EWG's Tap Water Database — 2021 UPDATE

picture of test tube and beaker in laboratory


November 2021


Nitrosamines are DNA-damaging, cancer-causing disinfection byproducts that form when water is treated with certain disinfectants, such as chloramine. Pollution of water sources with nitrogen-containing waste, such as discharge from municipal wastewater treatment plants and runoff from animal feeding operations, contributes to nitrosamine formation.

Nitrosamines may naturally occur in foods. They are also produced in the body after nitrate and nitrite, preservatives added to cured meats, are ingested.

Fifteen different nitrosamines are listed as carcinogens in the U.S. Department of Health and Human Services National Toxicology Program Report on Carcinogens. Yet the federal government has not set a legal limit for nitrosamines.

California has set a public health goal for one of the most common nitrosamines, N-nitrosodimethylamine, or NDMA, at 0.003 parts per billion, or ppb, in drinking water, a concentration that corresponds to an estimated one-in-a-million cancer risk.

How am I exposed to nitrosamines?

Nitrosamines form in drinking water as byproducts of the disinfection process, when nitrate or other nitrogen-containing compounds in water react with chlorine or chloramine. Because nitrosamines are not federally regulated, few water systems test for them. If tests are conducted, it is commonly for NDMA. Other nitrosamines may occur along with NDMA but might not be tested for.

For most people, diet is the largest source of exposure to nitrosamines. Nitrosamines are found in foods like cured and processed meats, and in beer; they also form when people consume food and water containing nitrate and nitrite. A diet rich in antioxidants like vitamin C can reduce nitrosamine formation in the body.

What are the toxic effects of nitrosamines?

Nitrosamines damage DNA and increase the risk of cancer. Most of these chemicals are known animal carcinogens, causing tumors in multiple organs, including the liver, stomach, lungs, kidneys and blood. Many nitrosamines have been listed by public health agencies as likely human carcinogens.

A 1999 study led by Paul Knekt at the National Public Health Institute in Finland found dietary NDMA exposures increased the risk of colorectal cancer in people. Dietary intake of nitrosamines has also been linked to stomach, esophageal and lung cancers.

What levels of nitrosamines are safe?

In the past, nitrosamine exposures were thought to come almost exclusively from food. More recently, scientists detected NDMA contamination in drinking water and pointed to the drinking water disinfection process as the cause of nitrosamine formation. The growing concern over nitrosamines in drinking water prompted the Environmental Protection Agency to list NDMA and four other nitrosamines as priority drinking water contaminants for review.

In California, water suppliers must notify customers if the levels of three nitrosamines – NDMA, N-nitrosodiethylamine and N-nitrosodi-n-propylamine – exceed 0.01 ppb. Massachusetts also has established a drinking water guideline for NDMA, at 0.01 ppb.

In 2006, California set a public health goal for NDMA in drinking water of 0.003 ppb. This level corresponds to a lifetime cancer risk of one in 1 million people exposed.

What can be done to reduce exposure to nitrosamines?

Once formed, nitrosamines are very difficult to remove from water and require specialized treatment, such as reverse osmosis. The best way to reduce nitrosamine levels in water is to remove their precursors and prevent their formation before water reaches the tap. This includes controlling pollution from the use of nitrogen-based fertilizers and industrial waste.

Since the majority of nitrosamine intake comes directly or indirectly from diet, limiting consumption of red, processed and cured meats is among the best things you can do to reduce nitrosamine exposures.


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