Phosphates: Environmental Constraints and Impacty

Caroline Sawyer
CHEM 2323 Organic Chemistry 2
Prof. P. Spellane
August 6, 2015
The Fate of Phosphorus: Why it is important for
organic chemists—and for everyone
An Overview

I: Chemistry of Phosphorus (P).
Atomic number 15; atomic weight 31; Group 5A on the periodic table, below nitrogen. Although it is a non-metal according to the periodic table, it is sometimes characterized as a metalloid (“metal-like”). Among its unusual properties, P has a large number of oxidation states: +1, +3, +4, +5 being the most common. P is almost always found bonded to three or more oxygen atoms. Owing to its affinity for oxygen, elemental phosphorus (industrially produced) when exposed to ambient oxygen will first glow with a greenish light and then combust spontaneously. This reaction, probably quite risky, is intriguing to watch in a YouTube video such as this one:

II. Where is P found?
A. Geologically, P comprises about 0.1% of the Earth’s crust. It is never found in its natural form; only as an oxide in minerals such as apatite, which are important natural resources. The five main countries where phosphates are extracted are: Morocco (particularly the Western Sahara, which it either comprises or occupies, depending on point of view), China, South Africa, Jordan, and the United States. Formerly bat guano from South American constituted an important source of phosphates, and new guano sources (feces of birds) have been discovered in eastern Africa.
B. Biologically, phosphates are essential to life.
1. In animals,
a. Phosphates are essential metabolic compounds: in the energy-storage molecule ATP; in nucleic acids such as DNA and RNA; in phospholipids making up cell membranes; cell 3. molecules such as cAMP; phosphate groups in phosphorylation of carbohydrates. Hormones such as Parathyroid Hormone (PTH) regulate phosphate balance, working with the kidneys’ exquisitely calibrated system for retaining and excreting exactly what is necessary.
b. Phosphate compounds, notably hydroxyapatite, are important components in the structure of bones and tooth enamel. As with calcium, with which it is found in association as calcium phosphate, in addition to a structural compound, P in bones serves as a reserve for metabolism. Of the phosphate that makes up about 1.2% of human body weight, about 85% is in bones and teeth.
2. In plants:
a. Phosphates perform similar metabolic roles as in animals. The energy-capture of photosynthesis transforms ADP to ATP. As every in every living organism, the encoding of plants’ physiology and growth is encoded by nucleic acids. Although we do not tend to think of plants as moving, they do move, continuously, in growth. P is necessary for growth, especially of roots of plants.
b. Cellulose, a carbohydrate, is one important component of a plant’s structure, but cell walls (which plants have instead of cell membranes) are another. Phosphates are an important component in plant cell walls.
3. Why? On the face of things, phosphorus, which has only a tenuous relationship with carbon, seems like an unlikely candidate for a substance so ubiquitous and essential to life. Perhaps one way to look at it is as a mediator between organic and inorganic. More provocatively, Butusov (p. 5) suggests that phosphorus saved the day for the evolution of living organisms by taking up the oxygen produced in photosynthesis, which otherwise would have poisoned cells compounds by oxidation. He argues that oxidation of hydrocarbon lipids would have rancidified them, making them useful. But phospholipids lock up oxygen, making cell membranes dynamic and viable.
III. Nutrition, the P cycle, and its problems.
A. Plants get P from the soil, but not by themselves. Fungi entwined around and penetrating their roots metabolize soil phosphates into a form that the roots can take in. (Plants provide the fungi nutrients in return, in these ecologically essential symbiotic relationships.) Whereas (vertebrate) animals store phosphates in their bones, plants store them in phytate, which will be discussed below. Plant seeds are particularly rich in phytate, also called phytic acid. (The root of these words, “phyte,” comes from the Greek for “plant,” because only plants produce these molecules.)
B. Animals get phosphorus from food; particularly from substances rich in protein. There are so many food sources for P that nutritional labeling does not even include that nutrient, even though a minimum daily requirement has been established of about 700 mg. But there is a catch, particularly for the majority of human beings who rely on agriculture for their food. The P in the phytates in plant seeds we eat—grains, beans, and nuts—is metabolically accessibly for us only to a very small degree. So this phosphate is wasted; excreted in urine.
C. Phosphate everywhere; yet not enough? Waste of phosphorus occurs at nearly every stage of its cycling between the realms of minerals and of organisms’ metabolism. The combined phenomena of agriculture, dense human settlement, population increase, and aspiration toward higher standards of living—including access to better quality food and to fuel resources—all put pressure on the phosphate resources that constitute the basis of agriculture.
1. In agriculture, soils produce plants that are removed en masse, so that the decomposed plant matter does not return to the ground. So nutrients such as P (and N and K) must be extracted or (in the case of N) synthesized to put back into the soil: fertilizer.
2. Reactive as it is, phosphate in fertilizer tends to run off before it can be used by plants. Runoff rich in phosphate causes considerable ecological damage, as in eutrophication of lakes, ponds and rivers (excessive organic growth that uses all the dissolved oxygen) and algal blooms that can make water toxic.
3. Excrement from animals raised for food can be an excellent source of fertilizer. But when animals are raised in very crowded conditions, too much excrement, or manure, is produced to be feasibly used. This unusable manure turns, essentially, to putrid toxin.
4. The economy of raising animals for food demands that they grow quickly, meaning they need supplemental phosphate. At a university in Canada, pigs (called “Ecopigs”) have been genetically engineered to produce enzymes enabling them to digest the phytates in their plant foods, meaning no need for supplements and less excretion of phosphate waste.
5. People, too, produce excrement—the more of it, the more people there are. For nitrogen and phosphorus, the less noxious form of excrement, urine, would be a good source, although it would have to be treated before being used as fertilizer. In wastewater treatment systems, a considerable amount of nitrogen can be captured as biogas, but phosphate is usually lost. A Belgian company, NuReSys, has developed a what they say is an economical method for capturing wastewater phosphate and turning it into slow-release fertilizer.
6. Phosphates play another important, and questionable role in agriculture as pesticides, particularly insecticides. These organo-phosphate compounds are effective because they block reuptake of Acetylcholine (ACh) in neural synapses, by inserting themselves into the active site of the ACh breakdown enzyme, ACh esterase. Agricultural workers who use or otherwise come in contact with organo-phosphate pesticides can suffer the same kind of death, from fast-acting toxicity, and there can be deleterious long-term consequences from exposure as well. In addition, obviously, organo-phosphate compounds also run off into water systems.
7. By some arguments, P is a critical limiting factor for the growth and prosperity of human populations—as critical a factor as petroleum fuels, perhaps. Others argue that, given the absolute abundance of phosphate resources, new methods will be found to extract, transport, apply, and recycle it economically.
IV. Wonders of the natural world: Not surprisingly, the phenomenon of bioluminescence depends on phosphorus—in form of energy shifts between ATP and AMP (actually). I hoped to be able to explain the chemical mechanism of firefly bioluminescence to you today, but it was too complicated. The word “phosphorescence,” of course, refers to phosphorus and its strange glow, sometimes even seen in mineral phosphates. The word is used even for the less usual types of luminescence in which phosphorus is not involved.
V. Phytate and its fate in the engine of phytase enzymes.
Phytate, a fascinatingly structured molecule, is illustrated in two ways, below. As mentioned about in connection with both plants and animals, for all its advantages as a storage molecule for plants, phytate poses some serious ecological problems. If we, like the “Ecopigs,” could produce enzymes to break down phytate from plant sources, we could make much more efficient use of the world’s phosphate resources and move toward more sustainable agricultural and waste systems.
The core of phytate is cyclohexanol with six alcohol groups, with stereochemistry that is important because of how the phosphoesters will be arranged when connected to those groups. In animals, the most important form of this compound, myo-inositol, is synthesized from glucose (actually glucose-6-phosphate) in the kidneys. Thus the stereochemistry is similar to the parent molecule’s:

Caroline Sawyer

CHEM 2323 Organic Chemistry 2

Prof. P. Spellane
August 6, 2015

The Fate of Phosphorus: Why it is important for

organic chemists—and for everyone

An Overview

I: Chemistry of Phosphorus (P).

Atomic number 15; atomic weight 31; Group 5A on the periodic table, below nitrogen. Although it is a non-metal according to the periodic table, it is sometimes characterized as a metalloid (“metal-like”).   Among its unusual properties, P has a large number of oxidation states: +1, +3, +4, +5 being the most common.   P is almost always found bonded to three or more oxygen atoms. Owing to its affinity for oxygen, elemental phosphorus (industrially produced) when exposed to ambient oxygen will first glow with a greenish light and then combust spontaneously. This reaction, probably quite risky, is intriguing to watch in a YouTube video such as this one:

https://www.youtube.com/watch?v=Oke8GinWDG8

  1. Where is P found?
  2. Geologically, P comprises about 0.1% of the Earth’s crust. It is never found in its natural form; only as an oxide in minerals such as apatite, which are important natural resources. The five main countries where phosphates are extracted are: Morocco (particularly the Western Sahara, which it either comprises or occupies, depending on point of view), China, South Africa, Jordan, and the United States. Formerly bat guano from South American constituted an important source of phosphates, and new guano sources (feces of birds) have been discovered in eastern Africa.
  3. Biologically, phosphates are essential to life.
  4. In animals,
  5. Phosphates are essential metabolic compounds:   in the energy-storage molecule ATP; in nucleic acids such as DNA and RNA; in phospholipids making up cell membranes; cell 3. molecules such as cAMP; phosphate groups in phosphorylation of carbohydrates. Hormones such as Parathyroid Hormone (PTH) regulate phosphate balance, working with the kidneys’ exquisitely calibrated system for retaining and excreting exactly what is necessary.
  6. Phosphate compounds, notably hydroxyapatite, are important components in the structure of bones and tooth enamel. As with calcium, with which it is found in association as calcium phosphate, in addition to a structural compound, P in bones serves as a reserve for metabolism.   Of the phosphate that makes up about 1.2% of human body weight, about 85% is in bones and teeth.
  7. In plants:
  8. Phosphates perform similar metabolic roles as in animals.   The energy-capture of photosynthesis transforms ADP to ATP. As every in every living organism, the encoding of plants’ physiology and growth is encoded by nucleic acids. Although we do not tend to think of plants as moving, they do move, continuously, in growth. P is necessary for growth, especially of roots of plants.
  9. Cellulose, a carbohydrate, is one important component of a plant’s structure, but cell walls (which plants have instead of cell membranes) are another. Phosphates are an important component in plant cell walls.
  10. Why?   On the face of things, phosphorus, which has only a tenuous relationship with carbon, seems like an unlikely candidate for a substance so ubiquitous and essential to life. Perhaps one way to look at it is as a mediator between organic and inorganic. More provocatively, Butusov (p. 5) suggests that phosphorus saved the day for the evolution of living organisms by taking up the oxygen produced in photosynthesis, which otherwise would have poisoned cells compounds by oxidation. He argues that oxidation of hydrocarbon lipids would have rancidified them, making them useful. But phospholipids lock up oxygen, making cell membranes dynamic and viable.

III. Nutrition, the P cycle, and its problems.

  1. Plants get P from the soil, but not by themselves. Fungi entwined around and penetrating their roots metabolize soil phosphates into a form that the roots can take in. (Plants provide the fungi nutrients in return, in these ecologically essential symbiotic relationships.) Whereas (vertebrate) animals store phosphates in their bones, plants store them in phytate, which will be discussed below. Plant seeds are particularly rich in phytate, also called phytic acid. (The root of these words, “phyte,” comes from the Greek for “plant,” because only plants produce these molecules.)
  2. Animals get phosphorus from food; particularly from substances rich in protein. There are so many food sources for P that nutritional labeling does not even include that nutrient, even though a minimum daily requirement has been established of about 700 mg. But there is a catch, particularly for the majority of human beings who rely on agriculture for their food. The P in the phytates in plant seeds we eat—grains, beans, and nuts—is metabolically accessibly for us only to a very small degree. So this phosphate is wasted; excreted in urine.
  3. Phosphate everywhere; yet not enough? Waste of phosphorus occurs at nearly every stage of its cycling between the realms of minerals and of organisms’ metabolism. The combined phenomena of agriculture, dense human settlement, population increase, and aspiration toward higher standards of living—including access to better quality food and to fuel resources—all put pressure on the phosphate resources that constitute the basis of agriculture.
  4. In agriculture, soils produce plants that are removed en masse, so that the decomposed plant matter does not return to the ground. So nutrients such as P (and N and K) must be extracted or (in the case of N) synthesized to put back into the soil: fertilizer.
  5. Reactive as it is, phosphate in fertilizer tends to run off before it can be used by plants. Runoff rich in phosphate causes considerable ecological damage, as in eutrophication of lakes, ponds and rivers (excessive organic growth that uses all the dissolved oxygen) and algal blooms that can make water toxic.
  6. Excrement from animals raised for food can be an excellent source of fertilizer. But when animals are raised in very crowded conditions, too much excrement, or manure, is produced to be feasibly used. This unusable manure turns, essentially, to putrid toxin.
  7. The economy of raising animals for food demands that they grow quickly, meaning they need supplemental phosphate.   At a university in Canada, pigs (called “Ecopigs”) have been genetically engineered to produce enzymes enabling them to digest the phytates in their plant foods, meaning no need for supplements and less excretion of phosphate waste.
  8. People, too, produce excrement—the more of it, the more people there are. For nitrogen and phosphorus, the less noxious form of excrement, urine, would be a good source, although it would have to be treated before being used as fertilizer. In wastewater treatment systems, a considerable amount of nitrogen can be captured as biogas, but phosphate is usually lost. A Belgian company, NuReSys, has developed a what they say is an economical method for capturing wastewater phosphate and turning it into slow-release fertilizer.
  9. Phosphates play another important, and questionable role in agriculture as pesticides, particularly insecticides. These organo-phosphate compounds are effective because they block reuptake of Acetylcholine (ACh) in neural synapses, by inserting themselves into the active site of the ACh breakdown enzyme, ACh esterase. Agricultural workers who use or otherwise come in contact with organo-phosphate pesticides can suffer the same kind of death, from fast-acting toxicity, and there can be deleterious long-term consequences from exposure as well. In addition, obviously, organo-phosphate compounds also run off into water systems.
  10. By some arguments, P is a critical limiting factor for the growth and prosperity of human populations—as critical a factor as petroleum fuels, perhaps. Others argue that, given the absolute abundance of phosphate resources, new methods will be found to extract, transport, apply, and recycle it economically.
  11. Wonders of the natural world: Not surprisingly, the phenomenon of bioluminescence depends on phosphorus—in form of energy shifts between ATP and AMP (actually). I hoped to be able to explain the chemical mechanism of firefly bioluminescence to you today, but it was too complicated.  The word “phosphorescence,” of course, refers to phosphorus and its strange glow, sometimes even seen in mineral phosphates. The word is used even for the less usual types of luminescence in which phosphorus is not involved.
  12. Phytate and its fate in the engine of phytase enzymes.

Phytate, a fascinatingly structured molecule, is illustrated in two ways, below. As mentioned about in connection with both plants and animals, for all its advantages as a storage molecule for plants, phytate poses some serious ecological problems. If we, like the “Ecopigs,” could produce enzymes to break down phytate from plant sources, we could make much more efficient use of the world’s phosphate resources and move toward more sustainable agricultural and waste systems.

The core of phytate is cyclohexanol with six alcohol groups, with stereochemistry that is important because of how the phosphoesters will be arranged when connected to those groups. In animals, the most important form of this compound, myo-inositol, is synthesized from glucose (actually glucose-6-phosphate) in the kidneys. Thus the stereochemistry is similar to the parent molecule’s.

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