An average smartphone contains 41 different elements - and last year alone 1.2 billion of the handsets were sold globally. This is causing an imbalance between the supply of  metals and metalloids and their demand from consumers - a concept referred to as 'criticality.' Researchers have now assessed the criticality of all 62 metallic-based elements on the Periodic Table to reveal which are most at risk and what that means for our gadgets in the long-term. Researchers from Yale University assessed the 'criticality' of 62 metals on the Periodic Table. They discovered at at least 33 of these (shown) are used for circuit boards. Criticality looks at which materials will become harder to find, which will have the highest environmental costs and which are irreplaceable . Metal criticality is analysed in three ways - supply risk, vulnerability to supply restriction (VSR) and environmental implications. Put simply, supply risk is the probability that a necessary raw material will run out. VSR is an index used to work out how likely a particular element will become restricted based on how much its used and how abundant it is. This index considers restrictions put upon supply from companies or countries, for example. Metal criticality is analysed in three ways - supply risk, vulnerability to supply restriction (VSR) and environmental implications. Put simply, supply risk is the probability that a necessary raw material becomes unavailable. VSR is an index used to work out how likely a particular element will become restricted based on how much its used and how abundant it is. This index considers restrictions put upon supply from companies or countries, for example. And in terms of the environment, researchers assess what costs mining certain materials, as well as the materials themselves, have on the environment and then the likelihood that this may also lead to restrictions. Lead, for example, was banned in many products after governments and companies learnt of its dangers to the environment and began prohibiting how much it was used. An overall score is awarded to each element within each category and the higher the score, the more at risk that element is. And in terms of the environment, researchers assess what costs mining certain materials, as well as the materials themselves, have on the environment and then the likelihood that this may also lead to restrictions. Lead, for example, was banned in many products after governments and companies learnt of its dangers to the environment and began prohibiting how much it was used. Using these three categories, researchers from Yale University led by Professor Thomas Graedel were able to see which metals and metalloids are most at risk within each group. Many of the metals traditionally used in manufacturing, including zinc, copper, and aluminum, are not at risk, explained Professor Graedel. However, the newer or less-common metals used in smartphones, infrared optics, and medical imaging, are vulnerable. The team's results show that the limitations for many important metals used in smartphones and other gadgets are largely those related to supply risk. These include gallium used in processor chips and selenium in transistors on these chips. Platinum group metals including gold and mercury have the highest environmental implications. While steel alloying elements, such as chromium and niobium, as well as elements used in high-temperature alloys including tungsten and molybdenum, scored higher in the vulnerability to supply restriction category. 'The metals we've been using for a long time probably won't present much of a challenge,' said Professor Graedel. This graphic reveals the 41 elements typically found in a smartphone's screen, electronics, battery and casing. Many metals traditionally used in manufacturing, including zinc, copper, and aluminum, are not at risk . The results  show that  many important metals used in gadgets are largely related to supply risk (A). These include gallium and selenium. Gold and mercury have some of the highest environmental implications (B). Chromium, niobium, tungsten and molybdenum scored higher for the vulnerability to supply restriction (C) 'We've been using them for a long time because they're pretty abundant and they are generally widespread geographically. 'But some metals that have become deployed for technology only in the last 10 or 20 years are available almost entirely as byproducts. 'You can't mine specifically for them; they often exist in small quantities and are used for specialty purposes. And they don't have any decent substitutes.' The researchers listed these as indium, arsenic, thallium, antimony, silver, and selenium. There is no substitute for indium, in particular, and this could impact our touchscreens. Factors affecting extreme criticality include 'concentration of primary production' and political instability. The study points to the fact that up to 95% of rare Earth metals come from China, and tantalum comes from areas of unrest such as the Democratic Republic of the Congo. Last year 1.2 billion smartphones were sold globally . Among the factors affecting extreme criticality include 'high geopolitical concentration of primary production' and political instability. The researchers point to the fact that up to 95 per cent of rare Earth metals come from China, while tantalum, used in phone micro-capacitors, comes from areas of unrest such as the Democratic Republic of the Congo. Professor Graedel also looked at the effect recycling can have on these elements and explained that lead is highly recyclable, but materials that are only used in trace amounts are harder to extract. 'I think these results should send a message to product designers to spend more time thinking about what happens after their products are no longer being used,' Professor Graedel added. 'So much of what makes the recycling of these materials difficult is their design. It seems as if it's time to think a little bit more about the end of these beautiful products.' The research is published in the journal PNAS.
Researchers assessed the  'criticality' of 62 metals on the Periodic Table . Criticality looks at which materials will become harder to find, which will have the highest environmental costs and which are irreplaceable . Paper found that supplies of gallium, arsenic and selenium are high-risk . These compounds are needed for circuit boards, batteries and more .