Any corn fed animal will have mercury, from the fungicides and pesticides used on the feed. also arsenic.

It's important to keep in mind that even if something is labeled 'organic', grown in the US or someplace where mercury or other toxins (unavoidable) in fungicides or pesticides is supposedly illegal, that that is not a guarantee of anything. Organic farms are popular now, but that is a recent trend. The same land that is now farmed 'organically' may have been farmed with heavy duty pesticides and fungicides up until just a few short years ago and the soil will remain contaminated for a long time. If vegetables are shipped from Mexico or elsewhere and then processed in the US there also is no guarantee as to quality in that regard.

Beef and chicken labled 'organic fed, no hormones, no antibiotics' is about the best i am able to find, and I am always aware that that does not guarantee 100% free simply because of toxin remnants in soil and elsewhere. I should go fishing more, there are rainbow trout right outside my door and I have been ignoring them. Where we live, the water is pretty clean, very clean matter of fact, on a mountain. But, down below us, about 50 miles away, they have issued mercury warnings about eating the fish from the lakes. Could be power plants, dental offices, even farmers doing the polluting, hard to say.