Detecting N-Nitrosamines in Alberta Drinking Waters at Nanogram per Liter Levels Using GC/MS Ammonia Positive Chemical Ionization

摘要

North American drinking water utilities are increasingly incorporating alternative disinfectants, such as chloramines, in order to comply with disinfection by-product (DBP) regulations. N-Nitrosodimethylamine (NDMA) is an unregulated, non-halogenated DBP associated with chloramination, having a drinking water carcinogenic unit risk two to three orders of magnitude greater than currently regulated halogenated DBPs. Development of a selective, sensitive and affordable bench-top analytical method for eight N-nitrosamine species, at relevant drinking water concentrations (ng/L) was the primary objective of this project. A dual media (Ambersorb 572 and LiChrolut EN), off-line solid-phase extraction method, capable of processing ten samples simultaneously was developed in conjunction with GC/MS ammonia positive chemical ionization (PCI). Ammonia PCI showed excellent sensitivity and selectivity for N-nitrosamines. An occurrence study of twenty Alberta municipal drinking-water distribution systems was undertaken. We detected NDMA (up to 100 ng/L) as well as N-nitrosopyrrolidine (4 ng/L) and N-nitrosomorpholine (3 ng/L)-two N-nitrosamines not reported in drinking water before. NDMA drinking water concentrations consistently over 100 ng/L are some of the highest ever recorded, without anthropogenic point source contamination. The described analytical method had high recoveries of standards and analytes and offers a valuable new approach for investigating several N-nitroso compounds at ultra-trace levels in drinking water. Risk trade-off issues involving alternative disinfection methods and unregulated DBPs, such as NDMA, are emerging as a major water quality and public health information gap.