates, some 84 percent of the total. The rest is found in various places in much smaller amounts, with 6 percent in China, 1 percent in the U.S., 1 percent in Jordan and the remainder spread among the rest of the world’s nations. These relatively limited supply lines could be vulnerable to disruptions, as was demonstrated in 2008 when China imposed a 135 percent export tariff on its phosphate rock. This geopolitical context has been further complicated by Morocco’s controversial occupation of Western Sahara since 1975, which has prompted some Scandinavian firms to protest by boycotting that region’s phosphate exports.

In addition to political considerations, poor transportation links limit the volume of fertilizer reaching farmers in some countries, where a correspondingly high price makes this input all the less accessible. Even without the dire threat of peak phosphorus, as growing population boosts demand for food, intensifying competition along narrow international supply lines could place fertilizers beyond the reach of many more farmers.

Faced with this challenge, sources like that tapped in Brave New World could take on a fresh appeal. In fact, though it does not yet extend to crematoria, phosphorus recovery is not consigned to science fiction.

One promising technology is a chemical reactor that can be installed in municipal wastewater streams, where human urine provides a rich supply of raw material. Urine forms the basis of ammonium magnesium phosphate, a white crystal known as struvite. Struvite cakes on the walls of sluiceways and sewers, hardening into a concrete-like consistency that is onerous to remove.

Struvite, if it can be extracted in a pure form, offers the basis for an effective fertilizer. For example, an extraction technology produced by Vancouver-based Ostara Nutrient Recovery Technologies Inc. has been installed in cities in Canada, the U.S. and the UK. The system, like others, aspires to provide a cost-effective means of capturing struvite for agricultural use.

The Other Half

The other half of the phosphorus predicament, ironically, is a problem of localized overabundance. Soils in many parts of North America have naturally high levels of phosphorus. Add too much more in an attempt to boost crop yields, and nutrients drain off the land to fertilize lakes and rivers. What often follows is the proliferation of algae in these waters, which then become oxygen-poor and inhospitable to plant or animal life. This process, known as eutrophication, can compromise aquatic ecosystems.

“We have understood the causes of eutrophication for more than 40 years, while the drivers have gotten worse,” says Stephen Carpenter, a professor at the University of Wisconsin’s Center for Limnology in Madison. “Increased planting of corn, increased livestock numbers and increasingly variable precipitation due to climate change are principal drivers of increased eutrophication. We decreased the discharge from sewage treatment plants, but at the same time the runoff of manure and overfertilized soil became much worse.”

Historical Sources of Phosphorus


Adapted from Cordell, D.; Drangert, J-O. and White, S. (2009). The story of phosphorus: Global food security and food for thought. Journal of Global Environmental Change 19(2):292–305.

Before the Green Revolution, most of the phosphorus used to boost crop growth came from animal waste. Today’s farmers rely mainly on phosphate rock mined from a few key hot spots around the world. View larger image