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In vivo Quantification of the Transition of Brain Extracellular Mercury after Thimerosal Administration


Monomethylmercury (MMHg) is recognized as one of the most potent neurotoxins. While the chemistry of ethylmercury (EtHg) is not fundamentally different from that of methylmercury, its toxicity has often been discussed as totally different. The ethylmercury moiety is part of thimerosal (TMHg), which is used as a preservative in vaccines to prevent fungal and bacterial growth since the 1930s. After injection into the body, the EtHg moiety is released from TMHg to the surrounding tissues and therefore should follow the same toxicological pathways as other ETHg absorbed into the body from other sources. While numerous studies exist, showing the strong toxic effects produced by EtMg, the use of TMHg in vaccines has not been associated with any clear connections with serious human neurodevelopmental disorders.

While the use of TMHg in vaccines in Europe and the US has been considerably reduced after 1999, especially for children and pregnant women, the worldwide use of TMHg-containing vaccines is still important. While the brain in general is protected against the inflow of many exotic toxic substances by the blood-brain barrier (BBB), mercurial substances can overcome the barrier and cause serious toxic effects. Therefore, the investigation of mercury concentrations between blood and extracellular fluid (ECF) of the brain following the administration of TMHg is important for improving the knowledge of the neurotoxicity of TMHg.

The new study:
Researchers from Taiwan now developed a method for the in-vivo determination of the transition of brain extracellular mercury after thimerosal administration. In order to cope with the extremely low available sample volume, the low Hg concentration and the high salinity of the sample matrix, a microfluidic approach was developed based on microdialysis for sampling and photocatalyst-assisted vaporization for sample introduction to the ICP-MS. Under optimal operation conditions, the developed analytical system provided limits of detection (based on 3s) of 2.7 and 1.7 ng/L for MMHg and TMHg.   

Using this system, the transport of mercury to the brain of adult male Sprague-Dawley rats was studied after intraperitoneal administration of MMHg or TMHg in saline solution with a time resolution of about 13 min. The system was able to monitor the  rapid change of mercurial concentration appearing in ECF. The results of the animal experiments with the two organomercurials indicated extremely similar transition trends. Thus the researchers concluded, that the BBB penetration behaviour of TMHg is very similar to that of MMHg although the transport mechanism of TMHg remains unclear.    

The original publication:

Cheng-Hsing Lin, Cheng-Kuan Su, Yuh-Chang Sun, Development of Online Microdialysis–Microfluidic-Based Photocatalyst-Assisted Vaporization Device–Inductively Coupled Plasma-Mass Spectrometry Hyphenated Analytical System for in vivo Quantification of the Transition of Brain Extracellular Mercury after Thimerosal Administration, Microchem. J., 154 (2020) 104569. DOI: 10.1016/j.microc.2019.104569

Used techniques and instrumentation:

Agilent Technologies Inc.- Agilent 7500 a ICP-MS

Related studies

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Related information

World Health Organization, Thiomersal.
European Medicines Agency, EMEA public statement on thiomersal in vaccines for human use–Recent evidence supports safety of thiomersal-containing vaccines.

 Related EVISA Resources

Brief summary: ICP-MS - A versatile detection system for speciation analysis
Link database: Toxicity of Organo-mercury compounds
Link database: Research projects related to organo-mercury compounds

Related EVISA News

January 14, 2013: United Nations Global Mercury Treaty: Fifth and final session
December 18, 2012: Pediatricians Argue to Keep Thimerosal in Some Vaccines
December 9, 2012: Mercury in fish more dangerous than previously believed; Scientists urge for effective treaty ahead of UN talks
October 12, 2012: Prenatal mercury intake linked to ADHD
July 15, 2012: World Health Organization Fails In Its Effort To Defend Mercury In Vaccines Before United Nations
October 28, 2011: WHO worries mercury treaty could affect costs and availability of vaccines
August 8, 2011: UNEP Global Mercury Treaty May Include Ban on Mercury in Medicine

last time modified: July 22, 2020


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