Arsenic is a toxic chemical element that is naturally found in the Earth’s crust in soil, rocks and minerals. The levels of arsenic found in drinking water systems and private water supplies across the United States vary widely.
Arsenic occurs naturally in the environment and as a by-product of some agricultural and industrial activities. It can enter drinking water through the ground or as run-off into surface water sources.
Some people who drink water containing arsenic in excess of the U.S. Environmental Protection Agency’s (EPA) standard over many years could experience skin damage or problems with their circulatory system, and may have an increased risk of developing cancer.
In 2001, EPA reduced the regulatory drinking water standard, called the Maximum Contaminant Level, from 50 micrograms per liter (ug/L) to 10 micrograms per liter (ug/L) based on bladder and lung cancer risks.
Nitrate and nitrite are nitrogen-oxygen molecules that can combine with various organic and inorganic compounds. Nitrate is the form commonly found in water, often in areas where nitrogen-based fertilizers are used. Vegetables, food and meat are the major sources of nitrate exposure. The greatest use of nitrates is as a fertilizer.
Nitrate and nitrite originate in drinking water from nitrate-containing fertilizers, sewage and septic tanks, and decaying natural material such as animal waste. Nitrate is very soluble in water, can easily migrate, and does not bind to soils. Nitrates and nitrites are likely to remain in water until consumed by plants or other organisms.
The U.S. Environmental Protection Agency (EPA) set levels of 10 milligrams per liter (mg /L) for total nitrate and nitrite, 10 mg /L nitrate, and 1 mg /L nitrite as drinking water standards. Infants under the age of 6 months who drink water containing more than 1 mg /L nitrite, or 10 mg /L nitrate, could become seriously ill and, if untreated, may die. In the body, nitrate converts to nitrite. Nitrite interferes with the oxygen-carrying capacity of blood. Symptoms, such as shortness of breath and blueness of the skin, can occur rapidly over a period of days.
Most public water systems use a disinfectant to kill viruses and bacteria that can cause illness, such as gastrointestinal disorders or diarrhea. Chlorine is the most commonly used disinfectant, sometimes used in combination with other disinfectants, such as ozone, chloramine, chlorine dioxide, and ultraviolet light.
Disinfection byproducts (DBPs) are a family of chemicals formed when these disinfectants react with naturally occurring organic matter and other substances in the source water. The disinfection byproducts included in Tracking data are the regulated haloacetic acids, known as HAA5 (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid) and the trihalomethanes, known as THMs (chloroform, bromodichloromethane, bromochloromethane, and bromoform).
The levels of disinfection byproducts depend upon the nature of the source water, the type of treatment to remove particles and organic matter, and type and concentration of disinfection.
The risk of illness from disinfection byproducts is much lower than the risk of illness from drinking most surface water and some groundwater sources that have not been disinfected. The major health risks from DBPs result from long-term exposures.
Surface water sources such as reservoirs and streams are more likely to have higher disinfection by-product levels than disinfected groundwater sources. If you get your drinking water from a private drinking water well, disinfection byproducts are unlikely to be present in the water.
EPA requires that water systems improve their treatment methods to keep the formation of disinfection byproducts to a minimum. The aim is to have a treatment method that uses enough disinfectant to protect people from waterborne disease while at the same time producing as few DBPs as possible.