Canned Foods--Is there any real risk?

Crabotanicals recommends avoiding canned foods unless the food cannot be found fresh or dried. Water chestnuts and black olives are well-liked by hermit crabs and are seldom available in any form but canned. There are many concerns related to canned food including human grade salt, preservatives, the leaching of metal, and now BPA. Even jarred food has some risk. Here's an interesting article.