Stevens Institute of Technology
This is based on an article that was published in Scientific American in June, 2009. The complete article can be found at: http://www.scientificamerican.com/article.cfm?id=phosphorus-a-looming-crisis. Additional resources can be found at http://personal.stevens.edu/~dvaccari/.
Every package of fertilizer prominently displays three numbers, such as 19-12-5. Those are the percentages of nitrogen, phosphorus and potassium, respectively. Where do these elements in fertilizer come from? We obtain nitrogen from the air, but we must mine phosphorus and potassium. The world has enough potassium to last several centuries. But phosphorus is a different story. High-grade global supplies may start running out by the end of this century. By then our population may already have reached what some say is the limit of what the planet can feed.
Supplies of phosphorus are even less evenly distributed than oil’s. The U.S. is the world’s largest producer and exporter of phosphorus, at 23 percent of the total, but 80 percent of that amount comes from a single source: pit mines near Tampa, Fla., which are running out. Meanwhile nearly 40 percent of global reserves are in a single country, Morocco, sometimes referred to as the “Saudi Arabia of phosphorus.” This imbalance makes phosphorus a geostrategic ticking time bomb.
My interest in phosphorus dates back to when I became involved in a NASA program for growing food for a long-term space mission. Our planet is also a spaceship; it has an essentially fixed amount of each element. In nature, weathering releases phosphorus from rocks, and it enters the food chain. Ecosystems recycle the phosphorus many times before it runs off into the sea. Over tens of millions of years tectonic uplift may return it to land. Agriculture short-circuits this cycle. Phosphorus is used once in the food that we eat, and then flushed away. Tilling accelerates land erosion, which is the biggest loss of phosphorus in our system.
There is estimated to be enough phosphorus rock to last a millennium. However, 90 percent of this is not currently economic to recover, either because of chemical composition, location at great depth or in sensitive areas, or due to the high levels of toxic or radioactive contaminants such as cadmium and uranium. Exploitable global reserves are enough to last about 90 years at the current usage rate.
Some geologists are skeptical about a crisis and reckon that estimates of resources are moving targets. As prices increase, deposits that were previously considered too expensive to access reclassify as reserves. Shortages can stimulate conservation efforts, new exploration efforts, or the development of new extraction technologies. Yet most of the phosphorus discovery in the past century has occurred in just two places: Morocco and North Carolina. And much of North Carolina’s resources are restricted because they underlie sensitive areas.
Like energy, phosphorus can be conserved. Soil conservation would have the greatest benefit. We can reduce our consumption of meat, especially beef, which is an inefficient use of grain. Unlike energy, there is no “alternative phosphorus.” But also unlike energy, it can be recycled. Only half of animal waste is effectively used today, and this should change. Waste from commercial and home food processing could be composted and recycled. The 1.5 grams per day of phosphorus that we excrete will need to be captured, either at the point of generation (the home) or in central wastewater treatment plants. Conservation would also help with the corollary problem of phosphorus in runoff and wastewater that pollutes our waters, including the Chesapeake.
We are running out of phosphorus deposits that are relatively easily and cheaply exploitable. There is a chance that the optimists are correct about the relative ease of obtaining new sources and that shortages can be averted. Considering that known deposits are so unevenly distributed and that this resource is critical to life and has no substitute, the findings to date are not enough to allay concerns. Given the stakes, we should not leave our future to chance.