There have been no long-term studies because no one is willing to fund them, and even if there were, some of this stuff hasn't been around long enough to conduct any.
How about employing common sense: why put substances into your body that do not exist in nature, have no know benefit to the body, in some cases are closely related to or made from substances that are known to cause harm, and in some cases have at least some short-term studies showing they themselves may cause harm?