Ndma Formation During Chloramination: Temporospatial Distribution Of Ndma Precursors, The Effect Of Lime Softening Treatment, And Precursor Identification Via Non-Targeted Analysis
2023-08
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Ndma Formation During Chloramination: Temporospatial Distribution Of Ndma Precursors, The Effect Of Lime Softening Treatment, And Precursor Identification Via Non-Targeted Analysis
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2023-08
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N-nitrosodimethylamine (NDMA), a byproduct formed in drinking water during chloramination disinfection, is notorious both for its potent carcinogenicity and toxicity. NDMA and other nitrosamine precursors are compounds containing secondary, tertiary, and quaternary amines, which can be released from diverse sources into the surface waters. There is still much to be understood, however, about the fate of these precursors in natural water and engineered water system. This work mainly addressed the seasonal variations and geographical occurrence of NDMA precursors in rivers, the effect of lime softening treatment on NDMA formation, and the identification of NDMA precursors via nontargeted mass spectrometric analysis. The seasonal and spatial variations in NDMA precursor levels in Crow River was assessed by approximately monthly sampling at twelve locations over 18 months. NDMA precursor concentrations was assessed as NDMA formation potential under Uniform Formation Test (UFC) conditions, which represent the average and realistic disinfection conditions. River water samples were lime softened in parallel. Raw water NDMAUFC concentrations (2.2 to 128 ng/L) exhibited substantial temporal variation but relatively little spatial variation. Lime-softening treatment typically resulted in an increase in NDMA formation using the UFC protocol likely due to the decrease in competition between precursors and NOM for chloramines and possibly reduced interactions of precursors with NOM.
The geospatial distribution of NDMA precursors in watersheds in Minnesota and its association with anthropogenic activities was investigated via geostatistical analysis. River water samples were collected from major watersheds in Minnesota in summer 2022. Representative regional fluorescence from excitation-emission matrix (EEM) spectroscopy was explored for its correlation with NDMAUFC. The results show the primary source of NDMA precursors is animal operations, followed by domestic wastewater discharge. The spearman correlation analysis between organic matter fluorescence and NDMAUFC suggests region IV is indicative of contributors to NDMA formation while organic matter in region V may serve as competitor for available chloramines during UFC testing.
The advancement of analytical techniques with higher mass resolution and accuracy facilitates the identification of NDMA precursors via a non-targeted approach. River water samples collected from Crow river were processed and loaded into mix-bed cartridges containing five different sorbents, which demonstrated effective extraction of NDMA precursors. Extracted samples were analyzed by liquid chromatograph quadrupole time-of-flight mass spectrometry. Following a non-targeted analysis workflow established on a pre/post chloramination sample comparison approach, twenty-eight compounds containing primary, secondary, tertiary, or quaternary amines were identified. Thirteen of these compounds were validated as nitrosamine precursors.
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University of Minnesota Ph.D. dissertation. August 2023. Major: Civil Engineering. Advisor: Raymond Hozalski. 1 computer file (PDF); xiv, 210 pages.
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Li, Jiaqi. (2023). Ndma Formation During Chloramination: Temporospatial Distribution Of Ndma Precursors, The Effect Of Lime Softening Treatment, And Precursor Identification Via Non-Targeted Analysis. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/258878.
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