Friday, 18 October 2013

One more shortage

This article will appear in the Kildare Nationalist next week.

If you’re reading this right now, your body is using up phosphorous; your cells depend on it to function. All life on Earth uses the double-helix of DNA, or something like it, as its blueprint – and the sides of the helix are held together by phosphorous bonds. No phosphorous, no life.

That’s not usually a problem, as small amounts of phosphorous circulate through the natural world the same way so many other elements do – it starts out as some chemical ingredient in rocks, and as the rocks are broken into smaller and smaller pieces by the elements, plants absorb the phosphorous through their roots. Herbivores eat the plants, carnivores eat the herbivores, they all generate waste, which goes back into the soil and brings the phosphorous back to the roots again.

Eventually, of course, erosion washes away the phosphorous, and a good rain washes it into streams, rivers, and finally the sea, where it fertilises plant life there. Finally it settles on the sea floor, where – in the very long term,  over tens of millions of years -- continents move slowly over it, lava melts the rocks, volcanos send them back to the surface again, and the exposed rocks become soil again. So far, so normal.

The thing to remember, though, is that there’s only so much phosphorous in the soil-plants-animals cycle, at this moment, like money in a paycheque, if you don’t get paid again for tens of millions of years.

Farmers long discovered that a bit more phosphorous in the soil boosts crop production, and for thousands of years this was done by adding human and animal manure back to the soil --- think of this as using one’s money well.

In the last couple of centuries, though, humans discovered that we could mine phosphorous and scatter it over soil to boost crop production. At first people mined guano – giant piles of bird droppings on isolated islands, or bat droppings in caves. Nations prized the resource so highly they fought wars over guano in the 19th century, and the USA still claims the right to annex islands with a store of guano.

Nowadays, we generally get phosphorous from mining rocks – using a credit card, in this analogy -- and it forms a major component of most fertilisers – many are labelled NPK, for Nitrogen (N) – Phosphorous (P) – Potassium (K, apparently because P was already taken). Phosphorous use rose six-fold between 1950 and 2000, and modern agriculture is now quite dependent on phosphorous mining.

One problem, though, is that rain continues to wash away the phosphorous, creating ocean dead-zones from excess phosphorous. Another problem is that number of phosphorous-rich rocks in the world is limited, and the supply has been shrinking.

None of this will be a problem if the supply of phosphorous-rich rocks never runs out, but according to a 2007 paper by Bart Anderson and Patrick Dery, we could be running out of such resources by 2027.

According to a recent article in Chemosphere, “we’ve now been forced to start mining the rocks that have lower quality phosphorus with higher rates of contaminants and are more difficult to access. We’re down to the tar sands equivalent of minable phosphorus, most of which is found in only five countries; Morocco, China, the USA, Jordan and South Africa. Maybe they can be the next OPEC cartel for phosphorus?”

To prevent this kind of crisis, the authors recommend keeping more phosphorous around – most of the phosphorous we use now, they say, is wasted. By preventing runoff and re-using animal and even human waste, they say, we could avoid this resource shortage hitting us around the same time that climate change kicks in and we have a billion or so more mouths to feed.

For more information: “A brief history of phosphorus use by humans and ideas on how we can prevent the global food security risk of ‘Peak Phosphorus’” 8 April 2011 Chemosphere Vol. 84 (2011) 737–746


Anonymous said...

No worries, volcanoes are spitting lots of phosphorus into the atmosphere..

Brian Kaller said...

Would you have any citations for that? Empirical studies, peer-reviewed papers or anything?