PAHs Sorption To Surface Sediments From The Yangtze Estuary And Nearby Coastal Areas And Fate Simulation

As an important area between land and ocean, the estuarine and coastal area is a complex ecosystem with special ecological value. Due to the interaction of land and ocean, the environmental factors change dramatically, making the estuarine and coastal area sensitive and fragile. With the development of economy, a large number of pollutants were brought to these areas and caused different extent of pollution. PAHs (Polycyclic Aromatic Hydrocarbons) had been frequently detected in estuarine and coastal area and caused great concern because of their carcinogenic and mutagenic features. In the present study, we take the Yangtze River estuarine and coastal area as the researching object, Phenanthrene sorption to surface sediment and the mechanism had been discussed, a multimedia model was established to simulate the fate of PAHs. The main conclusions are as follows:The concentrations of PAHs in surface sediments were in the range of 246.5～1493.5 ng/g (average value:661.2 ng/g). PAHs concentration is highest in SDK, and decreased from SDK to CM, JS has a relative higher concentration of PAHs among them. The 3～4 ring of PAHs are the dominated monomers in sediments of researching area. The highest proportion of the PAHs is Phenanthrene (23.2%), followed by Naphthalene (16.5%). The comparison with similar literatures showed that the contamination of PAHs in Yangtze River estuary and coastal area is much lower than foreign severely polluted estuaries and higher than most reported data of China. The LMV/HMV ratio indicated that PAHs of LHK, SDK, WSK are from the pyrogenic source while BLG, LG, FX, JS, CM are from the petrogenic source. Source apportionment by principal component analysis reflected PAHs derived from incompleted combustion and petroleum.In general, the Freundlich isotherms fit the best to the experimental sorption data for all the samples. Excluded BLG, FX and CM samples, the dual model comprising either Freundlich isotherm or Langmuir equation yield satisfied fitting, indicating two sorption domains in the samples studied. OC is one of the dominant sorbents in samples studied. TOC content showed significantly positive correlation with logKFr (R2=0.83,p<0.005) and n values in the Freundlich model,logQmax (R2=0.868, p<0.001) in the Langmuir model and logKFr,x (R2 =0.974, p<0.0005) and logQmax,x (R2=0.911, p<0.005) in the dual models, respectively. At SDK and WSK sites, Freundlich, linear and Freundlish inclusive dual model suggested the partitioning dominant sorption where foc>0.01. Using linear partitioning model, we get logKoc values higher than the predicted Kp values in dual models. Moreover the estimated Koc values at these two sites were higher than others, indicating the higher affinity of organic carbon than those in other samples where foc<0.01. The significance of BC was not concluded in this study. For other samples with foc<0.01, sorption coefficients higher than predicted Kp values suggested the occurrence of other sorbents besides OC. In spite of BC, the significance of minerals in the samples was concluded in this study. Previous studies has concluded that for sediments contained only small amount of OC (foc<0.001), mineral phase contributes significantly to sorption other than OC. In the present study, for LHK, LG, JS and CM sediment samples with foc in the range of 0.001 to 0.01, partitioning dominated sorption contributed by OC only at relatively high water concentration. Mineral phase adsorption dominated sorption at lower water concentration especially when Cw/Sw in the range of 0.0001 to 0.001 in the natural aqueous system.Sediment composition in the main factor control sorption. The result of sequential extraction experiments removing the inorganic and organic carbon showed that the sorption capacity decreased dramatically when organic carbon was removed, indicating that the organic carbon played an important role in sorption. The Freundlich parameter of H2O2 removed component showed that the n value is approximate to 1, in accordance with the characteristic of OC.Temperature is an environmental factor affecting the sorption of PAHs. The increase of temperature was not favorable to sorption, logKFr decreased along with the increasing temperature from 25℃to 55℃. The sorption results from the salinity effect showed that both logKFr and n value decreased with the increase of salinity in SDK and WSK, indicating that higher salinity will lead to higher sorption capacity and strengthen the non-liner trend. But this trend is not significant especially at CM, where mineral is one of the domain controlling sorption. The sorption results from NH4-N concentration effect showed the difference is not significant indicating NH4-N is not the main environmental factor affect PAHs sorption at Yangtze River estuarine and coastal area.A levelⅢmultimedia fate simulation model was established to simulate the transformation of PAHs in the Yangtze River estuarine and coastal area. The model was proved to be valid by comparing the simulated and measured data, and it can be used to study the environmental behavior of PAHs in the Yangtze River estuarine and coastal area.The simulating results showed that PAHs mainly enriched in vegetation and sediment phase; PAHs are transported to the study area by advection; the degradation rate of PAHs is fastest in the vegetation and slowest in sediment; the most predominant transportation fluxes are air-water and air-vegetation flux.