Combined Effects Of Different Functionalized Multi-walled Carbon Nanotubes And Atrazine On Rice Seedlings

The risk of materials entering into the environment is one of the present study hotspots.Atpresent,literatures indicated that carbon nanomaterials affected the growth of plants.Besides,the adsorption was very strong between carbon nanomaterials and the common organic pollutants.However,there were few studies on the risk of plant under the coexistence of carbon nanomaterials and environmental organic pollutants.In particular,there were hardly any investigations on the combined effects of colloidal carbon nanotubes and organic pollutants on plants.In this paper,three kinds of carbon nanotubes with different morphologies and functional groups(called Pristine-CNTs,Oxidized-CNTs,PEG-CNTs)were prepared by means of acid oxidation and ethylene glycol grafting.And the carbon nanotubes were characterized by TEM,FT-IR etc.Batch experiments were taken to explore the adsorption affinities between each carbon nanotubes and organic pollutant atrazine,while hydroponic experiments were applied to investigate the combined effects of each carbon nanotube(60mg/L)and/or atrazine(5mg/L)on growth,physiological and biochemical of rice seedlings.Germination rate,biomass,antioxidant enzyme activity(such as SOD,CAT,POD)and malondialdehyde(MDA)content were determined under different conditions.The results showed that:(1)the functionalized carbon nanotubes had large variation on morphology,for example the length was shorter,the wall was thinner,the pipe diameter was enlarged,the ends were opened,and the fracture surface was more.A large number of C-H was introduced to the surface of Oxidized-CNTs,and the number of Acyl chloride(-COCl-),hydroxyl(-OH),carbonyl(-CO-)was increased on the surface of PEG-CNTs.The functionalized carbon nanotubes showed better stability,dispersity and little agglomeration in aqueous solution.The effective particle size of three kinds of carbon nanotubes increased as follows:P-CNTs<O-CNTs<CNTs,while thedispersity and water solubility of them decreased as O-CNTs>P-CNTs>CNTs.The adsorption capacity of three kinds of carbon nanotubes was different.Compared with CNTs and O-CNTs,the adsorption capacity of P-CNTs was relatively weak.(2)For a single pollutant,CNTs with a concentration of 60 mg/L had no significant effect on seed germination of rice,but the functionalized carbon nanotubes inhibited seed germination.All of the CNTs andfunctionalized carbon nanotubes inhibited the root growth of plant while promote the growth of the upper part,as a result,the root to shoot ratio of the rice seedling became lower than control.All of the carbon nanotubes led to oxidation stress and resulted in the increase of protein content and the increase of antioxidant enzyme activities and MDA accumulation in the root and the aboveground parts of the plant seedlings.However,atrazine with a concentration of 5mg/L had no obvious effect on seed germination rate and seedling biomass.Compared with the control,the content of protein in the roots of rice seedlings increased,but in the shoot decreased significantly.The activities of antioxidant enzymes and MDA content in the roots were decreased,while those in the shoot increased.(3)Under the circumstance of combined pollution,the coexistence of each carbon nanotubes and atrazine had no obvious effect on seed germination rate,seedling root biomass,but promoting the growth of shoots.When CNTs and atrazine coexist,the proteincontent of the roots increased significantly,while that of shoot decreased significantly;however,when O-CNTs or P-CNTs coexist with atrazine,the root protein content did not change obviously,but that of the shoot decreased significantly.Compared with the control,under combined stress of three kinds of carbon nanotubes and atrazine,antioxidant enzymes activity and MDA content of root showed little change,but those of the shoot were higher.Furthermore,it was found that the atrazine coexist together.Moreover,P-CNTs seemed to promote the accumulation of atrazine in plant while O-CNTs seemed to reduce the accumulation.Generally speaking,the effect of MWCNTs on plant growth was related to the surface structure,physical and chemical properties of the nanomaterials.The functionalized MWCNTs had stronger inhibition effect on the growth of rice seedlings.When different functionalized carbon nanotubes coexist with atrazine,the adsorption interaction between carbon nanotubes and atrazine can alleviate the adverse effects on plant seedlings caused by each pollutant alone,and different functionalized carbon nanotubes also had different effects on the accumulation of pollutants in plants.Therefore,in the study of the ecological risk of carbon nanotubes,it is necessary not only to consider the carbon nanotubes with different properties,but also to notice the coexisting environmental pollutants.