| With the social and economic development, more and more pollutants with complex components are produced by human activity and natural process. Some trace pollutants which are persistent and biotoxic pose serious threat to the aquatic environmental. Persistent toxic substances are contaminants of strong biotoxicity and ecotoxicity, which are difficult to be degraded in the environment and constantly accumulate, enrich and magnify through the food chain in the ecosystem. Persistent toxic substances (PTS) can transport long distance in large scale via solid, gas and liquid. When PTS enter aquantic environment, they can affect living organisms directly through the overlying water, and also transport and transform among the overlying water-gap water-sediment through physical, chemical and biological processes of the water bodies. Thus, PTS have lasting impacts on the quality of the aquantic environment and furtherly affect the safety of the aquatic ecosystem. The persistent organic pollutants and heavy metal contaminant, two kinds of typical PTS in the aquatic environment, are hazardous to human beings and the nature since their impacts could be far-reaching and significant and their remediation is either hard and slow by nature process or costly and imperfect by artificial measures. Therefore, PTS in aquatic environment have been highly concerned worldwide.Wenruitang River, the "mother river" called by the local people, is the largest urban river network in Wenzhou City. Wenzhou is famous for its small-medium sized enterprises and family workshops, pollutants are disorderly discharged to the aquatic environment in the production process due to the loose environmental management. With the support of the National Major Project (2009ZX07317-006) and the National Natural Science Youth Foundation of China (41101471), this dissertation took Wenruitang River as the research object, investigated the PTS in the surface water, pore water and sediments from Wenruitang River by chemical analysis, determined the PTS pollution sources through statistical analysis, assessed the biological toxicity of the PTS via light-emitting bacteria and tropical Xenopus embryos. It revealed the spatial distribution characteristics of PTS (Cd, Cr, Pb, Hg, As, Cu, Zn, Ni and PAHs) in Wenruitang River, pollution sources, PTS biological toxicity and the response of model organisms to PTS, assessed the contamination degree and ecological risk of PTS in Wenruitang River, hopefully to provide a theoretical reference for river pollution treatment and the sustainable use and management of river water resources. The major conclusions of this research are listed as follows:(1) The average heavy metal content in the surface water and pore water from Wenruitang River was higher than the corresponding value in the level V of the surface water standard of China, which showed that the river was polluted by heavy metals. The content of Cd, Hg, Cr, Mn, Ni and Cu in the surface water was less than that in the pore water. Zn was an exception, for its concentration in the surface water from some of the sampling sites was higher than that in the pore water from the same place. The interval values (mg/kg) of heavy metals from the sediments of Wenruitang River were:Hg (0.18～7.31), Cd (0～149.53), Cr (43.9～1892.70), Pb (17.31～162.93), As (2.12～17.79), Cu (19.23～3393.81), Zn (119.27～4934.87) and Ni (16.72～1646.09). The sampling site with the maximum Cd and Zn contents located in the main channel of Wenruitang River where residential area and industrial area were overlapped, following by Sanyang wetland area where small smelting and plating factories used to concentrated there, and the minimum Cd and Zn contents in agriculture and exurban area. Vertical distribution characteristics of heavy metal in core sediment samples showed that heavy metal pollution caused by agricultural sources was reduced while pollution caused by industrial sources and residential sources were increasing. Heavy metals Cd, Cr, Pb, Cu, Zn, Ni and Fe were mostly in the form of residual fraction rather than other forms. The bioavailable state of these heavy metals were Cd (66.75%)> Mn (65.90%)> Ni (63.55%)> Cu (60.24%)> Pb (59.67%)> Zn (58.61%)> Cr (54.70%)> Fe (23.69%).(2) The evaluation result of the sediment single element pollution index (Cf1) was Cd (76.92)> Cu (17.4)> Hg (10.66)> Zn (9.19)> Ni (5.69)> Cr (4.30)> As (1.46)> Pb (1.43). The evaluation results of integrated Pollution Index (Cd) indicated that the numer of seriously, heavily and moderately polluted sampling sites was14,7and8, respectively. Among the seriously polluted sampling sites, Cd, Cu, Hg, Zn, and Ni belonged to the serious pollution level. The order of potential ecological risk index (Er1) was Cd (2307.47)> Hg (426.25)> Cu (87.03)> Ni (28.45)> As (14.58)> Zn (9.19)> Cr (8.60)> Pb (7.14). The results of the ecological risk index RI showed that there were17sampling sites of extremely strong ecological risk,7sampling sites of strong ecological risk and no site of low ecological risk. The highest ecological risk appeared at sampling site8#while the lowest was at sampling site25#. Hg and Cd had strong potential ecological risk.(3) The order of the average enrichment index of heavy metals in the sediment was Cd (126.7)> Cu (33.1)> Zn (16.3)> Hg (14.71)> Ni (10.7)> Cr (7.80)> As (2.63)> Pb (2.6). According to this order, As and Pb belonged to moderate pollution, Cr, Ni, Hg and Zn belonged to moderate to heavy pollution, Cu belonged to heavy pollution, Cd belonged to serious pollution. The entire river sediments were mostly polluted by Cd and Hg in term of polluted area with more than75.86%sampling sites were no less than the level of moderately to heavily contaminated, whereas As and Pb were leastly polluted with less than6.90%sampling sites were in the level of more serious pollution. Based on the Nemerow Pollution Index, a comprehensive geoaccumulation index was established. The geoaccumulation index showed that the sediments were polluted by Hg, Cd, Cu, Zn, Ni and Cr. The pollution level order of different region was machinery industrial park> main river city downton section> Sanyang Wetland> suburban areas> drinking water source areas. (4) Heavy metal pollution in Wenruitang River mainly affected by human activities. The anthropogenic contribution rate of each heavy metal was Hg (86.62%)> Cd (81.20%)> Zn (80.59%)> Cu (75.86%)> Ni (68.12%)> Cr (64.26%)> As (54.7%)> Pb (45.78%). The correlation analysis and principal component analysis indicated that Hg, Cd, Cu, Zn, Ni and Cr were significantly correlated. Heavy metals in Wenruitang River were mainly originated from anthropogenic sources, and affected by geochemical process at the mean time.(5) The minimum, maximum and mean concentration of polycyclic aromatic hydrocarbons in the surface river water was28.91ng.L-1,440.04ng.L-1and128.13ng.L-1, respectively. PAHs structure composed mainly by low ring (2+3). PAHs had higher concentration in machinery industrial park area, residential and industrial mixed area as well as the old city area. The maximum, mean and minimum concentrations of PAHs in interstitial water were1628.50ng.L-1,631.87ng.L-1and57.56ng.L-1, respectively. The average PAHs concentration in the interstitial water was greater than that in the surface water samples. The PAHs structure composed mainly by the low ring (2+3). The minimum, maximum and mean contents of PAHs in the sediments were152.85ng.g-1,3826.80ng.g-1and1314.58ng.g-1, respectively. PAHs monomer mainly composed by2～6rings, low ring (2+3) structure accounted for37.37%by average, middle ring (4) structure accounted for37.41%, high ring (5+6) structure accounted for25.22%. The order of PAHs content in sediments were machinery industrial park area> residential and industrial mixed area> the old city area> tributary confluence area> the main river stream and the river source area.The PAHs content in the sediment column sample showed that the first layer had higher PAHs than the second and third layers from samples1#,3#,10#,14#,18#and20#, which revealed that the pollution was aggravating. PAHs content in the first layer was lower than that in the second and third layers from samples2#,4#,7#,15#,16#,19#,21#and23#, which indicated that the pollution was reducing. (6) The TEQ values of surface water samples of Wenruitang River ranged from0.02to16.15ng.L-1. The average value was2.62ng.L-1, which is lower than2.8ng.L-1defined by the surface water quality environmental standards, meaning that the toxic equivalence was in security. There were7sampling sites with TEQ value higher than the surface water quality standards. These sampling sites would face higher ecological risk. The minimum risk value ranged from15.42to1684.28with the average value of315.06. The maximum risk value ranged from0.15to16.84with the average of3.15. There were4high-risk rating sties,17medium risk rating sites and8low risk rating sites. PAHs monomer concentration in sediments exceeding the ecological effects ERM was not found, so PAHs monomer in sediments was not liketly to induce ecological risk. The average biological toxicity by sediment toxicity equivalent methodwas158.2ng.g-1(ranged from9.49to1331.09ng.g-1). The average sediment minimum risk quotient is438.99, the risk quotient value ranged from55.36to2833.31. The samples had at least medium risk accounted for82.8%, indicating the possibility of potential ecological risk.(7) The cluster analysis and principal component analysis demonstrated that middle and high ring of PAHs monomer was generated by the heat source, the low ring with low molecular weight or alkyl substituted class of PAHs was originated from natural sources or oil spill. The FIu/(Flu+Pyr), Ant/(Ant+Phe) ratios indicated that the main source of polycyclic aromatic hydrocarbons was combustion sources, including23.1%oil combustion sources and76.9%fuelwood combustion source. The FIu/(Flu+Pyr), BaA/(BaA+Chr) ratios analyzed the sources of PAHs in the sampling sites, including4oil combustion sources,6oil, firewood and coal mixed source,12high-temperature fuelwood combustion sources. The cluster analysis showed that the high ring PAHs monomer in Wenruitang River sediments mainly originated from heating sources, the low ring PAHs or alkyl substituted class PAHs mainly originated from natural sources and oil spill. Principal component analysis of PAHs sources showed that PAHs were related to the emission from diesel, natural gas and gasoline combustion. This principal component can be regarded as traffic related pollution source, fuelwood class combustion source and volatile petroleum-related products source. Ant/(Ant+Phe) characteristic ratios illustrated there were six sites for the petroleum-based pollution sources. FIu/(FIu+Pyr) ratio illustrated source of fuelwood class combustion accounted for75.8%, and also the presence of oil burning and oil spill source. FIu/(FIu+Pyr), BaA/(BaA+Chr) ratio showed that82.8%of the samples mainly originated from the burning of fuelwood substance, the combustion and leak of petroleum substances mixed sources accounted for17.2%. TheFIu/(Flu+Pyr), Inp/(Inp+BghiP)eigenvalue showed that55%of the sampling sites were fuelwood combustion sources, the remaining were oil spill source.(8) The biological toxicity was measured by Qinghai Vibrio (Q7) against the surface water, interstitial water and sediment of Wenruitang River. Results showed that the average luminous intensity of the surface water was80.9%, belonging to slightly toxic; the average luminous intensity of interstitial water was69.7%, belonging to medium toxicity; the average luminous intensity of sediment was63.3%, belonging to medium toxicity. The order of relative luminous intensity was surface water>interstitial water>sediment. According to tropical Xenopus placed in sediment leaching, the toxicity results showed that the average hatching rate was75.98%, the average survival rate was83.77%, the average teratogenic rate was16.60%, and the average length was3.58cm. Sampling sites with complex pollution sources and serious pollution level had more significant toxic effect to the Xenopus embryo growth and development, whereas sampling sites with simple pollution source or sites in the river source area had less significant biological toxicity. |
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