Dear Colleagues,

As you know, three main forms of mercury (Hg) concern toxicologists: elementary Hg and inorganic and organic Hg (methyl- (Me) and ethyl-Hg, thiomersal). Extensive knowledge about Hg toxicology has been developed in these last decades. Yet, several questions are still pending:

• Is there a placental barrier against MeHg present at low environmentally relevant concentrations in food, as suggested by a recent study (Cambier et al., Food Chem Toxicol, 2018, 122:11-20)?
• Is the fetal-to-mother blood Hg ratio a proof of higher accumulation of Hg in fetal organs?
• Does this ratio rather reflect the greater affinity of fetal hemoglobin for MeHg compared to maternal hemoglobin and the fact that MeHg chelated by fetal hemoglobin does not allow MeHg accumulation in fetal organs (and is rather destined for excretion via the biliary tract)?
• Therefore, what could be the blood circulating mercurial species—and the molecules or proteins they are chelated to— that accumulate in the organs (fetal or adult) of mammals, birds, reptiles, amphibians, and invertebrates?
• What are the selenomercurial species formed in terrestrial mammals and other animals, besides those known in cetaceans?
• Do mercurial species from polluted environments have a role in the spread of emergent diseases such as multiple sclerosis, autism, Alzheimer’s and Parkinson’s diseases, and autoimmune diseases?

Other important issues are still being debated, and there is a need to update our knowledge in their regard:

• The huge gap between regulatory limits, for instance, the tolerable weekly intake and the reallowest-observed-adverse-effect level (LOAEL);
• The role of selenoneine in the protection against the various forms of Hg;
• The reason why bacteria devoid of the mer operon are 100 to 1000 times more sensitive to Hg(II) and MeHg than to other heavy metals such as Cd(II), Co(II), Ni(II), Pb(II), and Zn(II);
• New findings and development on the topic of Hg contamination of vaccines and dental amalgams.

The issues raised above do not pretend to be comprehensive, and proposals from authors and colleagues will be welcome.

Colleagues and authors are invited to submit their manuscripts to this Special Issue.

Prof. Dr. Jean-Paul Bourdineaud
Guest Editor

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• methylmercury
• divalent mercury
• elementary mercury
• fish
• dental amalgams
• vaccines
• selenoneine
• selenomercurial species
• bacteria
• bioavailable mercurial species