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A new study finds: Inorganic mercury stays in the brain for years if not decades


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.

liquid mercury formed to a skull
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 new study:
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.

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

James P.K. Rooney, The retention time of inorganic mercury in the brain — A systematic review of the evidence, Toxicol. Appl. Pharmacol., 274/3 (2014) 425-435. doi: 10.1016/j.taap.2013.12.011

Related studies (newest first)

L. Björkman, B.F. Lundekvam, T. Laegreid, B.I. Bertelsen, I. Morild, P. Lilleng, B. Lind, B. Palm, M. Vahter, Mercury in human brain, blood, muscle and toenails in relation to exposure: an autopsy study, Environ. Health, 6 (2007), p. 30. doi: 10.1186/1476-069X-6-30

I. Falnoga, M. Tusek-Znidaric, P. Stegnar, The influence of long-term mercury exposure on selenium availability in tissues: an evaluation of data, Biometals, 19/3 (2006) 283–294. doi: 10.1007/s10534-005-8642-2

G. Guzzi, M. Grandi, C. Cattaneo, S. Calza, C. Minoia, A. Ronchi, A. Gatti, G. Severi, Dental amalgam and mercury levels in autopsy tissues: food for thought, Am. J. Forensic Med. Pathol., 27/1 (2006) 42–45. doi: 10.1097/01.paf.0000201177.62921.c8

T. Lech, J.K. Sadlik, Total mercury levels in human autopsy materials from a nonexposed Polish population, Arch. Environ. Health, 59/1 (2004) 50–54. doi: 10.3200/AEOH.59.1.50-54

E. Hac, M. Krzyzanowski, J. Krechniak, Total mercury in human renal cortex, liver, cerebellum and hair, Sci. Total Environ., 248/1 (2000) 37–43. doi: 10.1016/S0048-9697(99)00474-X

M.B. Pedersen, J.C. Hansen, G. Mulvad, H.S. Pedersen, M. Gregersen, G. Danscher, Mercury accumulations in brains from populations exposed to high and low dietary levels of methyl mercury. Concentration, chemical form and distribution of mercury in brain samples from autopsies, Int. J. Circumpolar Health, 58/2 (1999) 96–107.

Y.K. Fung, A.G. Made, E.P. Rack, A.J. Blotcky, Brain Mercury in Neurodegenerative Disorders, Clin. Toxicol., 35/1 (1997) 49–54. doi: 10.3109/15563659709001165

M. Schuhmacher, L.D.I. Corbella, Mercury concentrations in autopsy tissues from inhabitants of Tarragona Province, Spain, Trace Elem. Electrolytes, 13/2 (1996) 75–78.

J.A. Weiner, M. Nylander, The relationship between mercury concentration in human organs and different predictor variables, Sci. Total Environ., 138/1–3 (1993) 101–115. doi: 10.1016/0048-9697(93)90408-X 

J. Tucek, M. Tucek, Contribution to the problem of environmental contamination with mercury, J. Hyg. Epidemiol. Microbiol. Immunol., 25/4 (1981) 354–363.

M. Sugita, The biological half-time of heavy metals. The existence of a third, “slowest” component, Int. Arch. Occup. Environ. Health, 41/1 (1978) 25–40.  doi: 10.1007/BF00377797

Related EVISA Resources

Link Database: All about dental amalgam
Link Database: Toxicity of mercury
Link database: Mercury exposure through the diet

Related EVISA News

December 13, 2013: Most Canadians having dental amalgam in their mouth are exposed to mercury at levels surpassing the reference exposure level (REL)
November 20, 2013: EPA Study: Mercury Levels in Women of Childbearing Age Drop 34 Percent
October 12, 2013: Minamata Convention is adopted
August 6, 2013: Bacterial methylation of mercury not only starting from oxidized mercury
March 22, 2013: Mercury isotope fractionation provides new tool to trace the source of human exposure
January 21, 2013: UNEP mercury treaty exempts vaccines for children
January 14, 2013: Mercury Levels in Humans and Fish Around the World Regularly Exceed Health Advisory Levels
December 24, 2012: Mercury in food – EFSA updates advice on risks for public health

December 9, 2012: Mercury in fish more dangerous than previously believed; Scientists urge for effective treaty ahead of UN talks
June 17, 2012: Factors Affecting Methylmercury Accumulation in the Food Chain

August 21, 2009: USGS Study Reveals Mercury Contamination in Fish Nationwide
June 17, 2009: 'Surprisingly High Levels' of Methylmercury Contamination found in Groundwater

February 11, 2009: Mercury in Fish is a Global Health Concern
October 30, 2008: Precautionary approach to methylmercury needed
March 11, 2007: Methylmercury contamination of fish warrants worldwide public warning
October 9, 2006: Linking atmospheric mercury to methylmercury in fish
September 23, 2006: Report Finds Mercury Contamination Permeates Wildlife Systems
August 16, 2006: Mercury pollution threatens health worldwide, scientists say
February 9, 2006: Study show high levels of mercury in women related to fish consumption

January 12, 2005: Number of fish meals is a good predictor for the mercury found in hair of environmental journalists
April 27, 2004: FDA/EPA recommends pregnant women to restrict their fish consumption because of methylmercury content

last time modified: December 29, 2013


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