Throughout human history, people have used arsenic, a naturally occurring element, as an alloy, a pigment, and a preservative. It has also been used as a poison. Because it has no odor or taste, can produce a confusing array of symptoms, and is usually very toxic, it has earned the nickname “the king of poisons.”

These days, many scientists are less concerned about intentional arsenic poisoning and more concerned about arsenic that occurs naturally in drinking water. In the early 1990s, a surprising case of arsenic poisoning in Bangladesh brought attention to this problem. Years before, international agencies sought to reduce epidemics of cholera in Bangladesh by drilling deep wells to replace surface-water wells deemed both unsafe and unreliable. Mysterious new illnesses emerged that were linked to the deeper wells. It turned out that these wells were tapping water that was contaminated by arsenic.

Contaminated drinking water has also become an issue of concern in the United States. In certain regions, including parts of New Hampshire, Maine, and Michigan, bedrock contains elevated levels of arsenic. There, arsenic can leach into groundwater through erosion and other natural processes.

Arsenic is a small molecule that can easily get into the body’s cells, interfering with cellular respiration and leading to multiple organ failure and death. Human exposure to arsenic can have both short-term and long-term health effects. Short-term, or acute, effects include nausea, diarrhea, and difficulty swallowing. These can occur within hours of drinking contaminated water. However, acute effects are unlikely to occur from U.S. public water supplies that comply with Environmental Protection Agency (EPA) standards. Of greater concern are long-term, or chronic, effects that occur over many years.

At lower exposures, arsenic interferes with the way cells communicate. Arsenic molecules may bind to hormone receptors and prevent them from responding to normal cell signaling. Because these signals are associated with a number of biological functions, this may contribute to the development of certain diseases, such as diabetes and vascular disease. Long-term arsenic exposure may also be linked with an increase in risk for different types of cancer. The mechanism is still not known, but it appears that arsenic does not act directly on DNA or genes the way many other known carcinogens do. Rather, it may change cells in ways that make them more likely to become cancer cells.

While arsenic levels in U.S. drinking water supplies are lower than those found in other parts of the world, they’re still high enough to raise health concerns. With new techniques to measure small amounts of arsenic in water, scientists can detect its presence with greater accuracy. Fortunately, arsenic can be removed with various types of filters. The key to safety is good testing and good water management.

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