In Situ Visual And Quantitative Studies On Retention Of Typical PAHs On Mangrove Root Surface

There are over 90%of PAHs occuring in the surface of sediment/soil in the environment.The uptake of PAHs by plant roots is an important part of the geochemical cycle of organic contaminants and also is an important factor affecting the migration and fate of PAHs in the environment.Mangrove is the dominant species of plants that were located in tropical and subtropical estuary,and plays an extremely important role to cleanup organic pollutants and maintain balance of inshore coast ecosystem.Owing to aerial roots and prop root of mangrove plant interspersed in the sediments/soil,the uptake of PAHs by roots can not be neglected.Numerous researchers have focused on the uptake of PAHs by plant root and its mechanisms.However,with the development of fluorescence microscopic techniques,it has been observed that the environmental behavior(including distribution and retention)of PAHs at macro-scale differs from that obtaind by sequential extraction techniques at micro-scale,and thus the uptake of PAHs by plant root needs to be further conducted at micro-scale.Based on the reviews on contamination of PAHs in mangrove sediments and in situ analytical methods of investigating PAHs in plant ecosystem,the MFSA,which has the potential to in situ determine and visualize the PAHs on the surface micro-zone,was used to establish a method for in situ quantification and visualization of the B[a]P,Pyr and Ant on the surface micro-zone of mangrove root.Then,retention of the B[a]P,Pyr and Ant on the K.obovata lateral root and taproot surface micro-zone were investigated in situ using the established method.Also,retention of the B[a]P,Pyr and Ant on the micro-zone of mangrove K.obovata lateral root and taproot surface were also studied in the presence of GO,know as a typical two-dimension CNMs.Last,the implications of salinity on retention of the B[a]P,Pyr and Ant on surface micro-zone of mangrove lateral root and taproot were investigated in situ in the present of GO.There is a novel in situ quantitative and visualization method provided for investigating the uptake of PAHs by plant root surface at micro scale.(1)The model PAH Ant and two kinds of fresh mangrove roots(K.obovata and A.marina)were selected to establish a novel method for in situ quantifying and visualizing PAHs adsorbed on root surface micro-zone using MFSA system.The results showed that there were good linear relationships between the amounts of Ant adsorbed on the surface micro-zone of the roots and their relative fluorescence intensities.The dynamic linear ranges of the established method were 5.3-63.2 and 10.5-52.6 pg/μm2,with the detection limits of 1.1 and 5.5 pg/μm2.The relative standard deviations of the established method were less than 12.5%(n=9),and the recoveries were 98.1-117.0%and 81.2-110.9%.Above results revealed that the MFSA system(set in the lab)has the ability to obtain quantitative information and fluorescence images of the PAH on surface micro-zone.(2)Based on above work,the MFSA system was used to establish the new method that in situ determine and visualize the B[a]P,Pyr and Ant on surface micro-zone of K.obovata lateral root and taproot in the simulated ecological conditions.Then,retention of individual B[a]P,Pyr and Ant on the surface micro-zone of K.obovata lateral root and taproot were investigated in situ.The results indicated that:(a)there existed good linear relationships between the amounts of B[a]P,Pyr and Ant on the surface micro-zone of the K.obovata lateral root and taproot and their relative fluorescence intensities.The detection limits of the proposed method were 44.2 ng/g for B[a]P,59.7 ng/g for Pyr,and 36.3 ng/g for Ant(lateral roots),and also the taproot roots were 42.8 ng/g for B[a]P,62.4 ng/g for Pyr and 39.1 ng/g for Ant;(b)Retention of B[a]P,Pyr and Ant on the surface micro-zone of the K.obovata lateral root and taproot had significant difference(p<0.05);there were also uneven distribution of B[a]P,Pyr and Ant both for the K.obovata lateral root and taproot,which were related to the uptake pattern of the the B[a]P,Pyr and Ant(passive or active uptake)and the surface polarity of the K.obovata root surface.(3)In the simulated ecological condition,the retention of the B[a]P,Pyr and Ant on the surface micro-zone of K.obovata lateral root and taproot in the present of GO were investigated in situ by the proposed method.The results showed that the GO improved the retained amounts of the B[a]P,Pyr and Ant on surface micro-zone of the K.obovata lateral root and taproot with the order of Ant<Pyr<B[a]P.Also,it has been observed that GO improved the amounts of B[a]P,Pyr and Ant in the K.obovata root tissue,which were related to the interaction of the individual B[a]P,Pyr and Ant with GO and also the effects of the co-exposure of GO and the PAH on the permeability of the root surface of K.obovata root.The salinity(represented by KCl)decreased the amounts of retention of the B[a]P,Pyr and Ant on surface micro-zone of K.obovata lateral root and taproot by improving the access of the individual B[a]P,Pyr and Ant into root tissue,being related to the active uptake of the B[a]P,Pyr and Ant by K obovata root.