Arsenic is the 52nd most abundant element on the earth, averaging 2 parts per million (ppm) of the earth’s crust. Arsenic is classified as a metal by the periodic table of elements. Elemental arsenic is a steel-gray colored mineral with a metallic luster that tarnishes in air to a black oxide. The free elemental form of arsenic is very rare. Arsenic is usually bound up in rocks with other minerals and leaches into water as arsenate (+5 oxidation state or pentavalent arsenic) or arsenite (+3 oxidation state or trivalent arsenic.) Arsenite is more difficult to remove from water because it has no charge in pH neutral water.
Both are known to be potent carcinogens in humans but arsenite or trivalent arsenic (the kind most likely to be found in unchlorinated private wells) it thought to be at least 60 times more toxic than pentavalent arsenic (the kind most likely to be found in chlorinated municipal water.)
Early civilizations in China, Greece and Egypt were familiar with arsenic-containing minerals that were mined along with co- existing native metal ores of lead, gold and copper. The arsenic minerals were used as pigments: yellow (orpiment) and red (realgar). The early Greeks identified metals with gender and called yellow orpiment “arsenikon” to associate it with “arenikos” meaning male. Between 2,000 and 600 BC during the Bronze Age, the Greeks used arsenic compounds to harden copper-tin alloy implements.
Arsenic is widely distributed in drinking water throughout the world. In the United States, it is a problem contaminant in the vast majority of drinking water supples, both in municipal water as well as private wells.
The NRDC analyzed data compiled by the U.S. Environmental Protection Agency on arsenic in drinking water in 25 states. Their most conservative estimates based on the data indicate that more than 34 million Americans drink tap water supplied by systems containing average levels of arsenic that pose unacceptable cancer risks.
It is likely that as many as 56 million people in those 25 states have been drinking water with arsenic at unsafe levels -- and that's just the 25 states that reported arsenic information to the EPA.
According to a 1999 study by the National Academy of Sciences, arsenic in drinking water causes kidney, bladder, lung and skin cancer, and may cause prostate and liver cancer. It also appears to make certain cancers more aggressive. The study also found that arsenic harms the central and peripheral nervous systems, as well as heart and blood vessels, and causes serious skin problems. It also may cause birth defects and reproductive problems.
Arsenic is considered an “accumulative enabler” because it makes people more likely to become ill from various cancers, diabetes, and high blood pressure. It may cause diseases related to the cardiovascular, pulmonary, immunological, neurological and endocrine systems within the body.
The table below shows the lifetime risks of dying of cancer from arsenic in tap water, based on the National Academy of Sciences' 1999 risk estimates (see our report for details on how we calculated total cancer risk).
The table below shows the lifetime risks of dying of cancer from arsenic
in tap water, based on the National Academy of Science
Arsenic Level in Tap Water (in parts per billion, or