Most Americans think they’re helping the earth when they recycle their old computers, televisions and cell phones. But chances are they’re contributing to a global trade in electronic trash that endangers workers and pollutes the environment overseas. While there are no precise figures, activists estimate that 50 to 80 percent of the 300,000 to 400,000 tons of electronics collected for recycling in the U.S. each year ends up overseas. Workers in countries such as China, India and Nigeria then use hammers, gas burners and their bare hands to extract metals, glass and other recyclables, exposing themselves and the environment to a cocktail of toxic chemicals.