All life needs phosphorus and agricultural yields are improved when phosphorus is added to growing plants and the diet of livestock. Consequently, it is used globally as a fertilizer – and plays an important role in meeting the world’s food requirements.
In order for us to add it, however, we first need to extract it from a concentrated form – and the supply comes almost exclusively from phosphate mines in Morocco (with far smaller quantities coming from China, the US, Jordan and South Africa). Within Morocco, most of the mines are in Western Sahara, a former Spanish colony which was annexed by Morocco in 1975.
The fact that more than 70 percent of the global supply comes from this single location is problematic, especially as scientists are warning that we are approaching “peak phosphorus”, the point at which demand begins to outstrip supply and intensive agriculture cannot continue to provide current yields. In the worst case scenario, mineable reserves could be exhausted within as little as 35 years.
So what is going on – and how worried should be?
In nature, phosphorus only exists bound to oxygen, which is called phosphate. It is in this form that it is mined. Chemists can remove the oxygens bound to it to get elemental white phosphorus, which glows in the dark, but it is so unstable that it spontaneously ignites on exposure to air.
Phosphate easily diffuses through soil or water and can be taken up by cells. When phosphate meets free calcium or iron, they combine to give highly insoluble salts.
In the first half of the 19th century, Justus von Liebig popularized the law of the minimum for agriculture, which states that growth is limited by the least available resource. It was soon discovered that this was often some form of phosphorus.
As a consequence, bones – comprised mostly of calcium and phosphate – from old battlefields were dug up to use in farming. Guano, large accumulations of bird droppings, also contains high concentrations of phosphorus and was used to fertilize crops. But supplies of this were soon depleted. As demand increased, supplies had to be mined instead.
But this applied inorganic phosphate fertilizer is highly mobile and leaches into watercourses. In addition, phosphate rock weathers and is also ultimately washed into the ocean where it either deposits as calcium phosphate or is taken up by marine organisms who also eventually deposit on the ocean floor when they die. Consequently, terrestrial phosphorus doesn’t really disappear, but it can move beyond our reach.
To complicate matters further, even the phosphorus we can use is largely wasted. Of the phosphorus mined as fertilizer, only a fifth reaches the food we eat. Some leaches away and some is bound to calcium and iron in the soil. Some plant roots have the ability to extract the latter, but not in large enough quantities to retrieve all of it.
In addition to these inorganic forms, phosphate is also converted into cellular compounds, creating organically-bound phosphorus, such as phospholipids or phytate. After the death of an organism, these organic phosphorus compounds need to be returned into the useable phosphate form. How much organically-bound phosphorus is present in soils depends on the number and activity of the organisms that can do this.
Agricultural soils are usually rich in inorganic phosphorus while in undisturbed ecosystems, such as forests and long-term pastures, organically-bound phosphorus dominates. But agricultural land is often depleted of phosphorus during harvest and land management practices such as ploughing, hence the addition of phosphate-containing fertilizers.
Spreading manure and avoiding tillage are ways of increasing microbial abundance in the soil – and so keeping more phosphorus in an organically-bound form.
The risks of peak phosphorus can be countered with some simple solutions. Eating less meat is a start as huge amounts are used to rear livestock for meat. The chances are that agricultural yields are limited by phosphorus availability and will be further stretched as the global population grows.
Humans are themselves wasteful of phosphorus, as most of what we take in goes straight out again. Fortunately, technologies have been developed to mine phosphorus from sewage, but at present are too expensive to be practical.
Peak phosphorus does not mean that phosphorus will disappear, rather that the reserves with mineable high concentrations are depleting. Instead, we are increasing the background concentrations of phosphorus and adding it to the ocean floor. More sustainable phosphorus use requires a greater appreciation and understanding of the many organisms that make up soils – and the part they play in phosphorus distribution – or we may no longer be able to feed the world at an affordable price.
The seventh row of the periodic table is complete, resplendent with four new names for the elements 113, 115, 117 and 118. The International Union of Pure and Applied Chemistry (the organization charged with naming the elements) has suggested these should be called nihonium (Nh); moscovium (Mc); tennessine (Ts) and oganesson (Og) and is expected to confirm the proposal in November.
The three former elements are named after the regions where they were discovered (and Nihonium references Nihon the Japanese name for Japan). And “oganesson” is named after the Russian-American physicist Yuri Oganessian, who helped discover them. Read More
Have you ever wondered how freshly baked bread gets its golden brown crust and why it smells so good? Or how nondescript green berries turn into beautiful brown coffee beans with a rich alluring aroma?
The answers to these questions lie in a series of complex of chemical reactions, known as Maillard reactions, which give many foods their familiar flavors and colors. These sensory properties even guide us in how we choose foods and help create our initial perceptions of their quality. Read More
Did you know that the discovery of a way to make ammonia was the single most important reason for the world’s population explosion from 1.6 billion in 1900 to 7 billion today? Or that polythene, the world’s most common plastic, was accidentally invented twice?
The chances are you didn’t, as chemistry tends to get overlooked compared to the other sciences. Not a single chemist made it into Science magazine’s Top 50 Science stars on Twitter. Chemistry news just don’t get the same coverage as the physics projects, even when the project was all about landing a chemistry lab on a comet.
So the Royal Society of Chemistry decided to look into what people really think of chemistry, chemists and chemicals. It turns out most people just don’t have a good idea of what it is chemists do, or how chemistry contributes to the modern world.
This is a real shame, because the world as we know it wouldn’t exist without chemistry. Here’s my top five chemistry inventions that make the world you live in.
by Richard Wrangham, as told to Discover’s Veronique Greenwood. Wrangham is the chair of biological anthropology at Harvard University, where he studies the cultural similarities between humans and chimpanzees—including our unique tendencies to form murderous alliances and engage in recreational sexual activity. He is the author of Catching Fire: How Cooking Made Us Human.
When I was studying the feeding behavior of wild chimpanzees in the early 1970s, I tried surviving on chimpanzee foods for a day at a time. I learned that nothing that chimpanzees ate (at Gombe, in Tanzania, at least) was so poisonous that it would make you ill, but nothing was so palatable that one could easily fill one’s stomach. Having eaten nothing but chimpanzee foods all day, I fell upon regular cooked food in the evenings with relief and delight.
About 25 years later, it occurred to me that my experience in Gombe of being unable to thrive on wild foods likely reflected a general problem for humans that was somehow overcome at some point, possibly through the development of cooking. (Various of our ancestors would have eaten more roots and meat than chimpanzees do, but I had plenty of experience of seeing chimpanzees working very hard to chew their way through tough raw meat—and had even myself tried chewing monkeys killed and discarded by chimpanzees.) In 1999, I published a paper [pdf] with colleagues that argued that the advent of cooking would have marked a turning point in how much energy our ancestors were able to reap from food.
To my surprise, some of the peer commentaries were dismissive of the idea that cooked food provides more energy than raw. The amazing fact is that no experiments had been published directly testing the effects of cooking on net energy gained. It was remarkable, given the abiding interest in calories, that there was a pronounced lack of studies of the effects of cooking on energy gain, even though there were thousands of studies on the effects of cooking on vitamin concentration, and a fair number on its effects on the physical properties of food such as tenderness. But more than a decade later, thanks particularly to the work of Rachel Carmody, a grad student in my lab, we now have a series of experiments that provide a solid base of evidence showing that the skeptics were wrong.
Whether we are talking about plants or meat, eating cooked food provides more calories than eating the same food raw. And that means that the calorie counts we’ve grown so used to consulting are routinely wrong. Read More