Be careful, mussels are used by biologists to test for pollution because they do such a good job of sponging up the heavy metals, and all the other pollutants.
I love mussels too, but I only pull on their wiskers when they're living in an area with clean ocean water and a good deal of current...even in the best of conditions I wouldn't eat them more than a couple of times a month.
Now scallops on the other hand
With these tasty little fellows you’re only eating the mussels mass and not any organs so they’re one of the safest delicacies to eat, plus they tend to only thrive in cleaner water to begin with.
Clams are another story.