metals in the body There are no metals normally present as such in the body, except those put there during surgery. Tantalum is used for sutures, and steel in artificial hip joints. Some children with congenital heart abnormalities have fine tungsten spirals inserted into the heart to plug small holes between the cavities of the two ventricles. The spirals are inserted, using fibre optic and catheterization techniques, via the femoral artery; the probes are fed through the circulation until the heart is reached. Fibrous growth around the spirals then seals the hole. People with artificial pacemakers have an electrode — which delivers the pulses — inserted into the heart, connected to a control unit placed under a skin flap in the abdominal region. The casing of the control unit is made of the finest steel and sealed to prevent attack by body fluids. In all instances the metals used in these artificial devices needs to be non-toxic, non-corrodable, and long lasting. The devices become part of the person and they forget about their presence, only to be reminded when they pass, for example, through metal detector screens at airports, where an artificial hip joint or a pacemaker control box will set off the alarm.

Three-quarters of all the hundred-odd elements that exist in the environment are metals. It is not surprising, therefore, that many of these metallic elements are found within the body, though mostly only in small amounts. Some of these are described as trace elements, vital for some body function. They do not exist in the body as elemental metal but as metal salts, or complexed with some organic component. An example is iron; complexed with haem it forms an essential component of haemoglobin, the oxygen carrier that gives red blood cells their colour. Many of the metallic elements exist in the body, without any function but at levels low enough to be tolerated. For example, 54 different elements exist in sea water, and people who live near the coast have detectable traces of all of these. Sometimes man does things that raises the levels of metal elements in the body to those which are unacceptable, and correction is needed. The yellow lines painted at the edges of roads to indicate no parking for vehicles originally contained bright yellow compounds of chromium, which has no known bodily function. The dust created by moving vehicles crossing the lines led to rising levels of chromium in the air and the practice was abandoned, non-chromium substitutes being found. After the Chernobyl disaster in Russia, sheep grazing in parts of Scotland were found to have raised levels of uranium in their bloodstreams. Uranium salts had been carried in the air and fell in rain on the Scottish highlands, becoming incorporated into the grass upon which the sheep grazed. For a while sheep from this region could not be used for food products. In a similar way many people in Europe stopped using dairy products in the Sixties at the time when atomic tests were carried out in remote parts of the world, because detectable amounts of radioactive strontium-90 could be detected in milk.

Which of the metal elements are essential for our existence? The list includes sodium, potassium, calcium, magnesium, manganese, iron, cobalt, copper, zinc, and molybdenum. In addition, small amounts of other metals are found which are unavoidably present, but have no known function. These include lead, aluminium, arsenic, mercury, cadmium, gold, bismuth, antimony, and beryllium. It is important to realize the extreme range of concentrations that exist among the metal elements found in the body — if the amount of arsenic equalled that of magnesium then you would have expired long ago. Perhaps the easiest way to consider the range is to give the value of 100 to sodium and potassium, then calcium and magnesium will have the value 1–2 (ignoring bone) and manganese, iron, cobalt, copper, zinc, and molybdenum will be in the range 0.1–0.001 (ignoring red cells). For all the others listed above the content will be even less. Beryllium, for example, is lethal at one part in a million of body weight. It is possible to have toxic effects even from those metallic elements which are essential for body function. For example, excessive intake of iron, often in those who self-medicate in the belief they can build up their strength, can lead to an abnormally high level in the blood, followed by deposition in the liver, pancreas and skin. Cooking in iron pots, as by the Bantu people, sometimes leads to iron intoxication.

How does the body use the metallic elements? The salts of sodium and potassium are the main providers of the osmotic strength of body fluids. It is not surprising that the compositions of body fluids are not unlike the milieu from which life evolved, namely the oceans. Yet the strength of sea water is far greater than that of blood. However, the sea has become increasingly salty over aeons of time as the rains have washed the soluble salts down from the mountains. Many sea creatures have evolved intricate mechanisms to keep the composition of body fluids constant in the presence of the increasing tonicity of their environment.

Calcium and magnesium are among the most abundant elements on earth, so they are imbibed as drinking water and as milk. Calcium is essential for the structure of bones and teeth, where it is kept in a highly insoluble form, and in milk production. It is an essential ‘second messenger’ in cell signalling and a requirement for muscle contraction and for blood clotting. If blood levels of calcium fall then calcium is withdrawn from bone, resulting in osteomalacia and osteoporosis. All phosphate-transferring enzymes, like those used in carbohydrate metabolism, require magnesium. Magnesium salts (e.g. magnesium sulphate, known as Epsom salts) were formerly used as osmotic purgatives. Our intake of manganese is through plants, spinach being a particularly rich source. This may explain why the well-known cartoon character Popeye and his companion Olive Oil always downed a tin of spinach before embarking on some heroic act. Manganese is an essential co-factor for many enzymes, and without it the growth of many green plants would fail and spinach would not exist. The body contains about 5g of iron, three-quarters of it in red cells complexed in haemoglobin, with half the remainder stored in the liver, kidneys, bone marrow, and spleen.

Cobalt is an essential part of the vitamin B₁₂ complex, which in turn is essential for red blood cell formation. B₁₂ cannot be made in the body and we depend on the diet for its supply, liver being the richest source. Cobalt is also a necessary activator of some important enzymes. Eating liver or shellfish gives us our intake of copper, essential for the synthesis of haemoglobin. Excess copper is excreted, but when copper handling is disrupted, copper is deposited in the eyes. In treating the rare condition of Wilson's disease, where there is an excess of copper, pencillamine is used to form a soluble complex with copper, which can then be excreted. Both zinc and molybdenum are necessary for the functions of many different enzymes.

What can be done if the concentration of metallic elements rises above the toxic threshold, particularly those that have no known function in the body? Some of these have been deliberately used as poisons, much beloved of Victorian melodramas, such as Arsenic and Old Lace, in which two seemingly sweet spinsters ran a boarding house, poisoning the lodgers with arsenic to relieve them of life's struggles. Yet some rather toxic metals, albeit in insoluble form, have been used as medicaments: Bismuth, for example, as an antacid. Yet others were intended to be absorbed; lithium salts for schizophrenia, antimony salts for protozoal diseases, mercury for syphilis. Other metallic elements have been inbibed en passant over a lifetime: lead, for example, picked up from old water pipes, and aluminium, from saucepans, the latter connected by some with Alzheimer's disease. Little can be done to reverse degenerative changes that have occurred consequent upon low level intake over many years. However, heavy metals can be removed from the body, whether they have accumulated chronically or by acute exposure. For this purpose chelating agents have been developed, some rather specific for certain metals. ‘Chelate’ means ‘to claw’, and it does exactly that: one or more chelate molecules combine with the metal atom to form a complex, with the metal held in the pincers of the claw. Chelates are generally very water soluble, so that the chelating agent containing the offending metal is excreted in the urine.

There are traces of many other metals in the body, and some of them will likely turn out to have essential functions in yet undiscovered bodily processes, but the amounts required will be infinitesimally small.

Alan W. Cuthbert