They're big, they're bulky, and they're full of chemicals that could be hazardous to the environment if they were introduced into a landfill. The best-case scenario is to prevent computers from hitting the landfills at all. That's where a lot of obsolete technology has been ending up, and it's a problem that's already reaching critical mass. The problem is not just the tremendous volume in landfills. It's also the components of computers that release toxic substances, which leach into soils and threaten ground water.
Computers are cornucopias of potentially hazardous chemicals.
Most computer components contain nickel, lithium, cadmium, chromium, and mercury. Not only that, but there is more and more plastic being used in computers, and less precious metals. Plastics, unlike metals, aren't worth much to recyclers. Computer monitors are the worst offenders of all. A standard glass cathode ray tube, or CRT, contains up to eight pounds of lead.