Drinking Water as a Proportion of Total Human Exposure to Volatile N‐Nitrosamines

Abstract

Some volatile N-nitrosamines, primarily N-nitrosodimethylamine (NDMA), are recognized as products of drinking water treatment at ng/L levels and as known carcinogens. The U.S. EPA has identified the N-nitrosamines as contaminants being considered for regulation as a group under the Safe Drinking Water Act. Nitrosamines are common dietary components, and a major database (over 18,000 drinking water samples) has recently been created under the Unregulated Contaminant Monitoring Rule. A Monte Carlo modeling analysis in 2007 found that drinking water contributed less than 2.8% of ingested NDMA and less than 0.02% of total NDMA exposure when estimated endogenous formation was considered. Our analysis, based upon human blood concentrations, indicates that endogenous NDMA production is larger than expected. The blood-based estimates are within the range that would be calculated from estimates based on daily urinary NDMA excretion and an estimate based on methylated guanine in DNA of lymphocytes from human volunteers. Our analysis of ingested NDMA from food and water based on Monte Carlo modeling with more complete data input shows that drinking water contributes a mean proportion of the lifetime average daily NDMA dose ranging from between 0.0002% and 0.001% for surface water systems using free chlorine or between 0.001% and 0.01% for surface water systems using chloramines. The proportions of average daily dose are higher for infants (zero to six months) than other age cohorts, with the highest mean up to 0.09% (upper 95th percentile of 0.3%).

Disinfection Processes

“…The use of chlorine dioxide before or simultaneously with free chlorine or monochloramine reduced THM and HAA levels by approximately 30% and 20%, respectively, in three natural surface waters (Shi, Ling, and Qiang, 2013 Nitrogenous DBPs. Hrudey et al (2013) estimated that drinking water contributes a low percentage of the lifetime average daily NDMA dose: 0.0002-0.001%…”

On Exposure Analysis for Volatile N‐Nitrosamines

“…estimated the average endogenous NDMA infusion in the range of 100 × 10 ‐3 –2,480 × 10 ‐3 mg/day. By adjustment through body weight, the daily average doses were estimated to be 1.4 × 10 ‐3 –35 × 10 −3 mg/kg‐day . These data showed an overall average intake of approximately 14.84 × 10 ‐3 mg/kg‐day (e.g., average of the values in Table IX of their article).…”

“…reported NDMA concentrations in 556 food samples and 75 beverages purchased in eastern France in 1987–1992. Hrudey et al . used these data to predict NDMA intakes considering U.S. Environmental Protection Agency (USEPA) exposure scenarios .…”

“…Concentrations in imported beer averaged 0.71 μg/L in 1991–1992 and 0.15 μg/L in 1994 . However, Hrudey et al . used a value of 0.2 μg/L of NDMA for the U.S.‐based intake assessment.…”

“…The justification for using a value of NDMA = 0.2 μg/L for the U.S. beers was not clear. My last, and most critical, concern is about endogenous doses of NDMA. Hrudey et al . estimated the average endogenous NDMA infusion in the range of 100 × 10 ‐3 –2,480 × 10 ‐3 mg/day.…”