Phosphorus
- Phosphorus is found in every cell and helps the body utilize Carbohydrates, fats and Protein for growth, maintenance and cell repair. It is needed for healthy nerves. Niacin and riboflavin cannot be digested without phosphorus.
- The main food sources are the protein food groups of meat and Milk. A meal plan that provides adequate amounts of Calcium and Protein also provides an adequate amount of phosphorus.
- Although whole-grain breads and cereals contain more phosphorus than cereals and breads made from refined flour, this is a storage form of phosphorus called phytin, which is not absorbed by humans.
- Fruits and vegetables contain only small amounts of phosphorus.
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[edit] Characteristics and Forms
Phosphorus is a nonmetallic element with an atomic number of 15, an atomic weight of 30.9738 and a valence of 3 or 5. White phosphorus, the most common phosphorus allotrope, has the following properties: melting point, 44.1°C; boiling point, 280°C; specific gravity, 1.82 g/cm3. Solid phosphorus has a tetratomic molecule (P4) with molecular weight 123.8952 atomic mass units (amu). Phosphorus occurs naturally in phosphates, especially in apatite - an impure calcium phosphate mineral found in phosphate rocks, in phosphorite, and many other minerals. There is almost 200 different phosphate minerals known.
It exists in three forms, or allotropic forms: white (or sometimes yellow), red, and black (or violet). The ordinary allotrope, called white phosphorus, is a poisonous, colourless, semitransparent, soft, waxy, yellow to white solid that glows in the dark and combusts spontaneously in air, producing dense white fumes of oxides, P4010. 50 mg constitutes a fatal dose. Its reactivity made its storage underwater practical; white phosphorus is nearly insoluble in water but very soluble in carbon disulfide. It is prepared commercially from phosphate rock in an electric furnace or blast furnace. Exposure to sunlight or heat, at 250 degrees Celsius and in the absence of air, converts white phosphorus to the more stable red phosphorus allotrope, a violet-red powder that does not phosphoresce, not poisonous, nor ignite spontaneously, unless it is heated to 200 degrees Celsius. This form appears as dull, reddish-brown cubic crystals or amorphous powder. Its specific gravity is 2.34. The red form is less dangerous than the white form, but should be handled with caution. It converts to white form at certain temperature and it emits highly toxic fumes when heated. Much less reactive and soluble than white phosphorus, it is used in manufacturing other phosphorus compounds and in semiconductors, fertilizers, safety matches, and fireworks. Black phosphorus, made by heating to white phosphorus to 200 degrees Celsius under a pressure of 12000 atmospheres, is lustrous and flaky, like graphite, and is electrically conductive material. It is insoluble in most solvents. Its specific gravity is 2.70.
[edit] Occurrence and Production
Phosphorus seldom occurs uncombined in nature due to its reactivity. Phosphorus forms the basis of a very large number of compounds, the most important class of which are the phosphates - in majority of its compounds, phosphorus is chemically bonded to four neighboring atoms. Research in phosphorus chemistry indicates that there may be as many compounds based on phosphorus as on carbon. Phosphorus has valence 3 or 5 in compounds, which have many uses in industry.There is a large number of compounds in which one of the four neighboring atoms is absent, and in which its place is taken by an unshared pair of electrons. There are also a few compounds in which there are five or six neighboring atoms bonded to the phosphorus. This last mentioned type of phosphorus compound is mostly very reactive and tend to be unstable. The usual method of production is energy intensive; phosphates, with sand and carbon, is heated in an electric furnace. The principal use of phosphorus is in compounds; for this reason, most of the phosphorus produced in furnaces is burned to make phosphorus pentoxide, a white powdery substance. While the pentoxide is used as a drying agent and chemical reagent, it is chiefly converted to phosphoric acid, H3PO4, also called orthophosphoric acid, by reaction with water. Another important source of phosphoric acid is from phosphate rocks by treatment with sulfuric acid; this is the so-called wet-acid process. The fertilizer mixture, superphosphate, is obtained by this sulfuric acid treatment. Phosphoric acid, in turn, is primarily used in the production of phosphate compounds. Safety regulations are strictly observed when working with phosphorus. Contact with skin may cause severe burns.
Elemental phosphorus is produced through the electrothermal reduction of naturally occurring phosphates (apatites or phosphate rocks) by coke at 1400°–1600°C in the presence of silica (quartz sand): 2Ca3(PO4)2 + 10C + nSiO2 = P4 + 10CO + 6CaO·nSiO2. Previously ground and dressed phosphorus-containing ore is mixed in given proportions with silica and coke and then charged into an electric furnace. Silica is necessary for reducing the temperature of the reaction and increasing the reaction rate. The latter effect is due to the bonding of the calcium oxide given off during the reduction process to form calcium silicate, which is continuously removed in the form of molten slag. Silicates and oxides of aluminum, magnesium, iron, and other impurities also enter the slag. Another component of the slag is ferrophosphorus (Fe2P, FeP, Fe3P), which is formed from the reaction of part of the reduced iron with phosphorus. Ferrophosphorus, as well as the small amounts of the phosphides of manganese and other metals that are dissolved in it, is removed from the furnace as it accumulates for use in the manufacture of special steels.
Phosphorus vapor is discharged from the electric furnace along with gaseous by-products and volatile impurities (CO, SiF4, PH3, steam, products of the pyrolysis of organic impurities in the charge) at a temperature of 250°–350°C. After being purified of dust, the phosphorus-containing gases are fed into condensation units, where at a temperature not below 50°C liquid commercial white phosphorus is collected under water. Most of the phosphorus that is produced commercially is processed into phosphoric acid and into the phosphorus fertilizers and commercial salts (phosphates) based on the acid.
[edit] Phosphorus and Biology
Phosphorus is essential to living organisms. The phosphorus content (mg per 100 g dry matter) in the tissues of plants is 230–350; it is 400–1,800 in marine animals, 1,700–4,400 in terrestrial animals, and approximately 3,000 in bacteria. Animal skeletons consist of calcium phosphate. In fact, in the human body, most phosphorus, 85%, is present in the skeleton and teeth as calcium phosphate, or hydroxyapatite, while the remainder is in intracellular phosphate anion, the phospholipids of cell membranes, in nucleotides, in nucleic acids, phospholipids, a number of coenzymes, and in a variety of metabolic intermediates, including ATP. Calcium phosphate, along with phosphorylated sugars and proteins, is termed inorganic phosphorus. Organic phosphorus occurs primarily in the form of phospholipids. Phospholipids are major structural components of cell membranes. Nucleic acids (DNA and RNA), which are responsible for the storage and transmission of genetic information, are long chains of phosphate-containing molecules. Adenosine triphosphate, or ATP, is an ester of sodium tripolyphosphate. Phosphates play an essential role in all energy-transfer processes such as metabolism, photosynthesis, nerve function, and muscle action. Practically every reaction in metabolism and photosynthesis involves the hydrolysis of this tripolyphosphate to its pyrophosphate derivative, called adenosine diphosphate (ADP). A number of enzymes, hormones, and cell-signaling molecules depend on phosphorylation for their activation. Phosphorylation, the addition of phosphoryls to various organic compound, is a prerequisite to metabolism. Conversely, detachment of the phosphoryl residue (dephosphorylation) precludes metabolic activity. The enzymes of phosphorus metabolism comprise the kinases, phosphorylases, and phosphatases. The important role of phosphorus in the regulation of metabolic processes derives from the extreme sensitivity of many enzyme systems in living cells to the action of organophosphorus compounds. Phosphorus also helps to maintain normal acid-base balance (pH) by acting as one of the body's most important buffers. Additionally, the phosphorus-containing molecule 2,3-diphosphoglycerate (2,3-DPG) binds to hemoglobin in red blood cells and affects oxygen delivery to the tissues of the body. In short, the functional roles of phosphorus include (1) the buffering of acid or alkali excesses, hence helping to maintain normal pH; (2) the temporary storage and transfer of the energy derived from metabolic fuels; (3) by phosphorylation, the activation of many catalytic proteins; and (4) the formation of bone matter.
The liver figures prominently in the conversion of phosphorus compounds in humans and animals. The parathyroid hormone controls the concentration of phosphate in the blood, mainly by modifying its excretion in the urine.
The calcium to phosphate ratio of infant foods is important as Vitamin D and calcium regulate the availability of phosphorus for bone formation. In fact, because phosphorus is so widespread in food, phosphorus deficiency, which lead to rickets and poor growth, is rare compared to the effects of calcium and vitamin D deficiency on bone development. The substitution of phosphate-containing soft drinks and snack foods for milk and other calcium rich foods represent a serious risk to bone health. Again, this risk is only observed in humans on diets that were low in calcium. Thus, a meal plan that provides adequate amounts of calcium and protein also provides an adequate amount of phosphorus.
| Age | Recommended Daily Intake | Tolerable Upper Intake (UL) |
|---|---|---|
| Adults (18 years and older, including pregnant and breastfeeding women) | 700 mg | for 19 to 70 years old, 4 grams; for adults 70 years and older, 3 grams; for pregnant women, 3.5 grams; for breastfeeding women, 4 grams. |
| Children (9 to 18 years old, including pregnant and breastfeeding females) | 1,250 mg | 4 grams; for pregnant females, 3.5 grams; for breastfeeding females, 4 grams. |
| Children (4 to 8 years old) | 500 mg | 3 grams |
| Children (1 to 3 years old) | 460 mg | 3 grams |
| Infants (7 to 12 months old) | 275 mg | Not clearly established; the source of intake should be from food and formula only. |
| Infants (0 to 6 months old) | 100 mg | Not clearly established; the source of intake should be from food and formula only. |
Rich sources of phosphorus include most meats and fish. Other sources include milk products, and cereals. Also, many polyphosphate food additives, such as organic phosphates, ferric phosphate, and tricalcium phosphate, are added to human foods. Phosphorus is present in most soft drinks as phosphoric acid. With animal feeds, dicalcium phosphate or sodium phosphate is added, though special devices are often necessary to get animals to take the required amounts. Dietary phosphorus is readily absorbed in the small intestine, and any excess phosphorus absorbed is excreted by the kidneys. Food phosphorus is a mixture of inorganic and organic forms. Intestinal phosphatases hydrolyze the organic forms contained in ingested protoplasm, and thus most phosphorus absorption occurs as inorganic phosphate. Adult needs about 1.3 grams of phosphorus per day. Note that dietary phosphorus derived from food additives is not calculated in most food databases, so the total amount of phosphorus consumed by the average person is not entirely clear. Also, phytic acid, or phytate, the storage form of phosphate is not bioavailable to humans as we lack enzymes (phytases) that liberate phosphorus from phytate. Yeasts possess phytases, so whole grains incorporated into leavened breads have more bioavailable phosphorus than whole grains incorporated into breakfast cereals or flat breads. As phosphorus is not irreversibly consumed in bodily processes and can be recycled indefinitely, the actual function of dietary phosphorus is first to support tissue growth (either during individual development or through pregnancy and lactation) and, second, to replace excretory and dermal losses. In both processes it is necessary to maintain a normal level in the extracellular fluid, which would otherwise be depleted of its phosphorus by growth and excretion.
Inadequate phosphorus intake, especially in cases of near-total starvation, results in abnormally low serum phosphate levels (hypophosphatemia). The effects of hypophosphatemia may include loss of appetite, anemia, muscle weakness, bone pain, rickets (in children), osteomalacia (in adults), increased susceptibility to infection, numbness and tingling of the extremities, and difficulty walking. Severe hypophosphatemia may result in death. Other individuals at risk of hypophosphatemia include alcoholics, diabetics recovering from an episode of diabetic ketoacidosis, and starving or anorexic patients on refeeding regimens that are high in calories but too low in phosphorus. Phosphate deficiency is common in livestock and gives rise to osteomalacia (also known as sweeny or creeping sickness). In less severe deficiency states there is pica, growth retardation, infertility and possibly retention of placenta. Sodium phosphate and potassium phosphate salts are used for the treatment of hypophosphatemia; their use requires medical supervision.
Phosphates are also used clinically to treat hypercalcemia (high blood calcium levels), as saline laxatives, and in the management of calcium-based kidney stones. They may also be of some benefit to patients with vitamin D resistant rickets, multiple sclerosis, and diabetic ketoacidosis.
Because phosphorus is not as tightly regulated by the body as calcium, serum phosphate levels can rise slightly with a high phosphorus diet, especially after meals. High phosphate levels in the blood reduce the formation of the active form of vitamin D (calcitriol) in the kidneys, reduce blood calcium, resorption of calcium from the bones and lead to increased PTH release by the parathyroid glands, and to decreased urinary calcium secretion. Even in the face of dangerous hyperphosphatemia, phosphorus continues to be absorbed from the diet at an efficiency only slightly lower than normal. These means phosphorus absorption in the human body is proportional to the dietary intake, unlike calcium, where absorption is inversely related to the logarithm of intake.
The most serious adverse effect of abnormally elevated blood levels of phosphate (hyperphosphatemia) is the calcification of non-skeletal tissues, most commonly the kidneys. Calcium deposition also occur in blood vessels, lungs, eyes and heart.Such calcium phosphate deposition can lead to organ damage, especially kidney damage. Because the kidneys are very efficient at eliminating excess phosphate from the circulation, hyperphosphatemia from dietary causes is usually only a problem in people with kidney failure (end-stage renal disease) or hypoparathyroidism. When kidney function is only 20% of normal, even typical levels of dietary phosphorus may lead to hyperphosphatemia. Pronounced hyperphosphatemia has also occurred due to increased intestinal absorption of phosphate salts taken by mouth as well as due to colonic absorption of the phosphate salts in enemas. Excessively high doses of calcitriol, the active form of vitamin D, or its analogs may result in hyperphosphatemia. Phosphorus absorption is reduced by ingestion of aluminum-containing antacids and by pharmacologic doses of calcium carbonate.
| High Phosphorus Foods | |
|---|---|
| Beverages | ale, beer, chocolate drinks, cocoa, milk drinks, canned iced teas, dark colas |
| Dairy Products | cheese, cottage cheese, cream soups, custard, ice cream, milk, pudding, yogurt |
| Protein | beef liver, carp, chicken liver, crayfish, fish roe, organ meats, oysters, sardines |
| Vegetables, beans and peas | baked beans, black beans, chick peas, garbanzo beans, kidney beans, lentils, limas, northern beans, pork 'n beans, soy beans, split peas |
| Other foods | bran cereals, brewer's yeast, caramels, nuts, seeds, wheat germ, whole grain products |
A much rarer case, due to absence of elemental phosphorus from the environment, is phosphorus poisoning. Poisoning can occur when working with white phosphorus; it is also possible during the thermoelectric sublimation of phosphorus and its compounds and during the production and use of the compounds. Poisoning causes severe gastroenteritis with vomiting and diarrhea and, in the case the victim survives the gastroenteritis, there is a subsequent acute hepatic insufficiency. The symptoms of acute poisoning include a burning sensation in the mouth and stomach, headache, weakness, nausea, and vomiting. After two or three days, jaundice manifests itself, and pain is felt in the epigastric region and right hypochondriac region. Chronic poisoning is attended by inflammation of the mucosa in the upper respiratory tract, symptoms of toxic hepatitis, disruption of calcium metabolism (development of osteoporosis; fragility and, sometimes, necrosis of the bone tissue, usually the mandible), and disorders of the cardiovascular and nervous systems. First aid in cases of acute poisoning, occurring most often through the mouth, includes pumping of the stomach and administration of cathartics and enemas. Solutions of glucose, calcium chloride, and other substances are administered intravenously. For skin burns, the affected area is treated with solutions of blue vitriol or soda. Eyes should be rinsed with a 2-percent solution of sodium bicarbonate. Safety measures are important in working with phosphorus, as are personal and oral hygiene and regular medical examinations.
| High Phosphorus Foods | mg | Low Phosphorus Substitute | mg |
|---|---|---|---|
| 8 ounce milk | 230 | 8 ounce nondairy creamer or 4 ounce milk | 100 or 115 |
| 1 ounce hard cheese | 145 | 1 ounce cream cheese | 30 |
| 1/2 cup ice cream | 80 | 1/2 cup sherbet or 1 popsicle | 0 |
| 12-ounce can of cola | 55 | 12 ounce of ginger ale or lemon soda | 3 |
| 1/2 cup lima or pinto beans | 100 | 1/2 cup mixed vegetables or green beans | 35 |
| 2 ounce peanuts | 200 | 1-1/2 cup light salt/low fat popcorn | 35 |
| 1-1/2 ounce chocolate bar | 125 | 1-1/2 ounce hard candy, fruit flavors or jelly beans | 3 |
| 2/3 cup oatmeal | 130 | 2/3 cup cream of wheat or grits | 40 |
| 1/2 cup bran cereal | 140 to 260 | 1/2 cup nonbran cereal, shredded wheat, rice cereals, or corn flakes | 50 to 100 |
Excessive intake of phosphates can cause potentially serious or life-threatening toxicity. Intravenous, oral, or rectal/enema phosphates may cause electrolyte disturbances including hypocalcemia (low calcium blood levels), hypomagnesemia (low magnesium blood levels), hyperphosphatemia (high phosphorus blood levels), or hypokalemia (low potassium levels). Calcification of non-skeletal tissues (particularly in the kidneys), severe hypotension (low blood pressure), dehydration, metabolic acidosis, acute kidney failure, or tetany can occur. Death has been reported in infants or adults with oral, rectal, or intravenous phosphates, particularly in those at increased risk for electrolyte disturbances. Late symptoms may include abdominal pain, vomiting of phosphorescent materials, bloody vomiting and diarrhea, headache, limb aches, tongue coating, foul breath, weakness, and yellow conjunctivae (whites of the eyes). Rare complications may include confusion, convulsions (seizures), headache, dizziness, numbness, tingling, pain, weakness, anxiety, increased thirst, muscle cramps, or fatigue. Abnormal heart rhythms, shortness of breath, foot/leg swelling, and weight gain have been reported. Dialysis can remove some phosphorus from your blood.
Aluminum-containing antacids reduce the absorption of dietary phosphorus by forming aluminum phosphate, which is unabsorbable. When consumed in high doses or used chronically, aluminum-containing antacids can produce abnormally low blood phosphate levels (hypophosphatemia) as well as aggravate phosphate deficiency due to other causes. On another case, potassium supplements or potassium-sparing diuretics taken together with a phosphate may result in high blood levels of potassium (hyperkalemia). Hyperkalemia can be a serious problem, resulting in life threatening heart rhythm abnormalities (arrhythmias). People taking such a combination must inform their health care provider and have their serum potassium levels checked regularly. Other drug interactions:
- Some anticonvulsants (including phenobarbital and carbamazepine) may lower phosphorus levels and increase levels of alkaline phosphatase. *Bile acid sequestrants such as cholestyramine (Questran®) and colestipol (Colestid®) can decrease oral absorption of phosphate. Therefore, oral phosphate supplements should be administered at least one hour before or four hours after these agents.
- Corticosteroids may increase urinary phosphorus levels.
- Potassium supplements or potassium-sparing diuretics taken together with a phosphate may result in high blood levels of potassium (hyperkalemia).
- Alcohol (ethanol) may increase urinary phosphorus. Wine may enhance absorption of phosphorus (as well as calcium and magnesium).
- Medications that may affect electrolyte levels should be used cautiously with phosphates. Examples include: amiloride (Midamor®); angiotensin-converting enzyme (ACE) inhibitors such as benazepril (Lotensin®), captopril (Capoten®), enalapril (Vasotec®), fosinopril (Monopril®), lisinopril (Zestril®, Prinivil®), quinapril (Accupril®), or ramipril (Altace®); cyclosporine; cardiac glycosides (Digoxin®); heparins; anti-inflammatory drugs; potassium-containing agents; salt substitutes; spironolactone (Aldactone®); and triamterene (Dyrenium®).
- Calcium may impair phosphates in the body, and result in calcium deposits in tissues.
- Excessive doses of calcitriol, the active form of vitamin D (or its analogs) may result in hyperphosphatemia (high phosphate levels).
In general, sodium, potassium, aluminum, and calcium phosphates are likely safe when used orally in recommended doses for short-term periods by people without hyperphosphatemia, impaired kidney function, or other health conditions known to increase the risk of hyperphosphatemia. Sodium phosphate is likely safe when used rectally for short-term periods in otherwise healthy individuals with normal kidney function. Long-term use or high doses used orally or rectally require monitoring of serum electrolytes. Intravenous phosphate is likely safe when used as an U.S. Food and Drug Administration (FDA)-approved prescription drug under medical supervision in people without hyperphosphatemia, impaired kidney function, or other health conditions known to increase the risk of hyperphosphatemia.
[edit] Serum Phosphate Test
The serum phosphorus test measures the amount of phosphate in the blood, particularly to check if you have a disorder known to cause abnormal phosphorus levels. Normal values range from 2.4 - 4.1 milligrams per deciliter (mg/dL). Procedure: (1) Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). (2) The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood. (3) The health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to a needle. (4) The elastic band is removed from your arm. (5) Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
