In this study biodegradation of 3 nitrosamines, N-nitrosodiethanolamine (NDELA), N-nitrosodimethylamine (NDMA) and N-nitrosopiperazine (NPz), were investigated at low concentrations in a biodegradation simulation test. The experiments were conducted with natural lake and river water as bacterial inocula, and over periods of 56 days (2 months). Biotransformation was determined by liquid chromatography – triple quadrupole mass spectrometry (LC-MS-MS-QQQ), and degradation rates determined by non-linear regression analyses. Biodegradation experiments with NDELA at different concentrations (100 to 1.0 µg/L) showed only small differences in biodegradation rates, with more than 80% depletion after 56 days and degradation half-lives of 28.5 to 33.1 days. Different water temperatures (5 to 20°C) affected biodegradation only moderately, with half-lives of 38.1 days at 5°C to 31.2 days at 20°C. However, the nitrosamines NDMA and NPz were significantly less biodegradable in water at low concentrations than NDELA under comparable conditions.