Now we have to worry about phosphorous

Phosphorous is an essential element for all living cells. Phosphorus compounds are used in explosives, nerve agents, friction matches, fireworks, pesticides, toothpaste and detergents.

But the most important use of phosphorus-based chemicals is the production of fertilizers. Without it, we don't eat. Now some are worried that the world may soon experience "peak phosphorous, " in other words, run out of the stuff. They say the world's reserves may be depleted in 50 to 100 years. And so far we don't have substitutes for it as we do for oil.

Worldwide, according to Dana Cordell, a Ph.D. candidate, and said Stuart White, director of the Institute for Sustainable Futures at the University of Technology in Sydney, Australia, five times more phosphorus is being mined than is being consumed. Stated another way, 15 million tons of phosphorus is mined yearly to grow food, but 80 percent never reaches the dinner table: It is lost to inefficiency and waste.

Farmers use too much fertilizer and it runs off the land, polluting streams, lakes and oceans. Industrial agriculture does not plow crop residues back into the soil after the harvest. In some countries, consumers throw away a third of their food, even when much of it is still edible.

Mature animals, including humans, excrete nearly 100 percent of the phosphorus they consume. But only half of animal manure — the largest organic and renewable source of phosphorus — is being recycled back onto farmland worldwide, studies show. And only 10 percent of what humans excrete is returned to agriculture as sludge or wastewater.

That's not a startlingly new idea.

The Urine Tax (Latin: vectigal urinae) was a tax levied by the Roman emperor Nero in the 1st century upon the distribution of urine. The lower classes of Roman society urinated into pots which were emptied into cesspools. The liquid was then collected from public latrines, where it was sold and served as the valuable raw material for a number of chemical processes: it was used in tanning, and also by launderers as a source of ammonia to clean and whiten woollen togas. The buyers of the urine paid the tax.

“We need to start talking about our pee and poo more seriously,” Cordell says.