PAHs And PCBs Biogeochemical Characteritics In The Sediments And Coupling With The Eco-environment In The Bohai Sea And The Southern Yellow Sea

The studies on the residue of Polycyclic Aaromatic Hydrocarbons (PAHs) and Polycyclic Biphenyls (PCBs) in the sediment environments are of important scientific and practical significance in revealing their sources, transition modes, contamination history and potential threat on environments. In this study, PAHs and PCBs in the sediments from the southern Yellow Sea and Bohai Bay, typical semi-enclosed seas, were analyzed with GC/MS. By virtue of systemic analyzing the coupling relationships between PAHs and PCBs concentrations and the sediment environment characteristics, as well as the factors controlling their adsorption and variation tendencies, were studies in detail, which were helpful to evaluate and establish sound scientifically priorities for future managements for them. Four conclusions were drawn as followed:The horizontal distribution pattern of PCBs in the sediments from the southern Yellow Sea was coincident with the sedimentation pattern and controlled by the mode of'sedimentation type-dynamical process-sources'. PCBs concentrations ranged from 518 to 5848 pg/g, with the average of 1715 pg/g. The horizontal distribution of PCBs followed the sequence: the middle area>the west coast>the east coast. PCBs concentrations increased with the sediment particle size decreasing and the clay contents increasing, moreover, PCBs concentrations positively linearly related with TOC contents, suggesting that the adsorption of PCBs were predominantly controlled by sediment texture and the organic matter. As well-known, the hydrodynamics conditions were the driving force to the particles sedimentation. Consequently, the driving factor controlling PCBs distribution was the hydrodynamics conditions of the southern Yellow Sea.From 1914 to 2004, PAHs and PCBs concentrations varied significantly, so that the past century was divided into three periods based on their concentrations variation. The vertical distribution illuminated that PAHs and PCBs levels declined with depth, indicating that their concentrations at present were much higher than in the early of this century with respect to sedimentation time. Therein, the concentrations of PAHs and PCBs kept in low constant level from 1914 to 1932. During the period of 1932~1962, PAHs and PCBs underwent huge variation with the variation range of 24~62%. Their discharge was up to the peaks in the periods of 1932~1944 and 1956~1962. From 1962 to 2004, PAHs and PCBs levels elevated slightly. PAHs compositions and isomeric compound ratios were generally used as the indexes to apportion PAHs sources. From 1920 to 1944, PAHs mainly derived from petroleum production; from 1944 to 1980, the predominant source was the production from grass/wood/coal combustion; and from 1980 to 2004, PAHs composition presented the multi-sources of petroleum and combustion.The distribution modes of PAHs, PCBs, DDTs and HCHs in the sediments collected from Bohai Bay were not in the same, indicating that difference existed in their biogeochemical behavior and sources. The concentrations of PAHs, PCBs, DDTs and HCHs were in the range of 149.0~375.3 ng/g, 360.8~1728.2 pg/g, 462.2~2007.3 pg/g and 4.3~33.8 ng/g. PAHs and PCBs concentrations were higher at the stations close to Majiahe River, Haihe River and Huanghe River. DDTs concentrations in the off-bay stations were higher than those in the in-bay stations, while no significant variations of HCHs concentrations were found. The isomeric compounds ratios suggested that PAHs in the sediments from Bohai Bay mainly derived from grass/wood/coal combustion and transferred into the aquatic environment through atomospheric movement. DDTs and HCHs compositions indicated that DDTs and HCHs were still in use after their legal banish.After comparing the POPs concentrations in the sediments from the southern Yellow Sea and Bohai Bay with the eco-risk thresholds, it was found that the quality of sediments of the southern Yellow Sea was clear and the potential risk rarely occurred. However, Fluorene and"dioxin-like PCBs"could probably pose risk on the environment of Bohai Bay.The original ideas of this paper were that: 1) The PAHs and PCBs distribution variation mode in the past century were studied for the first time, meanwhile, their sources and contamination history were traced and their potential eco-risk were evaluated. 2) The coupling relationships between PCBs and sediment environment were analyzed systemically, which was of precious scientific significance for assess their toxicity. 3) The sources, transition modes and contamination status of PAHs, PCBs, DDTs and HCHs in the sediments from Bohai Bay were analyzed in detail. The results could lay down the theorical foundation for developing and using the Bohai Sea properly and protecting the Bohai Sea environment.