| Owing to their toxicity(such as highly mutagenic and carcinogenic features)and widespread distributions in the global environment,persistent organic pollutants(POPs)have attracted the attention of environmental chemists,toxicologists and regulatory agencies for almost three decades.Recently,there has been a great concern about the POPs distribution research,which aim at establishing the trending model for the pollutants in the environment and researching for atmosphere-soil exchange.Many researching results show that,the monitoring results and calculation results from the model founded on the actual emission data are not be of much comparability,due to the limited data quantity of POPs gained from monitoring.Research for POPs environmental behavior and basical trending theory,such as the relative actions among pervasion,distribution,adsorption or transformation and long distances transportation,are all ideological hypothesis in laboratory,often fall under the predicament of too much variable in actual environment and have to revise the parameters difficultly,are lack of establishing model and validated researching in actual environment;researches on POPs environmental behavior are seldom or never reported for many special environment such as high altitude,deep sea or cave environment.Caves should act as a perfect experimental place to research the transportation model on POPs on account of its advantages as stable environment and no jamming.With the abundant cave source and the special terrain or physiognomy,Karst area has much ecological vulnerability and easiness to be contaminated.But the few reports for POPs in karst area is documented at home and abroad.This article take the selected karst caves as studying site in typical karst area—Guilin,fix on ubiquitous Organic chlorinated pesticides(OCPs)and Polycyclic aromatic hydrocarbons(PAHs)as aim compound and explore its environmental behavior in cave atmosphere or soil and their exchanges,in order to expose the particular characters of POPs exchanges between cave soil and atmosphere and therefore enhance the comprehensions on environmental behaviors and adscription of POPs,through simulating and validating the environmental behaviors of POPs in actual environment.Additionally,research on POPs pollution in karst area from the west of China also make a contribution to enriching Environmental Science in the tropical karst area.The first section of the article studied the OCPs and PAHs polluting characters in the soil and atmosphere from inner and outer area of Dayan Cave.Chosen 13 Sampling points of the soil and 10 Sampling points of atmosphere,atmosphere sampling time was 60 days continuously, have got 13 soil samples and 30 atmosphere samples totally.The result shows,the pollution of OCPs and PAHs in soil was slight,OCPs were abundant of chlordane and heptachlor.In the soil of outer cave,the pollutants were abundant of high molecular weight PAH(HMW),while light molecular weight PAH(LMW)was more in inner cave.OCPs and PAHs pollution in the atmosphere of outer cave were on middling level.OCPs concentration in atmosphere was comparable to the North Pole and South Pole,lower than some background locations in China. HCHs and endosulfan were the main OCPs pollutants detected.In the atmosphere both from inner and outer cave,LMW accounted for dominative proportion for PAHs.The analysis for DDTs and HCHs isomers implied probably fresh dicofol introduced while the of HCHs residues are from historical source.DDT degradation in the soil of outer cave is in aerobic condition contrary to anaerobic condition in inner cave.The indicative of PAH compound indicates that PAHs in atmosphere and soil derived from the complex contribution of oil and heat emission, among them,petrolic off-gas is the main source followed by fuel consumption and diesel engine.The second section of the article summarized the research of organic pollutants dynamic model firstly,informed the environmental conditions of karst cave,clarified the significances of the research of organic pollutants dynamic model by using karst cave as natural experimental place.Based on discussions,the author considered that the organic pollutants in cave atmosphere dynamic transformation should accord with the linear dimension hydrodynamic dispersion transformation model of "semi-infinite porous medium cylinder,one aspect is fixed concentration edge".Aiming at the very model,the article discussed the edge condition.The result were as follows:(1)Main HCHs compounds were accorded with the model,while contrary to the DDTs compounds.The reason was that the vapor pressure(VP)of HCHs was higher than that of DDTs, so it is difficult to be adsorbed by solid and liquid or any other matter in the cave and seldom is degradated with a stronger chemical stability;(2)Ten of PAHs compounds,from naphthol to chrysene,were accorded with transformation model primely.As for three kinds of PAH compounds,benzo[b]fluoranthene,benzo[k]fluoranthene and benzo[a]pyrene,were accorded with transformation model near the cave mouth,but disobeied from the model curve far from the cave mouth.It was through By discussing relations among DL and the different compounds characters parameters,the transformation capability of PAHs in caves was found related to the compounds characters,or was under its control.(3)The concentration value from the model in the cave mouth and actual concentration value of HCHs and PAHs determined was relative perfectly,which could be as the evidence on the conclusion of "POPs from outer cave atmosphere was the source of inner cave".Proposal are put forward to determine u value in the cave in the further work,and demonstrate t value for obtainning the absolute value of DL.The third section of the article described briefly the application and principle of Fugacity model and adsorption-isotherm model in soil-atmosphere exchange action,analyzed the distribution process existed probably for organic pollutants in karst cave environment.Because of a certain geological origin for PAHs,the contents of mineral matters in cave soil were analyzed in order to adjust the PAHs concentration come from rock formation process.The interaction of PAH between soil and atmosphere in the cave could be described by adsorption-isotherm equation.The ratio of soil-atmosphere concentration(Cs/a)was studied,from which the author found that the transferring process of polycyclic aromatic hydrocarbon in the cave soil was divided into three sections,they were:(1)Trap effect at cave mouth.Due to the severe temperature changes between inner and outer cave,there comes a trap domino offect to HMW PAH near the cave mouth,while LMW PAH can escape into the cave from the trap.(2) Chromatogram effect in the mid cave.For the constant temperature and higher humid conditions, the adsorption thermodynamic of PAH in the soil was accord with Freundlich adsorption isotherm equation.The research on the relation between Freundlich constant KiFand compound characters validated the reason of adsorption point ni provided by one.PAH has similar chromatogram effect in the soil and atmosphere.(3)Slope superposition effect in the deep cave.The soil near the deep cave(north cave mouth)breached color layer domino offect,and Cs/a value has gone up.That was due to the influence from the slope existed near the north cave mouth.According the PAH data determined in this study,the superposition quantity of inputting pollutants through slope and the slope volume were worked out,that is,the cave mouth volume is 16.5 time of the slope volume,which matched with the field survey.No obvious law was found in soil-atmosphere exchange action for OCPs in the studied cave due to its homologues degradation and transformation,which should be further researched.
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