N-nitrosodimethylamine (NDMA), a disinfection byproduct formed in drinking water following the addition of chloramines for disinfection, is known both for its potent carcinogenicity and toxicity. Although NDMA currently is not a regulated disinfection byproduct, various states have established guidelines and California has established a notification level of 10 ng/L (10 parts-per-trillion). High concentrations of NDMA precursors, with the potential to form more than 50 ng/L NDMA, have been found in samples of water from the Upper Mississippi River. Softening the water by addition of lime and inorganic coagulants, a process widely applied in drinking water treatment was found to “activate” the NDMA precursors in Crow river water samples, leading to an increased NDMA formation potential (-68% to 1184% with a mean of 96%) after lime softening treatment. To assess the seasonal variability of NDMA precursors in the Crow River and to identify the major sources of these precursors, a one-year sampling campaign was carried out along the length of the Crow River and Mississippi River upstream and downstream of the Crow. Seasonal dynamics in the formation potential appear to be related to flow, and potentially concentrations of precursors. Correlation between NDMA formation potential and water parameters including TOC, DOC, abs254, ammonia, nitrate, nitrite, TN, and DN will be discussed.

N-nitrosodimethylamine (NDMA) precursors occurrence in the Crow and Mississippi Rivers: Seasonal variation and effect of lime softening

ACS Spring 2022

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