Nitrosamines

Background

N-nitrosamine chemicals ("nitrosamines") are produced by numerous industrial sources such as the manufacturing of rocket fuel, rubber products, and other industrial process, and some nitrosamines have been identified by the National Toxicity Program as reasonably anticipated to be human carcinogens. Furthermore, the US EPA's IRIS Assessments classifies a number of nitrosamines as probable human carcinogens, including N-Nitrosodimethylamine (NDMA). 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").

In 1998, NDMA was found in a drinking water well in northern California. NDMA was subsequently found elsewhere (including groundwater recharge projects), and was also found to be a by-product of certain drinking water treatment processes (e.g. chloramination, chlorination, ozonation) (see studies).

As a result of these early findings, a notification level (then called an "action level") of 2 ng/L was established for NDMA in 1998. The notification level was then revised to 10 ng/L in 2002, in part to accommodate studies on NDMA's production in drinking water treatment and because 2 ng/L was below the capabilities of available analytical methods at the time.

In 2004, a notification level of 10 ng/L was established for N-nitrosodiethylamine (NDEA).

In 2005, a notification level of 10 ng/L was established for N-nitrosodi-n-propylamine (NDPA).

In 2005, US EPA published Method 521 for nitrosamines in drinking water and established a laboratory approval process before conducting the Second Unregulated Contaminant Monitoring Rule, which included NDEA, NDMA, NDBA, NDPA, NMEA, and NPYR.

In 2006, OEHHA established a Public Health Goal (PHG) of 3 ng/L for NDMA.

In 2020, OEHHA announced that they were initiating the process to update the PHG, and included the following information:

"NDMA is not currently produced or commercially used in the United States. Within the last five years, there have been numerous detections of NDMA in California public drinking water supply wells above the NL of 0.01 ppb. The update of the risk assessment for NDMA will consider the toxicology literature since the publication of the PHG in 2006 and will incorporate the application of updated risk assessment methodologies."

Recently, N-nitrosomorpholine (NMOR) has been detected in environmental and potable reuse water. Unlike several other nitrosamines, current research suggests that NMOR contamination in drinking water likely occurs from industrial sources, as opposed to being a by-product of certain disinfection processes.

Nitrosamines research and method development is ongoing.

Notification and Response Levels

Notification Levels and Response Levels have been established for three of the eight nitrosamines listed below. The levels of 1-in-1 million (de minimis) theoretical excess lifetime cancer risk are also presented in the table for comparison.

Nitrosamine

Public Health Goal (PHG) (ng/L)

Notification Level (ng/L)

Response Level1(ng/L)

Calculated 1-in-1 Million Cancer Risk Level2 (ng/L)

N-Nitrosodiethylamine (NDEA)

-

10

100

1

N-Nitrosodimethylamine (NDMA)

3

10

300

33

N-Nitrosodi-n-propylamine (NDPA)

-

10

500

5

N-Nitrosodi-n-butylamine (NDBA)

-

-

-

3

N-Nitrosomethylethylamine (NMEA)

-

-

-

1.5

N-Nitrosopiperidine (NPIP)

-

-

-

3.5

N-Nitrosopyrrolidine (NPYR)

-

-

-

15

N-Nitrosomorpholine (NMOR)

-

-

-

-

1 - DDW recommends removing sources from service if they exceed the Response Level. These levels correspond to a one in 10,000 cancer risk, or 10 times the Notification Level.

2 - Cancer risk levels for nitrosamines in drinking water can be derived from the 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. These calculations assumed drinking water consumption of two liters per day.

3 – The 1-in-1 million cancer risk level for NDMA was established by OEHHA's public health goal (PHG).

Origins and Occurrence of NDMA

NDMA is a chemical formed in industrial and natural processes and can be found in various foods and alcoholic beverages, as well as in cigarette smoke. It can also form in drinking water as a result of chloramine disinfection, and in chlorinated wastewater used for aquifer recharge. Historically, NDMA has been used in research, in the production of 1,1-dimethylhydrazine for liquid rocket fuel, and in a variety of other industrial uses.

NDMA has been detected in some California drinking water supplies. All drinking water occurrence from January 2011 through October 2023 is available on this spreadsheet. 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.