Occurrence, formation, and treatment implications of N-Nitrosamine risks in harvested waters

With growing freshwater scarcity, alternative sources such as harvested rainwater, atmospheric water, and stormwater are attracting increasing attention. However, their use may pose health risks due to contamination and the formation of carcinogenic N-Nitrosamines. This study systematically evaluated the occurrence and formation potentials (FPs) of nine N-Nitrosamines detected in harvested waters. Five N-Nitrosamines-N-Nitrosodimethylamine, N-Nitrosodiethylamine, N-Nitrosomorpholine, N-Nitrosopyrrolidine, and N-Nitrosodibutylamine-were consistently detected (2.2-23.1 ng L⁻¹) or formed during chloramination at concentrations ranging from 3.7 to 40 ng L⁻¹ , while N-Nitrosomethylethylamine, N-Nitrosodipropylamine, and N-Nitrosodiphenylamine were detected exclusively in stormwater samples. N-Nitrosopiperidine appeared only sporadically at low levels in rainwater. Spatiotemporal variability was most pronounced in stormwater, where first-flush events caused sharp increases. Correlation analysis indicated that N-Nitrosamine-FPs were strongly influenced by metals and bromide, and were closely associated with secondary amines and hydrophilic dissolved organic nitrogen fractions. Estimated lifetime cancer risks from chloraminated waters (2.69 × 10⁻⁵ to 1.08 × 10⁻⁴) exceeded the USEPA negligible risk level of 1.0 × 10⁻⁶ by 27-370 times. Pretreatment strategies prior to chloramination showed contrasting performances. Sand filtration achieved little removal, while Mn(VII) and UV/NH₂Cl sometimes increased N-Nitrosamine-FPs. In contrast, UV/HOCl achieved up to 90 % reduction under environmentally relevant conditions (oxidant dose ≤ 4 mg L⁻¹, UV fluence > 700 mJ cm⁻²), outperforming UV/H₂O₂, Fe(VI), and powdered activated carbon. Overall, harvested waters represent a significant N-Nitrosamine risk, but effective pretreatments can substantially mitigate formation. These findings highlight the need for integrated treatment and disinfection strategies to ensure safe water harvesting and reuse.