Study On The Feasibility And Biological Effect Of Starch Stabilized Nano Zero-valent Iron To Remediate Cr(?)contaminated Soil

Nanoremediationmaterials have wide applications in the treatment of polluted environments.Among them,nano zero-valent iron(nZVI)is a commonly used nanomaterial.Bare nano-zero-valent iron(B-nZVI)easily aggregates into clusters and oxidative deterioration and other instabilities,which affects the removal efficiency of pollutants,so the study of stabilized nZVI has attracted much attention.Due to the activity and mobility of nZVI,the transport,transformation and biological effects of nZVI in the soil have also caused considerable attention.In the present Cr(?)contaminated soil remediation experiments,the effects of starch stabilized nZVI(S-nZVI)dosage,soil moisture content,reaction time on the removal of Cr(?)in soil were studied.And the effects of S-nZVI and B-nZVI combined with biochar/humic acid on Cr(?)contaminated soil were compared.The effects of S-nZVI and B-nZVI combined with biochar/humic acid on plant growth,physiological biochemistry and soil microorganisms in Cr(?)contaminated soil were studied by pot experiments.The main results of this study are:(1)The results of Cr(?)contaminated soil remediation test showed that both S-nZVI and B-nZVI could effectively remove Cr(?)from soil,and the effect of S-nZVI was more significant at high dose(P<0.05).The increase of water contentand reaction time significantly enhanced the removal effect of S-nZVI on Cr(?).The removal rate of 250 mg/kg Cr(?)contaminated soil could reach 90% when 3.0g/kg S-nZVI and 70% water content were added at 60 days.The combined application of biochar or humic acid further enhanced the remediation effect of the two nZVI,but humic acid(HA)increased the availability of available Fe and available Cr in the soil.Considering the effect of Cr(?)removal and Fe release on plants,the combination of 100 mg/kg B-nZVI or S-nZVI with biochar is an ideal repair strategy.The results of Cr(?)contaminated soil remediation test showed that nZVI type,nZVI dosage,soil moisture content and culture days were the influencing factors of Cr(?)contaminated soil remediation effect.(2)The results of plant growth test showed that neither dose of B-nZVI inhibited or even promoted the growth of mung bean,while 1000 mg/kg of S-nZVI had high plant toxicity.The Cr content of the shoot and root of the plants treated with B-nZVI and S-nZVI were significantly reduced,and the content was reduced by about 50%.Compared with the control,the Fe content in the roots of B-nZVI and S-nZVI treated plants increased significantly under the action of high dose nZVI.TEM results showed that severe damage was observed in the root cells exposed to S-nZVI,such as lysozyme,cytoplasmic contraction,and cell membrane rupture,but the iron content in all seedlings was within the normal range(60 to 300 mg/kg).B-nZVI and S-nZVI showed significant difference on the chlorophyll fluorescence effect of plants.The high dose of S-nZVI led to the inactivation of the action center of the plant PSII and restriction of electron transfer in plants,and the leaf photosynthesis mechanism was destroyed.Moreover,the chlorophyll content of the high-dose S-nZVI treatment was significantly reduced,the cell chloroplast was enlarged,the starch granules in the chloroplast were obvious,and the volume and number of starch granules were increased,indicating that S-nZVI caused the destruction of photosynthetic organs and the reduction of photosynthesis.(3)The study found that the microbial effect of nZVI is related to the type of nZVI,the dose of nZVI and the accumulation of Fe.The effects of B-nZVI and S-nZVI on microorganisms showed significant difference.B-nZVI promoted the activity of catalase and phosphatase in soil,while S-nZVI inhibited catalase.Both biochar and humic acid promoted the enhancement of enzyme activity.Comparedwith other treatments,the composition of the community with 1000 mg/kg S-nZVI changed significantly,Gammaproteobacteria increased significantly,and the relative abundance of Alphaproteobacteria and Actinomycetes decreased.The reduction of Actinomycetes was not conducive to the conversion of soil nutrients and indirectly to the absorption and growth of plant nutrients.At the same time,high dose of S-nZVI led to serious damage to plant roots,and the absorption and balance of plant nutrients were disturbed.Furthermore,S-nZVI may cause plant nutritional deficiencies,interference with chlorophyll biossynthesis and photosynthesis,and ultimately inhibition of plant growth.