Study On Phytotoxic Effects And Mechanism Of Iron-based Remediation Materials

With the rapid development of nanotechnology,iron-based remediation materials have become one of the most widely used remediation materials in the field of environmental pollution remediation.Because of their active nature,it is easy to have a negative impact on organisms and ecosystems after entering the environment.Therefore,the fates and biological effects of iron-based remediation materials in the environment have attracted more and more attention.Here,seven iron-based remediation materials,including ferric chloride（Fe Cl₃）,micro-sized and nanoscale Fe₃O₄（i.e.,m Fe₃O₄and n Fe₃O₄）,bulk and bare nanoscale zero-valent iron（i.e.,m ZVI and n ZVI）,starch-supported n ZVI（S-n ZVI）,and activated carbon-supported n ZVI（A-n ZVI）,were studied their effects on mung bean and wheat.The phytotoxicity of iron-based remediation materials was studied through seed germination and seedling growth tests,and the effects of iron-based remediation materials on soil basic indexes,soil enzyme activities and soil microbial diversity were studied through laboratory experiment/culture experiments.The main results of the study are as follows:（1）The results of seed germination test showed that the iron-based remediation material delayed the seed germination.In the water environment,aggregates of iron-based remediation materials（except Fe Cl₃）were easily attached to seed coat and seedling roots to form a covering coating to affect the germination and growth of plants.The germination and growth of mung bean and wheat seeds were slightly promoted in m Fe₃O₄and n Fe₃O₄suspensions.The effects of four zero-valent iron materials on the length and weight of mung bean and wheat seedlings were different in plant species.S-n ZVI and A-n ZVI significantly affected the growth of mung bean seedlings,while m ZVI and n ZVI significantly affected wheat seedling growth.Among all materials,Fe Cl₃solution increasingly inhibited the germination rate,length and weight of mung bean and wheat seeds with the increase of iron concentration（p<0.05）.In soil environment,the effect of iron-based remediation materials on the germination and seedling growth of mung bean seeds was significantly lower than in water,and the root dry fresh weight of mung bean was significantly inhibited by iron based remediation materials at high dose（1000 mg/kg）（p<0.05）.The results showed that the species and dosage of iron-based remediation materials,plant species and environmental media were important factors affecting seed germination and growth,and the attachment of iron based aggregates on plant seed coat and seedling roots was the key factors to delay seed germination and affect seed growth.（2）Seedling growth test results showed that iron-based remediation materials could significantly change the growth of mung bean seedlings.Under high dosage（1000 mg/kg）condition,plant height and weight of mung bean seedlings were significantly decreased（p<0.05）.The application of iron-based materials promoted the absorption of Fe by mung bean roots,and damaged the chlorophyll composition and photosynthesis of mung bean.Among them,the transfer of S-n ZVI and A-n ZVI to the ground of mung bean not only increased the concentration of Fe in mung bean leaves,but also reduced chlorophyll content and chlorophyll fluorescence parameters.Meanwhile,the application of iron-based remediation materials significantly changed antioxidant enzyme activity in mung bean leaves（p<0.05）.The activities of superoxide dismutase（SOD）and peroxidase（POD）in mung bean seedlings exposed to iron-based materials increased,while the activities of catalase（CAT）decreased.According to the results,the species and dosage of iron-based remediation materials were important factors affecting the growth of mung bean seedlings.The accumulation and transfer of Fe in mung bean roots and shoots damaged the photosynthetic mechanism and chlorophyll composition of mung bean plants.The application of iron-based remediation materials induced a large amount of active oxygen free radicals（ROS）,which affected the activity of antioxidant enzymes in leaves and inhibited the growth of mung bean seedlings.（3）The results of laboratory experiment/culture experiments showed that the application of iron-based remediation materials could increase the content of available iron（DTPA-Fe）,decrease the soil p H value,promote the activitied of soil urease and catalase.The presence of plant roots alleviates the effect of iron-based remediation materials on p H and enhanced soil enzyme activities.Compared with the control,the application of iron-based remediation materials increased the relative abundance of soil Firmicutes,and decreased the relative abundance of Chloroflexi and Acidobacteria.Therefore,the species and doses of iron-based remediation materials significantly affected the soil microenvironment.In conclusion,the species and dosages of iron-based remediation materials were important factors affecting seed germination,seedling growth and soil microenvironment.In the water environment,the attachment of iron based aggregates on plant seed coats and seedling roots was a key factor affecting seed germination and growth of plants.The main reasons of phytotoxicity of iron-based remediation materials were the absorption,accumulation and translocation of iron in plants,and the changes of chlorophyll content,photosynthetic mechanism and antioxidant enzyme activities in plants caused by iron-based remediation materials.In addition,iron-based remediation materials also affected soil basic properties,soil enzyme activities and relative abundance of soil microorganisms.Therefore,the selection of appropriate species and dosages of iron-based remediation materials in practical applications can effectively reduce the secondary effects on organisms and ecosystems.