What it is:
• The nitroso chemical unit is N=O; the nitrosamine unit is N=N=O. Nitrosamines and related N-nitrosated amides and nitrosated ureas are readily formed from reaction of oxynitrogen species and the appropriate organic nitrogen compound.
• The organic nitrogen chemical could be a secondary amine like dimethylamine, an amide or protein, and several other chemicals. The reactant can be HNO2, NO, NO2, N2O3, N2O4 and possibly others.
• The chemical structure of nitrosodimethylamine (NDMA), also commonly called dimethylnitrosamine, is (CH3)2N=N=O. Several nitrosamines have been detected in some drinking waters either from industrial discharges or as byproducts of drinking water treatment, especially chloramination.
Occurrence:
• Nitrosamines are commonly found at nanogram to microgram levels in several foods, like cheeses, milk, sausage, bacon, cured meats and beer. They are also generated during cooking because the precursor amines and nitrogen oxide reactant (especially nitrite) are often present. Fermentation and heating processes contribute to nitrosamine formation.
• Tobacco smoking is a source of nitrosamine exposures. Nitrite-containing cutting fluids produce nitrosamines.
• Drinking water surveys have demonstrated the presence of nitrosamines, predominantly NDMA, in some surface waters at ppt (ng/L) levels; ~1/3 of chloraminating systems; ~3 percent of chlorinating systems. Ninetieth percentile chlorinating was 9.4 ppt; median 3.3 ppt (90th percentile chlormaninating was 15.2 ppt; median 4.1 ppt).
• Nitrosamines and other nitroso compounds are also endogenously generated in our bodies at microgram+ levels from standard chemical processes that occur in vivo. NO and nitrite are the predominant nitrosating agents that our bodies produce. Nitrate is reduced to nitrite in vivo.
• Interestingly, the quantity of endogenously produced nitrosamine far exceeds our exposures from food and water sources, on the order of >99 percent endogenous, <1 percent food and <0.1 percent drinking water.
• Nitrosamines in drinking water occur predominantly in surface water systems that utilize chloramination. Upstream wastewater discharges provide organic nitrogen precursors like dimethylamine that can react with dichloramine in a process that leads to ppt amounts of nitrosamines, mostly NDMA.
• The original detections of nitrosamines in treated drinking water were caused by polyDADMAC coagulant aid nitrosamine precursors.
Health effects:
• Most nitrosamines are considered to be animal carcinogens and probable human carcinogens. Some like NDMA are very potent, but others like diphenylnitrosamine are weak carcinogens.
•The Environmental Protection Agency’s (EPA) Health Advisory for NDMA calculates a hypothetical lifetime 1/10,000 risk at 0.00007 mg/L (0.07 ug/L).
Water treatment:
• The nitrosamines found in drinking water tend to be the low molecular weight types such as NDMA. Thus, they are not efficiently removed by reverse osmosis — on the order of 60 percent.
• The nitrosamine functional group is a chromophore so it is susceptible to photolysis by both low and medium pressure UV lamps.
• Advanced oxidation processes involving peroxide and UV are also used, but the data indicates that most of the nitrosamine decomposition is from direct UV photolysis rather than hydroxyl radical chemistry.
Regulation:
• Nitrosamines are not currently regulated by the EPA, but regulatory development is underway and a proposal is likely in the next few years.
• The World Health Organization (WHO) Drinking Water Guideline for NDMA is 100 ppt (ng/L) estimated to be a 1/100,000 lifetime risk. California has a reporting level of 10 ppt (ng/L). Given the very minute contribution to total daily exposure from those drinking waters containing nitrosamines at ppt levels there is a serious policy question whether there would be any realistic benefits worth the costs from drinking water regulation, as well as whether the risk trade off that might occur from changes in disinfection (chloramine use) would result in net benefits to consumers.
Dr. Joseph Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He holds a Ph.D. in Physical Organic Chemistry and is a member of the World Health Organization’s Guidelines for Drinking-water Quality Committee and expert advisory groups on drinking water quality, desalination, wastewater and water reuse. He is a former director of the U.S. EPA Drinking Water Standards Division.
