What surprised me most about this is that the clams are caught wild and returned to nature after a while. I would have guessed that they'd be bred for this and "used" until they died.,(reply>), Only in America, but we'd never do this because there's not enough profit in it. Imagine if this was implemented in Flint Michigan,(reply>), Probably to prevent the clams from being changed or adapted to dirty water. They are caught in a known clean lake and changed frequently to keep the samples stable.