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Facts about arsenic

Arsenic is a naturally occurring substance. It occurs in several forms, often in compounds with other chemical elements. Arsenic and all of its compounds are poisonous but the toxicity varies. For example, inorganic arsenic - arsenic combined with oxygen, chlorine or sulfur - is thought to be the most toxic, while most organic forms of arsenic are relatively less toxic.

In its solid state arsenic appears as a silver-gray, brittle semi-metal that tarnishes in the air. It is about the 52nd most common chemical element on the earth.

Natural background levels of arsenic in Washington

The Washington State Department of Ecology and the United States Geological Survey have determined that the natural background level of arsenic in Puget Sound soil is 7 ppm (parts per million). The state average is also 7 ppm, and levels are 9 ppm and 5 ppm in the Spokane Basin and Clark County respectively.

For more information on the study that determined these background levels consult the Ecology publication: "Natural Background Soils Metals Concentrations in Washington State" Publication #94-115.

Human uses for arsenic

Arsenic has been known since ancient times, though probably in compound form rather than in its pure state. It is used in combination with other materials in pigments, poison gases and insecticides (such as Paris Green, calcium arsenate and lead arsenate) and is well known from former use as a rat poison.

Arsenic has a long history of medical applications; before penicillin was developed an arsenic compound was used to treat syphilis and yaws.

Arsenic is used in ammunition manufacturing because it helps to create harder and rounder bullets. Arsenic is used in small quantities in semi-conductor manufacturing. It is used as a preservative in tanning and taxidermy, as well as on the exterior of wood such as deck and playground materials.

In short, though arsenic is an extremely poisonous substance it has numerous industrial applications and has been used widely for many years.

Another potential source of arsenic in our environment is as a byproduct of copper smelting - arsenic occurs naturally in copper ores. During copper processing, arsenic passes from the solid state into the gaseous state and leaves the smelter through the smokestacks in the form of toxic dusts.

Tacoma Smelter Plume

In western Washington a source of arsenic contamination was the Asarco copper smelting plant, which operated from about 1890 to 1986. It was located at Ruston, near Tacoma. The area immediately surrounding the Ruston plant is an EPA superfund site because of the serious arsenic and lead contamination from the smelter. However, arsenic and lead smokestack releases were likely carried by wind and spread over wide parts of King County and surrounding regions. The heavy metals settled into the soils. Public Health - Seattle & King County and the state Department of Ecology are working together to determine the extent of arsenic and lead contamination in King County.

More information about the Tacoma Smelter Plume project

How arsenic is regulated in Washington state

Washington law requires that arsenic-contaminated soils be cleaned up to specific levels. The state Department of Ecology regulates soil contamination under the Model Toxics Control Act (MTCA). Learn more about MCTA visit the Ecology website.

Arsenic clean-up levels, which are measured in ppm (parts-per-million), vary according to the type of contaminated property. The strictest clean-up standard is known as "Method A." The Method A clean-up level for arsenic is:

Residential: 20 ppm
Industrial: 200 ppm

Testing your soil for arsenic

You are not required to test soils, but may be interested in knowing if their soils are contaminated. If you wish to test your soils, do a search online for "testing laboratories".

Guidelines for testing your soils

  • Ask if the laboratory is certified by the Washington State Department of Ecology.
  • Get approved soil collection jars from the laboratory.
  • Work with the lab staff on which areas of your property to sample.
  • Wear gloves while sampling.
  • Base your sample method on the information you want. For example, if you only want to know about arsenic levels in your garden, only collect samples in the garden plot and to the depth of the lowest roots.
  • If your soils show arsenic levels above background follow the guidelines below to minimize your exposure.

Arsenic and your health

Inorganic arsenic is extremely toxic. Produced as a byproduct of industrial production such as copper smelting, it can cause both acute and long-term health effects. One of the problems with arsenic exposure is that many of the symptoms may result from causes other than arsenic - so a person who has been exposed may not suspect arsenic. Therefore, if you believe you may potentially be exposed to arsenic in the soil it is important to take steps to reduce your exposure to this toxic substance.

Since arsenic in soils can be a health hazard, gardeners and others who work or play in contaminated soils should take precautions to limit and reduce the amount of soil they swallow or breathe.

  • Acute (short-term) arsenic poisoning may cause nausea, vomiting, diarrhea, weakness, loss of appetite, shaking, cough and headache. Chronic (long-term) exposure may lead to a variety of symptoms including skin pigmentation, numbness, cardiovascular disease, diabetes, and vascular disease. Arsenic is also known to cause a variety of cancers including skin cancer (non-melanoma type), kidney, bladder, lung, prostate and liver cancer.
  • Doctors may prescribe arsenic tests that analyze arsenic levels in urine, blood, and hair. Tests may either test for the different types of arsenic or just the "total arsenic" in the body. Arsenic tests may be difficult to interpret because health experts are not sure what "normal" levels of arsenic in the body are. Furthermore, different people may react to arsenic in different ways - some people are more susceptible to arsenic than others. Since we do not know who is most likely to be sensitive to arsenic, it is prudent for anyone who thinks they might be exposed to arsenic in the soil to follow the guidelines for reducing exposure to arsenic.

Gardening around arsenic: Best practices

The goal of these suggestions is to reduce the amount of contaminated soil that you unintentionally swallow or breathe in while gardening or working around your home. Follow these guidelines to reduce your exposure:

  • Wear gloves while gardening.
  • Wash all vegetables carefully and peel vegetables where possible. Be sure to remove particles of soil on the food item. Wash inside crevices (e.g. broccoli and cauliflower).
  • Though there is evidence that vegetables and fruits may take up small amounts of arsenic into their roots or leaves, a more serious problem could come from eating fruits and vegetables that have bits of contaminated soils stuck to them.
  • Add clean soils or soil supplements such as compost or mulch to your existing garden. Clean soils are ones that are known to be contaminant-free. If you are unclear whether your new soils are clean you may consider testing.
  • Consider establishing a raised bed using clean soils.
  • Do not garden in soils with arsenic in excess of 20 ppm (parts per million). Bring in clean soils and build a raised bed instead.
  • Dampen soils with water before you garden to limit the amount of dust you inhale.
  • Follow guidelines below to reduce your exposure to contaminated soils.

Guidelines for reducing your exposure to contaminated soils

Arsenic does not decompose, biodegrade or move downward through soils and will remain permanently in the top layers of soil unless it is removed. Therefore, if you suspect your soils are contaminated you should take the following exposure reduction measures:

  • Keep children from playing in contaminated dirt. The most likely way to become exposed to arsenic is from ingesting (eating) dirt; toddlers and young children tend to play in dirt and then put their hands/toys/other items in their mouths. Some children (over two years old) and adults eat dirt on purpose.
  • Frequently wash toys, pacifiers and other items that go into children's mouths.
  • Cover bare soils with grass or other material.
  • Wash hands and face thoroughly after working or playing in the soil, especially before eating. Do not eat, chew or smoke in areas with contaminated soil.
  • Wash garden vegetables and fruits carefully to remove all soil particles. Take care to get dirt out of the crevices of vegetables such as broccoli.
  • Remove work and play shoes before entering the house.
  • Wash soil-laden clothes separately from other clothes.
  • Damp-mop floors and wipe down counters, tables and window ledges regularly. Do not use a vacuum as a method to keep contaminated dust under control. Vacuum cleaners DO NOT reduce dust and tend to stir it up into your breathing zone. If you prefer to use a vacuum cleaner, use one with a HEPA (high efficiency particulate air) filter.
  • Prevent pets from tracking contaminated soils into your home. Keep them out of areas with exposed dirt.
  • Consider wearing a mask if you spend time in dusty environments.

Additional resources