N

Nitrate-Nitrite

CASRN 7440-38-2

Physical Properties

Nitrate is a compound of one nitrogen atom bound to three oxygen atoms; nitrite is a compound of a nitrogen atom joined to two oxygen atoms. In nature, nitrates are readily converted to nitrites and vice versa. Both are anions (ions with a negative charge). They tend to associate with cations (ions with a positive charge), to achieve a neutral charge. Microbial action in soil or water decomposes wastes containing organic nitrogen into ammonia, which is oxidized to nitrite and nitrate.

Uses

Nitrates are used primarily to make fertilizer, but also to make glass and explosives. These compounds are used in various chemical production and separation processes. Nitrites are manufactured mainly as a food preservative. Both nitrates and nitrites are used extensively to enhance the color and extend the shelf life of processed meats.

Sources of Exposure in Iowa

The main source of exposure for nitrites is food, especially processed or preserved meats. Although vegetables are seldom a source of acute toxicity, they account for more than 70% of the nitrates in a typical human diet. Cauliflower, spinach, collard greens, broccoli, and root vegetables have naturally greater nitrate content than other plant foods. One possible source of exposure to nitrates is shallow domestic wells installed in areas where nitrogen-base fertilizers are widely used. Since Iowa is an agricultural state, drinking water is a potential source of nitrate exposure.

Health Effects from Large Acute Exposures

Nitrates themselves are relatively nontoxic. When swallowed, they are converted to nitrites that can react with hemoglobin in the blood, oxidizing its divalent iron to the trivalent form and creating methemoglobin. Methemoglobin cannot bind oxygen, which decreases the capacity of the blood to transport oxygen from the lungs to body tissues. This is a condition known as methemoglobinemia. Infants younger than 4 months of age are more susceptible to developing methemoglobinemia, because the pH of their gut is normally higher than in older children and adults. The higher pH enhances the conversion of ingested nitrate to the more potent nitrite. Normal individuals have low levels (0.5 to 2%) of methemoglobin in their blood. When this level increases to 10%, the skin and lips take on a bluish tinge (cyanosis), and levels above 25% can cause weakness and a rapid pulse. At levels above 50 to 60%, a person may lose consciousness, go into a coma, and die. Levels of methemoglobin above 50% are extremely rare. Some children and adults who ate food or drank fluids that contained unusually high levels of nitrite have experienced decreases in blood pressure, increased heart rate, headaches, abdominal cramps, and vomiting.

Cases of methemoglobinemia are required to be reported to the Iowa Department of Public Health (IDPH).  Since 2010 there has been between one and six cases of methemoglobinemia reported to IDPH each year – none of these reported cases were infants and none were associated with exposure to elevated nitrate or nitrites in drinking water.  There has not been a case of infant methemoglobinemia in Iowa caused by elevated nitrates or nitrates within drinking water for over 30 years.

Health Effects from Smaller, Chronic Exposures

Long-term exposure to lower levels of nitrates and nitrites can cause diuresis (increased urine, and starchy deposits and hemorrhaging of the spleen). There is limited evidence that nitrite may cause some cancers of the gastrointestinal tract in humans. Cancer could result from reactions between nitrite and certain other chemicals that may produce cancer-causing substances.  The International Agency for Research on Cancer (IARC) determined that there is inadequate evidence for the carcinogenicity of nitrate in food or drinking water and limited evidence for the carcinogenicity of nitrite in food (based on association with increased incidence of stomach cancer).

Protection from Exposure

All regulated public water supplies must be tested for the presence of nitrate and nitrite. Regulated public water supplies must maintain levels of nitrate in drinking water below 10 parts per million (ppm) and levels of nitrite below 1 ppm. Health studies indicate that exposure to nitrate and nitrite below these levels will not cause adverse health effects, even in children. Some shallow private wells may contain elevated levels of nitrates due to agricultural runoff; therefore, water from these wells should be tested for nitrate and nitrite. Bottled water should be used for mixing infant formula if a shallow private well is the source of drinking water. Ion exchange or reverse osmosis may be used to reduce nitrate and nitrite levels in drinking water.

Nitrogen Oxides

CASRN 10102-43-9, 10102-44-0

Physical Properties

Nitric oxide or nitrogen oxide (NO) and nitrogen dioxide (NO2) both are nonflammable and colorless to brown at room temperature. Nitric oxide is a sharp sweet-smelling gas at room temperature, whereas nitrogen dioxide has a strong, harsh odor and is a liquid at room temperature, becoming a reddish-brown gas above 70°F. These two compounds can be found in both outdoor and indoor air.

Uses

Nitrogen oxides are used in the production of nitric acid, lacquers, dyes, and other chemicals. Nitrogen oxides are also used in rocket fuels, nitration of organic chemicals, and the manufacture of explosives.

Source of Exposure in Iowa

The general population is primarily exposed to nitrogen oxides by breathing in air. People who live near combustion sources such as coal burning power plants or areas with heavy motor vehicle use may be exposed to higher levels of nitrogen oxides. Households that burn a lot of wood or use kerosene heaters and gas stoves tend to have higher levels of nitrogen oxides in them when compared to houses without these appliances. Nitric oxide and nitrogen dioxide are found in tobacco smoke, so people who smoke or breathe in second-hand smoke may be exposed to nitrogen oxides. Workers employed in facilities that produce nitric acid or certain explosives like dynamite and trinitrotoluene (TNT), as well as workers involved in the welding of metals may breathe in nitrogen oxides during their work.

Health Effects from Acute or Large Exposures

Breathing high levels of nitrogen oxides can cause rapid burning, spasms, and swelling of tissues in the throat and upper respiratory tract. Exposure to high levels of nitrogen oxides can cause reduced oxygenation of body tissues, a build-up of fluid in your lungs, and death.

Health Effects from Smaller, Chronic Exposures

Low levels of nitrogen oxides in the air can irritate your eyes, nose, throat, and lungs, possibly causing you to cough and experience shortness of breath, tiredness, and nausea. Nitrogen oxides have not been classified as to their potential to cause cancer.

Protection from Exposure

The U.S Environmental Protection Agency has established a National Ambient Air Quality Standard for nitrogen dioxide of 100 parts per billion (ppb) for a one-hour exposure. Maintaining low indoor levels of nitrogen oxides can be made by proper maintenance of furnaces, stoves, heaters, and chimneys. Keeping gas appliances properly adjusted will limit the exposure to nitrogen oxides. Consider purchasing a vented space heater when replacing an unvented one. Use proper fuel in kerosene space heaters. Install and use an exhaust fan vented to outdoors over gas stoves. Open flues when fireplaces are in use. Choose properly sized wood stoves that are certified to meet EPA emission standards. Make certain that doors on all wood stoves fit tightly. Have a trained professional inspect, clean, and tune-up central heating system (furnaces, flues, and chimneys) annually. Repair any leaks promptly. Do not idle the car inside a garage. Farm families should not allow children to play near silos that contain silage.