Multi-media Distribution And Sources Identification Of Polycyclic Aromatic Hydrocarbons (PAHs) In The Yangtze Estuarine And Coastal Ecosystem

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic to humans, and a number ofPAH compounds have been identified as either carcinogenic or mutagenic to both terrestrial and aquatic organisms. PAHs accumulated in different environemtal media, such as air, waters and organisms, are introduced into the coastal environment by long distance transportation. The estuarine and coastal area, as a typocal transitional zone between land and ocean, is a multifunctional and complex ecosystem with special ecological values and potential resources. Due to the interaction of land and ocean, the estuarine and coastal area is characterized by intense hydrodynamic conditions, frequent sediment transport and material exchange, steep physiochemical gradients and high biodiversity. In addition, the estuarine and coastal area is one of highly human activities zone where response to global changes sensitively. So taking the Yangtze estuarine and coastal ecosystem as a research object, multi-media distribution of PAHs, PAH transport and partition mechanisms near the interface between particle and water, sources identification and its input pathways, ecological risk assessment have been discussed in this work. The main findings are as following:Based on analyzing the temporal and spatial distribution of PAHs in overlying waters, suspended particles and sediments respectively, the present work revealed temperature and resuspension condition of estuarine system were the main factors influenced the variation of PAH compounds in the study area. Because of the complex hydrodynamic condition of the Yangtze Estuary and coastal pollution discharge, the effect of water salinity and sediment grain size on PAHs distribution was not significant. In addition, human activities, such as the sewage discharge, commercial shipping and fishing, also play an important role on PAH multi-media distribution. Ecological risk assessment showed that some PAH compounds had the primary potential impacts on the Yangtze tidal flat ecosystem.Through the discussion of PAH transport and partition process near the interface between particle and water, the results demonstrated that organic carbon in the suspended particles had weakly lipophilic characteristic, and the partition process of PAHs was controlled by a heterogeneous mixtures of soot carbon. The exsisting equilibrium partitioning model that incorporated soot carbon phase could well predict the partition of PAHs in situ. Thus, the sources of PAHs and particle properties should be involved when studying the partition behavior of PAHs in the estuarine coastal area. One further implication of the environemntal soot-associated PAHs is that current laboratory-based practices in sorption-desorption and toxicity testing may not realistically reflect the actual availability of in situ PAHs to participate in such process. To further constrain the proposed extension of the hydrophobic partitioning model to include soot-phase partitioning, K_sc should be evaluated under controlled conditions. This direct investigation on the quantitative relationship between in situ PAH distribution and the presence of soot phases indicates that understanding this link may prove crucial to elucidating the biogeochemical cycling og such combustion-derived compounds.Given the large number of potential sources of PAHs to the multi-media of this highly intense human activities urban estuary, multiple techniques are helpful to identify specific sources of this contminants. By applying the general techniques (e.g., LMW/HMW, isomer ratios), PAHs in the Yangtze estuarine and coastal area were indicative of incompleted combustion at low to moderate temperatures as well as some uncombusted petroleum products. The primary potential inputing sources, such as sewage discharge, coastal rivers draining and road dusts in urban central area, were also proposed by general techniques. By applying the sources specific techniques (CSIA), identification of dominant PAH sources is PAHs that associated with different types of soot carbon, including wood combustion soot, coal soot, car soot, tyre soot and domestic soot. In addition, PAHs derived from wood incompleted combustion was also contributed PAHs to surface sediments.BaA/Chry index inferred that most volatile PAH compounds could enter the water body via air-water exchange, partition into suspended particles, and deposit onto the sediments. Compared with that original source information in potential regions, both BaA/Chry index and isotopic values indicated that PAHs derived from wood incompleted combustion could reach the coastal sediments from rivers and pollution discharge. Those PAHs associated with wood and coal soot which enriched in road dusts could enter coastal area via surface runoff after being washed out by rainstorm. In addition, PAHs associated with car soot in road dusts from urban traffic district, commercial district and culture and education district, were imported mainly via atmospheric transport in dry season and rainstorm wash out in flood season.Sources apportionment by principal component analysis reflected PAHs derived from incompleted combustion. As for dissolved PAHs, coal, petroleum and diesel oil combustion accounted for 74.3%, coke source accounted for 9.5%. As for PAHs in suspended partcles, coal and oil combustion accounted for 77.1%, petroleum combustion accounted for 10.5%. And PAHs in sediments had 67.1% coal and oil combustion, 11.0% petroleum and diesel oil combustion, and 8.6% coke combustion.Separation and quantification of organic carbon and soot carbon is the key to estimate the environmental behavior and effects of combustion-derived PAHs in estuarine and coastal area. Particel and sedimentary organic carbon and soot carbon presented in the Yangtze estuarine and coastal area were the characteristic of combustion origin. Sources identification revealed that particle organic carbon mainly came from organism processes or diagenesis, and imput directly from coastal river and discharge, and had poor affinity to PAHs compared with soot carbon which generated from incompleted combustion. Combustion was the main source for sedimentary organic carbon and soot carbon whose affinity were stronger than particle organic carbon and soot carbon. Sedimentary organic carbon should be washed out by rainwater during transportation and soot carbon could not soluble in water which resulted in sedimentary soot carbon was more abundant than organic carbon.