| Persistent organic pollutants (POPs) are a series of toxic organic pollutants, they have longhalf-lives, and hard to degrade once released to environment. They are semi-volatile, can betransported to remote regions even polar regions by wind or water. Moreover, they are likelyaccumulated in organism by food chain, which will be disadvantageous for the health of humanand organism. They are toxic to liver, kidney, nerve, and incretion, which cause cancer and otherproblems. Hence, there are more concerns on POPs, and the problem of POPs has been a globalenvironmental issue.Due to their physicochemical properties, POPs are subject to long-range atmospherictransport. Therefore, POPs released to the source region could be dispersed rapidly by air andwater, and tend to be redistributed at a bigger or global scale. Recently, many studies haveshowed that atmospheric transport from tropical and subtropical which are high POPs emissionregions across the Pacific Ocean to high latitude regions, such as Canadian and Arctic regions.Similarly, high mountain areas usually have relatively low daytime air temperature andrelatively high precipitation compared with lowlands, and most experience long-lasting snowcover. Wind speed and solar radiation flux are higher than in adjacent low lands, whereasatmospheric pressure is lower in high mountains. Many of these characteristics will influence theenvironmental behavior of organic chemicals, which favor for mountain areas act as a "tank" or"reservoir" for POPs. On the other side, mountains have a high degree of habitat diversity and theyare main water source for low altitude regions. The pollution of mountains will be potential threatsto sensitive aquatic and terrestrial ecosystems. So it is of great importance to study the pollutionlevel and pollution process in mountains. Tibet Plateau is of great ecological signification due to its vast water source and lots of sparse animals and plants. The intergrades of mountains linkedTibet and lower land in Sichuan Basin (the west edge of Sichuan Basin) is the necessary path forwater supply and for pollutants transport to high mountains. However, at present, few studies havebeen focused on this region. Hence, in this thesis, a typical region between Tibet and SichuanBasin-Chengdu Economic Region was chosen. The concentration of POPs in this region, seasonaland spatial air-surface exchange and transport characteristics of selected POPs in basin-mountainregion of west edge of Sichuan Basin and the contribution fluxes of POPs from lower land tohigher altitude region were studied.Part one: The regional soil pollution level and distribution characteristics of POPs inChengdu Economic Region (CER)The half-lives of POPs in soil were longer than in other environmental media, so theconcentrations in soil were used to represent the general distribution and pollution level of POPsin CER. Gridding method was used to collect the surface soil samples. In sum, 245 soil sampleswere collected in April, 2006. The concentrations of OCPs and PAlls in soil were analysed.1. The regional pollution level and distribution characteristics of OCPs in CER(1)The concentration order of OCPs was: DDT> HCB >HCH. The concentrations of OCPs atthe centre of CER, like Chengdu, Deyang and some other places in Mianyang were higher thanplaces at surrounding mountains; (2) For HCHs, the concentrations were less than those in northand east of China, but higher than in less developed region, like Guiyang. The concentrations ofDDTs were more than reports on southeast and southwest of China and less than concentrations innortheast of China. Comparing with different mountains in the world, the level of OCPs washigher than those in mountains in Europe and South America; (3) The ratios ofα-HCH/γ-HCH andp,p'-DDE/p,p'-DDT indicated illegal OCPs was still used in some places of CER.2. The regional pollution level and distribution characteristics and geochemicalsignifications of PAHs in CER(1)The average concentration of total 16 PAHs in soil was 3233.92 ng g-1. HMW-PAHs weremajor fractions of total PAHs in CER. Higher concentration was showed at the centre of CER andhigh mountains near Ya'an City; (2)The average concentration of total PAHs was one order ofmagnitude higher than that of south China, was equivalent to that in north China. Compared toother regions in the world, the concentration was much higher than those of background regions inAntarctic and European high mountain soils, and higher than in some Europe residential and arablesoils; (3) The ratios of different PAHs indicated grass, wood and coal combustion was the main source of LMW-PAHs in high mountains, traffic and industry petroleum combustion was the mainreason of high level PAHs in the centre of CER.3. The influences of environmental variables on Distribution of OCPs(1) Generally, the concentrations of OCPs in the subtropics and temperate zones were higherthan in frigid zones; (2) The concentrations of HCHs and HCB in plain and hilly land were higherthan in mountain area, while the concentrations of DDTs in mountains were higher; (3) In arableland, forests and artificial land, HCHs and DDTs concentrations were higher than in grasslandareas; (4) For most HCHs, the concentration had high positive relationship with soil TOC;however, for DDTs and HCB there was no such tendency; (5) The concentrations of OCPs in acidsoils were higher than in alkali and neutral soils; (6) The concentrations of OCPs in spinney forestwere higher than in conifer forest and broad-leaved forest.4. The influence of environmental variables on distribution of PAHs(1) The concentrations of PAHs were higher in warm temperate zone and subtropical zonethan in low temperature zone; (2) The concentration in plain, hilly land and Ya'an mountainousregion were higher than in other places; (3) The concentration in paddy fields, dry land andforests were higher than in artificial land and grass; (4) There was positive correlation betweenthe concentration of PAHs and TOC. The correlation was more obvious for 4-rings PAHs thanfor 5-, 6-rings PAHs; (5) The concentration of PAHs in acid soils was higher than in alkali andneutral soils; (6) The concentrations in conifer and spinney forest were higher than inbroad-leaved forest.Part two: The temporal and spatial distribution characteristics of POPs at Basin-MountainTransect (BMT).After the regional investigation, the typical basin-mountain transect from Daying toQingping was selected for studying the temporal and spatial changes, air-surface exchange andtransport of POPs. 10 pairs of soil and air deposition sites along this transect were deployed. Thesamples were collected nearly every three months. The monitoring time was from Jun, 2007 toJun, 2008. 39 soil samples and 38 couples of wet and dry deposition were analysed. Theconclusions in this part were:1. General concentration characteristicsThe general tendency of concentration of OCPs was: in soil samples, the order was DDTs>HCB>HCHs; in rain waters, the order was HCB>HCHs>DDTs; and in dry particles, the orderwas HCB>DDTs>HCHs. For PAHs, the concentration of total HMW-PAHs (4-6 rings) were higher than those of total LMW-PAHs (2-3 rings).2. Seasonal characteristicsIn soils, the concentrations of HCH and HCB were higher in winter and autumn than inspring and summer; on the contrary, high level DDTs was showed in summer and spring. Forrainwater samples, the concentrations in autumn and winter were higher than in other seasons.For dry deposition particles, high concentrations were found in winter and spring for most OCPs,and a notable high concentration forγ-HCH in summer. The concentrations of PAHs in winterand spring samples were mostly higher than the sample collected in summer and autumn.However, there was high concentration of PAHs in summer rain water.3. Spatial characteristicsFor HCH, the concentration in soil increased as altitude increasing, while the highestconcentrations of HCB and DDT and DDE were at low altitude site. For wet and dry deposition,the concentrations in low altitude were higher than in high altitude. There were positiverelationships between LMW-PAHs soil concentrations and altitude. However, there was noobvious relationship between wet and dry deposition and altitude.4. The deposition characteristics of POPsThe deposition levels of p.p'-DDE and p,p'- DDT were lower than those of HCB and HCH.The depositions at low altitude were more than those at high altitude region. For HCH and HCB,the depositions in spring and summer were more than in other seasons. Wet deposition was moreeffective than dry deposition for more volatile compounds HCH and HCB, while dry depositionwas important for less volatile chemicals.The depositions of PAHs were more than those of OCPs. Wet deposition was moreimportant for Nap than dry deposition, and dry deposition was important for HMW-PAHs,indicating wet deposition is more important for more volatile compound, while dry deposition ismore important for less volatile compounds. Spatially, highest deposition level was showed atthe middle of this transect. Seasonally, the depositions in winter and spring were higher thanthose in summer and autumn.5. The influence of environmental factors on the distribution of POPs at BMTThe impact of soil properties on POPsHigh volatile compounds like HCH and HCB had obvious relationship with the content ofTOC in soils. For HCH, negative relationship was observed with the percentage of calcite in soil,but positive relationship betweenγ-HCH and illite in soil. For low volatile p,p'-DDE and p,p'- DDT, no evident relationship was found between their concentration in soil and TOC, butpositive correlation of them with montmorillonite and chlorite.For PAHs, there was no strong relationship between PAHs concentrations and soil mineralcomposition. While positive relationships were found between PAHs concentration and TOC,PAHs concentration and altitude. TOC was dominating factor for retaining of PAHs in soil.The impact of meteorological factors on POPsMeteorological parameters did not significantly affect the concentration of OCPs in soil.Dry deposition ofγ-HCH had a positive relationship with precipitation, temperature andhumidity. While dry depositions of HCB, p,p'-DDE and p,p'-DDT had a negative correlationwith those factors. Wet deposition of OCPs had a positive relationship with precipitation,temperature, humidity and wind speed, especially for HCB,γ-HCH and p,p'-DDE.There were obvious negative relationships between dry deposition of PAHs and temperatureand humidity. Negative relationship was also found between wet deposition of Nap and humidity,wet deposition of BghiP and wind speed.Part three: The spatial and temporal characteristics transport model of POPs atBasin-Mountain Transect (BMT)Mountain cold trapping has been proved by monitoring data; however, there were spatialand temporal differences due to complex physicochemical properties, environmental andmeteorological parameters. A four compartments dynamic fugacity model was used to explainthe spatial and temporal characteristics, and no emission and constant emission scenarios wereconsidered for OCPs and PAHs respectively.Sensitivity analyse showed the varying of soil and temperature were the most importantparameters influenced the modeling result. Modeling results indicated that soil was the source ofPOPs in other media. Sediment was a more stable compartment for the store of POPs. Theconcentrations in air and water varied seasonally, with concentration of high volatile compoundswas higher than those of low volatile compounds. The comparison of modeling concentrationand initial concentration showed that high volatility compounds were more difficult to reducecomparing with high volatility compounds. The reduction ratio in high temperature seasons washigher than that in cold winter. The calculated air transport fluxes indicated more volatility willresult longer transport distance. And there was seasonal difference; the fluxes in winter weremuch less than those in other seasons. In spatially, the fluxes ofα-HCH at basin sites were lessthan those at high altitude mountains, while the result of p,p'-DDE was reverse, that high air transport fluxes were found at basin (low altitude), while the fluxes at high altitude were verylow, indicating more volatility will result longer transport distance. There was no obvious spatialdifference for PAHs. However, great difference was showed between different compounds. Thefluxes of PAHs were higher than those of OCPs. The order of fluxes for PAHs was:Phe>Pyr>BghiP. The difference of PAHs also proved there was strong positive relationshipbetween the transport capability and volatility at BMT. |
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