| Oxygen | Oxygen atoms are present in water (H2O) and water is essential to all life. Oxygen and is present in many organic compounds. Most organisms use oxygen for respiration. While oxygen (O2) is necessary for life, oxygen as ozone (O3) is highly toxic. On the other hand, ozone is an important component of the atmosphere (the ozone layer) and helps to shield us from harmful ultraviolet rays from the sun. |
| Carbon | Carbon is key to life and by definition is present in all organic compounds. The study of life is known as biological chemistry or biochemistry. Ethene gas (C2H4) helps to ripen tomatoes. |
| Hydrogen | Hydrogen makes up two of the three atoms in water and water is absolutely essential to life. Hydrogen is present in all organic compounds. A form of water in which both hydrogen atoms are replaced by deuterium ( 2H, or D) is called "heavy water" (D2O) and is toxic to mammals. Some bacteria are known to metabolise molecular hydrogen (H2). |
| Nitrogen | Nitrogen is a key component of biological molecules such as proteins (which are made from amino acids, and nucleic acids. The nitrogen cycle in nature is very important. |
| Calcium | Calcium is essential for all life. It forms part of cell walls and bones. It is important for blood clotting. |
| Phosphorus | Phosphorus is a key component of biological molecules such as DNA and RNA. Phosphorus is a component of bones, and teeth, and many other compounds required for life. Chronic poisoning of people working unprotected with white phosphorus leads to necrosis of the jaw ("phossy-jaw"). |
| Sulphur | Sulphur is essential to life. It is a minor constituent of fats, body fluids, and skeletal minerals. Sulphur is a key component in most proteins since it is contained in the amino acids methionine and cysteine. Sulphur-sulphur interactions are important in determining protein tertiary structure. Hydrogen sulphide (H2S) replaces H2O in the photosynthesis of some bacteria. In people, hydrogen sulphide in very small concentrations can be metabolized, but in higher concentrations it kills quickly by preventing respiration. It is insidious in that it deadens the sense of smell quickly, meaning victims may be unaware of its presence. It is more toxic than cyanide. Remarkably, sulphuric acid (H2SO4) is present in the digestive fluids of sea squirts (ascidians). |
| Potassium | Potassium salts are essential for both animals and plants. The potassium cation (K+) is the major cation in intracellular (inside cells) fluids (sodium is the main extracellular cation). It is essential for nerve and heart function. A normal diet containing reasonable amounts of vegetables contains all the potassium necessary. |
| Sodium | Sodium is a vital element. The human diet must contain a sensible amount of sodium. The sodium cation is the main extracellular (outside cells) cation in animals and is important for nerve function in animals. The importance of sodium as salt in the diet was recognized well before sodium itself was understood to be an element. This recognition formed the basis of trading of salt deposits lining the Dead Sea in biblical times by the Romans. Prolonged sweating results in sodium ion loss in sweat and it is most important that the sodium ion is replaced through proper diet. |
| Chlorine | Chlorine as chloride (Cl-) is essential for mammals and plants. Digestive juices in the stomache contain hydrochloric acid. |
| Magnesium | Magnesium is an important element for plants and animals. Chlorophylls (responsible for the green colour of plants) are compounds known as porphyrins and are based upon magnesium. Magnesium is required for the proper working of some enzymes. The adult daily requirement of magnesium is about 0.3 g day. |
| Silicon | Silicon is probably essential in higher plants and perhaps to mammals. Diatoms, some protozoa, some sponges, and some plants use silicon dioxide (SiO2) as a structural material. Silicon is known to be required by chicks and rats for growth and skeletal development. Silicon is not particularly toxic but finely divided silicates or silica cause major damage to lungs. |
| Iron | Iron compounds are essential to all life. For example, it is an iron atom in hemoglobin that is responsible for carrying oxygen around the blood stream. |
| Flourine | Fluorine as fluoride (F-) is probably an essential element for humans and certainly is for some molluscs. In some areas, fluoride ion is added to drinking water (in very low concentrations) since it renders tooth enamel relatively immune to bacteriological attack. It does this by replacing the OH group of hydroxyapatite with fluoride. In other areas, fluoride is not added to water, despite the benefits, as a consequence of protests from civil rights activists who object to the addition of anything to water. |
| Zinc | Zinc is essential in the diets of plants and animals. Zinc shortage in soils around the world is an important problem. Zince is the key component of many enzymes. The protein hormone insulin contains zinc. Zinc plays a role in reproduction and also sexual maturation. Zinc deficiency resluts in stunted growth and in male sexual immaturity. This is reversed on the addition of zinc in the diet. Some organisms seem to accumulate zinc. |
| Rubidium | Rubidium has no biological role but is said to stimulate the metabolism. It can accumulate ahead of potassium in muscle. |
| Strontium | Strontium has no biological role. |
| Bromine | Bromine may be an essential trace element for red algae and possibly mammals. It is found in the mollusc pigment "royal purple", although its role is not understood. Excessive bromide intake leads to depression and of weight loss. |
| Lead | Lead has no biological role. Lead affects the gut, central nervous system and causes anaemia. |
| Aluminum | Aluminium may be involved in the action of enzymes such a succinic dehydrogenase and d-aminolevulinate dehydrase (involved in porphyrin synthesis. Aluminium compounds are toxic to most plants and somewhat toxic to mammals. Aluminium has been linked to Alzheimer's disease (senile dementia). |
| Copper | Copper is essential for all life, but only in small quantities. It is the key component of redox enzymes and of haemocyanin. |
| Boron | Boron is probably not required in the diet of humans but it might be a necessary "ultratrace" element. Boron is required by green algae and higher plants. |
| Cadmium | Cadmium might be a necessary element in very, very, small quantities in rats. Inhalation of cadmium dust causes problems for the respiratory tract and for the kidneys. Death may follow. Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver and the kidneys. |
| Barium | Barium has no biological role. The British Pharmaceutical Codex from 1907 indicates that barium chloride ["barii chloridum", BaCl2.2H2O] has a stimulant action on the heart and other muscles. It was said that it "raises blood pressure by constricting the vessels and tends to empty the intestines, bladder, and gall bladder". Its poisonous nature was also pointed out. Barium sulphide (BaS) was used as a depilatory agent (removes hair). Barium sulphate (BaSO4) is insoluble and used for body imaging (barium meal). |
| Manganese | Manganese compounds are essential to life. They are essential for the action of some enzymes. Soil deficiencies lead to infertility in mammals and to bone malformation in growing chicks. |
| Tin | Tin might be a necessary element in very, very, small quantities in rats. Organotin compounds are used as bactericides and fungicides in marine environments but cause environmental concern as they cause severe problems to local wildlife. |
| Iodine | In nature, iodine exists as iodide ions, I-, and it is as iodide that it is taken into our bodies. Iodine is an essential component of the human diet and in fact appears to be the heaviest required element in the diet. Iodine compounds are useful in medicine. Lack of iodine in the diet is a cause of goitre (Derbyshire neck). This condition is rare now as table salt is dosed with a little iodide. |
| Nickel | Nickel is an essential trace element for many species. Chicks and rats raised on nickel-deficient diets have liver problems. Enzymes known as hydrogenases in bacteria contain nickel. Nickel is also important in plant ureases. |
| Molybdenum | Molybdenum is a necessary element, apparently for all species. Only very small amounts are required. Molybdenum plays a role in nitrogen fixation, (a process by which the normally unreactive nitrogen gas is turned into other compounds) enzymes, and nitrate reduction enzymes. |
| Gold | Gold has no biological role but does form the basis of some drugs (possibly toxic) used to treat rheumatoid arthritis. Its mode of action appears not to be understood. |
| Arsenic | Arsenic, despite its poisonous reputation, may be a necessary ultratrace element for humans. It is a necessary ultratrace element for red algae, chickens, rats, goats, and pigs. A deficiency results in inhibited growth. |
| Selenium | Selenium is essential to mammals and higher plants, but only in small amounts. Selenium is said to stimulate the metabolism. It may help protest against free radical oxidants and against some heavy metals. Livestock grown in areas containing high amounts of selenium in the soil and in which a plant called Astragalus ("loco weed" in USA) is present are poisoned. This is because Astragalus concentrates selenium. On the other hand, sheep grown in areas containing deficient amounts of selenium in the soil develop "white muscle disease". |
| Zirconium | Zirconium has no biological role. The tolerance of human tissues to it makes the metal suitable for some artificial joints and limbs. |
| Lithium | Lithium seems to have no biological role, but does have an effect on the body if swallowed. Sometimes, lithium-based compounds such as lithium carbonate (Li2CO3) are used as drugs to treat manic-depressive disorders. The dose is around 0.5 g - 2 g daily. |
| Vanadium | Vanadium is essential to sea squirts (ascidians). The concentration of vanadium in sea squirts is a million times higher than in sea water as a consequence of their ability to concentrate vanadium. Vanadium is a necessary part of the diet of rats and chicks, but only is very small amounts. Deficiencies cause reduced growth and impair reproduction. |
| Chromium | Chromium is an essential trace element and has a role in glucose metabolism. It seems to have an effect in the action of insulin. In anything other than trace amounts, chromium compounds should be regarded as highly toxic. |
| Cobalt | Cobalt salts in small amounts are essential to many life forms, including humans. It is at the core of a vitamin called vitamin-B12. Grazing animals do not to do well in areas where there is little cobalt in the soil. |
| Cesium | Cesium has no biological role. However it is capable of replacing potassium in the body to some extent because of its chemical similarity. Ingestion of any cesium compounds is therefore to be avoided. Because of this similarity, the isotopes 134Cs and 137Cs (present in the biosphere in small amounts as a result of radiation leaks) are very toxic. Rats fed cesium in place of potassium in their diet die. |
| Uranium | Uranium has no biological role. |
| Beryllium | Beryllium has no biological role. In fact, compounds containing beryllium are poisonous. |
| Radium | Radium has no biological role. |