Ethyl Mercury vs. Methyl Mercury: What’s The Difference?


Home / Ethyl Mercury vs. Methyl Mercury: What’s The Difference?

Mercury can accumulate in fish. Photo by Doomster photostream.

MeHg cannot be easily eliminated from living organisms; therefore, it accumulates over time. Such bioaccumulation, or accumulation in the body systems, is particularly high in aquatic species higher up in the food chain, such as fish; this can have very negative effects on the life of these species. Moreover, if we eat the fish, mercury can also accumulate in our bodies, affecting our health as well.

According to the Environment Protection Agency (EPA), high MeHg levels in the human body can cause poisoning and damage the nervous system; moreover, in the case of pregnant women, the babies could have serious nervous problems and be born with disabilities.

The Reference Dose for Chronic Oral Exposure (RfD) for humans is 0.0001 milligrams per day per kilogram of weight. For instance, a safe dose for a person who weighs 70 kg, or a little over 154 pounds, would be 0.007 mg per day.


The main source of ethylmercury, or EtHg, is thiomersal (or thimerosal), an organic compound which is used as a preservative in vaccines, and which degrades to give EtHg.

EtHg does not bioaccumulate, or build up in the body; from this point of view, therefore, it is less dangerous than MeHg.

In recent years, however, there has been a lot of controversy about the possible effects of ethylmercury on the health on children who were injected with thiomersal-containing vaccines. It has been suggested that EtHg exposure may cause neurological problems and autism; the studies on this topic, however, were inconclusive. Some investigations showed a correlation between these vaccinations and the development of autism; in other cases, however, no definitive link was found.

Mercury in Vaccines

Today, thiomersal has been almost completely eliminated from vaccines, with children’s flu vaccine being a notable exception; other preservatives are used instead. A report issued by the US Food and Drug Administration covers this issue in detail.

Up to date, no specific exposure limit has been established for EtHg; for this reason, often the value considered is the same as that of MeHg.


Environmental Protection Agency. Mercury: Human Exposure. (2012). Accessed February 4, 2013.

Environmental Protection Agency. Organic Mercury: TEACH Medical Summit. (2007). Accessed February 4, 2013.

US Food and Drug Administration. Thimerosal in vaccines. (2012). Accessed February 4, 2013.

Environmental Protection Agency. Methylmercury. Iris. (2012). Accessed February 4, 2013.

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