| The estuary is the main channel for terrigenous pollutants to enter the ocean,it is affected by both terrestrial runoff and ocean tides.Studying the pollution characteristics of pollutants at estuaries is of great significance for analyzing the geochemical behavior of pollutants.Persistent organic pollutants(POPs)have the characteristics of slow degradation and large-scale migration,and they are a class of pollutants that have attracted worldwide attention.In this thesis,two types of chlorinated POPs.organochlorine pesticides(OCPs)and polychlorinated biphenyls(PCBs)in the typical subtropical river-sea interface of Jiulong River Estuary are discussed.Temporal and spatial distribution characteristics and compositional differences explore possible sources of pollutants.Based on this,the distribution and partition of pollutants in different environmental media are studied,and their possible influence factors are analyzed.The potential health risks of pollutants in the water environment and the ecological risks caused by sediments are evaluated.The result shows that:(1)The dissolved OCPs concentration in maximum turbidity zone of Jiulong River Estuary during the flood season was 0.42～60.98 ng/L,and the PCBs content was 0.31～20.49 ng/L.The concentration at the center of maximum turbidity zone was the highest,and average concentrations of OCPs and PCBs were 15.41 ng/L and 7.39 ng/L,respectively.The concentration of pollutants at the center of maximum turbidity zone during the dry season increased significantly.The OCPs concentration ranged from 35.94 to 119.56 ng/L,with an average value of 68.86 ng/L.The PCBs concentration ranged from 3.02 to 52.15 ng/L,with an average value of 20.11 ng/L.Statistics have shown that the runoffs during the flood and dry seasons were several times different,and the dilution of surface runoff during the flood season was an important reason for the difference of pollutants concentration between different seasons.(2)The concentrations of OCPs and PCBs showed a trend of midstream>upstream>downstream within the Jiulong River Estuary maximum turbidity zone.As the surface runoff of the Jiulong River passed through the maximum turbidity zone,due to the"filtration effect" of the estuary,a large amount of pollutant was trapped at the center of the maximum turbidity zone where the salty and fresh water were most severely mixed,forming a high-value pollution zone.The salinity in the downstream was slightly higher than that in the middle reaches.After a small amount of pollutants entered the downstream area,they were affected by the dilution of low concentration seawater and the "salting out effect",which further reduced the concentration of pollutants.The concentration variation of pollutants in the maximum turbidity zone was controlled by reciprocating flow.During the entire tidal cycle,the concentration was relatively lower at high tide and higher at low tide.(3)The concentrations and compositions of OCPs and PCBs in the flood season differed greatly between water bodies at different depths.Due to the strong runoff effect during the flood season,the sea water and fresh water masses at the river-sea interface impinged on the formation of saltwater wedges in the mixing process,forming vertical gradient differences in the water.Because the composition of pollutants carried by fresh water was different from that of seawater,the proportion of trichlorobiphenyls on the vertical gradient in this region gradually decreased with water depth,and the proportion of pentachlorobiphenyls gradually increased.In addition,the proportion of HCHs in OCPs also showed gradual decrease with depth.In the dry season,the runoff was small,the salty and fresh water were entirely mixed,and the estuarine water showed weak salinity gradient.The concentration and composition of pollutants in the surface and bottom water bodies were both relatively close.(4)The compositions of OCPs and PCBs in different water depths were similar,but the content in the particulates were different.The pollutants per unit mass gradually decreased with the water depth.The size distribution of OCPs and PCBs in the particles showed seasonal differences.The adsorption capacity was balanced among the particle of different size in the flood season,and the enrichment ability of the fine particle in the dry water season was stronger.As suspended particles were dominated by particles of 0.7 to 10 μm,70%of total pollutants were concentrated in this size range.The particle-water partition process was controlled by various factors such as water salinity,OC,EC and so on.During the flood season,the partition process was significantly affected by the organic carbon content.The normalized partition coefficient indicated that,except for HCHs,other OCPs and PCBs had not reached the theoretical equilibrium state of partition.(5)According to the ratio analysis,y-HCH was the dominant pollutant of HCHs in dissolved phase during flood season,while the characteristics showed mixed sources in the dry season.In the particulate phase,β-HCH content was high,indicating that the pollutants on the particulate matter were mainly historical residues.The relative content of o,p’-DDT in the dissolved phase was relatively high,which was affected by the input of dicofol.However,most of DDT in the particulates had been degraded,and the relative content of the degradation product DDE was higher.Principal component analysis of PCBs showed that the main source of PCBs in water bodies was the mixed pollution of industrial products Aroclor1248 and Aroclor1254.In the surface layer and middle layer particulates during flood season,there were also input of Aroclor1260 in addition to Aroclor1248 and Aroclor1254.(6)The concentrations of OCPs and PCBs in the sediments were lower than that of suspended particle.In terms of the distribution of the whole estuary,OCPs showed a tendency of enrichment in the sediments of the maximum turbidity zone,while PCBs had a higher concentration in the sediments of Haimen Island.(7)The risk assessment of pollutants showed that OCPs and DL-PCBs in the central of maximum turbidity zone had certain health risks,which may cause cancer to both adults and children.Among them,α-HCH monomer has a higher carcinogenic risk,and its highest value exceeded the risk threshold 10"6 specified by USEPA.In the sediment,p,p’-DDD and γ-HCH had certain ecological risks,and their concentrations exceeded ecological risk threshold. |
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