Photochemical attenuation of N-nitrosodimethylamine (NDMA) and other nitrosamines in surface water.

The aqueous photolysis of seven alkyl nitrosamines was studied by irradiation in a solar simulator. Nitrosamines included N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosodi-n-butylamine (NDBA), N-nitrosopiperidine (NPip), and N-nitrosopyrrolidine (NPyr). Direct photolysis at irradiations of 765 W/m2, representing Southern California midsummer, midday sun, resulted in half-lives of 16 min for NDMA and 12-15 min for the other nitrosamines. The quantum yield for NDMA was determined to be phi = 0.41 and phi = 0.43-0.61 for the other nitrosamines. Quantified products of NDMA photolysis included methylamine, dimethylamine, nitrite, nitrate, and formate, with nitrogen and carbon balances exceeding 98 and 79%, respectively. Indirect photolysis of nitrosamines in surface water was not observed; increasing dissolved organic carbon (DOC) slowed the NDMA photolysis rate because of light screening. Removal of NDMA measured in tertiary treated effluent flowing in a shallow, sunlit engineered channel agreed with photolysis rates predicted based on the measured quantum yield and system parameters. Because biodegradation is relatively slow, aquatic photolysis of NDMA is generally expected to be more significant even at relatively low levels of solar irradiation (t(1/2) = 8-38 h at 244-855 W/m2, 51 degrees N latitude, 1 m depth).