I came across a relevant piece at New Scientist. Debora MacKenzie writes about the long term effects of sarin, saying:
Proof that some of Saddam Hussein’s chemical weapons still exist finally came on Monday, when a chemical shell containing sarin was discovered in Baghdad. It had been rigged to booby-trap a US military convoy and exploded before it could be disarmed, resulting in “minor exposure” for two bomb disposal experts.
The two “showed some minor indications of nerve poisoning” said Army general Mark Kimmitt on Monday. “However, it was so minor that the doctors already have these people released.” The two were probably treated with atropine, the standard antidote for life-threatening exposure to sarin.
New Scientist then went further:
New Scientist contacted the departments of Defense and of Veterans Affairs in Washington DC and Central Command in Baghdad, but was given no indication that personnel have or will be tested for paraoxonase. Robinson says: “They can contact us, and we can point them in the right direction to get help.”
These long-term effects are caused by the agent’s effect on brain receptors, not the receptors in muscle and the lungs that make higher doses of sarin lethal. But nothing is yet available for soldiers or anyone else in Iraq who has been exposed to Saddam’s leftover sarin – or is in the future.
I think Hewitts arguments are a small bit on the thin side. One shell, perhaps over a decade old, is not sufficient reason to invade an entire country.