Indirect photodegradation of sulfadiazine in the presence of DOM: Effects of DOM components and main seawater constituents.

The presence of pharmaceuticals and personal care products in coastal waters has caused concern over the past decade. Sulfadiazine (SD) is a very common antibiotic widely used as human and fishery medicine, and dissolved organic matter (DOM) plays a significant role in the indirect photodegradation of SD; however, the influence of DOM compositions on SD indirect photodegradation is poorly understood. The roles of reactive intermediates (RIs) in the indirect photolysis of SD were assessed in this study. The reactive triplet states of DOM (3DOM∗) played a major role, whereas HO· and 1O2 played insignificant roles. DOM was divided into four components using excitation-emission matrix spectroscopy combined with parallel factor analysis. The components included three allochthonous humic-like components and one autochthonous humic-like component. The allochthonous humic-like components contributed more to RIs generation and SD indirect photolysis than the autochthonous humic-like component. A significant relationship between the indirect photodegradation of SD and the decay of DOM fluorescent components was found (correlation coefficient, 0.99), and the different indirect photodegradation of SD in various DOM solutions might be ascribed to the different components of DOM. The indirect photolysis rate of SD first increased and then decreased with increasing pH. SD photolysis was enhanced by low salinity but remained stable at high salinity. The increased carbonate concentration inhibited SD photolysis, whereas nitrate showed almost no effect in this study.

Composition variations and spatiotemporal dynamics of dissolved organic matters during the occurrence of green tide (Ulva prolifera blooms) in the Southern Yellow Sea, China.

Seawater samples were collected from April 6 to September 6, 2017 in the Southern Yellow Sea, China where green tides often occurred, and analyzed for nutrients, dissolved organic carbon (DOC), and fluorescent dissolved organic matter (FDOM). The DOC concentrations increased significantly in the green tide areas by approximately 1.2 times compared to those in the non-green tide areas. From the large-scale outbreak to the complete dissipation of the green tide, the fluorescence intensities of the four FDOM fluorescent components identified in the green tide areas were significantly higher than those in the non-green tide areas. During the extinction period, the fluorescence intensities of the three humus-like components and one protein-like component were approximately 1.8 and 1.3 times higher than those in the non-green tide areas, respectively. These findings suggested that the outbreak of green tide could release DOM into water and affect the biogeochemical cycle in green tide regions.

[Indirect Photodegradation of Sulfamethoxazole in Water].

Indirect photodegradation is one of the primary approaches for the removal of pharmaceutical contaminants from water. This degradation process is dominated by chromophoric dissolved organic matter (CDOM). After illumination, CDOM produces many reactive intermediates, which can react with drug pollutants to achieve indirect photodegradation. In this article, we focused on four different sources of CDOM and factors affecting indirect sulfamethoxazole (SMZ) photolysis. The results show that the indirect photodegradation effect of SMZ is significantly influenced by CDOM. This indirect photodegradation has a dual nature. It promotes the indirect photodegradation of SMZ through the formation of various reactive intermediates and at the same time inhibits the photodegradation of SMZ through light shielding and masking of reactive intermediates. The indirect photodegradation of SMZ is mainly controlled by active intermediates such as 3CDOM*, HO·, and 1O2 produced by CDOM; 3CDOM* is the main participant in indirect photodegradation of SMZ. In addition, the pH, salinity, and nitrate ions have a significant effect on the indirect photodegradation of SMZ, while bicarbonate ions have no significant effect on the indirect photodegradation of SMZ.