[No Blue States]

The main threat of a "dirty bomb," however, would be fear itself. A "dirty bomb" detonation in New York City at midday could cause a mass exodus from the city in panic.

Additionally, families and businesses might be reluctant to live, work, and go to school in an area that has been potentially contaminated. This could create conditions that could eventually lead to the demolition of tens of square miles of real estate and local economic hardship. Further, the cost of cleanup and decontamination would likely be billions of dollars.

[No Blue States]

Dirty bomb’s biggest hazard: panic Experts say radiation would play on public fears.

http://www.globalsecurity.org/org/news/2002/020610-nuke1.htm