Historically most of the research and concern regarding mercury's toxic effects on humans and in particular on fetal development have focused on methylmercury, rather than mercury vapor or inorganic mercury. This has been due to a combination of factors, but basic misunderstandings of the differential nature and effect mechanisms of the different forms of mercury appears to have played a role in this. There have been highly publicized major acute poisonings affecting many people and infants of those exposed through fish in Japan and food in Iran.Methylmercury has also been shown to be extremely neurotoxic, much moreso than inorganic forms that do not as readily cross cellular membranes such as the blood-brain barrier, even though they are also very neurotoxic. Additionally, doctors and researchers have traditionally tended to use blood tests to test for mercury exposure, without the understanding from more recent experience that has found blood tests mainly relevant to methylmercury, not mercury vapor or inorganic mercury body burden. Mercury vapor has been found to have an extremely short half-life in the blood[8-10] since the vapor form rapidly crosses cellular membranes including the blood-brain barrier and placenta, where it is rapidly oxidized to inorganic forms. While the half life of vapor in the blood has been found to be about 3 seconds[8], the inorganic form does not readily cross cellular membranes resulting in accumulation in the body organs, especially the brain where the half life can be over 20 years[11,12].
The form of mercury found in the blood by blood tests is thus mostly organic[9,13], while most of the mercury in body organs and urine is mostly inorganic. However, unfortunately there is no simple or commonly accepted test methodology for inorganic mercury body burden, other than post-mortem autopsies which have verified the accumulation of inorganic mercury in the brain and other organs [12,14,15,127].
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