Designers of everything from mobile phones to electric car batteries should make their products far easier to recycle.
Products should be made to become "designer minerals" at the end of their lifetimes so they can more simply be broken up and stripped of metals ranging from copper to gold, according to the twin studies.
"Global metal needs will be three to nine times larger than all the metals currently used in the world" if demand in emerging economies rises to levels of rich nations, said Achim Steiner, head of the U.N. Environment Programme.
The total amount of steel in use in the United States, for instance, was an estimated 11 to 12 metric tonnes per person in 2010, compared with 1.5 tonnes in China.
"Product designers need to ensure that materials such as rare earth metals in products ranging from solar panels and wind turbine magnets to mobile phones can still be recovered easily when they reach the end of their life," he said in a statement.
Recycling rates are low in most nations and electronic waste alone is estimated at between 20 to 50 million tonnes a year, or between three and seven kilos (7-15 pounds) per person.
Most ends up dumped or burned, contaminating air, water and soil.
A third report by a non-governmental organisation quoted estimates that about 130 million mobile phones are thrown away annually in the United States.
Collectively, they weigh about 14,000 tonnes and include almost 2,100 tonnes of copper, 46 tonnes of silver and 3.9 tonnes of gold.
A mobile phone alone can contain more than 40 elements including copper, tin, cobalt, indium, antimony, silver, gold, palladium, tungsten and yttrium.
Most are in tiny amounts but recycling would take pressure off mining.
The two reports by the United Nations' International Resource Panel urged governments to agree on best available recycling technologies.
So far, recycling laws are limited mostly to developed nations.
Manufacturers also should start with ease of recycling in mind, the reports said, for instance avoiding mixes of metals that are hard to separate.
Platinum group metals, for instance, can effectively dissolve when mixed into steel.
"Some combinations are harder and uneconomic to separate," Markus Reuter, lead author of the report on metals recycling, said.
He likened some mixes to trying to separate a cup of coffee into water, milk, sugar and coffee.
Rising demand for metals will also have to be curbed with lighter-weight designs.
In the European Union, for instance, the average weight of cars rose to 1.2 tonnes in 2001 from 0.85 tonnes in 1981.
Recycling could also cut energy demand and greenhouse gases compared to mining, which often uses 10 to 100 times more energy than recycling for the same amount of metal.
"Metals use seven to eight per cent of the world's total energy in their primary production. That's larger than anyone had thought," Ester van der Voet, lead author of the other report on metals and environmental challenges, said.
The third study, by the Gaia Foundation, said the world's growing addiction to throwaway consumer electronics was putting enormous pressure on resources such as metals, minerals, water and ecosystems.
In the United States, it said, 80 per cent of electronic waste was shipped to developing countries in Asia or Africa where it was handled in bad social and environmental conditions.
"In failing to create effective recycling systems, we are thus outsourcing our toxic waste and turning parts of the world into digital dumps," van der Voet said.