| Pharmaceuticals, personal care products, food additives, hormones and sterols, are biologically active but still unregulated or not commonly regulated contaminants. These are collectively classified as emerging organic contaminants (EOCs). EOCs are ubiquitous in the environment. Moreover, EOC concentrations may persist or become pseudo-persistent in aquatic environments. Even at low concentration (ng/L), they may still pose a high risk to the aquatic ecosystem. In this study, forty-two EOCs (e.g. antibiotics and endocrine disrupting compounds) were measured in the Yangtze Estuary (i.e. the overlying water in intertidal zone), China due to their high prescription rates or quantities, high consumption and the availability of reliable analyzing methods, as well as their frequent detection in aquatic environments. This study investigated the occurrence and the seasonal and spatial distribution of these selected EOCs in the study area. To gain further insight of the impact of colloids on the behavior of EOCs in water, the water samples were further isolated into soluble phase and colloidal phase using cross-flow ultrafiltration (CFUF). Moreover, the role of colloids on the occurrence, distribution and behavior of EOCs in Yangtze Estuary (i.e. typical wastewaters and estuary) was examined. The purpose is to understand the interaction between EOCs and colloids by establishing correlations between colloidal geochemical properties, physicochemical properties of the water, and EOCs, especially for the colloidal size-fractionation from the typical wastewaters. The results provided the important data for pollution control and risk assessment of EOCs in the aquatic environments.In the tidal flat of the Yangtze Estuary, the dissolved oxygen (DO) and dissolved organic carbon (DOC) were both negatively related to the temperature. The DOC concentrations in filtrate, soluble (<1kDa) and colloidal phases (1kDa-1μm) were0.4-12.8mg/L,0.3-9.5mg/L, and0.1-1.9mg/L, respectively. The particle sizes and zeta-potential values of estuarine colloids in October2011ranged from454nm to 1610nm and from-6.5mv to-16.5mV, respectively. A strong positive correlation was found between the size and zeta-potential of the colloids (R=0.94, P=0.001). Heterogeneous particles with different aggregate shapes were visible, including anomalous spherical, lens-shaped or fibrous objects and cellular structures. In addition, colloidal properties, including hydrodynamic size, zeta-potential and some important fluorophores (TYLIS:tyrosine-like substances; TPYLIS:tryptophan-like substances; HULIS:humic-like substances) were all significantly negative related to salinity, indicating the vital role played by salinity in estuarine areas.In addition, water samples from an urban wastewater treatment plant (WWTP) and the river influenced by concentrated animal feeding operations (CAFOs) were taken as the typical domestic and livestock wastewater sources of EOCs. In order to gain more information of the effect of colloid on the behavior of EOCs in typical wastewater, the filtrates were further separated into different particle size fractions i.e.300kDa-1μm,10-300kDa,5-10kDa, and1-5kDa. The corresponding colloidal organic carbon (COC) concentrations in these fractions were2.1-6.3mg/L,0.4-2.2mg/L,0.2-1.5mg/L and0.03-0.4mg/L, respectively. It indicated that the COC concentrations were dominated in the300kDa-1μm fraction. A positive significant correlation was found between COC concentration and the colloidal concentrations. Unlike the colloids in Yangtze Estuary, no significant correlation was found between the size and zeta potential of the colloids in the typical wastewater. The morphological structure was dominated with the sheet, branched-chain, and network structure composing of the anomalous spherical particles. The heights of the single particles were less than5nm with relative high value found in livestock wastewaters. In addition, the results of fluorescence indexes show that the colloids in the wastewaters were generally terrestrial and autochthonous particles. When the intensity of TYLIS and TPYLIS increased, HIX values decreased, while BIX values increased, due to the decrease of humification. The occurrence and distribution of EOCs in the tidal flat of Yangtze Estuary were further studied in October2011. The result revealed that the selected EOC concentrations ranged from<LOQ (limit of quantification) to89.1ng/L. Of the42EOCs,70%EOCs were detected with thiamphenicol, florfenicol, sulfadiazine, sulfamethoxazole, sulfamethazine, diclofenac, and paracetamol as the dominant EOCs among all the compounds. The contribution of chloramphenicols, sulfonamides and non-steroidal anti-inflammatory drugs were4.7-27.0%,4.0-54.4%,14.3-66.2%, respectively. The highest concentrations of antibiotics and estrogens were both found in January, which may be due to the relative low water flow and temperature in winter. The highest concentrations were mainly observed at the sampling sites influenced by the confluence of rivers (WSK and LHK) and WWTPs effluent (BLG), indicating that the input of contamination from the rivers and WWTPs upstream is the primary cause for the higher concentration of EOCs occurring at these sampling sites. Furthermore, a significant positive correlation between DOC contents and the total EOC/antibiotic/estrogen concentration suggest that DOC may play a significant role in the behavior of the EOCs in the estuarine system. Risk assessment showed that the RQ values for most of the selected EOCs in the Yangtze Estuary were below0.01, indicating little risk to the relevant sensitive aquatic organisms posed by the target compounds in any season. However, sulfapyridine, sulfamethoxazole and indomethacin could cause medium risk to daphnid in some sampling sites of the Yangtze Estuary, while sulfadiazine, sulfamethoxazole, sulfamethazine,4-tert-octylphenol, paracetamol and diazepam could pose low risk to daphnid of fish in some sampling sites of the Yangtze Estuary.The previous studies, although limited, suggest that colloids can act as a significant sink for selected EOCs, which are confirmed in this study. The average percentage of the selected EOCs associated with colloids was up to42.3%. Moreover, it was found that the contributions of estrogens and NSAIDs in colloidal phases were higher compared to other EOCs. The average organic carbon normalized partition coefficient values (logKcoc) ranged from5.75to7.80. In addition, colloidal properties, including hydrodynamic size, zeta-potential and organic carbon composition were found to be the key factors controlling the association of EOCs with aquatic colloids. Moreover, these colloidal properties were all significantly related to salinity, indicating the critical role played by increasing salinity in EOCs-colloids interaction in an estuarine system.In the wastewaters, less EOC were generally bound with the colloids with compared to colloids in the Yangtze Estuary, which could be attributed to the higher portion of the smaller particles in natural water. The logKcoc values for most EOCs compounds were decreased with molecular weight increased, i.e. Kcoc-1> Kcoc-5> Kcoc-10Kcoc-300.It could be due to the different composition or structure of organic carbon in the different size fractions. Among different size fractions,5-10kDa and10-300kDa fractions displayed a relative higher total absolute concentration of EOCs (i.e. the total EOC mass per gram of colloids), and1-5kDa fraction showed the lowest total absolute concentration among all the colloidal size fractions. It indicated that colloidal concentration was also a vital factor that could affect the distribution of EOCs in the aquatic environment. To fully evaluate the aquatic behavior of EOCs in the wastewater, the mass balance was calculated by including all the colloidal fractions and soluble phases. Overall, the colloidal contribution to the total concentrations of most EOCs ranged from10%to30%. Furthermore, a significant positive correlation was found between the logKow value and the contribution of EOCs in different colloidal fractions, demonstrating that hydrophobicity might be an important factor controlling the behavior of EOCs in the aquatic environment. In addition, pairwise correlation analysis between fluorescence properties (i.e. the intensity of TYLIS and TPYLIS and the fluorescence indexes of HTX and BIX) and the parameters of EOCs behavior (i.e. logKcoc, the absolute concentration and the colloidal contribution) showed that quite a portion of EOCs compounds were related to the fluorescence properties.In addition, the effect of ultraviolet (UV) light on the direct photodegradation behavior of EOCs at low initial concentration (ug/L level) and the effect of colloids on the photodegradation of EOCs in water were elucidated, by studying the photodegradation kinetics in different water fractions (filtrates, soluble phase and colloidal phase). The results reveal that more significant decomposition of most EOCs occurred in the quartz reactor, indicating that UV light was more effective than the other visible light on the photolysis of EOCs. The effect of colloids on the photolysis of EOCs was found to be dependent on the sources, physicochemical properties and concentrations of colloids. In general, compared to ultrapure water, the photolysis rates of most EOCs in permeate were generally accelerated, while inhibited in the retentates (concentrated colloidal fractions). Moreover, the degradation rates of EOCs in domestic wastewater were lower than those in livestock wastewater. |
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