Come on now. Let's use a little common sense.
You actually think that al Qaeda and company HAVEN'T thought about poisoning the food and/or the water???!!!
It's NOT as easy as it may seem, and can be detected early on. Besides, they (al Qaeda) aren't likely to go for killing small amounts of people, which is all that it would effect before detection would occur, they want the big numbers of deaths (bang for the buck), like deadly chemicals spread through the air over and around large cities.
No sense panicking on this kind of crap.
I remember at the beginning of the WOT, there was an article that mentioned the terrorists had threatened to poison imported canned tomatoes, I believe. I imagine alot of euro muslims work in canneries, just doing the work the euros don't want to do.