Good catch. Perhaps there was a modicum of hyperbole there. Rather than "probably", I'd more accurately have said "could". Some meat monitoring programs have found mercury levels in meat that are the same order of magnitude as those found in fish.

Assuming that cows only eat grass is a little bit naive, though. Mad cow disease was probably initiated by the practise of feeding sheep to cattle, and it was probably propagated by the persistence of feeding cattle to cattle.

There are a number of variables that moderate the mercury level in fish, but it's pretty clear than certain species are probably not a good idea to eat. Some tuna (there are a number of tuna species), swordfish, shark.....top predators, generally, are not good food souces, due to mercury contamination. Certain water bodies are polluted, making any seafood sourced there unwise to eat. However, for the "average American" person, only 20% of mercury intake from food is from fish. Where is the other 80% coming from?

I like this brief quotation from a World Health Organization publication, "For mercury, average intakes were below the PTWI (300 micrograms/person; 200 micrograms/person or 3.3 micrograms/kg bw as methylmercury) for adults and for breast-fed infants. Contributions from fish varied from 20 to 85%; in some countries because of different dietary habits, cereals or meat may contribute similar amounts. Because of inadequate data on food other than fish, intake estimates are biassed and sometimes based solely on typical levels in fish."

Fish get a lot of scrutiny. Other sources do not. It's not that mercury is in the soil that grows the grass that the cow eats, but it's in the industrial dust and deposits that settles everywhere. It's in the supplements fed that cow. The older the cow, the more likely it is to become a hamburger. And as we know, age is a factor in bioaccumulation. We just don't have good evidence for 80% of the total mercury consumed in food. Fish aren't "contaminated" while meat is somehow "clean". Fish are good for you. Almost without exception. And we know which ones we should consider exceptions.

300 metric tonnes of mercury go towards making amalgam tooth fillings every year. Now that's a mercury problem. But, we're drifting away from the subject matter.....

Lar