What happens when you toss your old cellphone or computer monitor in the Dumpster? First, you’re contributing toxins like mercury, lead and cadmium into the environment. By some estimates, there are 500 million discarded cellphones in the U.S. alone. Second, you’re wasting precious resources: Electronics contain small amounts of precious metals like gold, silver and coltan, all of which can be reclaimed to reduce often environmentally destructive mining operations. What can you do? Plan your electronics purchases wisely—think about a new phone every three or four years, instead of every six months—and always drop your e-waste off at a recycling center.