The typical computer monitors in use today are likely to be either LCD screens or their increasingly obsolete cousins -- sturdy, old, workhorse CRT monitors. While CRT monitors contain more of the stuff that keeps environmentalists up at night than do LCD monitors, each type of display contains material, including lead, that should be dealt with properly. Let's first discuss CRTs.
Your CRT monitor screen, for those of you who still have them, contains lead, but it is no threat, so you can touch it without any risk to your health. In its ordinary, functioning state, it's not dangerous. However, lead itself is a toxic metal, and even a very small amount can cause poisoning. As such, you should try to avoid touching a broken CRT screen. The trouble with this type of monitor and its dangerous contents comes when you finally decide to upgrade to a newer monitor, or you decide you want to toss the old CRT paper weight sitting on the floor in a corner of your home office. You can't just toss it in a landfill: First, because it's against EPA regulations and second, because its just too harmful to the Earth to do so. Not only do CRTs contain lead but they also have cadmium, mercury and phosphorous. When the CRT monitor is smashed in a landfill, these materials ooze into the landfill and risk one day showing up in the water supply. And the lead in the monitor glass, when the screen gets crushed, releases harmful particles into the air [source: Advanced Recovery].
As for LCD monitors, some of these newer leaders of the computer display world have screens and backlighting with lead and mercury in them, so tossing them indiscriminately in a landfill runs some of the same risks as putting CRTs there. They're safe during normal use though, just like the CRTs.
In either case, then, you should find a responsible recycling facility to dispose of these monitor types. Check with your local county or state government about recycling alternatives, or see if a nearby box retailer takes monitors off to recycling heaven (recycling a monitor usually comes with a nominal fee attached, but it's worth it). You may even consider donating them if they still work. You might not find as much of a "freecycling" market for your old seven-ton CRT, but it's hard to imagine not being able to give away a working LCD monitor.
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