Arsenic in Drinking Water
Extension, College of Agriculture & Life Sciences, The University of Arizona
Jeff Schalau, Agriculture & Natural Resources Agent
Arsenic is the twentieth most abundant element in the earths
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.
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.
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.
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.
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.
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 arsenics 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.
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.
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 18002345677 ext 4536 16022074536
Agency for Toxic Substances and Disease Registry Division of Toxicology
1600 Clifton Road NE, Mailstop E-29 Atlanta, GA 30333 1404639-6000
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.
Document located http://cals.arizona.edu/pubs/water/az1112.html
Published August 1999
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