So what is the difference between thimerosal and straight mercury? Is it more or less harmful?
Thimerosal is an organic compound and so it will hold to it's Hg atom somewhat. Hg as a free metal is a poison as it catalyzes some unwanted reactions or it simply stops some important ones. If the Hg atom is already bound then it's less poisonous or has a very small chance to be poisonous.
Just like cyanide. In our cells there are many compounds that hold onto the -CN bond.
Thimerosal is not suitable for little children so there are some poisonous effects, and from what I've read it' mainly used externally.
Thimerosal is an ethyl mercury compound with a salicylate group attached. The compound http://mercury-freedrugs.org/docs/071130_Geier_etal_PublishedReviewOfThimerosalPaper1.pdf" [Broken], a well-known mercury toxin. That said, the likelihood of thimerosal causing excessive toxicity is low since it is not something that one is chronically exposed to as opposed to methyl mercury, for example.
"Straight mercury" is not sufficiently descriptive to compare with thimerosal. If you are referring to elemental, metallic mercury, the answer is it depends on the route of exposure. If the mercury is inhaled over a period of time (as you might get in a closed room or lab that has had a mercury spill) the toxicity is certainly greater for elemental mercury in that case. If you ingest it or handle it, it has a much lower toxicity. http://www.idph.state.il.us/envhealth/factsheets/mercuryhlthprof.htm" [Broken]
In general it's the other way around.
Elemental liquid mercury is insoluble and although toxic it is difficult to absorb a serious dose - heated mercury vapour is more easily absorbed and so more dangerous.
Organo-mercury compounds are often a lot more soluble and much more readily absorbed - hence much more dangerous.
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