| Polycyclic aromatic hydrocarbons(PAHs)are important persistent organic pollutants(POPs).They are pervasive in the environmental medias,including atmosphere,soil,water and sediments.PAHs can migrate between different medias.In recent years,research on PAHs sources and their environmental effects has become one of the hotspots at home and abroad.As the sink of material migration in the watershed,sediments can record the ecological evolution information continuously and high-resolution.The increase of organic matter content in the sediments will promote the capacity of enriching external pollutants,resulting in increasing of the ecological risk in the watershed.Among them POPs are the most typical.Southwest China is located in the Yunnan-Guizhou Plateau.With the rapid development of industry and agriculture,the internal and external sources of organic pollutants in the watershed have increased accordingly,causing a serious threat to the environment and human health.Therefore,from the perspective of ecological security and sustainable development of the region,quantitative analysis of PAHs content,sources,influencing factors and assessment of ecological risks in typical small catchment are of great significance for the management of this region.In this study,two small catchments in the southern part of Dianchi Lake in southwestern China were selected as the research targets.The characteristics of the organic matter contents,particle size and PAHs contents in the modern sediments were analyzed.Various methods,such as radionuclide dating techniques,multivariate statistical analysis,molecular ratios and so on were used accordingly.The level of contamination and potential risks of PAHs were discussed.The sources of PAHs were identified.We reconstructed the historical trend of PAHs pollution in the study area.Here are the main conclusions we obtained:(1)Characteristics of sedimentary environment in the small catchment are obvious.The time series of sediments in the small catchment were established based on the activity of 210Pbex in the sediments(verification by 137Cs activity).The results show that the sedimentary periods was from 1867 to 2011 and the average sedimentation rate was 0.62 g/cm.The particle size analysis show that the silt content in the sediments was high(59.89%),which enhance particles to carry organic matter.It can be also proved by the concentrations of TOC,TN and TP ranged between 4.86?43.47g/kg,0.58?5.194g/kg,0.08?1.23g/kg,respectively.In addition,the changes in sedimentation rates at different periods reflected the impact of human activities on the ecological environment after the construction of water conservancy facilities in the catchment.Before 2000,the climate in the area was relatively humid,but in recent years,the precipitation has decreased.(2)The contents and composition of PAHs in the sediments of the small catchment vary with deposition period.The concentrations of PAHs in the sediments ranged from 102.47 to 653.57 ng/g(mean value 230.18 ng/g).In the composition of PAHs,2-3 ring PAHs accounted for 74.29%of the major components.As for individual PAH,the Phe content was highest(average concentration 55.13 ng/g),followed by Flu(average concentration 54.22 ng/g).PAHs shows a rising trendency over time.The deposition records of PAHs in the sediments in a hundred years can basically be divided into three stages.From 1867 to 1982,PAHs concentrations were stable and low at this stage,which was related to the sluggish economic development and frequent wars at that time.In the second stage,from 1982 to 1998,the PAHs increased steadily.China implemented the policy of "reform and opening" policy in 1978,in line with the fact that a large number of new factories and fossil fuels were used in the study area.In the Early 1990,the adjustment of agricultural planting structure in Yunnan province is of great important.The third stage is that after 2000s,The PAHs content is gradually increasing but slowly,which may be related to the policy of large-scale conversion of farmland to forests implemented by Yunnan Province in 1998 and the improvement of industrial structure and pollutant treatment measures.(3)The sedimentary PAHs are mainly from the incomplete combustion of fossil fuels.The results of the qualitative analysis by molecular ratios in the small catchment show that PAHs mainly come from the mixture input of combustion and petroleum.Quantitative analysis was based on PMF modal,which shows coal and biomass combustion source,oil source,coke source and Gasoline and diesel combustion source account for 36.73%,23.68%,21.67%,17.91%,respectively in the Chaihe catchment.While in the Shuanglong catchment was 34.48%,25.82%,22.33%and 17.37%,respectively.(4)The ecological risk of PAHs in small catchment is low.The concentrations of PAHs in the small catchment were all above 100 ng/g,indicating that the historical pollution level of PAHs was mainly within the range of moderate pollution.The ecological risk assessment of individual PAH showed that the risk coefficients of Ace and Flu were 1.76 and 3.62,while the rest were far less than 1.Toxicity of 16 PAHs(US EPA)ranged from 0.77 to 32.29 ng TEQ/g.It shows that the potential ecological risk of small catchment in southwest of china is low.(5)Human activities have a greater impact on the environmental behavior of PAHs.The concentration of PAHs is positively related to human activity.Phosphorus mining has a great influence on the content of PAHs(R2=0.67,P<0.001).Increase of organic matter content in the catchment will accelerate the enrichment of PAHs.The comprehensive analysis of organic matter sources by C/N(2.46?10.82)and ?13C(-24.88 ‰?-21.72 ‰),it can concluded that the organic matter mainly comes from terrestrial C3 plants and algae.TOC contents had positive correlation with ?PAHs(R2=0.72,P<0.001)and 4-ring(R2=0.80,P<0.001).It reveals that human activities causes the increase of TOC content,affects the distribution and fate of PAHs in sediments. |
PDF Full Text Request