Most people have mercury in their blood – is it harmful?

A new report from the CDC shows that most people have measurable levels of mercury in their blood and urine. What are the dangers?

chemistryA new report from the US Centers for Disease Control and Prevention (CDC), reveals that scientists have found measurable levels of mercury in most of the 8500 persons who recently took part in a national health and nutrition survey. In the comprehensive research program scientists analyzed blood and urine samples in order to measure the total mercury content of the large number of participants.

The report from the CDC concluded that:

* Most of the participants had a measurable amount of mercury in their bodies.

* Mercury levels tended to increase with age.

* All blood mercury levels were less than 33 µg/L.

* Blood and urine mercury in the US population were similar to levels seen in other developed countries.

Although the mercury levels caused by dental fillings are not thought to be harmful to the human body, the CDC scientists admitted that determining what constitutes “safe” levels is still a question that needs to be researched more.

Determining safe levels of mercury exposure is of utmost importance since even small amounts of blood mercury content is suspected of causing neurodevelopmental effects in children. These effects include mental retardation, ADHD, autism and other neurological disorders.

The toxicity of mercury

There are different kinds of mercury, which are not all thought to be equally harmful to humans. Elemental mercury is found in many of the goods that we are exposed to every day such as thermometers, some light bulbs and dental amalgams. Elemental mercury is also used in industry and mining where it gets into the air when coal and other fossil fuels are burned. When we breathe in air that contains mercury vapour, elemental mercury enters our bodies.

In the body, elemental mercury usually forms inorganic compounds. Elemental mercury has not been proven harmful in small doses. However, very high levels of vapour concentrations can lead to severe lung damage, and exposure to low vapour concentrations over a long period of time can cause neurological disturbances, memory problems, skin rash, and kidney abnormalities.

Methyl mercury – the real cause for concern

The kind of mercury which causes the most concern is the kind which is called methyl mercury. Methyl mercury is formed, when microorganism in the marine environment “eat” and metabolize elemental mercury. These microorganisms and their methyl mercury content are then eaten by larger fish and other organisms and the methyl mercury is thus accumulated as it travels up through the food chain. At the top of the food chain we, the humans, are exposed to the methyl mercury when we eat fish or shellfish. Methyl mercury is especially harmful for pregnant women, because of its ability to pass through the placenta into the developing fetus where it might cause neurological damage.

Mercury from dental fillings is thus not as harmful to humans while it is in the mouth (elemental mercury) as it becomes when it ends up in the environment and is transformed into methyl mercury. As neurological defects in children continue to be on the increase however, scientists continue to study the toxicity of chemicals such as mercury and to question the existing “safe” levels of exposure to these.

“National Report on Human Exposure to Environmental Chemicals.”
CDC, National Center for Environmental Health, 2009.
US Department of Health and Human Services.