A Study On The Distribution Features And Release Rules Of PCBs In Surface Sediments Of The Grand Canal (North Section Of Jiang Su)

As the main water transport passage of the South-to-North Water DiversionProject, the Grand Canal （North Section of Jiang Su） would directly influence theeffects of the quality of water transport. After the water transport, the environmentalconditions and water power conditions would change and break the equivalent state ofpollutants of sediments and previous aqueous phase, especially the persistentorganisms would re-enter the previous aqueous phase and thus influence the waterquality of water transport. PCBs is one of the persistent organic pollutants, which canretain in the environment and organism as residuals for a long time and function as theteratogenic, carcinogenic and mutagenic causes; therefore, PCBs is classified into thefirst batch of “The Stockholm Convention” as one of the controlled pollutants. Thestudy on the distribution features and release rules of PCBs in surface sediments ofthe Grand Canal （North Section of Jiang Su） is of vital importance and provides dataand references for prevention and control of organism pollution of the Grand Canal.Sponsored by the Innovation Fund of Jiang Su Province, the paper hassystematically introduced the current studies of PCBs of sediments at home andabroad, collected the specimens of sediments on spot, and carried out the research ofPCBs in surface sediments of the Grand Canal （North Section of Jiang Su） with thefollowing research findings:1. By analyzing37samples of surface sediments collected from the main channel ofthe Grand Canal （North Section of Jiang Su）, the relevance ratio of PCBs is94.6%,the content is between nd²6.819ng/g（dry weight） and average value is9.316ng/g.Two monitoring spots containing the peak value of PCBs content out of37monitoringspots are both located in Xu Zhou Section. As for the space distribution, it is obviousthat the concentration is gradually rising from south to north and from downstream toupstream. The average content of Xu Zhou Section is higher than that of Yang ZhouSection and Su Qian to Huai An Section, and the pollutants are mainly lowchlorinated PCBs. There are three water-passing lakes of the Grand Canal （NorthSection of Jiang Su）, Hong Ze Lake, Luo Ma Lake and Wei Shan Lake respectively, inall which PCBs are detected. The average concentration of PCBs in the sediments ofHong Ze Lake comes first as9.451ng/g, second comes as4.240ng/g in Wei Shan Lake, and the concentration of Luo Ma Lake is lowest, which is only3.542ng/g.2. By adopting the Characteristics of Compound Ratio Method and the PrincipalComponent Analysis, the PCBs in the Grand Canal （North Section of Jiang Su） andthree water-passing lakes are examined to check the source apportionment with thefollowing findings: the PCBs in the main channel mainly stem from the commercialproducts of pentachlorobiphenyl and hexachlorobiphenyl and then from the waste gasout of the high temperature process of coal burning and combustion of urban garbage;the PCBs in Hong Ze Lake mainly come from the commercial products of PCB1andPCB6, and then from the high temperature process; the PCBs in the Luo Ma Lakemainly come from the high temperature process and then the lower chlorinated PCBscommercial products; the PCBs in Wei Shan Lake mainly come from thepentachlorobiphenyl commercial products, such as Aroclor1242, while theby-products of the high temperature process have relatively less impact on Wei ShanLake.3. By adopting the Potential Ecological Harm Index Method and the Toxic EffectEvaluation Method, the author has conducted an ecological risk evaluation of thePCBs in both the main channel of the Grand Canal and the water-passing lakes. Itindicates that the Potential Ecological Harm Index Method is simple and fast butcovers less comprehensive reaction of authentic toxicity; it is better to adopt the ToxicEffect Evaluation Method to reflect the authentic potential risk of ecology. Thepotential ecological risks in Yang Zhou Section are relatively slight, but the moretoxic homologues of PCB126and PCB169cause the more serious ecological risk ofYang Zhou Section than those in Huai An-Su Qian Section and Xu Zhou Section. Thepotential ecological risks in two water-passing lakes （Luo Ma Lake and Wei ShanLake） are relatively low, which has little influence upon biology; while the ecologicaltoxicity of PCBs in surface sediments of Hong Ze Lake is the highest. Totallyspeaking, the ecological risks of these three lakes are far below the ecological risk ofthe main channel of the Grand Cannel.4. By utilizing home-made release simulation device, the PCBs in the sediments areconducted with a simulation release experiment. The results indicate that the first5to9days are the fast-release stage, during which the emission amount of PCBs accountsfor a large proportion of the total emission amount, and then follows the slow-releasestage. During the fast-release stage, the emission ratio and the total emission amountare positively related to speed of stirring device in the water while it is not obvious in the slow-release stage. Two surfactant （SDS and OP-10） in the experiment havefunctions of solubilization and promotion of release, among which OP-10has asignificant effect, especially when it is above the critical micelle concentration （500mg/L and700mg/L）; while the concentration is below the critical micelleconcentration （100mg/L）, it will suppress the release of PCBs in the sediments. Thereleases of sediments with different particle size indicate that the amount of PCBs insediments with small particles（<0.45mm） are obviously higher than those in thelarge particles（0.45-1.25mm）.5. By adopting the PCBs pollutants release dynamics experiment of static shakingflask, the emission process of PCBs in the sediments match with the model offirst-order two compartments and an emission dynamics model is set up as follows:Cw（0）=Cs（0）·Ms/V-Cs（0）·Ms/V·Frap·e^-krap^t-Cs（0）·Ms/V·（1-Frap）·e^-kstow^tThe constants （krap）of the fast release ratio of PCB118,114and126are0.1154d-1、0.1850d-1、0.1403d-1; the constants （krap）of the slow release ratio are0.0057d-1，0.0057d-1and0.0031d-1; the amount of the fast release（Frap） accountsfor67.81%,71.59%and73.97%.6. According to testing and release experimental results, the author puts forwordsuggestions for pollution preventions concerning the future release effect of PCBs insediments of the Grand Canal （North Section of Jiang Su） upon the water quality ofthe South-to-North Water Diversion Project.