Effects Of Engineered Nanoparticles On The Transport And Transformatiom Of Racemic-Metalaxyl In Soils

As the nanoscience and nanotechnology developing fast nowadays,the engineered nanoparticles(ENPs)are widely used on agriculture,medicine,electronic equipment,clothing and coating.At the meantime,the ENPs inevitably enter the environment during its productive,transportational and applied process.Most of the ENPs have good stability,which lead to its continuously rising of concentration in soils.The microbial communities and the environmental behavior of the organic pollutants in soils can be subsequently affected.Metalaxyl,used as the proxy of the chiral pesticide,was studied in this paper.The effects of three typical ENPs(nano-SiO2,nano-TiO2 and nano-ZnO)on the transport and transformation of metalaxyl agents and preparations in agricultural soils were investigated.And based on the difference of soil microbial abundance and community structure in different experiment conditions,the preliminary mechanism about how ENPs affect the soil microorganisms and the transport and transformation of organic pollutants was presented.The main findings and conclusions are:(1)Nano-SiO2 adsorbed metalaxyl fast and strongly.It can promote the adsorption of metalaxyl in soil and reduce its mobility when nano-SiO2 enter the soil.The adsorption on nano-SiO2 or soil showed no enantio-selectivity.Nano-SiO2's adsorption capacity of metalaxyl decreased when it enter into the soil,mainly due to the homoaggregation,the competitive adsorption of organic matter,and the interactions with the soil particles.(2)Under simulated solar irradiation,the transformation of metalaxyl in soil was promoted by nano-TiO2.Nano-TiO2 mainly promoted the chemical transformation of metalaxyl in soil through phototransformation process,and the promotion amplitude depended on the type of nano-TiO2 and its interaction with soils.The promotion capacity of nano-TiO2 decreased when it was in soils pretreated with autoclave sterilization,or "aged" in soils.Neither the enantio-selectivity of transforming metalaxyl nor the microbial structure and abundance were affected by nano-TiO2 in soils,which showed that the biotransformation of metalaxyl in soils was not influenced by nano-TiO2.(3)Different ENPs showed different effects on the enantio-selectivity transformation of metalaxyl in soils.Under simulated solar irradiation,nano-ZnO promoted the transformation rate of metalaxyl and showed influence on the enantio-selectivity.It also significantly changed the bacterial structure in the mixed soil.Nano-TiO2 exhibited chemical promotion on the transformation of metalaxyl in soils without changing the enantio-selectivity.Nano-SiO2 suppressed the transformation of R-metalaxyl a little,and the enantio-selectivity was affected in a certain extent.The influence of ENPs on soil microbial structure might be the main reason for the change of the enantio-selectivity of transforming metalaxyl.The influence of ENPs on the transport and transformation of organic pollutant in soils was the result of some complex interactions.The findings in this work may help people to understand the interactions in ENPs-soil microorganism-organic pollutant,and show a further understanding about the environmental risk of ENPs when it enter soils.