Effect Of Representative Engineered Nanoparticles On Transportation And Transformation Of Cadmiun And Metalaxyl In Soil-rice System

With the development of nanotechnology,there are growing concerns and studies about potential environmental risks of engineered nanoparticles.Soil is one of main sink for engineered nanoparticles,and is the prime nursery for agricultural crops as well.It is of concern for agricultural,environmental and food safety to understand transportation and transformation processes of engineered nanoparticles and effects of engineered nanoparticles on coexisting contaminations in agricultural soil environment.In this research,three representative engineered nanoparticles(C60,nano Ti2,nano SiO2)are chosen to study:aggregation and adsorption of nC60 in soil,uptake,transportation and interaction of C60 and cadmium in soil,effect of nano TiO2 and nano SiO2 on enantioselective behavior of metalaxyl in soil-rice system.The main research contents and conclusions are shown as follow:1.Aggregation of C60 nanoparticles(nC60)under the influence of Ca2+ and humic acid was studied.CCC of Ca2+ for nC60 was 3.5 mM.The influences of three humic acids on aggregation of nC60 under same Ca2+ concentration are significantly different.In fluorescence quenching titration experiments,nC60 quenched fluorescence of humic acid through a steady quenching machanism,whereas hydrophilic C60-OH showed barely influence on the fluorescence.The difference between effects of nC60 and C60-OH on humic acid's fluorescence testified that the main interaction machanism between nC60 and humic acid was hydrophobic interaction other than ?-? interaction.nC60 could be adsorbed by soil particles.However,the adsorption of nC60 on soil accounted for a minor ratio compared with the aggregation of nC60 in soil leachate.So,the main form of nC60 in soil was aggregates with a large size.2.Four rice cultivars were cultivated in soil spiked with different concentrations of C60 and Cd to evaluate uptake and transportation of C60 and Cd during whole life period.Exposure of C60 barely changed the biomass of rice during whole life periods.All four rice cultivars could adsorb and transport C60 from soil to panicles,but different cultivars showed different capabilities to adsorb and transport C60.Uptake and transportation of Cso in Japonica rice Nipponbare's root and stem were significantly different from three Indica rice cultivars,which might cause by the differences of physiological characteristics between Japonica rice and Indica rice.C60 concentration in organs of rices except Luo You 8 increased significantly with the increased exposure level of C60.Compared with low exposure of Cd,higher level of exposure inhibited uptake and transportation of C60 in there cultivars.In soil with a low level of Cd,exporsure of C60 promoted roots and stem of four cultivars to adsorb and transport Cd.However,in soil with a high level of Cd,exposure of C60 decreased the content of Cd in root,stem and panicle of Yuetai B.In different growth periods,the degree of uptake and transportation of C60 and Cd in rice were distinct.In conclusion,in the process of uptake and transportation in rice,C60 and Cd could affect each other,which was decided by exposure level of Cd and C60,and differences between rice types.3.Effects of nano TiO2 and nano SiO2 on metalayxl in soil were studied.The addition of nano TiO2 or nano SiO2 increased the adsorption coefficient of racemic metalaxyl onto an agriculture soil,and the adsorption was nonenantioselective.R-metalaxyl transformed faster than S-metalaxyl.Biotransformation was the predominant pathway for the elimination of R-metalaxyl,while abiotic and biotransformation made a comparable contribution to the degradation of S-metalaxyl.Metalaxyl acid was the main transformation intermediate.The enantiomer fraction of metalaxyl decreased with an increase in its initial spike concentration or the presence of the coconstituents(mancozeb)in metalaxyl commercial products.Adjuvants(?-cyclodextrin,sodium lignosulphonate)hardly influence on transformation of metalalxyl.In dark incubation,nano TiO2 and nano SiO2 did not affect the transformation.Under simulated solar irradiation,the presence of nano TiO2 promoted the overall transformation kinetics through enhanced biotransformation and extra photoinduced chemical reactions,whereas nano SiO2 showed baraly influence.The promotion was enantioselective and thereafter changed the enantiomer fraction.In soil incubated outdoor,transformation of commercial metalaxyl was enantioselective as well,and its transformation was significantly faster than the reaction in indoor incubation soil.In soil-rice system,nano TiO2 promoted transformation of metalaxyl,and enantioselectivity of the transformation were influenced by incubation conditions,type of nano TiO2 and coexisting materials.The results obtained in this study showed that some achiral parameters,although they have no direct impact on enantioselective reactions with enantiomers,could significantly affect the enantioselective transformation of racemic metalaxyl.