A drinking water concentration of 0.7 ng/L of NDMA is associated with a theoretical 10-6 lifetime excess cancer risk. The U.S.
Environmental Protection Agency (EPA) is expected to make a
regulatory determination on NDMA and several other nitrosamines in the near future.
NDMA is a DBP preferentially formed by chloramines. Sources
of NDMA precursors include treated wastewater effluents and
Chloramines have been shown to minimize the formation
of THMs and HAAs (in general), but they favor the formation of
N-nitrosodimethylamine (NDMA). Results from the Unregulated
Contaminant Monitoring Rule 2 (UCMR2) indicated that NDMA
was present in at least half of U.S. chloraminated drinking waters
on an annual average basis, with 12% of these waters having
10 ng/L or more of NDMA.
While no federal regulations have been established for nitrosamines, California and Massachusetts have a 10 ng/L public
notification or regulatory level for NDMA. 1 Recently, Canada
set a 40 ng/L maximum acceptable concentration for NDMA.
Controlling the Formation
Stuart Krasner, Metropolitan Water District of Southern California; William A. Mitch, Stanford
University; Paul Westerhoff, Arizona State University; Djanette Khiari, Water Research Foundation
Utilities in the United States are increasingly switching from chlorine to alterna- tive disinfectants to minimize the formation of trihalomethanes (THMs) and haloacetic acids (HAAs), while achieving adequate pathogen inactivation. Of particular interest is the increasing use of chloramines for secondary disinfection.
1 California also has regulatory levels for two other nitrosamines.