Posted by Larry Hoover on October 4, 2009, at 9:00:18
In reply to Re: Elemental mercury vs. mercury salts, posted by NKP on October 3, 2009, at 18:37:05
> The person (who I'm not sure is a "he") plays with elemental mercury in their bare hands.
Sounds like a woman to me.
> I was asking a real question about the toxicity of elemental mercury, since I used to play with the stuff as well when I was a child (I obtained it from thermometers which I broke open to remove the mercury).
The problem isn't so much in playing with it. It's from the potential for long-term exposure to mercury vapours from spills. Even small droplets of mercury take a long time to evaporate, and during that time there would be an elevated mercury vapour pressure in any closed airspace, such as a room in a house. Inhaled mercury vapour is absorbed from the lungs.
> I was hoping that somebody knowledgable on the subject might confirm or refute the person's claims. From what I've read on the internet, I am under the impression that elemental mercury is at least *less* toxic than mercury salts - but I am not very knowedgeable on these matters, which is why I was hoping that a more knowledgeable person might be able to shed some light.
You're absolutely correct in your understanding; elemental mercury is less toxic than mercury salts. We don't very often come in contact with true salts of mercury, however, but we instead are most often exposed to organic mercury compounds. In those organics, mercury has the same electron configuration as it does in the salts, but it has different bonds to the other atoms.
There is a contextual element to environmental mercury exposure that is often left out of discussions; the selenium/mercury ratio is as critical a factor to consider as is the absolute mercury exposure.
For predators at the apex of the food chain, the top order predators, absolute mercury exposures can be extraordinarily high. Polar bears have shown tissue mercury levels so high that they exceed our theoretical thresholds for acute toxicity (from one-time exposure), but these are levels from chronic exposure. And yet, these animals are reproducing normally, have normal lifespans, etc. The key to their survival is that they also have extremely high exposure to selenium.
When laboratories conduct the assays for absolute mercury content in tissue samples, the individual chemical forms of the mercury are entirely lumped together. There is no way to separate out mercury that has been wholly inactivated by selenium from mercury that is still in a toxic form. When we see these incredibly high mercury contents, we misunderstand what we're seeing unless we also identify what chemists call the speciation of the mercury, i.e. the actual chemical structures in which it was found. Those include elemental mercury, various organic mercury structures, chelated mercury ions, and also Se-Hg (the covalent selenium/mercury compound).
I suspect that mercury has always been found in high concentrations in fish and marine mammals of the high Arctic. Traditional foods of the Inuit such as muktuk (various spellings, but it is the skin of small whales) are extraordinarily abundant sources of selenium. The people may not have a chemistry-based understanding of why it is important to eat that particular food, but those who did, and passed on the behaviour to their heirs, are with us today.
So, if you're worried about mercury exposure, make sure you get selenium.
Lar
poster:Larry Hoover
thread:918589
URL: http://www.dr-bob.org/babble/20091001/msgs/919652.html