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What are heavy metals: mercury and arsenic?

Mercury, arsenic, and lead are found naturally in the earth, but just because they’re natural chemical elements doesn’t mean they’re harmless. They are heavy metals with a long history of industrial and personal use—and just as long of a history of harming human health.

How am I exposed?


  • Mercury is in our air from the combustion of diesel, jet fuel, and heating oil. It deposits on land and water, then concentrates in the food chain.
  • Mercury is also emitted by coal-burning power plants, and by manufacturers, oil refineries, medical waste disposal facilities, dental offices, and cremation facilities.
  • When mercury gets into water, bacteria convert it to toxic methylmercury, which builds up in fish. When we eat fish that contain mercury, it tags along and settles in our bodies.
  • Mercury is in many consumer products, including: fluorescent light bulbs, electrical fixtures, auto switches, thermostats, medical equipment, and dental amalgam fillings. Mercury is also used in thermometers, although this use in many areas is being phased out in favor of non-mercury digital thermometers.


  • Until 2002, arsenic compounds were used to treat wood to prevent rot. The arsenic leaches out into soil and rubs off the wood on to people or animals.
  • Arsenic is also in the soil from smelters and some pesticides.
  • Arsenic compounds are still used to make special glass, semi-conductors (gallium arsenide), some paints, dyes, metals, soaps, and drugs.
  • Seafood can contain arsenic (although in a less-toxic form), as does drinking water in some locations.

Why should I be concerned?

Mercury exacts its most devastating toll on the developing brain.

  • Children with above-average mercury exposures have learning difficulties.
  • Recent studies also suggest that arsenic can harm the developing brain.

Many other health effects of these metals are well-known.

Metal Common Health Effects (some occur only at high exposure levels)
Mercury blindness and deafness

brain damage

digestive problems

kidney damage

lack of coordination

mental retardation

Arsenic breathing problems

death if exposed to high levels

decreased intelligence

known human carcinogen: lung and skin cancer

nausea, diarrhea, vomiting

peripheral nervous system problems

What can government and industry do?

Only relatively recently have people begun to take action to curtail the use of mercury and arsenic.  Local advocacy and legislation have made a difference in reducing continued pollution with these metals.

Mercury – A number of states, including Washington and Oregon, have passed legislation to address mercury use in products such as thermometers and thermostats. The Washington State Department of Ecology credits the legislation and its action plan with reducing mercury emissions by 14,000 pounds between 2003 and 2008. Major sources such as coal burning continue.

King County has had tremendous success in reducing mercury pollution from dental offices by cracking down on dentists to keep mercury out of their wastewater. Mercury in dental offices comes from amalgam fillings, which are about half mercury by weight. State law requires dentists to use devices called separators, which remove mercury from wastewater, but compliance in the past has been poor. By conducting inspections and threatening fines, King County was able to achieve 97% compliance and a 50% reduction in mercury in wastewater between 2000 and 2003 (King County 2005).

Arsenic – Arsenic-treated wood was extremely widely used before manufacturers agreed to phase it out.

The following actions would reduce ongoing exposure to these toxic heavy metals:

  • Mercury and arsenic should be phased out of products.
  • Coal burning should be replaced with conservation and cleaner sources of fuel for energy production. In the meantime, existing coal-fired power plants should be required to install the best technology to limit mercury emissions.
  • Contaminated sites should be cleaned up promptly and fully. Where a large geographic area is contaminated, state government should take measures to ensure facilities such as schools and day care centers are not sited on contaminated soil.
  • Solid-waste and medical-waste incinerators should be shut down and replaced with waste and toxicity reduction, reuse, recycling, and composting programs.
  • Health care facilities, including hospitals and dental offices, should phase out mercury-containing products in favor of safer alternatives.
  • Manufacturers of compact fluorescent light bulbs should find alternatives to the mercury contained in those bulbs.
  • Government agencies should expand programs to remove, collect, and safely store mercury from thermostats, thermometers, and switches.

How can I reduce my exposure?

We come into contact with lead, mercury, and arsenic in many ways, but there are some steps we can take to reduce our exposure.

Remove treated wood. Remove wood treated with the preservatives CCA or ACZA, which contain arsenic. If removing arsenic-treated wood is not an option, you can paint or seal the wood to reduce leaching and contact exposure. Choose semi-transparent deck stains for deck surfaces and play structures, and latex paint for fences, tables, and other furniture. Reapply the coating when it shows signs of deterioration.

Choose fish wisely. Avoid fish high in mercury, such as king mackerel, tilefish, swordfish, orange roughy, and marlin. Limit consumption of tuna, especially steaks and canned ‘white’ albacore. Lower-mercury choices include wild salmon, sardines, anchovies, Atlantic herring, Dungeness crab, Pacific cod, Alaskan black cod, farmed striped bass, farmed catfish, clams, mussels, and Pacific oysters.

If you eat sport-caught fish, check for specific guidance on mercury levels in Washington water bodies or coastal waters. Fish and shellfish advisories are available from the Washington State Department of Health

Limiting mercury intake from fish is especially important for young children and women who are pregnant, nursing, or of child-bearing age.

You can find additional guidance on fish choices at the following websites:

Environmental Defense’s Oceans Alive: Best and Worst Seafood

Environmental Working Group: Mercury in Seafood (includes Tuna Calculator):

Fish are an excellent source of nutrients, including protein, omega-3 fatty acids, and vitamin D, and we encourage people to continue eating fish following these precautions.

Make sure medicines are free of toxic metals. Some home remedies, as well as drugs and cosmetics, can contain these metals. Look at ingredient lists, talk to your doctor, and avoid folk remedies and other medicines that contain arsenic or mercury.

Be cautious with mercury-containing products. When possible, choose products without mercury, such as digital thermostats and thermometers. Be careful not to break fluorescent light bulbs, mercury thermometers, or other household items containing liquid mercury. These products release harmful mercury vapors when broken. If they do break, use appropriate clean-up methods (see the EPA’s web site).

Check paints and art supplies. Avoid paints containing mercury compounds, which are still found in some paints as pigments. Information on some products containing mercury ingredients is available from the Household Products Database. Otherwise, ask the manufacturer.

Skip herbicides with arsenic. Avoid arsenic-containing herbicides, which have ingredients listed as monosodium methanearsonate (MSMA), calcium acid methanearsonate, or cacodylic acid.

Consider composite fillings. Consider choosing composite dental fillings rather than mercury-containing amalgam fillings.