Dissipation Mechanism Of Polycyclic Aromatic Hydrocarbons In Submerged Plant Rhizosphere At Millimeter Level

Polycyclic aromatic hydrocarbons(PAHs)are typical persistent organic pollutants in sediments,and the toxicity of the hydroxyl group(OH-PAHs)is stronger than that of the parent.It is a hot research topic in the research of the plant repair technology of PAHs,but the research on the degradation mechanism of organic pollutants in sediments is still lack.This paper first established the analysis method of OH-PAHs in the soil or sediment,then used Vallisneria spiralis and Myriophyllum spicatum as tested plants,submerged multi compartment root chamber box as experimental installation,of reduction mechanism of submerged plants rhizosphere PAHs.The main conclusions are as follows.This paper established a method for determination of 1-hydroxypyrene by a high-performance liquid chromatography with ultrasonic extraction.The optimum conditions of ultrasonic extraction are the methanol: dichloromethane(V:V=35:65)as extraction liquid,the volume of 10 mL,ultrasonic time of 20 min,ultrasonic times of 3 times.Among the conditions,the volume ratio of methanol and dichloromethane are the main factors affecting the extraction efficiency.The pH(5.7~9.8)of soil or sediment and 1-hydroxypyrene recovery(83.3%~6.6%)were significantly negative(r=-0.928,n=5,p=0.023),and the lower the pH,the higher the recovery rate of 1-hydroxypyrene.For soil or sediment with similar pH values,the recovery rate of the ultrasonic extraction method was significantly higher than that of the literature value.The research results of PAHs reduction mechanism in submerged plant rhizosphere showed that the plant rhizosphere could really promote PAHs degradation,and the range of rhizosphere effect was the distance to the root surface 4 mm,and the PAHs content in the plants and the control group were significantly different(p<0.05).The rhizosphere effect of Vallisneria spiralis was significantly greater than that of Myriophyllum Spicatum(p<0.05).There was a negative correlation between PAHs and total PLFAs content,G+ and total bacterial amount(p<0.05).At the same time,the removal rate of PAH-degrading bacteria and PAHs was significantly positive(p<0.05).In addition,the redox potential(Eh)of sediment has a gradient descenting law in the rhizosphere spatial,and the plant root system can significantly enhance the Eh value especially stronger on the root surface.Furthermore,the correlation analysis showed that the higher Eh value could increase the number of PAH-degrading bacteria,and significantly increased the PAHs reduction of the soil.In the rhizosphere,the content of 1-hydroxypyrene and pyrene was significantly positively correlation(p<0.05),while the rhizosphere dissipation of PAHs,it also reduced the concentration of OH-PAHs,that is to reduced the environmental pollution and potential risks.