Toxicity-Weighted Multi-Criteria Decision-Making for the Prioritization of Nitrosamines in Drinking Water Using a Fuzzy Aggregation Framework.

Nitrosamines are among the most concerning nitrogenous disinfection by-products in drinking water because of their high carcinogenic potency and frequent occurrence, particularly in chloraminated systems. However, current risk assessments are predominantly compound-specific and often rely on N-nitrosodimethylamine (NDMA) as a surrogate, limiting the interpretation of multi-compound exposure scenarios. In this study, a toxicity-weighted multi-criteria decision-making framework based on the fuzzy analytic hierarchy process (fuzzy AHP) was developed to prioritize nine commonly reported nitrosamines: NDMA, N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosodibutylamine (NDBA), N-nitrosomethylethylamine (NMEA), N-nitrosopyrrolidine (NPYR), N-nitrosopiperidine (NPIP), N-nitrosomorpholine (NMOR), and N-nitrosodiphenylamine (NDPhA). The framework initially considered toxicological properties, exposure indicators, environmental prevalence, evidence availability, data reliability, and practical management considerations. Following fuzzy weighting, the final aggregation was driven by oral slope factor, mean concentration, chronic daily intake (CDI), and toxicity-data reliability. To account for dataset heterogeneity, three contexts were evaluated separately: Formation potential, distribution network, and treatment plant effluent. NDEA ranked first in all three contexts, primarily because of its high carcinogenic potency. NDMA ranked second in the formation-potential and treatment-plant-effluent contexts but third in the distribution-network context, where NDPA ranked second. The high priority of NDMA reflected its combined contributions from carcinogenic potency, concentration, and CDI, whereas the priority of NDPA was largely driven by its comparatively high CDI. Mid-ranked compounds showed context-dependent variation: NPIP and NMOR received relatively higher priorities in the treatment-plant-effluent and formation-potential contexts, while NMEA ranked higher in the distribution-network context. Across all three contexts, the lowest rank was consistently assigned to NDPhA. Overall, the findings demonstrate that nitrosamine prioritization requires the joint consideration of toxicity and exposure and that the proposed framework provides a transparent and transferable tool for risk-informed monitoring and management in drinking-water systems.