Swamp Gas
Unprotected travelers without environmental protection must make a save versus poison of 12 or higher every fifteen minutes spent in the fog or suffer from the following penalties: Reduce speed by half and -2 to all combat actions.  Effects of the gas are a burning, itching sensation on the skin and laboured, heavy breathing.

Radiation
Travelers without the benefit of radiation shielding face the risk of serious illness due to prolonged exposure to the marshlands.  As once moves closer to the centre of the marsh, and enters the ruins of the fuel processing plants, the likelihood of developing serious health complications increases exponentially.  For every half hour spent in the marsh (or five minutes spent in the epicentre) characters must make a save versus disease of 14 or higher or begin to suffer the effects of radiation poisoning.