It’s a common question – particularly during flu season, since multi-dose vials of the flu vaccine contain thimerosal, or methyl mercury: “What is the difference between methyl mercury and ethyl mercury? Are they toxic or dangerous for humans and environment?” To answer this question, we’ll describe the structure and the properties of the two mercury-based compounds, focusing on their possible sources and their effects on human health.
What is Mercury?
Mercury (Hg) is a metallic element present in nature; its main characteristic is that it is the only metal which is liquid, not solid at room temperature.
Hg toxicity, such as in mercury in dental fillings is well known and documented. In recent years mercury has been used less than in the past, and it has been replaced in some applications by other metals and chemical compounds.
Despite this, however, mercury is still present in the environment from man-made sources as well as natural ones. Hg can be a contaminant in coal or in industrial residues – they they are burnt, Hg is released into the atmosphere and it can be successively transported to the water, soil, and other parts of the physical environment.
Mercury occurs in the metallic form, but that is not its only configuration; it can also chemically bond to other elements, to form more complex molecules. When Hg is bonded to carbon atoms, we have what is normally called organic mercury.
Two of the most common organic mercury compounds are methylmercury (MeHg) and ethylmercury (EtHg), where Hg forms a bond with a methyl (CH3) or ethyl (CH3CH2) group, respectively; their formulas are shown in the picture on the side. X– is an anion, or an ion with more electrons than protons, which compensates for the positive charge in both species.
Methylmercury and Bioaccumulation
MeHg can be formed by the reaction of metallic mercury with organic molecules or fragments of them; bacteria present in water, for instance, can favour this conversion.
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