Priority Substances List Assessment Report for N-Nitrosodimethylamine (NDMA)

Synopsis

N-Nitrosodimethylamine (NDMA) is the simplest dialkylnitrosamine, with a molecular formula of C₂H₆N₂O. There are no industrial or commercial uses of NDMA in Canada. NDMA is released to the Canadian environment as a by-product and contaminant from various industries and from municipal wastewater treatment plants. Major releases of NDMA have been from the manufacture of pesticides, rubber tires, alkylamines and dyes. NDMA has also been detected in drinking water and in automobile exhaust. Sources of release of NDMA may occur across Canada, but releases have been quantified only in Ontario. NDMA may also form under natural conditions in air, water and soil as a result of chemical, photochemical and biological processes.

Photolysis is the major removal pathway from surface water, air and land. However, in surface waters with high concentrations of organic substances and suspended matter, photodegradation is much slower. In subsurface water and in soil, biodegradation is the removal pathway of importance. NDMA is unlikely to be transported over long distances in air or to partition to soil and sediments. Because of its solubility and low partition coefficient, NDMA has the potential to leach into and persist in groundwater. It is metabolized and does not bioaccumulate. NDMA is generally not detectable in surface waters, except for localized contamination from industrial sites, where end-of-pipe effluent concentrations as high as 0.266 µg/L have been measured.

Acute and chronic toxicity data are available for aquatic organisms. The most sensitive toxic effect was a reduction in the growth of algae at 4000 µg/L. Concentrations of NDMA in Canadian surface waters are less than the threshold for adverse effects estimated for aquatic organisms. No data on concentrations of NDMA in sediments or in soil have been identified in Canada. NDMA is not involved in stratospheric ozone depletion and is not an important contributor to climate change or photochemical smog formation.

NDMA has not been detected in ambient air, except in the vicinity of industrial sites, in small surveys of several cities in southern Ontario. Low concentrations of NDMA have been measured in drinking water in Ontario, where sources have included the contamination of groundwater with industrial effluents and the formation of NDMA in water treatment plants. The presence of NDMA has been demonstrated in some foods in Canada, most frequently in beer, cured meat and fish products, and some cheeses, although levels of NDMA have decreased in these products in recent years owing to changes in food processing. Some of these changes have been mandated under the Canadian Food and Drugs Act and Regulations.

Based upon laboratory studies in which tumours have been induced in all species examined at relatively low doses, NDMA is clearly carcinogenic, with a very strong likelihood that the mode of action for the induction of tumours involves direct interaction with genetic material. Qualitatively, the metabolism of NDMA appears to be similar in humans and animals; as a result, it is considered highly likely that NDMA is carcinogenic to humans, potentially at relatively low levels of exposure.

Based on the information available, it is concluded that NDMA is not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity, or that constitute or may constitute a danger to the environment on which life depends. NDMA is considered to be entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health. Therefore, NDMA is considered to be "toxic" as defined in Section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999).

While there have been a number of measures taken to limit exposure of the general population in Canada to NDMA in foodstuffs, cosmetics and consumer products, recent data on the NDMA content of foodstuffs and rubber-containing products in Canada other than infant feeding bottle nipples and pacifiers have not been identified. Moreover, with the exception of monitoring conducted in Ontario in the early 1990s, potential for exposure to NDMA in the vicinity of point sources in Canada is also largely unknown, although stakeholders under the voluntary Accelerated Reduction/Elimination of Toxics (ARET) program have committed to reducing total emissions of NDMA from 6000 g in 1993 to 87 g by the year 2000.

Continued monitoring of levels of nitrosamines (including NDMA) in Canadian foodstuffs to verify reduction of content seems warranted. Determination of the potential presence of nitrosamines (including NDMA) in rubber products other than infant feeding bottle nipples and pacifiers may also be warranted, particularly for those products with which infants (who exhibit mouthing behaviour) may come into contact.

On the basis of limited information from short-term monitoring surveys of ambient air and water near industrial facilities, the priority for investigation of options to reduce exposure to NDMA in the vicinity of such point sources is considered high. It is recommended, therefore, that there be additional investigation of the magnitude of exposure of populations in the vicinity of point sources to assist risk management actions.

Optimization of drinking water treatment to minimize formation of NDMA is also recommended, though such measures must not compromise human health protection.

Since NDMA may be released directly to the environment through the application of certain pesticides, the levels of this nitrosamine in products regulated under the Pest Control Products Act should also continue to be monitored. Monitoring by the Pest Management Regulatory Agency has shown that the review standard of 1 µg/g is rarely exceeded.

Owing to the common practice in Canada of applying sewage sludge to agricultural lands and the potential for uptake by plants, it is recommended that concentrations of NDMA in such sludge be monitored to determine the potential of this practice to contribute to the exposure of humans and non-human organisms.

Since NDMA is likely to be carcinogenic to humans at relatively low levels of exposure and is not currently used in commerce in Canada, it is recommended that the manufacture, import and use of the substance be banned in order to prevent its introduction into the Canadian market.