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　　What happens to those old computers once theyve been abandoned for newer models? The refuse from discarded electronics, also known as e-waste, often ends up in landfills instead of being recycled. And that means toxic substances like lead and mercury that are commonly used in these products can contaminate the land, water and air. The United States generates more e-waste than any other nation. Some of that waste is recycled. For example, steel, aluminum and copper are often stripped from outdated machines and reused in newer models. But even recycled parts come at a price. An estimated 50 to 80 percent of e-waste collected in the United States for recycling is exported to areas such as China or India or Pakistan, where workers taking apart the old machines are handling toxic chemicals that can pose serious health problems. Luckily, some manufacturers are beginning to assume greater responsibility for what happens to their products after they become out-of-date.