Effects Of Various Components Of Root-soil Multi-media Interface On Phenanthrene Environmental Behavior

Polycyclic aromatic hydrocarbons(PAHs)are a class of highly hydrophobic organic pollutants in the environment,which are easily combined with soil organic matter and deposited in the soil.Because the carcinogenic,teratogenic and mutagenic PAHs can easily accumulate in human body through food chain transfer,the removal of PAHs has become central in the field of soil remediation.PAHs undergo a series of environmental behaviors in the process of migration from soil to plant,including soil desorption,plant root surface adsorption,plant absorption and diffusion,and finally degradation.This process is dominated by other substances in the farming soil,which are able to alter the bioavailability of PAHs and their distribution in the food chain.In order to minimize the safety risk of crops produced in polluted soils,it is necessary to systematically study the important factors in the soil that may affect the migration of PAHs to plants.Since phenanthrene(Phe)is ubiquitous in nature and has a fused ring angle structure,it is used as a theoretical model for PAHs research analysis.Based on the actual circumstances in agricultural production,this paper studied the desorption effects of biochar,organic acid,organic matter and organic fertilizer on soil PAHs.In addition,the wheat root surface and the bacterial biofilm established by Phenanthrene degrading bacteria were used to evaluatethe adsorption,degradation and diffusion behaviors of phenanthrene.The detailed research results are as follows:(1)The addition of biochar can effectively promote the inactivation and prevent the desorption of phenanthrene in the soil.The addition of organic fertilizer also reduces the desorption of phenanthrene,but this mainly result from the degradation of phenanthrene by the microorganisms in the organic fertilizer.The addition of fulvic acid,citric acid and DL-malic acid are all able to promote the desorption and desorption of phenanthrene from soil,thus improving the extraction efficiency of phenanthrene.(2)Under the wheat hydroponic culture system,the addition of citric acid and fulvic acid can promote the degradation of phenanthrene in solution to different extents.Moreover,they promote the formation of root surface bacterial biofilm on wheat by the phenanthrene-degrading bacteria JM2-gfp,and enhance the surface hydrophobicity and stability of the bacterial biofilm.The biofilm of the degrading bacteria prevents the migration and accumulation of phenanthrene in plants by function as a biological barrier and participate in the degration of phenanthrene,(3)The two-photon laser confocal microscope and inverted fluorescence microscopy showed that phenanthrene was transported and distributed differently in root and stem of wheat.The results showed that phenanthrene was transported from the root surface of wheat into the root tissue mainly through the symplast pathway.After 48 hours,it reached the rhizome binding site and continued to transport in the stem through the apoplast pathway.The study also found that the addition of citric acid can accelerate the migration of phenanthrene to wheat,while humic acid delays its migration.Based on the above results,it can be seen that different organic matter components have different effects on the environmental behaviors such as desorption,migration and degradation of phenanthrene in the root-soil multi-media interface.The formation of biofilms using degrading bacteria on the root surface of plants can change the environmental behavior of phenanthrene at the root surface.At the same time,as a biological barrier,the biofilm can reduce the migration and accumulation of phenanthrene in crops,which is beneficial to improve the safety of agricultural products.This study provides some technical guidance for effectively controlling the PAHs pollution of crops in contaminated farmland soil,and also provides an effective method for bioremediation of contaminated farm soil.