Revealing a Size-Resolved Fluorescence-Based Metric for Tracking Oxidative Treatment of Total N-Nitrosamine Precursors in Waters from Wastewater Treatment Plants

N-Nitrosamines make up a nonhalogenated group of disinfection byproducts that form during chloramination, particularly in drinking waters impacted by wastewater treatment plant (WWTP) effluents. Here, we reveal a size-resolved fluorescence-based precursor surrogate for tracking total N-nitrosamine formation potential (TONOFP) through oxidative treatment. Samples were collected at seven WWTPs, at the finished effluent and prior to final disinfection (i.e., secondary effluent). Asymmetric flow field-flow fractionation (AF4) with inline fluorescence detection at excitation and emission wavelengths of 280 and 340 nm, respectively (i.e., I280/340), showed protein-rich natural organic matter peaks between 10–445 and 445–1500 kDa. TONOFP was measured by chemiluminescence on samples dosed with 250 mg L–1 Cl2 monochloramine at pH 7 for 7 days. Metrics from AF4 I280/340 (i.e., area under the curve and peak height) and I257/277 from whole water excitation–emission matrices were leveraged in multivariate models to develop correlations with TONOFP. The TONOFP of the finished effluent divided by that of the secondary effluent (i.e., the TONOFP Ratio) was strongly correlated (R2 = 0.996; p = 0.000) to a model of AUC for the 10–445 kDa peak, maximal peak height, and I257/277. This TONOFP precursor surrogate requires 2 mL of sample and is transformational with respect to assessing the impact of oxidative treatments on N-nitrosamine precursor concentrations.