I and my fellow stormwater professionals have spent decades obsessed with Phosphorus. We have developed formulas and spreadsheets that tell us how many pounds of Phosphorus will run off of a parking lot or yard. We have explained the various ills created by too much Phosphorus flowing to rivers, lakes, and the Chesapeake Bay. We build contraptions called BMPs to trap it and disarm it. The Chesapeake Bay TMDL admonishes us to limit Phosphorus to 12.5 million pounds per year.
Given all that, I have struggled with actually envisioning Phosphorus. What does a pound of Phosphorus actually look like, much less 12.5 million pounds? I can’t look into a river and declare with any certainty, “there goes some Phosphorus” (except of course for the occasional algae left in its wake). What exactly is this sinister substance called Phosphorus?
I have a good image in my mind of a pound of pasta or a pound of butter (which, by the way, go pretty well together for those willing to forego both low-carb and low-fat). However, after all these years of collecting samples of it and modelling its removal in stormwater practices, I still can’t conjure with any clarity a pound of Phosphorus. This led me to undertake some research.
Most phosphorus in the world today is derived from Phosphate rock that looks something like this:
Source: Minerals Education Coalition
Before Phosphorus was extracted from rocks, it was made by evaporating urine (do not try this at home) and heating the residue. This process was pioneered in 1669 by Hennig Brandt in Hamburg, Germany. Apparently, when Brandt was not evaporating urine, he was trying to turn base metals into gold.
In the natural world, Phosphorus does not exist in its elemental form, but manifests as the compound, Phosphate. In the environmental field, we are most familiar with the use of Phosphorus in fertilizers and detergents, and thus its ill affects on rivers and lakes when there is too much of it. However, here is an astonishing list of some of the other uses of Phosphorus: matches, and match books, pyrotechnics, incendiary shells, warning flares, high strength/low allow steel, light emitting diodes (LEDs), animal feed, rust removers, corrosion preventers, dishwasher tablets, gasoline additives, lubricating oil, flame retardants, insecticides, weed killers.
The two primary forms of Phosphorus are white and red. If you are trying the envision Phosphorus, white Phosphorus is undeniably the more flamboyant of the two: it glows in the dark, is dangerously flammable, and is a deadly poison. Do not mess with white Phosphorus!
Red Phosphorus, on the other hand, is friendlier and helpful around the house; it is the stuff stuck to the side of matchboxes and formed around match heads. It is the quintessential “Light Bringer,” as the term Phosphorus can be translated loosely from the Greek.
As there are so many uses for Phosphorus, some have even speculated that we will be reaching “Peak Phosphorus” around the year 2050. Similar to “Peak Oil,” this is when the raw material of Phosphorus bearing rock would be running on low, which would be rather detrimental for all of the aforementioned uses, unless we start evaporating a lot of urine.
We all know that Phosphorus is a nutrient, and, as such, it has important functions in the human body. According to the Linus Pauling Institute at Oregon State University, Phosphorus is an essential structural component of cell membranes and nucleic acids but is also involved in several biological processes, including bone mineralization, energy production, cell signaling through phosphorylation reactions, and regulation of acid-base homeostasis.
Returning to the stormwater context, urban runoff contains both particulate and soluble forms of Phosphorus. Sources of Phosphorus in stormwater include leaf litter, grass clippings, eroded soil, pet waste, fertilizer, road salt, atmospheric deposition, and other sources. Stormwater BMPs are capable of removing the particulate-bound Phosphorus (associated with organic matter), but the soluble forms tend to sneak through. This is significant because around 45% of total Phosphorus can be in this soluble form (mostly orthophosphorus), a figure that will vary based on watershed characteristics. When it reaches a waterbody, soluble Phosphorus is readily available for the growth of algae and aquatic plants (Minnesota Stormwater Manual, Wiki).
This is why a new generation of BMPs is experimenting with strategies to capture soluble Phosphorus, such as adding Iron or Aluminum amendments to bioretention soil media (see, for example, the Chesapeake Stormwater Network report on “performance enhancing devices,” link in Related Links below).
If, after reading this, you are hungry for more information about Phosphorus, I recommend strongly that you watch the following short video featuring a couple of professorial types from the University of Nottingham. Watch in particular for the fellow with irrepressible hair and a Periodic Table necktie. He helpfully explains that Phosphorus could easily make our bodies explode, but that our bodies thankfully use it up before that can happen.
Minerals Education Coalition
Royal Society of Chemistry, Periodic Table
Linus Pauling Institute, Oregon State University
Minnesota Stormwater Manual, Wiki site
Chesapeake Stormwater Network, Performance Enhancing Devices