The amino acid cysteine is very high in foods that we call sulfur foods. One of the things that is fairly common in people were mercury toxic is the enzyme that breaks down Cysteine gets screwed up.
I can speak to this from personal experience. Within a year after getting my mercury fillings removed which in retrospect I did not educate myself fully enough before I had them removed. ..I developed chronic diarrhea that I went on for eight months before I finally figured out that all the foods that are high in sulfur I was totally reacting to foods that before my fillings removed I never had trouble with.
Sorry to drop this kind of bomb on you but it could be worth checking out. Here's a website you might want to check out