Lightbulbs break all the time. So why would a single broken bulb in a Maine household trigger the state's
Department of Environmental Protection to refer the homeowner to a decontaminator?

The answer lies in the type of bulb that broke—a compact fluorescent lightbulb—and what was inside that bulb. Compact fluorescents, like their tubular fluorescent precursors, contain a small amount of mercury—typically around five milligrams. Mercury is essential to a fluorescent bulb's ability to emit light; no other element has proved as efficient.

As effective as it is at enabling white light, however, mercury—sometimes called quicksilver—is also highly toxic. It is especially harmful to the brains of both fetuses and children. That's why officials have curtailed or banned its use in applications from thermometers to automotive and thermostat switches. (A single thermostat switch, still common in many homes, may contain 3,000 milligrams (0.1 ounce) of mercury, or as much as 600 compact fluorescents.)

The problem comes when a bulb breaks. Mercury escapes as vapor that can be inhaled and as a fine powder that can settle into carpet and other textiles. At least one case of mercury poisoning has been linked to fluorescents: A 1987 article in Pediatricsdescribes a 23-month-old who suffered weight loss and severe rashes after a carton of eight-foot (2.4-meter) tubular bulbs broke in a play area.


http://www.scientificamerican.com/article.cfm?id=are-compact-fluorescent-lightbulbs-dangerous