Ryegrass Remediation For Cadmium And Pyrene Co-contaminated Soil Enhancing By Chelating Surfactant

In recent years,the problem caused by polycyclic aromatic hydrocarbons(PAHs)and heavy metals combined pollution in soils has become more and more serious.Comparied with other soil remediation technologies,the development of improved jointly repairing methods connected with phytoremediation has emerged as a new way to control soil contaminations.Chemical-assisted phytoremediation technologies has received great attention and made some research progress in the past decade.In this study,N-dodecylethylenediamine triacetate(LED3A),a novel and easily degradable chelating surfactant,was used as chelating solubilizing and activating reagent to study the enhancement effect of LED3A on phytoremediation of contaminated soil.The effect of LED3A on increasing dissolution and absorption of Cd and pyrene in soil was preliminarily explored to analyze the feasibility of using LED3A to enhance phytoremediation.The effects of LED3A on the growth,physiological indexes and soil properties of ryegrass were studied by pot experiment.LED3A enhanced the effect of ryegrass on the remediation of single and compound polluted soil;The interaction of pollutants coexistence on remediation and the detoxification mechanism of ryegrass to Cd;Combined with the analysis of soil pollutant morphology changes before and after remediation,the mechanism of LED3A enhancing Cd enrichment and pyrene degradation of ryegrass was explored.The main conclusions are as follows:(1)LED3A has a good desorption effect on Cd and pyrene in single and combined contaminated soil,with a desorption equilibrium time of 16 h,and a high desorption efficiency under alkaline conditions.LED3A can promote the desorption of exchangeable Cd from soil particles,promote the conversion of adsorbed pyrene to bioavailable pyrene,and improve the bioavailability of Cd and pyrene,indicating that LED3A can promote the activation of Cd and pyrene in soil,which is conducive to inducing plant remediation of contaminated soil.(2)After the treatment of LED3A,the changes of plant height,biomass,malondialdehyde(MDA)content and antioxidant enzyme activity of ryegrass showed a certain stress response,but did not affect the normal growth of ryegrass on the whole.The results indicate that LED3A can promote the enrichment and degradation of Cd/ pyrene in the soil without causing obvious plant toxicity.Ryegrass roots could provide a suitable rhizosphere environment for soil microorganisms and promote the activities of soil microorganisms,soil dehydrogenase and sucrase.However,the addition of LED3A can stimulate the change of soil microorganism and enzyme activities due to the improved bioavailability of pollutants,so as to effectively promote the absorption or degradation process of pollutants by ryegrass.(3)After the application of LED3A,the maximum removal rate of Cd in single and combined contaminated soil increased by 85.29% and 55.41% compared with that of ryegrassonly.With the increase of LED3A concentration,ryegrass increased the enrichment coefficient(BCF)of Cd,but had little effect on transfer coefficient(TF).LED3A strengthens the cell wall precipitation and vacuolar area isolation of Ryegrass on Cd,and effectively avoids the damage of Cd to organelles.Ryegrass combined with LED3A improved the removal efficiency of pyrene in soil.At the maximum concentration of LED3A(0.8 g·kg-1),the maximum remediation efficiency of single and combined contaminated soil was 86.25%and 84.63%,and the degradation efficiency of pyrene increased 88.91%and 204.63%compared with ryegrass alone.LED3A significantly promoted the biodegradation of pyrene.Principal component analysis and correlation analysis showed that LED3A concentration was significantly positively correlated with Cd enrichment,and the removal effect of pyrene was significantly positively correlated with soil microorganisms and dehydrogenase.(4)The combination of LED3A and plants can significantly promote the transformation of reducible and oxidizable Cd to exchangeable Cd,improve the bioavailability of Cd,and promote the absorption and extraction of Cd by ryegrass.The content of bioavailable pyrene decreased significantly with the increase of LED3A concentration,because ryegrass and LED3A enhanced soil microbial and enzyme activities,thus promoting the biodegradation process of pyrene in soil.