I'm guessing it is part of the glue that manufactures process these foods. Take for instance a food pellet, how in the heck it stays good for so long without spoiling and that matter how does it shape into a pellet? Flake food, can you imaging what it takes to make a flake and hold together? What about that mush you make? I made a food mush this weekend, at the store they have what you call a gumbo mix (just for us Louisianans) if was a mixture of clams,shrimp oysters and a few others. I'm imaging these creatures have metals in them, just imagine what they eat, and how polluted is our waters from which they live and eat in?