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Description

Nitrates are a normal part of the diet, but can cause problems at excessive levels, particularly for infants.

Nitrates can build up in soil and groundwater, and they are taken up by plants as they grow. The usual sources of nitrate contamination are human sewage, animal manure (especially from feedlots), nitric oxides, and in particular nitrogen-based fertilizers, of which potassium nitrate and ammonium nitrate are the most common. The dangers of nitrate are related to their formation of nitrites in the body.

Both nitrates and nitrites are used as food additives in cured and processed meats and some smoked fish (see How Common Exposures Occur, below). They give cured meats, like bacon and hot dogs, a pink color. They may also protect against botulism. (But there are safer alternatives.)

Infants under four months of age that drink water or eat food contaminated with high levels of nitrates or nitrites are particularly at risk for health effects. For all children, nitrites are generally worrisome because they can interact with other substances in the body to form potential cancer-causing chemical called nitrosamines.

Health Effects

Immediate Health Effects

If SWALLOWED, nitrite, nitrate is Not Available
If ABSORBED THROUGH SKIN, nitrite, nitrate is Not Available
If INHALED (SNIFFED OR BREATHED IN), nitrite, nitrate is Not Available

Longterm or Delayed Health Effects

This chemical is considered an Unclassifiable Carcinogen by the World Health Organization, the U.S. Environmental Protection Agency, or another agency.

Other

Rarely, a baby may develop methemoglobinemia, or blue baby syndrome. This can occur if water (particularly well water) containing high levels of nitrates is used to prepare infant formula, and very rarely if infants eat nitrate-rich spinach which has broken down into nitrite during storage. Nitrites can cause blood to lose its ability to transfer oxygen from the lungs to tissues, which rapidly can result in coma and death if not recognized and treated appropriately. The first symptoms are a blue-gray skin color, shortness of breath, rapid pulse, and irritability or lethargy. Infants with infections or with bacterially-contaminated drinking water are most at risk.
A number of studies consistently find an association between frequent consumption of cured meat by pregnant women and brain tumors in children. The evidence is suggestive but not conclusive. Some studies suggest a link between meets and childhood leukemia, either from parental occupation in meat handling or consumption of cured meats by pregnant women or children. The U.S. National Academy of Sciences does not consider that there is adequate evidence to support an association between nitrates or nitrites in drinking water and increased cancer rates.
Swallowing nitrate-based fertilizers can cause severe abdominal pain, bloody stools and urine, weakness, and collapse. Eight to fifteen grams of sodium or potassium nitrate is fatal for adults.
Frequent urination and hemorrhaging of the spleen from chronic exposures.
Some, but not all, epidemiological studies have found a link between nitrate-contaminated drinking water and stomach cancer.
Nitrate or nitrite exposure at high doses during pregnancy may adversely effect the unborn child. Evidence in humans is considered suggestive by some, but inadequate by others.

How Exposures Occur

From Drinking Water

Nitrate levels are regulated in public water supplies. But drinking water coming from private wells, particularly in agricultural areas can be contaminated with higher levels of nitrates, primarily from runoff of fertilizer, animal manure, and human sewage from septic tanks. Drinking water typically only contributes 2-3% of average total daily intake of nitrate and nitrite; however, in cases of well water contamination, up to 69% of daily nitrate exposure can come from water.

If you draw your water from a private well, water testing is advised, particularly if you have a baby or are pregnant (see Detection, below).

From Vegetables

For most people, the highest daily nitrate exposure is through its natural occurrence in vegetables, particularly beets, celery, lettuce, parsley, broccoli, carrots, radishes, rhubarb, spinach, melons and turnip greens. However, these foods contain ascorbic acid (vitamin C) and other vitamins that protect against nitrate poisoning and against the formation cancer-causing nitrosamines. Eating a diet rich in vegetables and fruits is the best way to reduce your overall cancer risk. Note that, while vegetables do make up about 85% of daily exposure to nitrates, they only make up about 16% of daily exposure to nitrites.

Significant Statistics

Nine percent of residential wells in farming areas contain nitrate levels exceeding the U.S. Public Health Service recommended limit of 10 milligrams of nitrate per liter of water, according to the U.S. Geological Survey.

Holton, Conard. “Nitrate Elimination,” Environmental Health Perspectives, Vol. 104, No. 1 (January 1996).http://ehpnet1.niehs.nih.gov/docs/1996/104-1/innov.html

An estimated 40 percent of the nitrogen applied to fields as fertilizers is converted into nitrates and enters water sources as run-off and leachate.

Wetzlich, Scott. “Water: Better Late Than..., Part II: Nitrates,” Cooperative Extension University of California, Environmental Toxicology Newsletter, Vol. 11, No. 1 (1991).http://ace.orst.edu/cgi-bin/mfs/01/newsletters/n111_91.htm

There were about 2,000 cases of methemoglobinemia in infants reported between 1945 and 1970, with approximately 160 being fatal.

Approximately 700 tons of nitrites are added to the 4 million tons of cured meats (ham, bacon, frankfurters, bologna, and sausage) and cured fish consumed in the United States each year.

Solutions

How to detect nitrite, nitrate

Nitrates and nitrites are regulated under the Safe Drinking Water Act. This law requires that community water systems monitor nitrate and nitrite levels, and make public when levels exceed the set Maximum Contamination Level (MCL). The MCL for nitrates has been set at 10 mg/liter, or 10 parts per million (ppm), and for nitrites at 1 mg/liter, or 1 ppm.

Community water systems are required to produce annual consumer confidence reports and mail them to every water customer.

If your water source is a well, your water is not monitored for contaminants as is required for public water supplies by the Safe Drinking Water Act. Private testing of the water is necessary.

Even if your water comes from a community water system, contaminant levels can vary from house to house. You can have your water tested by sending samples to a certified laboratory.

You can search for water quality reports from your water provider, obtain information on well water testing and find a list of state-certified drinking water laboratories at the U.S. EPA’s Office of Water’s website or call the EPA’s Safe Drinking Water Hotline, 800-426-4791.
Read labels. As a precaution, you can limit or avoid your family’s consumption of packaged meats, such as hot dogs and bacon, that contain sodium nitrite as a preservative.

How to minimize exposure to nitrite, nitrate

If you draw your water from a private well with water that exceeds the permitted level of 10 mg. of nitrates per liter of water (or 1 mg. of nitrites) and if you are pregnant or with an infant, you may want to filter your drinking water, use bottled water for infant formulas, and breastfeed your baby.

Only the following types of water filtration methods have been approved by EPA for removing nitrates: ion exchange, reverse osmosis, or electrodialysis. Water filtration devices with only carbon or activated charcoal filters will not remove nitrates. A database of water filters certified by NSF International and the contaminants they remove from water is on NSF’s website.
Eat a diet high in antioxidants, such as vitamins C (ascorbic acid) and E, which reduce the conversion of nitrates into more toxic nitrites, and stop the breakdown of nitrites into carcinogenic nitrosamines.
Refrigerate your raw greens and vegetables, especially spinach, which is particularly rich in nitrates. Storing vegetables at room temperature causes their naturally-occurring nitrates to break down more quickly into nitrites, which are more toxic.

Alternatives

Breastfeed your infant, particularly if the water you would use to make infant formulas is drawn from a private well that may contain elevated nitrate and nitrite levels. Breastfed infants receive very little nitrate/nitrite exposure.
Eat fresh produce (locally-grown vegetables are freshest), or those that have been frozen, as nitrates will not convert to nitrates when foods are frozen.
Instead of processed meats, serve nitrite-free, certified organic meats or soy or wheat gluten meat-substitute sandwich meats, hot dogs, and bacon. They are available at most natural foods stores and many supermarkets.
Use natural, and therefore slow-release, fertilizers in place of synthetic nitrogen-based fertilizers, such as ammonium nitrate and potassium nitrate, to minimize your contribution of nitrogen to groundwater.

For More information

Books, articles, factsheets and reports

Hot Dogs: Questions and Answers. Cancer Prevention Coalition, 1994.

http://www.preventcancer.com/patients/children/hotdogs.htm

National Primary Drinking Water Regulations: Consumer Factsheet on Nitrates/Nitrites. U.S. Environmental Protection Agency, Office of Water, Ground Water and Drinking Water, Updated November 26, 2002.

http://www.epa.gov/safewater/dwh/c-ioc/nitrates.html

Chemical Cuisine: CSPI's Guide to Food Additives. Center for Science in the Public Interest.

http://www.cspinet.org/reports/chemcuisine.htm#Alphabetical

Other government agencies

U.S. Environmental Protection Agency

Office of Ground Water and Drinking Water
Ariel Rios Building
1200 Pennsylvania Avenue NW
Washington DC 20460-0003

http://www.epa.gov/safewater/

U.S. Food and Drug Administration

Center for Food Safety and Applied Nutrition
5600 Fishers Lane
Rockville, MD 20857-0001
888-INFO-FDA (1-888-463-6332)

http://www.cfsan.fda.gov

Nonprofit organizations

Environmental Working Group

1718 Connecticut Ave. N.W., Suite 600
Washington DC 20009
202-667-6982

http://www.ewg.org

Center for Science in the Public Interest

1875 Connecticut Ave. NW
Suite 300
Washington DC 20009
202-332-9110

http://www.cspinet.org/index.html

NSF International

789 Dixboro Road
P.O.Box 130140
Ann Arbor, MI 48113-0140
800-NSF-Mark

http://www.nsf.org

Other websites

Other

The toxic effects of nitrate are closely related to its conversion to nitrite by bacteria in the mouth and stomach, and depends not only on dose, but also on the concentration and type of bacteria present. The stomach of infants is less acidic than that of adults and is thought to be more favorable to nitrate-converting bacteria, which is one reason for the heightened susceptibility of babies to nitrate-induced methemoglobinemia. Infants have also been found to be more likely to contract methemoglobinemia when they have diarrhea.