That is well known, but there are other ways of taking glutathione which gets around this problem, such as transdermally (which I use), or rectally. I buy reduced glutathione in bulk powder form, and then just apply the power to my skin. I know it is absorbed, because I find transdermal glutathione provides me with a mild mood-boosting antidepressant effect. Rich Van Konynenburg talks about the various methods of glutathione administration here. In the case of mopping up mercury, the bloodstream is where you'd want the glutathione to be, as this is where the displaced mercury is found.