Unless you're going around licking the tubes or using them for Wine Decanters then they are safe.
I think the issue is when they are busted up and ground to bits, then the Lead can leach out into the ground and cause contamination.
Here's an interesting article on Lead leeching in CRT's. I've never heard anything about Mercury in CRT's, LCD flat panels do have mercury, probably in the fluorescent back lighting. AFAIK Plasmas contain neither Lead or Mercury.
http://www.pca.state.mn.us/index.php....html?gid=4865