Amalgams and fish mercury may cause many conditions which are not easily recognized as an illness:excess intestinal gas,oily skin, acne,bad breath,emotional instability,anger problems,sensitivity to light or sound,brain fog,nightmares,etc. Mercury may make various forms of mental illness worse.
There are thousands of clinical trials on various health issues. Only two seemed relevant to mercury: One was about eskimo children and the other NOrwegian children. They will study the effects of toxic metals in the environment. No doubt these might take 20 years to complete. There are of course zero studies on amalgams, or fish, or mercury in vaccines.