# Peak phosphorus - what are the sinks?

The minable phosphorus reserves are limited. Where is the mined phosphoprus landing, what are the global phosphorus sinks?

I would assume that most phosphorus is used for fertilizer and ultimately ends up in the water (via consumption by plants, than animals or humans and then wastewater or faeces). The most likely candidate in water would be phosphate ($PO_4^{-3}$). I would assume that phosphate is fixed in microorganisms and that those ultimatly form sediment and get mineralized. But this is a wild guess.

How does the phosphorus cycle actually work after phosphorus is used by humans and emitted into the environment? What are major processes, and in what forms is phosphorus mineralized?

• I wonder whether this is on-topic here... AIUI your question is not about where phosphorus reserves are, which would clearly be on-topic, but about where phosphorus ends up after use. It might be argued that this is earth science when considered at a global level, but it probably wouldn't be otherwise... I'm not going to vote to close or anything, but I wonder whether it'd be worth also asking on sustainability.SE. – Semidiurnal Simon Apr 22 '14 at 10:04
• I think the question is fine here. Geochemistry is a big part of the Earth sciences. @mart is interested in a part of the phosphorous cycle where it is used as a resource. But for global budgets and rates this part of the cycle is also on-topic. As a non-native speaker I just think that an edit for clarity would help. – tobias47n9e Apr 22 '14 at 10:15
• please review if the new wording is clearer. – mart Apr 23 '14 at 11:52
• @Spießbürger fair enough :-) – Semidiurnal Simon Apr 23 '14 at 12:03

The phosphorous sinks are the ocean and ocean sediments.

The ocean holds $3 \times 10^{15}$ moles of phosphorous.

The annual amount of phosphorous input into the ocean, as well as the amount of burial of phosphorous as sediment is on the order of $10^{10}$ moles.

The sediment is of three categories:

1. Phosphorous associated with calcium carbonate
2. Organic phosphorous (associated with organic carbon)
3. Apatite

See Phosphorous Accumulation in Marine Sediments and the Oceanic Phosphorous Cycle for a detailed analysis.

• $10^{10}$ moles inventory in the sediment? – mart May 14 '14 at 13:02
• not inventory, ~$10^{10}$ moles per year become ocean sediment. It is rate (amount/year) rather than an amount. – DavePhD May 14 '14 at 13:12
• On the whole, are 1 and 3 phosphorus that's been part of a marine organism, and 2 includes terrestrial runoff and sediments that might go directly to being buried? – cphlewis Apr 28 '15 at 0:53

It is very likely that there will always be phosphorous for mining, because rising demand will increase prizes, and make more mining sites profitable (This is like the golden rule of mining and seen for example with oil sands suddenly being profitable).

From a crystalline-rock perspective (this is just a partial answer) the phosphate minerals are a huge phosphorous sink. Prominent members of this group are Apatite, Monazite and Xenotime, which occur widely in granitic rocks. The problem with these minerals is that they can contain high percentages of radioactive elements and submicroscopic inclusions with even higher radioactivity. This has already contributed to the rise of radioactivity on fertilized fields and rivers that run from them (http://link.springer.com/article/10.1007%2FBF00747688). This is relevant to your question because radioactivity and the isotopes that produce it, can be used as a tracer for phosphorous.

• thanks, but my question was about sinks after mining and usage. – mart Apr 22 '14 at 8:48
• You correctly point out that saying "there will always be phosphorous for mining" is like saying "there will always be oil for drilling / otherwise extracting". Both statements are clearly untrue. – Semidiurnal Simon Apr 22 '14 at 9:38
• @SimonW It is probably a whole question in its own. But for the foreseeable future I think it holds true. In the case of oil it might be that global demand will sometime be larger than production, but that would in my opinion just result in alternative technologies picking up that money. – tobias47n9e Apr 22 '14 at 10:00
• That first paragraph sounds like an economist! In the case of oil for energy, there also becomes a point where it takes more energy to extract than is released - something economists forget! – winwaed Apr 23 '14 at 13:02
• @winwaed I am no economist, but I think that the point where extraction becomes unprofitable is not dependent on the (energy used/energy mined)-ratio. It all depends on how much money can be earned with the commodity (gems are essentially worthless, but get insane revenues). Climate change and environmental damage are also left out of economists equations, but they are actually borrowed money from future generations and nature. The history books of the future will not be proud of us :/ – tobias47n9e Apr 23 '14 at 17:53