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As some of the most active regions of water interaction among the large river systems inthe world, the Yellow River Delta (YRD) and the intersection of Yangtze and Hanjiang River(YHR) gain increasing concern on its environmental conditions and changes. However,insufficient studies on polycyclic aromatic hydrocarbons (PAHs) have been reported forthese areas, especially for the YRD which is a newly born wetland with an abundance ofwetland vegetation and aquatic biological resources. In this work, the pollution status ofPAHs was investigated for the YRD area, and by analyzing the transport affecting factors,the PAH transport characteristics in aqueous environment were studied for the concernedareas. The PAH concentrations in the YRD were found to be at relatively low or mediumlevels (121.3 ng L" in water, 209.1 ng g"1 in suspended particulate matter (SPM), and 150.9ug kg" in sediment on average) comparing to other water bodies. The PAH compositionshowed that low and moderate molecular PAHs were the major species in water phase,whearas the SPM and sediment showed a different propotion of each PAH composition. Aninteresting result was found that low-ring PAHs and salinity in this land-ocean interactionarea had a positive relationship (R=0.609). The ecological risk assessment of PAHs showedthat adverse effects would rarely occur in the YRD based on both the average ERL quotientsand the probability risk assessment. The PAH compositions and the principal componentanalysis (PCA) with multiple linear regression (MLR) uniformly presumed that the mixedsources of pyrogenic and petrogenic deriving PAHs were identified in the YRD. For the study of PAH transport characteristics and mechanisms, factors affecting thetransport process were identified. Firstly, the role of carbonate and organic matter in thesorption and desorption process of PAHs was studied勿using a sequential separationprocedure. Five PAHs were used as multi-sorbate and their sorption and desorptioncharacteristics in separated samples were investigated. Generally, the sorption of larger sizePAHs was dominated partitioning to the organic carbon. For smaller size PAHs, bothadsorption and partition play an important role in the sorption process. The desorption massof PAHs was very low for all the three solid samples, especially for larger size PAHs. Forsmaller size PAHs, carbonate mainly affected their sorption and desorption process due to itsinfluence on the physical characteristics of sediment.
Organic fractions remarkably affected the behavior of PAHs in the sorption妙determining the dominating uptake process. For providing insight into the sorptionproperties of organic contaminants, demineralized organic matter (DM), condensed organicmatter (COM), and black carbon (BC) were isolated from original bulk sediment and thesorption parameters were characterized by batch equilibration experiment. Based on thecomparison of sorption behavior of different sorbents, the solid physical structure wasconcluded to play an important role in the PAH sorption. The organic carbon normalizeddistribution coefficient K measured for DM was 0.8 to 3.0 times higher than that of thebulk sediment, indicating that the mineral structure may physically protect the favorablePAH sorption domains. The comparison of surface area normalized Ko values showed thatthe differences between COM and BC in their sorption capability were largely caused bytheir surface areas, additionally indicating the importance of solid physical structure. Whenconsidering the specific r-n interaction with the PAHs, mature organic fractions withpolyaromatic sheets may be affected by this specific interaction, whereas the DM samplewhich contains the electron repulsive group of N-H stretching was considered to hardly sorbPAHs via，二interaction. After eliminating the hydrophobicity effect, sorption affinity ofindividual PAHs showed an increasing order of Fla>Phe>Pyr>Flu>Ace, with the exceptionalPyr showing medium uptake although it has the largest size and is most electrically active.This was attributed to the solid-phase condensation mechanism with part of sorbed Pyr notexisting as liquid phase as other PAHs due to its higher melting temperature.
In aqueous environment, temperature is also considered to play an assignable role in thesorption process of PAHs, and its influence on the sorption equilibrium is indicative of thesorption strength and mechanism. For providing insight into the temperature-dependentsorption process, sorptions of five PAHs on three heterogeneous sorbents including the YHRriver sediment, the YRD estuary sediment, and the treated sediment with organic matterremoved (IM) were also carried out at a range of temperature from 5 0C to 35 0C. Strongersorption was observed at lower temperature, with the equilibrium sorption coefficient凡increasing 2 to 5 times with a decrease in temperature of 30 0C. The increase of Ka value wasattributed primarily to the change of PAH water solubility which predicted 40％ to 75％ ofthe Kd increase in the sorption process. For providing insight into the sorption mechanism,enthalpy change (CHs) for the sorption process was calculated and the values were observedto be negative for all of the interactions, suggesting that the exothermal sorption of PAHsinversely dependents on the temperature. Based on the values of 01Ys, van der Waals forceswere inferred as the main sorption mechanism for the PAHs especially on the YHR sedimentwhich contained more organic matter. For larger size PAHs on the sorbents with low organicmatter, specific interactions other than van der Waals forces were deduced to contribute tothe overall sorption.
For the PAH transport simulation study, sediments from YHR and YRD were subjectedto artificial resuspension under simulated hydrodynamic conditions by using an improvedsyntonic turbulence-simulation device (TSD).艺PAHs concentrations in particles on volumnnormalization increased 74.1％ and 18.5％ for the YRD and YHR samples, respectively, andthe same increasing trend was observed for individual PAHs. On mass weight basis,艺PAHswere observed to decrease for both the YRD (from 2039.5 ng g" to 1149.7 ng g) and YHR(4222.7 ng g"1 to 2914.2 ng g") samples. Interestingly, concerning on different heights of theTSD, the YRD associated PAHs showed an opposite behavior comparing with the YHRbound PAHs, due to the remobilization of less contaminated, larger size particles for theYRD samples which skewed the PAH concentration downward. The distribution of PAHsbetween solid and liquid phases was found to be affected by both organic carbon contentsand surface areas of the remobilized sediments. A modified prediction model with addictiveconsideration of surface properties was developed to exhibit the distribution of PAHs inhydrodynamic system.