Environmental Behavior Of Typical Pharmaceutical Residues In The Yangtze Estuary And Optimization Of Monitoring Technology

Pharmaceutical residues in natural waters are of great concern, of which antibacterials are important representatives. These pharmaceutical residues have been widely detected in the environment. Some of them are characterized by pseudo persistence, low concentration and high ecological risk. This study selected 27 kinds of pharmaceuticals as targets, which had high production and consumption in China in recent years, strong environmental stability and potentially high ecological risk, including 7 sulfonamides,3 chloramphenicols,2 macrolides, and 15 non-antibacterial pharmaceuticals. The Yangtze Estuary is an important area of land-ocean interaction, and the environmental behavior of pharmaceutical residues need further study.In this study, the dynamic behavior of dissolved pharmaceuticals over tidal cycles in the Yangtze Estuary was studied to assess the tidal impact on the fate of pharmaceutical residues. The results show that most pharmaceuticals were frequently detected with concentrations from below detection to 27.2 ng/L, with sulfamethoxazole, sulfamethazine, erythromycin, thiamphenicol, and florfenicol dominating. During tidal cycles, pharmaceutical concentrations decreased during tidal rise, then increasing during tidal receding for all locations, except at site S2 which showed an opposite trend due to unique water movement there. It was observed that most compounds showed a non-conservative behavior, while diazepam and sulfamethoxazole displayed a conservative behavior. The pharmaceutical concentrations were found to increase with dissolved organic carbon (DOC) concentration, suggesting DOC as a carrier of pharmaceuticals. In addition, many compounds showed a significant negative relationship with suspended particulate matter (SPM) concentration, indicating SPM-water interactions as a control of pharmaceutical behavior in estuarine environment.After studying the dynamic behavior of pharmaceutical residues, this research estimated seasonal fluxes of pharmaceuticals to the Yangtze Estuary and analyzed their sources. The occurrence and seasonal variation of dissolved pharmaceuticals in the sections of Datong (the tidal limit of the Yangtze Estuary), Xuliujing (the bifurcation node of North and South Branches of the Yangtze Estuary), and Wusongkou (the estuary of the Huangpu River into the Yangtze River) were studied. The results show that various pharmaceuticals were detected with concentrations from below detection to 535.2 ng/L. Sulfadiazine, erythromycin, thiamphenicol, and paracetamol were the main residues in the group of sulfonamides, macrolides, chloramphenicols, and non-antibacterial pharmaceuticals, respectively. During the same period, the concentrations at the sites of Wusongkou were generally higher than Datong and Xuliujing, which were mainly due to the dilution of the Yangtze River. Compared to the concentrations at Datong, chloramphenicols at Xuliujing were significantly higher in the autumn and winter, while macrolides were lower in the spring. Based on the flux estimation and the detected concentrations at Xuliujing and Wusongkou, about 37.1 tons of sulfonamides,17.4 tons of macrolides,79.2 tons of chloramphenicols, and 14.1 tons of non-antibacterial pharmaceuticals were discharged into the Yangtze Estuary during the period of June 2013 to May 2014. However, the total flux from the Huangpu River only accounted for 5%. The pharmaceutical sources can be speculated by analyzing the seasonal variations of pharmaceutical concentrations and fluxes at different sites. Both environmental factors and social factors may affect the fluxes.According to the concentration levels of pharmaceuticals and hydrological conditions of the Yangtze Estuary, learning from the existing diffusive gradients in thin films (DGT), a novel passive sampling technique based on the two-dimensional diffusion model was developed and optimized. In addition, in the selection process of the adsorption material for passive sampling, the process and mechanism of adsorption of pharmaceuticals on multi-walled carbon nanotubes (MWCNTs) had be discussed. The adsorption behavior of 3 chloramphenicols,7 sulfonamides, and 3 non-antibacterial pharmaceuticals on five types of MWCNTs, and the underlying factors were studied. Adsorption equilibrium was reached within 12 h for all compounds, and well fitted by the Freundlich isotherm model. The adsorption affinity of pharmaceuticals was positively related to the specific surface area of MWCNTs. The solution pH was an important parameter of pharmaceutical adsorption on MWCNTs, due to its impacts on the chemical speciation of pharmaceuticals and the surface electrical property of MWCNTs. The adsorption of ionizable pharmaceuticals decreased in varying degrees with the increasing ionic strength. MWCNT-10 was found to be the strongest adsorbent in this study, and the Freundlich coefficient (KF) values were 353-2814 mmol1-n-Ln/kg,571-618 mmol1--n-Ln/kg, and 317-1522 mmol1-n-Ln/kg for sulfonamides, chloramphenicols, and non-antibacterial pharmaceuticals, respectively. The different adsorption affinity of sulfonamides might be attributed to the different hydrophobic of heterocyclic substituents, while chloramphenicols adsorption was affected by the charge distribution in aromatic rings via substituent effects.