Processed tuna is often colored and treated with carbon monoxide gas to appear fresh and contains heavy metals.

“There was recently a lot of interest in the process of making AI tuna look fresh and look this deep reddish orange color. And what they're doing with a lot of this AI that's old, it's kind of old and brown and gray and they're cutting off the old brown gray parts. They're actually adding coloring to it in the factory of various types. And they're filling it with a carbon monoxide gas in freezers to make it look this fresh red color. So, I'm not a huge fan of a tuna in general because it's very high in heavy metals.”