From what I have read on the mustard gas it was old and stored improperly. It looked like it was buried and forgotten. Not something you want to write home about.
One shell could do some mass destruction if it were unleashed on the USA. This is the reason we took Saddam out. Now they are using WMD on the troops. We were totally justified in going to Iraq to destroy WMD. See, we already destroyed one shell and there are sure to be thousands of more.