Phosphorus

Discovered in 1669 by Brand, who prepared it from urine. Phosphorus exists in four or more allotropic forms: white (or yellow), red, and black (or violet). White phosphorus has two modifications: α and β with a transition temperature at –3.8°C. Never found free in nature, it is widely distributed in combination with minerals. Twenty-one isotopes of phosphorus are recognized. Phosphate rock, which contains the mineral apatite, an impure tricalcium phosphate, is an important source of the element. Large deposits are found in the Russia, China, Morocco, and in Florida, Tennessee, Utah, Idaho, and elsewhere. Phosphorus in an essential ingredient of all cell protoplasm, nervous tissue, and bones. Ordinary phosphorus is a waxy white solid; when pure it is colorless and transparent. It is insoluble in water, but soluble in carbon disulfide. It takes fire spontaneously in air, burning to the pentoxide. It is very poisonous, 50 mg constituting an approximate fatal dose. Exposure to white phosphorus should not exceed 0.1 mg/m3 (8-hour time-weighted average — 40- hour work week). White phosphorus should be kept under water, as it is dangerously reactive in air, and it should be handled with forceps, as contact with the skin may cause severe burns. When exposed to sunlight or when heated in its own vapor to 250°C, it is converted to the red variety, which does not phosphoresce in air as does the white variety. This form does not ignite spontaneously and it is not as dangerous as white phosphorus. It should, however, be handled with care as it does convert to the white form at some temperatures and it emits highly toxic fumes of the oxides of phosphorus when heated. The red modification is fairly stable, sublimes with a vapor pressure of 1 atm at 417°C, and is used in the manufacture of safety matches, pyrotechnics, pesticides, incendiary shells, smoke bombs, tracer bullets, etc. White phosphorus may be made by several methods. By one process, tricalcium phosphate, the essential ingredient of phosphate rock, is heated in the presence of carbon and silica in an electric furnace or fuel-fired furnace. Elementary phosphorus is liberated as vapor and may be collected under water.

Phosphorus is an essential constituent of plants and animals, being present in deoxyribonucleic acid (DNA), bones, teeth and other components of high biological importance. Phosphorus does not occur in its elemental state in nature, as it readily oxidises and therefore is deposited as phosphate rock. The remaining elements of group 15 are mostly obtained from minerals, but can also be found in their elemental form in the earth’s crust.

White phosphorus is a highly poisonous substance. The toxic routes are ingestion, skin contact, and inhalation.
Inhumansasingleoraldoseof70–100 mg can cause death. The toxic symptoms are nausea, vomiting, severe abdominal pain, diarrhea, coma, and convulsions. The other harmful effects from ingestion are liver damage and jaundice. An amount as small as 5–10 mg of white phosphorus can exhibit some of the foregoingtoxic effectsinhumans from an oral intake. The lethal doses and symptoms for other species varied with the species. The toxic symptoms were somnolence, convulsion, and lung injury. The lethal doses ranges from 3 mg/kg for rats to 50 mg/kg for dogs.
Inhalation of its vapors can cause irritation of respiratory tract. The chronic poisoning from inhalation (or ingestion) severely affected the lungs, kidney, and liver in test animals. The toxic symptoms were bronchopneumonia, bone changes, necrosis of the jaw (“phossy” jaw), anemia, and weight loss. Since the vapor pressure of white phosphorus is low [0.026 torr at 20°C (68°F)], the acute health hazard from a short exposure to its vapors under normal conditions of its handling and uses should be low..