Introduction
Copper is a naturally hygienic metal that slows down the growth of germs such as E-coli (the 'burger bug'), MRSA (the hospital 'superbug') and legionella. This is important for applications such as food preparation, hospitals, coins, door knobs and plumbing systems.
Copper is both good and bad for living things. At very low concentrations, it is useful. But when the concentration increases, it becomes toxic and interferes with cell metabolism.
In this section, we'll look at how copper is essential for life and how it can be used as a biocide.
Vital Copper
Copper is essential for our bodies to work properly. It is one of several micronutrients. These are minerals that are found in very small, but vital, quantities in our bodies.
Copper is found in enzymes and in other biological molecules involved in respiration. It is, therefore, important for most animal life.
It's a slug's life
Copper has another biological function in animals such as snails, lobsters and spiders. It is part of their blue blood!
Vertebrates (including humans) have red blood. The colour comes from a special molecule called haemoglobin, which is found in red blood cells. Haemoglobin carries oxygen around the body and its key element is iron.
On the other hand, some invertebrates rely on a molecule called haemocyanin to carry oxygen around their bodies. Snails, lobsters and spiders actually have blue blood (properly called haemolymph). The colour comes from the haemocyanin molecule, which is blue. It is dissolved directly into their 'blood' instead of being enclosed in blood cells.
Plants
Plants and crops, such as wheat, also need very small amounts of copper to grow. We say that it is a trace element in their diet. Their roots take in soluble copper compounds from the soil.
Putting the copper in
Only a small amount of copper in the soil is found in soluble compounds. However, as plants only need it in tiny amounts, there is usually enough for their needs. But farm animals feed on these plants. We say these animals are further up the food chain. The small amount of copper taken in by the plants is often not enough for normal growth in these animals. Copper is quite often added as a nutrient to feeds for cattle, pigs and poultry. This prevents deficiencies which reduce their growth.
In some parts of the country, not enough copper gets into the agricultural food chain through plants. Certain breeds of cattle and sheep are more likely to suffer from copper deficiency because of the grass they eat. To supplement their diet, farmers provide mineral licks, which contain essential elements such as copper.
Clean pipes
Copper is used for water pipes and central heating systems (tanks and pipes). This is because it doesn't corrode and its ductility makes it easy to shape and install. It also protects against the growth of unwanted, pathogenic bacteria such as legionella, which thrive in stagnant water storage units.
Copper in the kitchen
A copper work surface can be used in the kitchen for food preparation. It reduces the growth of bacteria (e.g. E-coli) and lowers the possibility of food poisoning.
Copper is used for saucepans because of its durability, corrosion resistance and good thermal conductivity.
Alloys and Coins
Alloys
Sometimes it is better to make an alloy of copper to change or improve its properties. For example, an alloy might be stronger, have better corrosion resistance or a brighter colour.
Brass, which is made by melting together copper and zinc, is harder, stronger, more corrosion resistant and has an attractive gold colour. It still keeps its anti-bacterial properties, which make it an ideal material for door knobs, handrails and plumbing fittings.
Healthy coins
Copper has been used to make coins for centuries. These stay around for years and it is impossible to guess how many times they have been passed from hand to hand.
Normally we don't wash our hands before and after handling money. Yet this is potentially a good route for infections to spread. Copper, with its antimicrobial properties, helps to stop this from happening. Bacteria do not survive on copper coins and since it is a non-allergenic material, people don't get a rash from handling them.
Coins and alloys
Mixing copper with other metals produces alloys of different colours. 184,000 tonnes of copper were used for the first production of the eight new Euro coins.
The €1 coin has a golden coloured outer ring made of an alloy called nickel brass. This is 75% copper, 20% zinc and 5% nickel. The centre is silver coloured made from nickel coated with an alloy of 75% copper and 25% nickel.
The €2 is similar with the alloys reversed, the 10, 20 and 50 cent coins contain 89% copper and the 1, 2 and 5 cents are copper-coated steel.
Electrical conductivity
Vending machines that sell drinks, crisps, chocolate etc. always check that the correct coins have been put in. One of their tests is to measure the electrical resistance of the coins. The composition of the new Euro coins was selected to give them exactly the right electrical resistance.
Longer lasting
Copper's corrosion resistance properties mean that these coins don't tarnish easily - i.e. they stay nice and shiny for a long time. The Euro coins are expected to last for 30 years.
Copper can be recycled when the coins reach the end of their useful life. The coins can be melted down to make new copper alloys or it is possible to refine them using electrolysis to make very high purity copper (99.9% pure). They can then be used for the highest quality electrical applications.
