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Arsenic in Drinking Water
Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona

Written by
Jeff Schalau, Agriculture & Natural Resources Agent

Arsenic is the twentieth most abundant element in the earth’s crust and frequently occurs in rock formations of the Southwestern United States (including Arizona). If aquifers are in contact with rocks and minerals containing arsenic, then water pumped from these sources may contain detectable amounts of arsenic. Arsenic remains in the environment over long periods and when it occurs in high concentrations, can be toxic to many life forms. Interestingly enough, arsenic has been shown to be an essential nutrient for many animal species and may be essential to humans (in very small amounts) as well.

Inorganic Arsenic

Under natural conditions, arsenic usually occurs at low levels and is chemically bonded with other elements such as oxygen, chlorine, and sulfur. These are called inorganic arsenic compounds. Inorganic arsenic is the form that can occur in domestic water supplies.

Organic Arsenic

Arsenic found in plants and animals is chemically bonded with carbon and hydrogen. This is called organic arsenic and is usually less harmful to other life forms than inorganic arsenic.

Water Testing

Municipal water suppliers should have their water tested regularly and the resulting mineral content data available to the public upon request. If you obtain domestic water from a well or other untested source, water samples can be collected and analyzed for arsenic content by an environmental testing laboratory for $20.00 to $30.00. Cooperative Extension offices have a list of testing laboratories.

Current Standards

The Environmental Protection Agency (EPA) has set the Maximum Contaminant Level (MCL) for inorganic arsenic in drinking water at 0.05 mg/L (mg/L = parts per million or ppm). Drinking water that meets the current standard is associated with little or no risk and should be considered safe with respect to arsenic. However, this standard is currently under review and the MCL may be decreased in the future.

Human Health

In most cases, the human body can tolerate infrequent ingestion of small amounts of inorganic arsenic (below the MCL). Here, the arsenic would be converted to the organic form and excreted in the urine. Research has shown arsenic’s effects on human health to be variable depending on sex, ethnicity, concentration, and length of exposure. Arsenic poisoning may be acute or chronic. Acute poisoning occurs when high levels (over 60 mg/L) of arsenic are ingested over short periods of time. This is more likely to occur in settings where arsenic has been concentrated by industrial processes or at waste sites. Chronic poisoning occurs when moderate or small amounts of arsenic are ingested over long periods. Chronic poisoning could potentially occur where groundwater containing inorganic arsenic in excess of the MCL is consumed daily for extended periods. Low levels of exposure may cause the following symptoms: gastrointestinal irritation, decreased production of red and white blood cells, abnormal heart rhythm, blood vessel damage, and “pins and needles” sensation in hands and feet. Long term exposure may lead to changes in fingernails and toenails, darkening and/or thickening of the skin and the appearance of small corns or warts on the palms, soles and torso. Arsenic is a known carcinogen and long term ingestion may increase the risk of skin cancer and tumors of the bladder, liver, kidney, and lungs. Direct skin contact may cause redness and swelling at high concentrations.

Human Testing

There are tests available that can measure exposure to high levels of arsenic. Urine is the most reliable test for arsenic exposure. However, arsenic stays within the body only a short time and urine testing must be done directly following exposure. Analysis of hair and fingernails can also measure exposure to high levels of arsenic over the past 6-12 months. These tests can only measure high level exposure and will not predict the likelihood of harmful health effects. Persons exhibiting the previously mentioned symptoms or who are concerned about arsenic exposure, should seek the advice of a medical doctor.

Plant Tolerance

Plants vary widely regarding their tolerance to arsenic. For example, sudan grass can grow in arsenic concentrations as high as 12 ppm while rice can tolerate only 0.05 ppm. Little is know about arsenic poisoning risk associated with crops grown in areas of elevated arsenic concentrations (soil or water).

It is known that arsenic can accumulate in plant root systems. Certain plants may grow normally while accumulating toxic levels of arsenic in the roots. Gardeners may choose to avoid growing root crops such as carrots, beets, potatoes or onions if the area is suspected of containing high levels of arsenic. Furthermore, gardeners wishing to avoid arsenic ingestion altogether should grow flowers and non-edible plants.

Removing Arsenic from Water

The most reliable water treatment processes for arsenic removal are reverse osmosis and distillation. Of the two processes, reverse osmosis devices are less costly, take less time, and use less energy than distillation devices. Reverse osmosis devices can be installed at the point of entry (for the entire household water supply) or for drinking water only. Treating all of the household water will be considerably more expensive than treating drinking water only. Many water treatment companies sell or rent reverse osmosis devices and offer maintainence agreements.
Cooperative Extension is not responsible for plant or human health problems associated with high arsenic levels in plants, soil or water.

For Further Information Contact:

Arizona Department of Environmental Quality 3033 N. Central Ave.
Phoenix, AZ 85012 1–800–234–5677 ext 4536 1–602–207–4536

Agency for Toxic Substances and Disease Registry Division of Toxicology 1600 Clifton Road NE, Mailstop E-29 Atlanta, GA 30333 1–404–639-6000

The University of Arizona is an Equal Opportunity/Affirmative Action Employer. Any products, services, or organizations that are mentioned, shown, or indirectly implied in this publication do not imply endorsement by the University of Arizona.
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Published August 1999
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