Evidence from modeling studies based on autopsy tissue data point to a half-life of inorganic mercury in human brains of several years to several decades, contradicting older radioisotope studies that estimated half-lives in the order of weeks to months in duration.
The new study
Biological half-life is an important pharmacokinetic parameter. The biological half-life or elimination half-life of a substance is the time it takes for that substance to decrease its concentration in a given body compartment by 50% and this relationship is observed to hold true for a given substance provided the assumption of first order kinetics is valid. Additionally, a steady state concentration is arrived at after a time of approximately 5 times the elimination half-life for a given substance (assuming first order kinetics)—the ultimate concentration reached depending on the elimination half-life, the rate of exposure and the volume of distribution for the particular substance. Consideration of these concepts allows for modelling and analysis that can be used to address important practical issues, such as maximum safe daily exposure levels for a given toxic substance.
The U.S. Environmental Protection Agency and the U.S. Agency for Toxic Substances and Disease Registry launched its “Don’t Mess with Mercury” video in an effort to protect people -- especially children -- from the dangers of mercury.
To see the video, and for more information about mercury, visit: www.dontmesswithmercury.org/
Inorganic mercury itself cannot access the brain, however as elemental mercury, ethyl-mercury and methyl-mercury are all metabolised to inorganic mercury within the brain, knowledge of its half-life is important in the modelling of the toxicity of all forms of mercury in humans.
The author of the new study reviewed existing data on the concentration of mercury found in human and animal tissues. Out of more than 16.500 papers dealing with mercury poisoning, 984 papers were found dealing with autopsy studies, out of which 81 were dealing with human studies. Eighteen human mercury poisoning cases were followed up long term including autopsy. Brain inorganic mercury concentrations at death were consistent with a half-life of several years or longer. Estimates from modelling studies appear sensitive to model assumptions, however predications based on a long half-life (27.4 years) are consistent with autopsy findings. The author concluded that shorter estimates of half-life are not supported by evidence from animal studies, human case studies, or modelling studies based on appropriate assumptions.Comment
This finding carries important implications for pharmcokinetic modelling of mercury and potentially for the regulatory toxicology of mercury. It follows that given a longer half-life, the phenomenon of mercury bioaccumulation may be observed—i.e. the slow increase in tissue levels of mercury with time at constant exposure—even at very low exposure levels. Such bioaccumulation at very low exposure levels is questioning all those statements on "safe" exposure limits resulting from different mercury sources such as dental amalgam, mercury compounds in vaccines or contaminated seafood. The original study
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last time modified: December 29, 2013