Background Risks Associated With Exposure to N-Nitrosodimethyamine (NDMA): Is Something Amiss in the Regulation of This Chemical. P. J. Sheehan, D. Mathur, D. Dodge, and D. J. Paustenbach, ChemRisk Service, McLaren/Hart, Inc., 1320 Harbor Bay Parkway, Suite 100; Alameda, CA 94502-6578
NDMA belongs to a class of compounds called nitrosamines that are found in many types of foods, beverages and other household products. NDMA is also produced in the body when we eat foods such as fish that are rich in amines. On the other hand, NDMA has not been produced for commercial use in the United States since 1976. Prior to that it was synthesized as an intermediate in the production of rocket fuel. NDMA is therefore a common constituent in foods but a rare environmental contaminant. As an environmental contaminant, the USEPA considers NDMA a probable human carcinogen and has assigned a cancer risk level of 1 in 1,000,000 for a NDMA concentration in water of 0.0007 ppb assuming a consumption rate of 2 liters per day for 70 years. In addition, the California EPA under the Safe Drinking Water and Toxic Enforcement Act of 1986, have established a no significant risk level of 0.04 (g/day of exposure to NDMA. These are relatively stringent criteria for a chemical that is a found as a contaminant at only a few sites, but is common in our diet for. For instance, according to USEPA criteria consumption of one glass of milk daily with the average reported NDMA concentration (0.12 ppb) may pose an incremental lifetime cancer risk of approximately 2 in 100,000. Consumption of two meals of bacon a week from adolescence to age 70 may pose an incremental cancer risk of approximately 4 in 100,000. Consumption of 3 bottles of beer or malt whiskey drinks a week with an average NDMA concentration (2.5 ppb) for 40 years may pose an incremental cancer risk of approximately 1 in 10,000. A total estimated dietary intake of NDMA, 1 (g/day, may pose a cancer risk of approximately 1 in 1,000. To add further perspective, the total dose of all nitrosamines in the diet is more than 100 times the daily dose of NDMA. There are, however, no epidemiological data regarding carcinogenic effects in humans associated with NDMA exposures. This analysis indicates that the risk from background daily dietary exposure to naturally occurring or formed NDMA is likely to be high relative to the risk that may come from exposures to NDMA in contaminated soil or water. Secondly, and perhaps more importantly, this analysis raises questions about the applicability of the cancer potency criteria current assigned to NDMA, in the evaluation of risks of exposures to NDMA as an environmental contaminant.
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