I haven't heard that mercury can cause bloody stools. Are you taking a vitamin K supplement? If not, then I suggest that you take 100 mcg a day longer term just as a preventative. I am taking 100 mcg a day, as many of the herbs I am taking have a slight anticoagulant effect.

I did have a slight bit a blood in my stool a few times over the years, some of those times were when I was taking plenty of vitamin E(perhaps 800 IU a day?), and probably all those times were when I wasn't taking vitamin K. Now I just take the vitamin E that is in my multi which is just 200 IU, and I don't even take this every day. I take many of the vitamins individually anyway, so don't really need the multi so much.