Long-range Atmospheric Transport And Transformations Of Organochlorine Pesticides (OCPs) In The Qinghai-Tibet Plateau

Organochlorine pesticides?OCPs?is a class of persistent organic pollutants.Most OCPs have been banned in production and usage in agriculture activities,due to their adverse and toxic effects in humans including immunological,carcinogenesis and reproductive disorders.With the decrease of the primary emission,the re-emission from the environmental media,as well as the global distribution and environmental fates of OCPs have attracted great concern.The long-range atmospheric transport?LRAT?and natural degradations of OCPs are two important contents.Furthermore,these two environmental behaviors closely correlate with each other.The degradations happen all the time during the LRAT of OCPs,and the metabolites of OCPs can also undergo LRAT as they have similar physico-chemical properties?such as semi-volatilities and persistence?with parent compounds.The concentrations and compositions of OCPs in remote areas are results of the degradations and LRAT of OCPs.However,as far as we know,all LRAT field studies had idealized or ignored the effect of degradations.If the influence of degradations is idealized or ignored directly,an untrue or even wrong LRAT conclusion based on the concentrations and compositions of OCPs might be got.Furthermore,most of the degradation researches of OCPs were carried out under lab-controlled conditions,usually in minimal media or marine sediments,the natural degradations of OCPs have been rarely studied.With time,more and more metabolites will appear and become more abundant.The study on the LRAT and natural degradations of OCPs is essential for better understanding the global distribution and environmental fates of OCPs.In the natural environment,many environmental factors have great impacts on the LRAT and degradations of OCPs.Among them,black carbon?BC?is one of the most important factors.Many field studies have suggested that BC might have a great impact on the LRAT and degradations of OCPs.However,few lab studies have been conducted for explaining detailly the influence of BC on the transport and transformation of OCPs.This thesis concluded field studies and a lab study.For studying on the LRAT and obtaining various metabolites of OCPs,the field studies?the first and second parts of this thesis?have been carried out in a long transect?ca.1000 km?from the Sichuan Basin to the Yellow River source?Qinghai-Tibet Plateau?,Western China.Along this transect,soil and seasonal air samples were collected.Twenty-four OCPs and metabolites of DDT?a typical OCP compound?were analyzed with a gas chromatography triple quadrupole tandem mass spectrometer?GC-MS/MS?.Based on the result of the field studies,¹⁴C-Lindane and ¹⁴C-HCB were chosen as target compounds for the lab study?the third part?.In the lab study,soils were mixed with BC concentrations?0%¹0%?,100 Bq/g dw¹⁴C labeled compounds and 100 ng/g unlabeled compounds,and incubated for 103 d.Soils were collected after 1,7,14,28,56 and 103 d for extracting different fractions and analyzing ¹⁴C-activities with a liquid scintillation counter.In the first part,based on the concentrations and compositions of OCPs along the transect of the Sichuan Basin-the Yellow River source?Qinghai-Tibet Plateau?,the pathway,mode and status of OCPs'LRAT were studied.Concentrations of?OCPs in the soil and air were in ranges?mean?of 175⁶9229?4844?pg/g dw and 17.8³85?70.5?pg/m³,respectively.HCB,HCHs,DDTs and SULPHs?including endosulfan-I,endosulfan-II and endosulfan sulfate?were abundant both in the soil and air.Along the transect,concentrations of OCPs in soils of the forest/basin area were significantly higher than those in soils of the plateau area,while atmospheric OCPs concentrations were similar along the transect.The cold trapping effect couldn't explain the spatial distribution of OCPs in the soil and air along the transect.The spatial distribution of OCPs in the soil,spatial and seasonal distribution of OCPs in air,and the correlation analysis between OCPs concentrations and the environmental factors?including total organic carbon?TOC?,BC,temperature and precipitations?,suggested that the distributions of OCPs in the soil and air might be influenced by the vegetation filter and the cold trapping effects,rather than by just one.The forest filter effect was relatively stronger in autumn and winter.Compared with that in spring and summer.TOC,BC,air temperature and precipitation jointly explained 54%and 63%of the total variation in soil concentrations of OCPs in the plateau and forest/basin areas,respectively.TOC and BC were the predominant factors in controlling the distributions of OCPs in soils of the plateau and forest/basin areas,respectively.The distributions of atmospheric OCPs might be predominately influenced by other environmental factors rather than air temperature and precipitation.Based on air circulation,isomeric and metabolic ratios,fractionation and principal component analysis,a two-way transport system was determined.One flowed from the Sichuan Basin to the Qinghai-Tibet Plateau comprising HCB,HCHs,and DDTs,while the other flowed reversely from the Qinghai-Tibet Plateau to the Sichuan Basin dominating by SULPHs and CHLs?including Heptachlor,Heptachlor epoxide,trans-chlordane,and cis-chlordane?.Multiple linear regression analysis demonstrated greater average contributions?85.9%?of the Sichuan Basin sources onto the soil?OCPs than that of the Qinghai-Tibet Plateau source?14.1%?.In the second part,DDT and relative metabolites were detected in the soil and air along the transect of the Sichuan Basin-the Yellow River source?Qinghai-Tibet Plateau?.Firstly,we concluded the p,p'-dicofol detection limitations of GC system,and suggested that concentrations of p,p'-DBP and/or p,p'-dicofol reported in previous field studies were likely to be false positive.Concentrations of?₁₀DDTs in the soil were in a range?mean?of 37.7⁷0097?4204?pg/g dw,dominated by p,p'-DDT,p,p'-DDE and p,p'-?dicofol+DBP?.?₁₀DDTs in soils of the forest/basin area were significantly higher than those in the plateau area.The atmospheric?₁₀DDTs ranged from 1.23 to 70.5 pg/m³,with a mean of 13.3 pg/m³.p,p'-?dicofol+DBP?was the most dominant compound.The highest atmospheric?₁₀DDTs were found in spring and summer in the basin area,which might be attributed to the cultivation activities in spring and higher BC emission in winter.Accounting to the isomer ratios and mass balance,along the transect,avg.95%and 79%of DDT in soils and air respectively originated from the historical usage of technical DDT.The degradations of DDTs contributed 77%and 31%p,p'-?dicofol+DBP?in soils and air respectively.The higher contributions of commercial dicofol on DDT and p,p'-?dicofol+DBP?in air were probably attributed to the spraying way of pesticides in China,higher mobility of the air,higher uncertainty of the air data and the difference of degradation pathways in soils and air.In the air,the contribution fraction of the DDTs degradations on the p,p'-?dicofol+DBP?concentrations was only avg.30.6%,which was lower than that in soils.The ratio values of p,p'-DDX/p,p'-DDT?p,p'-DDX is the sum concentration of all metabolites?suggested that p,p'-DDT in the soil and air was widely and highly degraded.Because of the presence of other metabolites,the improper use of?p,p'-DDD+p,p'-DDE?/p,p'-DDT ratio would increase?more than one time?the fresh input scale of DDT.This suggested that the ratio of?p,p'-DDD+p,p'-DDE?/p,p'-DDT was not universally applicable anymore and was indicative of the more and more importance of metabolites.Based on previous researches and the correlation analysis,degradations of p,p'-DDT,p,p'-DDE and p,p'-DDD,and the formation of p,p'-DDMU widely occurred in soils along the transect.The degradation pathways were found decreased in areas close to the Yellow River source.The pathways of p,p'-DDT?p,p'-DDE and p,p'-DDD were not significant in plateau areas close to the Yellow River source,which might due to the significant reduction of the parent p,p'-DDT concentrations,the decrease of the oxygen in the air and the greater contribution of the LRAT than that of the degradations on the DDTs concentrations.p,p'-?dicofol+DBP?in the soil was diagnosed to be a metabolite of p,p'-DDT.However,p,p'-?dicofol+DBP?in soils along the transect was found from the LRAT,but not from the degradation of p,p'-DDT in local soils.In the air,the significant degradations of DDTs were investigated in spring and winter in the forest/basin area.The formations of p,p'-?dicofol+DBP?were widely happened,which was in agreement with the dominant degradation source of p,p'-?dicofol+DBP?in air around the Sichuan Basin in spring and winter.PCA and MLRA analysis showed that degradations in the soil and LRAT were two important behaviors?contributing avg.38.3%and 61.7%,respectively?influencing the residues of DDTs in soils of the plateau area.Although the mean contribution of degradations in the soil was lower than that of LRAT,its impact on the DDT residues in the remote area cannot be ignored.The DDTs residues in soils of the forest/basin area were influenced by the degradations in the soil,degradations in air and LRAT,with avg.contribution fractions of 60.1%,31.3%and8.58%,respectively,suggested the predominant influence of the degradation behaviors on the distribution of DDTs in soils.In the third part,a lab experiment was set up to investigate the influence of BC on the fractions and transformations of ¹⁴C-Lindane and ¹⁴C-HCB in the soil,which revealed the impact of BC on the LRAT and degradations of OCPs.In each soil,the volatile rate of Lindane and HCB was constant throughout the aging time,and the volatile content was increased linearly.After 103 d,the volatile contents of Lindane and HCB from the soil without BC were 54.9%and 84.8%,respectively.According to these trends,Lindane and HCB in the natural soil would completely volatilize into the air.BC could rapidly and significantly decrease the volatile and water-soluble fractions of Lindane and HCB by up to three orders of magnitudes,which indicated the significant suppression effect of BC on the LRAT and water transport of Lindane and HCB.The suppression effect of BC on the volatile and water-soluble fractions also suggested the suppression effect of BC on the photolysis and bio-degradation of Lindane and HCB.BC could increase the organic-extractable fractions of Lindane and HCB,revealed that BC facilitated the transport and degradation potentials of both chemicals.The non-extractable fraction of HCB in the soil with 10%BC was>50 times higher than that in the soil without BC,suggested the significant suppression of BC on the bio-degradation of HCB in the soil.Differ from the effect on HCB,the non-extractable fractions of Lindane were oppositely decreased with higher BC concentrations,suggested that BC could not suppress the bio-degradation of Lindane through decreasing its non-extractable fraction.The correlation analysis demonstrated that the volatile fractions of Lindane and HCB were transformed from the water-soluble and acetonitrile/water-extractable fractions with time.The influence of BC on the volatilizations of Lindane and HCB were deemed through impacting the water-soluble and acetonitrile/water-extractable fractions.The non-extractable fractions of both chemicals originated from the transformations of acetonitrile/water-extractable fraction.The presence of BC in soils weakened the transformation extents and rates of Lindane and HCB with time.BC was showed higher affinity for HCB than for Lindane.In summary,distinct from the single LRAT,this thesis suggested the two-way LRAT mode along the transect of the Sichuan Basin-Yellow River source?Qinghai-Tibet Plateau?and highlighted the different source-sink roles of the Qinghai-Tibet Plateau and the Sichuan Basin for different OCP compounds.Furthermore,this thesis suggested the different degradation pathways of OCPs in different zones and found the non-negligible influence of the degradation on the OCP residues in soils along the transect,which could be very helpful for obtaining the proper conclusions of LRAT in field studies.The lab experiment detailly revealed the significant suppression effect of BC on the LRAT and degradations of OCPs,which could prove specific explanations and evidence for the influence of BC on the global distribution and environmental behaviors observed in field studies.