Geochemical Characteristics Of POPs In Soils And Sediments From Small Cathcments In The North Of Dianchi Watershed

Dianchi Lake is located in the central of Yun-gui plateau with surface area of 2920 km2.Dianchi Lake is a plateau lake that has always been classed as comprehensive restoration water areas in China,and the eutrophication was the research focus of water pollution control.With the continuous development of industrialization and urbanization,human activities have increased the nutrients to lakes,reservoir and other closed water area.Eutrophication has become one of serious global water quanlity problems.Persistent organic pollutants?POPs?are organic compounds of natural or anthropogenic origin,which are characterized by hard degradation,bioaccumulation,semi-volatility and high toxicity.As a result,POPs pose a serious threat to human health and the ecological environment.With the development of agriculture and chemical industry,because of their serious harms,POPs in the environment have drawn increasing attention globally.In recent years,scientists have been focusing their intention on the research of POPs.Polycyclic aromatic hydrocarbons?PAHs?are a group of persistent organic pollutants?POPs?which have carcinogenic,teratogenic and mutagenic.Although PAHs in the environment is minimal,PAHs may enter the body through a variety of ways in generation,migration,transformation and degradation process.PAHs have the greatest threats to human health.The problem of PAHs pollution has caused a great attention.Polycyclic aromatic hydrocarbons?PAHs?and organochlorine pesticides?OCPs?are the persistent organic pollutants?POPs?controlled by the Stockholm Convention.Organochlorine pesticides?OCPs?as an important class of typical persistent organic pollutants in the environment,it is difficult to oxidation,degradation of long cycle and high toxicity,the pollution and harm to ecological environment and human health has caused widespread concern around the world.So,The organic pollutants analysis,history tracing and environment risks evaluation are very important for people to comprehend the time-space distribution,the pollutant source,the composition character and the contaminations caused by human activities of organic pollutants in that area.This study chose 2 small catchment of Dianchi watershed as research area and 2 typical kinds of POPs?PAHs,OCPs?as study objects.The level of Persistent Organic Pollutants?POPs?pollution in sediments can directly affect the health of human and other creatures in research area.This paper probed the level of pollution,distribution of the POPs in soils and sediments.In order to do deeply research on the Baoxianghe catchment,in this paper,several representative sampling points which from the soils and sediments were selected to study the residue levels,the distribution characteristics as well as the composition features of this area.The possible sources of the contamination were discussed here,and the potential ecological risks were evaluated.Through the analyses and measures of the vertical distribution and contamination characters of POPs in the sedimentary cores,set up the corresponding time index by Cs and Pb dating to rebuild the aggrading history of the POPs in Baoxianghe catchment.The results of this paper are as follows:1.The pollution level of POPsThe level of pollution and distribution of PAHs in soils and sediments show that:the 16 US EPA PAHs were detected,and PAHs compounds were mainly 3 ring PAH.Occurrence and distribution of OCPs in the soils and sediments:HCHs and DDTs were analyzed.The concentrations of OCPs which were mainly DDTs,reached the peak value in the deep of 30cm in the soils.OCPs in the sediments were mainly from HCHs which were mainly P-HCH,and the concentration reached the peak value at 25cm depth.The results of risk assessment show that:the residues of PAHs in the soils were lower than the national standards of Canada by assessing risk of soil safety in this study.The pollution level of PAHs in the sediments was similar with the same type domestic area,higher than the areas which have weaker human activity.The results of risk assessment show that:the risks evaluation of OCPs in the soils is in the safe range,but there exists some compounds over the ERL in the sediments,which have potential impact of the investigated area.2.The source of POPsAccording to the analysis the PAHs,the PAHs in the soils were mainly from the burning of coal;The PAHs in the sediments originated from combustion concluding liquid fossil fuel combustion,domestic coal and biomass combustion,which was mainly from the combustion process of domestic coal and biomass.Through characteristics of the degradation products of the compound,the result showed that DDTs pesticide mainly came from historical accumulation of the technical DDTs.However,the new input DDTs are transferred to the circumjacent area,which may relates to the usage of Dicofol.HCHs pesticide in the soils came from the combination of historical accumulation of technical HCHs,as well as a newly input of Lidane.And HCHs in the sediments was mainly from a newly input of Lidane.3.The sedimentary records of POPsBase on detection data by using ²¹⁰Pb and ¹³⁷Cs,the temporal and spatial distributions of POPs were obtained.The POPs sedimentary record was reconstructed and the contamination history was investigated.According to the vertical distribution of the OCPs in the sediment core,the use of OCPs in this area began in the earlier 1950s.Then the concentration reached to the highest level in the 1980s.Due to the forbidden of OCPs,the residue of the OCPs then declined.In the later 1980s to 2006,the increasing trend of DDTs concentrations related to the local economic development,leading to the increase of OCPs.The HCHs contamination was mainly from historical residues though new input,such as Lindane,might have occurred before 1990s.The composition analysis results showed that there was still new input of DDTs after 2000.Concentrations of 16 US EPA PAHs ranged from 162.3 in 1945 to 762.2 ng·g-1 in 2013.Local population and Gross Domestic Product?GDP?were significantly correlated with PAHs concentrations in the sediment core during the period between1962 and 2004.Source apportionment results suggested that PAHs originated primarily from combustion processes.A change of source from Biomass or domestic coal combustion)to liquid fossil fuel combustion was observed in 1980s?1990s.The pollution history of POPs corresponded to the industrialization,urbanization,and social and economic development.4.The effect of TOC on POPs in the environmentThrough the analysis of SPSS,the results showed that there was significant correlationship between PAHs,OCPs and TOC in sediments.It suggested that TOC was an important factor in the effects of PAHs and OCPs in the sediment environment.There was significant correlationship between HCHs,OCPs and TOC in soils,suggesting that TOC was an important factor in the effects of HCHs,OCPs in the soil environment.However,there was no significant correlationship between DDTs and TOC.