Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Fairey, Julian L.

Committee Member

Zhang, Wen

Second Committee Member

Pifer, Ashley

Keywords

Biofilm-related Materials as Total N-nitrosamine (TONO) Precursors and Hydroxylamine-based Interferences in TONO and N-nitrosodimethylamine (NDMA) Measurements

Abstract

In this study, a chemiluminescence-based total N-nitrosamine (TONO) assay was adapted to include a solid-phase extraction (SPE) step to assess the role of biologically derived materials as N-nitrosamine precursors. Methanol was determined to be a suitable solvent for the SPE-TONO assay, with N-nitrosodimethylamine (NDMA) losses estimated to be 30% by SPE alone and an additional 15% from concentration of the methanol extracts by N2-gas blowdown. Three biofilm-derived materials - poly-N-acetylglucosamine (PNAG), Pseudomonas aeruginosa, and tryptophan - were individually chloraminated and dose-response relationships were observed with the SPE-TONO assay, indicating biofilm are potential N-nitrosamine precursors. The role of hydroxylamine - a nitrification intermediate - was assessed as a function of five sample treatments related to the TONO assay (Untreated, HgCl2 only, sulfanilamide [SAA] only, HgCl2 + SAA, and HCl) in terms of aqueous phase TONO, SPE-TONO and NDMA by GC-FID. A series of batch reactor experiments were performed with various combinations of 3.52 mM hydroxylamine, 35.2 mM dimethylamine (a known NDMA precursor) and 3.52 mM monochloramine. However, several analytical interferences were discovered, associated with excess hydroxylamine in the samples, which obscured results from the TONO assay, GC-FID (for NDMA), and ion chromatography (for nitrite). In the aqueous phase with dimethylamine present, hydroxylamine was catalyzed by (1) HgCl2 to nitrite and NDMA and (2) HgCl2 + SAA to NDMA only, as any nitrite formed was removed by SAA. In the methanol phase, hydroxylamine and dimethylamine were catalyzed to NDMA on the activated carbon in the SPE cartridges. However, these experiments revealed a previously unconsidered NDMA formation pathway, in which hydroxylamine is catalyzed to peroxynitrite (ONOO-) in the presence of dissolved oxygen and subsequently reacts with dimethylamine to form NDMA. Recommendations are provided to guide the design of N-nitrosamine formation pathway experiments.

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