Not sure they are as deadly as nukes, but think of releasing some bug with 50% fatal outcome and nice spread rate at Grand Central in Mahattan, between 8 and 10. Some serious economic impact, no? Whole fleet of beer trucks hitting key people on key projects in a lot of financial orgs.
The real bio and chemical weapons are hard to get, though. The crap we read about in "terrorist plot" warnings is not real. That's some amateurs dinking around in their kitchen while talking tough. The real thing, which is in possession of countries like North Korea or may be Siria, is not available to the terrorists yet. We'll have to wait a bit longer.