I do know that having a lack of digestive enzymes is a bad thing, and often associated with mercury. That's why so many people with mercury toxicity have heartburn.

To stop the heartburn, you simply need to increase your digestive enzymes through supplementation. That's what I did a couple years before my amalgams were removed and it stopped my heartburn 9 of 10 times. Here is what I took: Food Enzymes

If you have plenty of digestive enzymes, that may be a good sign.