Occurrence and mass loads of N-nitrosamines discharged from different anthropogenic activities in Desheng River, South China

Abstract N-nitrosamines are widespread in various bodies of water, which is of great concern due to their carcinogenic risks and harmful mutagenic effects. Livestock rearing, domestic, agricultural, and industrial wastewaters are the main sources of N-nitrosamines in environmental water. However, information on the amount of N-nitrosamines these different wastewaters contribute to environmental water is scarce. Here, we investigated eight N-nitrosamines and assessed their mass loadings in the Desheng River to quantify the contributions discharged from different anthropogenic activities. NDMA (8.5 ± 5.2 ng/L), NMEA (0.1 ± 0.4 ng/L), NDEA (1.2 ± 1.0 ng/L), NPYR (1.6 ± 4.1 ng/L), NMOR (7.0 ± 7.1 ng/L), NPIP (0.3 ± 0.7 ng/L), and NDBA (7.8 ± 3.8 ng/L) were detected. NDMA and NDBA were the dominant compounds contributing 89% and 92% to the total N-nitrosamine concentrations. The mean cumulative concentrations of N-nitrosamines in the livestock rearing area (26 ± 11 ng/L) and industrial area (24 ± 4.8 ng/L) were higher than those in the residential area (16 ± 6.3 ng/L) and farmland area (15 ± 5.1 ng/L). The significant negative correlation between NDEA and dissolved oxygen indicated the light-screening effect. The mean concentration of N-nitrosamines in the tributaries (22 ng/L) was slightly higher than that in the mainstem (17 ng/L), probably due to the dilution effect of the mainstem. However, the mass loading assessment suggested the negligible mass emission of N-nitrosamines into the mainstem from tributaries, which could be due to the small water flow of tributaries. The average mass loads of N-nitrosamines discharged into the mainstem were ranked as the livestock rearing area (742.7 g/d), industrial area (558.6 g/d), farmland area (93.9 g/d), and residential areas (83.2 g/d). In the livestock rearing, residential, and industrial area, NDMA (60.9%, 53.6%, and 46.7%) and NDBA (34.6%, 33.3%, and 44.9%) contributed the most mass loads; NDMA (23.4%), NDEA (15.8%), NPYR (10.1%), NPIP (12.8%), and NDBA (37.8%) contributed almost all the mass loads in the farmland area. Photodegradation amounts of NDMA (0.65 ~ 5.25 µg/(m3·day)), NDEA (0.37 ~ 0.91 µg/(m3·day)), and NDBA (-0.06 ~ 0.66 µg/(m3·day)) were also calculated according to the mass loading. Quantifying the contribution of different anthropogenic activities to the river will provide important information for regional river water quality protection.