Study On The Environmental Behavior Of Typical Persistent Organic Pollutants In Lanzhou Area

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 In addition, when POPs be emitted to the environment, they can have serious effects on the environmental fate and health exposure risk because of some behaviors and characteristics including transfer and transformation between different environmental media.Semi-volatile POPs can easily evaporate into air from soil and water, and exist in the vapor phase and absorpt into particles phase or aerosol. Moreover, once the POPs have been discharged into the environment they can stay in the environmental media for a long time due to their characteristic of non-degradation. Because of the two characteristics of semi-volatility and non-degradation of POPs, they can emit into air and,then deposit, futhermore evaporate into air and then deposit again, so they will be transported through atmosphere for a long-range distance and can be found in the global environmental media. Therefore, to study the pollution situation, to know the characteristics of pollutants concentration level and distrubution, and to identify the souces, transfer potential and fate become the hotspot problems in environmental field in recent years.Lanzhou is located in the semi-arid area of China, in which the sandstorms commonly occur all over the year. Lanzhou city also has special meteorological and geographical conditions, so it is significent to reveal the characteristics of environmental behaviors of POPs in Lanzhou area. Organochlorine pesticides are a kind of tapical POPs and were used as insecticides in large quantities in Lanhou area previously. Recent researches have revealed that there are still some residual in environmental media in Lanzhou area. In addition, the development of heavy industry, the large-volume fossil fuel combustion and other human activities result in the remarkable increase in discharge quantity of poly cyclic aromatic hydrocarbons,dioxin and other pollutants in Lanhou area.This paper tries to chooses several typical POPs as aim compounds and Lanzhou city as study area, and to study their pollution characteristics of air and soil, the air-soil exchange, and the environmental behaviors of long-range transport and overall environmental persistence. Therefore, this study will provide some scientific data for the ecological risk assessment and pollution contron of typical POPs in semi-arid Lanzhou area.The research methods and contents in this paper are as follows:The aims of this work are to collect the air and top-soil samples in winter,spring and summe, respectively, in Lanzhou area, to analyse the concentration levels of TSP, four isomers of HCH (α,β,γandδ-HCH),the isomers and metabolite of DDT (4,4'-DDE,2,4'-DD,4, 4'-DDD和4,4'-DDT) from these samples, to identify their variation trends of concentrations with season, to reveal the gas-particle partitioning characteristic in air, and the initially sources and sinks of DDTs in the soil by using the ratio of DDTs and its metabolite, to analyse the variation trends of concentrations of HCH and DDTs in the air and soil samples in recent years, to compare the pollution levels of HCH and DDTs between the Lanzhou city with other cities by refering the relevant literature data, to investigate the states of air-soil exchange of HCH and DDT in soil of Lanzhou area by using the concept of fugacity and the criteria of fugacity quotient and fugacity fraction, to discuss the uncertainties or potential errors by using fugacity quotient as the criteria; to estimate the long-range transport potential (LRTP) and overall persistence (Pov) of typical POPs (2,3,7,8-TCDD,γ-HCH,BaP,HCBand p, p'-DDT) through air and water in semi-arid Lanzhou area by TaPL3 model, to discuss the relationship between the characteristic travel distance (CTD) and Pov, to compare the results with foreign researches, to examine and evaluate the model uncertainties against physical/chemical properties and environmental paramaters by a sensitivity study and the Monte Carlo method for 2,3,7, 8-TCDD.The conclusions are summarized as follows:(1) The concentrations of HCHs and DDTs in the atmosphere of Lanzhou tend to decrease largely in recent years by comparing the study data with literature data. The concentration of HCH and DDT in Lanzhou are under intermediate level by comparing the concentrations in air of winter and spring of Lanzhou with the data of other cities, and as a results, the air pollution is lightly in Lanzhou area. In this study, there are ten air samples results can be granted the two-level of The National Ambient Air Quality Standards in all the twenty-four air samples, and the mean TSP concentration is 426μg/m3. For other pollutants, the gaseous concentrations obviously vary with the alternation of season except forβ-HCH, in addition, and the gaseous concentrations showed an increasing trend from larger to small in order of winter,spring and summer, namely the air concentrations increasing depend on the temperature rising. The HCHs and DDTs in the air samples mainly exist in the gas phase with about 85% percent of total air concentrations.(2) The average concentrations of HCHs and DDTs in soil of Lanzhou area meet the one-level of The National Soil Quality Standards, which reveals that the residual amounts of HCHs and DDTs in soil show relatively low level since they have been banned. The residual amounts of HCHs and DDTs in soil of Lanzhou area are lower compared with that of other cities. The concentrations variations of HCHs and DDTs don't have obvious seasonality according to the monitoring results of samples in March and June. The ratio of p, p'-DDT/p, p'-DDE is more than one in three sampling sites and the highest ratio is p, p'-DDT/p, p'-DDE in Anning sites, which indicate that it is possible that there are new DDTs uses after their prohibition. The residual levels of HCHs and DDTs in soil of Lanzhou area already have been declined to from 1 to 3 orders of magnitude compared with that of 1982, moreover, some pollution levels for other aim compounds have also been declined compared with that of 2004.(3) The study results of air-soil exchange for tapical POPs in Lanzhou are as follows:4, 4'-DDD is absorbed to soil from air, which indicate that it displays a net deposition from air to soil. Forδ-HCH, the air-soil exchange probably close to the equilibrium. And for other pollutants (α-HCH,β-HCH,γ-HCH,2,4'-DDT,4,4'-DDE和4,4'-DDT), they have obvious deviation trend from air-soil equilibrium, which suggest that the air-soil exchange probably show a net volatilization from soil to air, namely soil is source.(4) The Simulating results for LRTP and Pov of typical persistent organic pollutants in Lanzhou area suggest that the CTD values of 2,3,7,8-TCDD,γ-HCH,BaP,HCB and p, p'-DDT are 126,934,117,13 307 and 122 km, and the Pov values are 1421,1082,1413,3949 and 1387 d in atmosphere, respectively. Meanwhile, the CTD values of 2,3,7,8-TCDD,γ-HCH,BaP,HCB and p, p'-DDT are 6633,119000,16249,16658 and 20667 km, and the Pov values are 1584,1551,2711,4428 and 3988 d in water, respectively. In addition, there is not obvious relationship between LRTP and Pov, and the distributions of the CTD values in atmosphere of 2,3,7,8-TCDD are more intentionally than those in water, but the distributions of the Pov values of 2,3,7, 8-TCDD in atmosphere are similar to those in water. Futhermore, comparing with study results of foreign researches, the CTD values of 2,3,7,8-TCDD in atmosphere is lower considerably than that in water but the Pov in both air and water are relatively higher.