Forms of Mercury
Elemental mercury has been used in a wide variety of equipment and consumer products, such as thermometers, blood pressure cuffs, barometers, switches, pressure regulators, and in some types of light bulbs.
Elemental mercury that is not in a closed container will slowly give off vapor and can accumulate in indoor air. For example, a broken fever thermometer that is not properly cleaned up (especially in carpet or on fabric) can leave behind elemental mercury that will give off low levels of vapor for many years. Breathing in low levels of mercury vapor for months to years can be harmful, especially for the developing fetus, infants and children.
Elemental mercury vapor easily moves from the lungs to the bloodstream. Heating elemental mercury speeds up evaporation and can quickly lead to dangerous vapor levels in a very short time and at high levels can be very harmful, even fatal.
On the other hand, eating a small amount of elemental mercury, like the amount in a fever thermometer, is not a serious concern because very little elemental mercury is absorbed through the stomach and intestines. (However, if you do swallow elemental mercury, please contact the poison control center at 1-800-222-1222.)
Methyl mercury easily passes from the stomach and intestines into the bloodstream and then can cause damage to the nervous system, especially when the nervous system is developing in fetuses, infants and children.
When elemental mercury in the air falls onto lakes and streams, certain bacteria chemically combine it with carbon to form methyl mercury. Fish accumulate methyl mercury from their food. Fish that feed on other fish - such as walleye, northern pike, shark and swordfish - have the highest amounts of mercury. Fish that don't eat other fish, for example sunfish and salmon, have low levels of methyl mercury. Older, larger fish also have higher amounts because methyl mercury builds up in fish over time.
Fish provide many health benefits. Fish are an excellent source of low fat protein, omega 3 fatty acids and other nutrients. If you follow MDH’s advice, the methyl mercury in the fish you eat will be safely eliminated between meals. For advice on how to choose which fish to eat and how often, see Fish Consumption Advice from MDH.
Other forms of Mercury
Mercury naturally occurs in the environment in a salt form or in rock, such as cinnabar. Some inorganic mercury compounds were commonly used in the United States as medicine, but most are no longer in use.
Mercury compounds have been used in some products including fungicides, antiseptics or disinfectants. Some traditional medicines, such as skin lighteners or freckle creams, can contain high levels of mercury. All medicines with unknown ingredients should be avoided.