Sources, Accumulation And Distribution Of Dioxin-like PCBs In The Typical Plants From Yellow River Delta

Polychlorinated biphenyls(PCBs) are a group of persistent organic pollutants (POPs).Being persistent,semivolatile,bioaccumulted and high toxic,PCBs are listed in the 12 primary group pollutants in "Stockholm Convention on Persistent Organic Pollutants".Dioxin-like PCBs(DL-PCBs) are referred to the non-ortho and mono-ortho PCBs,including 12 congeners.DL-PCBs are the most toxic group of compounds in the PCBs.Though the concentrations of DL-PCBs in the environmental and biological matrices are low,they contribute much to the total toxic value of pollutants.Therefore,DL-PCBs are more important than the other PCB congeners for the study of PCBs in biological matrices,and are becoming a research hotspot in the world.In this study,firstly the analysis method of dioxin-like PCBs(DL-PCBs) was set up based on the review of related literature,secondly the pollution conditions and sources of DL-PCBs in the typical plants from Yellow River delta were studied, thirdly the accumulation characteristics of DL-PCBs in plants were explored,finally, DL-PCBs the distribution patterns of DL-PCBs in plants were given out.(1) Research on the analysis method of trace DL-PCBs in plantsThe analytical difficulties in the analysis of PCBs in plants are due to the complex components of plants,trace concentration of DL-PCBs in plants,etc. Current studies about analysis of trace DL-PCBs in plants are seldom reported,so convenient and rapid methods to determine the trace DL-PCBs in plants are required. By study of pretreatment technology and experimental parameters improvement,a rapid and accurate analysis method of trace DL-PCBs in plants were developed in this study.Samples pretreatment.The parameters of Soxhlet extraction was studied,the results are as follows:200mL mixed solvents hexane/acetone(1:1,V/V) were used to extract 20-30g dry weight of plant samples,Soxhlet time was 24h,the reflux speed was 4 circles/h.The extraction was then concentrated and treated with concentrated sulfuric acid and potassium permanganate solution,and the Florisil column was used for purification.DL-PCBs analysis.Dual-column system with low and intermediate polarities combined with GC/MS was used analyze DL-PCBs in plant samples.The method can separate 12 DL-PCBs from the bulk PCBs and organochlorine pesticides,and effectively analyze DL-PCB congeners in the plant samples.The results found the spiked recovery of this method was in the range of 75.56%-87.42%,the relative standard deviation(RSD) of repeated plant samples was in the range of 3.60%-14.53%,meeting the US EPA standard of recoveries(70%-140%) and RSD of repeated samples(＜20%).(2) Loadings and sources of DL-PCBs in typical plants from Yellow River deltaTo investigate the loadings and sources of DL-PCBs in plants from Yellow River delta,five typical plant species were chosen to determine the DL-PCBs concentrations in October,2006,including Imperata cylindrical var.major, Phragmites australis(Cav.) Trin.ex Steud,Suaeda Heteroptera,Tamarix chinensis Lout.,Salix matsudana Koidz.The total concentrations of DL-PCBs in plants were 575.48-819.23 ng/kg, DL-PCBs congener concentrations measured in plants were 2.32-237.36 ng/kg;the total concentrations of DL-PCBs in the associated soils were 147.75-505.58 ng/kg, and DL-PCBs congener concentrations in the associated soils were 2.48-403.58 ng/kg.The total concentrations or congener concentrations of DL-PCBs in plants and associated soils from Yellow River delta were far lower than those about other area in the published reports.To identify the sources of DL-PCBs in plants,correlation analysis of congener concentration of DL-PCBs in plants and those in the corresponding soils were carried out.The results show the concentrations of DL-PCBs in the plants were not significantly related to those in the corresponding soils.This indicates that the source of DL-PCBs in plants from Yellow River delta was not from soil.Combined with the related studies,considering the octanol-air coefficients(K_oa) and octanol-water coefficients(K_ow) of DL-PCBs,it can be concluded that air was the main source of pollutants.(3) Characteristics of DL-PCBs accumulation in plants from Yellow River deltaThe DL-PCBs concentrations in three annual plants(I.cylindrical,P.australis, S.Heteroptera) and two perennial plants(T.chinensis,S.matsudana) were compared to explore the interspecies variance of DL-PCBs accumulation in plants. Octanol-air coefficients,plant taxonomy and growth time were studied as factors resulted in the variance of pollutants accumulated in plants of different species.①Total concentrations and congener concentrations of DL-PCBs in different plant speciesThe total concentration of DL-PCBs in I.Cylindrical was the lowest among the five species(575.48 ng/kg),and the other four species was not significantly different from each other.All the 12 DL-PCB congeners were detected in each plant sample, only PCB126 did not show different accumulation among species.PCB77,PCB81, PCB114,PCB123 and PCB156 concentrations were found be significant different among at least three species.The congener with largest variance was PCB 81,whose concentration in T.chinensis was 72 times higher than that in I.Cylindrical.②Influence factors of DL-PCBs accumulation in plantsInfluence of DL-PCBs K_oa on pollutant accumulation in plants.Relations of log K_oa and CP/CI(DL-PCB concentrations in P.australis,S.Heteroptera,T.chinensis, S.matsudana versus that in I.cylindrical) was investigated.When log K_oa was 8.46, CP/CI was 2.0-72.3,When log K_oa was 11.25,CP/CI was 0.7-1.5。Thus,the interspecies variance of plants decreased with increasing log K_oa of DL-PCBs.K_oa was an important factors resulted in DL-PCBs accumulation variance in different plant species.Influence of plant types on DL-PCBs accumulation in plants.Hierarchical cluster analysis of the five plant species labeled by the concentrations of DL-PCBs congeners was conducted.The results show that I.cylindrical and P.australis, which belong to the same family--Gramineae,had the most similar patterns of DL-PCBs accumulation among the five species.This is because only I.cylindrical and P.australis belong to the same family in this study,leading to the smallest variance of their accumulation patterns among the five species.Influence of growth time on DL-PCBs accumulation in plants.Correlation analysis of log K_oa and DL-PCBs concentrations in the five plant species was carried out.A positive correlation between log K_oa and DL-PCBs concentrations of three annual species(I.cylindrical,P.australis and S.Heteroptera) was found,with Pearson correlation coefficients of 0.390,0.464 and 0.354(p＜0.05) respectively.But in the perennial species(T.chinensis and S.matsudana),the correlation between log K_oa and DL-PCBs concentrations was not significant.The results indicate different uptake mechanism of PCBs by annual and perennial plants.This can be explained by the various DL-PCBs accumulation properties of annual and perennial tissues in perennial species,and annual tissues occupied low proportions of the biomass of whole perennial plants,therefore,correlation between log K_oa and DL-PCBs concentrations in the perennial species was not significant.(4) The DL-PCBs distribution in the plant tissues from Yellow River delta and influence factorsAn annual plant(S.Heteroptera) and a perennial plant(S.matsudana) were collected in November,2007.The above-ground and under-ground parts of S. Heteroptera,the leaves,roots and branches of different growth time were determined for the DL-PCBs concentrations,exploring the distribution patterns of DL-PCBs in plants.①DL-PCBs distribution in different parts of S.HeteropteraThe total amount of DL-PCBs concentrations in the above-ground parts (1263.33 ng/kg) of S.Heteroptera was higher than that in the under-ground parts (833.47 ng/kg).On the congener level,PCB 81,77,123,118,114 were more accumulated in the above-ground parts of S.Heteroptera than that in the under-ground parts,which indicated that the low-chlorinated PCBs are more likely to be absorbed by the above-ground parts of S.Heteroptera.②DL-PCBs distribution in different parts of S.matsudanaThe total DL-PCBs concentrations in the leaves,roots,four kinds(primary, secondary,three-level and four-level) of S.Heteroptera were determined,which were 3054.64 ng/kg in the leaves,704.28 ng/kg in the roots,538.58,770.75,714.65,552.59 ng/kg in the four kinds of branches.The results indicate that total DL-PCBs concentrations were the highest in the leaves,which in the branches were secondary＞three-level＞four-level＞primary,and the total DL-PCBs concentrations in the roots are similar to that in the third-level branches and differed significantly from the other tissues.On the congener level,DL-PCBs concentrations in the leaves were significantly higher than that of other tissues,but no significant difference was found in the rest tissues.③Influence factors of DL-PCBs distribution in plantsCorrelation Analysis of total values of DL-PCBs concentrations of S. Heteroptera and S.matsudana and lipid concentration in different plant tissues was conducted,and no significant correlation was found.The DL-PCBs concentrations of S.Heteroptera and S.matsudana in different plant tissues were found to be significantly negatively related to total organic carbon concentration.This can be explained that accumulation of DL-PCBs was not as fast as that of the total organic carbon,the growth dilution effect resulted in the phenomenon that the organs with high carbon concentration have less DL-PCBs.