What is Thimerosal

     The other day I was idly browsing my facebook feed and encountered an image regarding the presence and safety of mercury in vaccines.

      The image is in two parts; both are satirical. The top half was created in favor of the anti-vaccination movement declaring that the presence of mercury in vaccines is dangerous. The bottom section is an equally sarcastic rebuttal to the former; stating that the original author has no idea what he is talking about. The image itself is actually terribly incorrect on a few points; though it does invite a few interesting question for discussion. What is thimerosal? What is it for? Does it contain mercury? Is it dangerous? Am I an ignorant idiot? Let us find the answers for ourselves.

      I will start by going over the image itself first and then digging into the real meat of the subject. The second section of the image states “This is how I would normally handle chlorine... but when it is in the form of table salt, it is completely safe.” True to what is meant to be implied chlorine is pretty dangerous. Chlorine is gaseous under normal temperature and pressure; it is irritating to the lungs at 15 parts per million (ppm) and lethal at 50 ppm. Thus the reason the scientist is carefully holding that beaker away from his face; though I do feel the need to comment on his lack of a respirator and hazmat suit.

      The second half of that statement, regarding table salt, has a few misleading points. It correctly says that when chlorine is in the form of table salt, sodium chloride, it is completely safe. In fact, it is not only completely safe but even necessary for the human body to survive.

      The reason for this is simple: notice the chemical name of table salt, sodium chloride. Particularly, notice the 'ide' part of chloride. Chloride is completely safe for humans; whereas chlorine is deadly. The difference between the two is small, yet significant. When chlorine gains an extra electron it has an over all negative charge; this makes the anion of chlorine, chloride. Anions cannot freely exist: they must bond with another element to maintain chemical balance. That negative charge from the extra electron cannot just hang out by itself. Certain other elements tend to get a positive charge; sodium is one of these.

      There is an important distinction to make here. Chlorine is not simply present in table salt; it is in an entirely different form. Additionally, sodium chloride does not break down into its' base elements in the human body. If the second author of the image is correct then mercury must be in a different, safe, form when present in thimerosal and it must be stable when metabolized in the human body.

      Now we can dig into what thimerosal actually is. Thimerosal is a compound used as a preservative in vaccines; it is created by reacting ethylmercuric chloride with thiosalicylic acid. When present in the body, especially the bloodstream, thimerosal breaks down back into thiosalicylate and ethylmercuric chloride.

      Thiosalicylate can be dismissed easily enough. It is not dangerous to the human body and is only used as a reactant to create other compounds (like thimerosal) and as a dye. On the other hand ethylmercuric chloride is quite a bit nastier. You may be thinking, 'Hey, we just talked about chloride! That stuff is good for us!' This is absolutely correct; however the important part of this particular molecule is the ethylmercuric bit. I looked up ethylmercuric chloride on the website of a scientific chemical supplier. The notable part of the entry is in the safety and documentation section of the webpage. Out of the list of warning labels I found H300, H310, and H330 to be of particular interest. Those abbreviations are the supplier's codes for hazards: fatal if swallowed, fatal in contact with skin, and fatal if inhaled, respectivally. The Center for Disease Control states that ethylmercuric compounds are safe. Out of the two sources here, I think I would rather trust the one that does not have a vested interest in proving that ethylmercuric chloride is safe.

      Mercury, in any organic form, is dangerous to the human body. When it is absorbed into the bloodstream mercury is carried into the brain. Once there, it wrecks havoc on the nerve cells; causing headaches, memory loss, sensory impairment, lack of coordination, and death. Naturally the dose makes the poison here; although many people would rather avoid the 'mild' symptoms as well.

      The estimated lethal dose (obviously, nobody can really test this legally) of organic mercuric compounds, such as ethyl mercuric chloride, is 20 milligrams (0.000705479 oz.). For the average adult weighing 72 kilograms (157 lbs) the lethal dose is 1,440 milligrams (0.05 oz.) of mercury. Not something any sane person should want in their body in any amount.

      The natural reaction upon learning this information is to ask how much mercury is actually in thimerosal and how much is actually being injected with vaccines. Checking the Material Safety Data Sheet (MSDS) for thimerosal tells us that the compound is 49.55% mercury by weight, a little bit less than half. Finding how much thimerosal is in a vaccine shot is a rather difficult question to answer as it happens. Just by browsing the Center for Disease Control and the Food and Drug Administration websites I found answers ranging from less than 1 microgram all the way up to 125 micrograms. Other sources claim amounts around 300 micrograms; some vaccine critics claim as much as 900 micrograms. My personal opinion is that more mercury is bad; I would just as soon avoid any amount of it at all. However, the purpose of this post is not to recommend or discourage the use of vaccines; only to inform on what thimerosal is and to try and discourage some bad science.

      Finally, we are ready to answer our questions from earlier. What is thimerosal? A compound made out of thiosalicylic acid and ethylmercuric chloride. What is it for? As a preservative in vaccines. Does it contain mercury? Yes, in the organic form of ethylmercuric chloride. Is it dangerous? Yes. Am I an ignorant idiot? We do not know. Perhaps that is a discussion for another time.

      Hopefully I have given you, the reader, a bit more knowledge on the subject. Thimerosal is indeed not mercury. However it does contain mercury and, most importantly, breaks down into that same compound in the human body. Perhaps the original image is correct: knowing a few basic chemistry concepts before commenting on them is a good idea. I would like to add that it is a good idea to discuss differences of opinion with well thought debate rather than a single sentence captioning a picture. Otherwise, you too run the risk of looking like an ignorant idiot.

WORKS CITED

“Thimerosal.” Hawley's Condensed Chemical Dictionary. 12^Th ed. 1993. Print.

“Ethylmercuric Chloride.” Hawley's Condensed Chemical Dictionary. 12^Th ed. 1993. Print.

“Thiosalicylic Acid.” Hawley's Condensed Chemical Dictionary. 12^Th ed. 1993. Print.

Emsley, John. The Elements 3^rd ed. New York: Oxford University Press Inc., 1998. Print.

Newton, David E. Chemical Elements: From Carbon to Krypton Vol. 1. Farmington Hills: UXL, an Imprint of Gale. 1999. Print.

Newton, David E. Chemical Elements: From Carbon to Krypton Vol. 2. Farmington Hills: UXL, an Imprint of Gale. 1999. Print.

Brown, Theodore L., Lemay, H. Eugene jr., Burson, Bruce E. Chemistry: The Central Science. 10^Th ed. Upper Saddle River: Peorson Education inc. 2006. Print.

“Ethyl Mercuric Chloride” Sigma-Aldrich. Sigma-Aldrich, n.d. Web. 18 May 2016.

“Thimerosal in Flu Vaccine” CDC. Centers for Disease Control and Prevention, n.d. Web. 18 May 2016.

“Frequently Asked Questions about Thimerosal.” CDC. Centers for Disease Control and Prevention, n.d. Web. 18 May 2016.