NDMA and Other Nitrosamines - Drinking Water Issues


In 1998 N-nitrosodimethylamine (NDMA) was found in a drinking water well in northern California. NDMA was subsequently found elsewhere (including groundwater recharge projects), and also found to be a byproduct of drinking water treatment (see studies). There's more on the NDMA history page.

As a result of these early findings, the Drinking Water Program in the Department of Health Services (now the Division of Drinking Water) established a notification level in 1998 for NDMA.

After NDMA was first found, there were only a few laboratories capable of detecting NDMA at very low concentrations—on the order of just a few nanograms per liter (ng/L), or parts per trillion. Subsequently, US EPA published Method 521 for nitrosamines in drinking water (part of list 2 of unregulated contaminants for which monitoring is required), and established a laboratory approval process. (Click here for more information).

NDMA and other nitrosamines are considered "emerging contaminants." More information about emerging contaminants is here.

Other Nitrosamines

The National Toxicology Program's 13th Report on Carcinogens contains background information on the uses, production, and occurrence of a number of nitrosamines. NDMA, for example, has been used in research, in the production of 1,1-dimethylhydrazine for liquid rocket fuel, and in a variety of other industrial uses. It's been reported in foods, beverages, drugs, and tobacco smoke and to be an air and water contaminant.

In 2004, a notification level was established for another nitrosamine, N-nitrosodiethylamine (NDEA), and in 2005, after findings of N-nitroso-n-propylamine (NDPA) and NDMA associated with the evaluation of a disposable resin for drinking water treatment, NDPA was added to the list of chemicals with notification levels (see history).

The release of nitrosamines from some resins that may be used in drinking water treatment suggest a need for continued vigilance, so that a treatment approach to remove one contaminant does not inadvertently introduce another.

Health Concerns

NDMA and other nitrosamines can cause cancer in laboratory animals. The NTP identifies a number of them as reasonably anticipated to be human carcinogens (NTP, 201), and US EPA classifies a number them as probable human carcinogens (see US EPA's IRIS).

NDMA and other nitrosamines are among the chemicals known to the state to cause cancer [Title 27, California Code of Regulations, Section 27001], pursuant to California's Safe Drinking Water and Toxic Enforcement Act of 1986 ("Proposition 65").

Cancer risk levels can be calculated for nitrosamines in drinking water. For example, the concentrations in drinking water that correspond to de minimis cancer risks for some nitrosamines are presented in the following table:

10-6 Risk Level (ng/L)
Notification Level1 (1ng/L)
Response Level2 (ng/L)
N-Nitrosodiethylamine (NDEA)3,4
N-Nitrosodimethylamine (NDMA)3,5
N-Nitrosodi-n-propylamine (NDPA)3,4
N-Nitrosodi-n-butylamine (NDBA)3,4
N-Nitrosomethylethylamine (NMEA)3,4
N-Nitrosopiperidine (NPIP)4
N-Nitrosopyrrolidine (NPYR)3,4

1 - Notification levels for NDEA, NDMA, and NDPA are established at 10 ng/L, somewhat above the de minimis level, to take into account the very low detection limits and their potential presence in association with drinking water treatment.
2 - "Response levels" are levels at which DDW recommends removing the source from service. They correspond to a 10-4 risk, 100 times the de minimis ( 10-6) value.
3 - Chemical is on US EPA's List 2 of Unregulated Contaminants Requiring Monitoring.
4 - Risk levels for nitrosamines in drinking water can be derived from the 10-5 lifetime cancer risk levels in 27 CCR §25705, which sets forth "no significant risk" levels of carcinogens for purposes of Proposition 65, in terms of daily exposures. From these, de minimis cancer risks (i.e., lifetime cancer risks of 10-6), commonly used by DDW for notification levels for other carcinogens can be calculated, using an assumed drinking water consumption of two liters per day.
5 - OEHHA's public health goal (PHG) for NDMA is established at the 10-6 risk level.

Future Plans

Given the NDMA detections associated with drinking water sources and treatment, NDMA is a good candidate for future regulation (i.e., establishment of a drinking water standard, also known as a maximum contaminant level or MCL). Thus, we requested a PHG from the Office of Environmental Health Hazard Assessment (OEHHA). A PHG is the first step in the regulatory process (for more about PHGs, click here). OEHHA (2006) established a 3-ng/L PHG for NDMA.

An MCL for NDMA will likely not be available for several years, so the 10-ng/L notification level will continue to be used to provide information to local governing agencies and consumers.