Phosphorus, the Bringer of Light
A Toxic Element that is Essential to all Living Things
Aug 14, 2008
As a result of this observation, Brandt named his new discovery phosphorus, meaning ‘bringer of light’.
Phosphorus belongs to the same family of elements as nitrogen, arsenic and antimony. The pure element is extremely poisonous, a fatal dose being as little as 0.1 gram. In contrast, like nitrogen, it is indispensable for all living organisms. Combined with oxygen, it is widely distributed in phosphate minerals from which it can be extracted. It has also been obtained from bones and the droppings of sea birds, known as guano.
Allotropes of Phosphorus
Phosphorus exists in three forms, or allotropes, depending on the arrangement of molecules in the solid. White phosphorus is a pale yellow, waxy substance that is stored in water. It smoulders in air, and if warmed, bursts into flames, producing thick, acidic smoke. Red phosphorus is more stable and need not be kept in water. Black phosphorus is unusual as a non-metal in that, like graphite it can conduct electricity.
Phosphorus is an Inflammable Element
The ready inflammability led to its use as the main constituent in the heads of matches. In the 19th and early 20th centuries, workers in match factories suffered from a painful, disfiguring disintegration of the jawbone, known as ‘phossy jaw’, as a result of inhaling phosphorus vapour.
During World War II, thousands of tonnes of phosphorus were dropped in incendiary bombs onto German cities. The resulting firestorms killed more people than did the atomic bombs in Hiroshima and Nagasaki. Ironically, one of the cities thus destroyed was Hamburg, where the element was first discovered.
Phosphorus in Living Organisms
A molecule of fat or oil is formed by a combination of the alcohol, glycerol, with three fatty acid molecules. If a phosphate group replaces one of these fatty acids, then a phospholipid is formed. These compounds make up the outer membranes of all living cells. Within the cells the transfer of energy from foods such as sugars and fats is mediated by adenosine triphosphate, ATP, which also stores energy during photosynthesis in plants. It plays a part in the transmission of signals along nerves and in the synthesis of nucleic acids. The genetic code, carried by DNA depends on the sequence of linked bases, supported on both sides by backbones consisting of sugar units and phosphate groups.
The largest concentration of phosphate in animals’ bodies is as hydroxyapatite, a form of calcium phosphate, in bones and teeth. Phosphate is needed in the human diet to the extent of around 0.8 gram per day. A balanced diet normally contains between one and two grams per day, the richest sources being fish, lean meat, eggs and cheese. Calcium phosphate is present in self-raising flours, while phosphoric acid is used as flavouring in some soft drinks.
Importance and Dangers of Fertilizers
While other minerals are also necessary for healthy plant growth, the availability of phosphorus is often the limiting factor. Phosphates are therefore an important component of fertilizers. When conifer forests grow on phosphorus-poor soils, these nominally evergreen trees readily drop their leaves to replenish this essential element.
Excess phosphorus can be damaging. Phosphates are used in detergents, to soften hard water and to suspend dirt. The waste water often finds its way into rivers and lakes, along with sewage and fertilizer run-off from fields. The result is excessive growth, particularly of algae, in the rivers. When the plants die, their decomposition by bacteria removes oxygen from the water and thus kills other aquatic life.
Reference: John Emsley, The Shocking History of Phosphorus, Macmillan 2000
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