I am not a doctor and do not offer medical advice. Also, I did not say that if you drink kefir, you will be cured. I only made a hypothesis, which, if proved to be true, could be beneficial to many people.
Having said that, to the best of my knowledge, kefir can do no harm. Furthermore, a healthy gut is absolutely necessary for the elimination of heavy metals from the body. Without a healthy intestinal flora, the body cannot eliminate toxins or metals.
Also, I heard it said that kefir is needed in large quantities (1 lt/day) for therapeutic purposes.
Here is a link discussing the possible effects of aerobic bacteria on Mercury. (http://www.asknature.org/strategy/1ee340b8e77682d012ce1f61ab65df68)
Please use the information provided with caution and always consult your doctor/physician.