None. I was my own group. I'm one of those people who doesn't need to read books to understand that having mercury in the mouth is dangerous. I was an industrial chemist for a while before switching to law, and had been exposed to lots of mercury. I always knew it bad, but the event that kicked me off was
having to wear eyeglasses, when all the 90 year olds in my family on both sides do not need eyeglasses.
Plus, I found myself crying one day in my office, for no apparent reason. I had changed my diet to really eating healthy, which included lots of fish, but I was unaware of the methylmercury issue and I was eating a LOT of fish. Swordfish and tuna, 4 times a week or more for a long time. It probably kicked me over the threshold, from being symptom-free, to having symptoms. Everybody has a different threshold probably.