Effects Of Carbon Nanotubes On The Transport And Ecotoxicity Of Organic Pollutants In Riverine Sediment

Carbon nanotubes have broad application prospects in the filed of polymer composite materials,electrical and electronic engineering,energy,environment,medicine,chemical industry,architecture,aerospace,military equipment,and so on,due to their unique physical and chemical properties.As the production and applications continue to increase,carbon nanotubes will inevitably be released into the environment.Carbon nanotubes can enter the environment through wastewater discharge,waste treatment,product applications,and many other ways during the manufacturing,processing,transportation,use,and recycling stages,and become emerging nano-pollutants.The environmental behaviors and risks of carbon nanotubes are not completely clear,which is one of the important factors restricting the development of carbon nanotube-based products and technologies.It is of great significance for the sustainable development of carbon nanotubes and related industries to conduct research on the environmental effects of carbon nanotubes.The aquatic sediment is an important sink of carbon nanotubes in the environment,and it also accumulates many pollutants in the aquatic ecosystem.Because carbon nanotubes have strong adsorption affinity for a variety of organic and inorganic pollutants,carbon nanotubes in the sediment may affect the mobility,toxicity,and bioavailability of coexisting pollutants.Based on this,the effects of carbon nanotubes on the transport and ecotoxicity of organic pollutants in riverine sediments were investigated in this study,in order to improve the understanding of potential risks of carbon nanotubes and coexisting pollutants in the aquatic environment,and clarify the environmental relevance and ecological significance of the interaction between carbon nanotubes and coexisting pollutants.The specific research work and results of this paper include the following five sections:The 1st section describes the study about the effects of multi-walled carbon nanotubes(MWCNTs)on the transport of sodium dodecyl benzene sulfonate(SDBS)in riverine sediment.The effects of MWCNTs on the adsorption of SDBS by riverine sediment were studied by adsorption experiments.Based on this,column experiments were conducted to investigate the effects of MWCNTs on transport of SDBS in riverine sediment.The existence of MWCNTs in the sediment increased the adsorption capacity of the sediment mixture for SDBS,thereby retarding the transport of SDBS in riverine sediment.The estimated retardation factor based on the convection-dispersion equation model increased with the addition of MWCNTs in water or sediment,and had a high correlation with the content of MWCNTs in sediment.Whether MWCNTs were in the water or in the sediment,the accumulation of SDBS in the top sediment increased,and MWCNTs in the sediment retarded the transport of SDBS to deeper sediment.The 2nd section presents the study about the effects of MWCNTs on the phytotoxicity of riverine sediment contaminated with phenanthrene.The binding ability of phenanthrene by sediment with different MWCNT content was analyzed by the adsorption experiments and the determination of phenanthrene concentrations released from the sediment.The existence of MWCNTs could increase the adsorption of phenanthrene by riverine sediment and reduce the release of phenanthrene into the overlying water.The toxicity on plant seed germination and seedling growth were used to explore the effects of different doses and particle sizes of MWCNTs and the contact time with MWCNTs on the phytotoxicity of phenanthrene in riverine sediment.The addition of MWCNTs had no significant effect on the germination of mung bean and radish seeds sowed in phenanthrene-contaminated sediment,and the root growth of these two plant seedlings was more sensitive to changes of pollutant concentrations than their fresh weight.The existence of MWCNTs reduced the inhibitory effects of phenanthrene-contaminated sediment on root growth and biomass production,and the effects were more significant with higher dose and smaller particle size of MWCNTs.The 3rd section introduces the study about the effect of MWCNTs on microbial community in the riverine sediment contaminated with 2,4-dichlorophenol(2,4-DCP).The effects of MWCNTs on the adsorption of 2,4-DCP by riverine sediment were investigated by adsorption experiments.Chloroform fumigation extraction,enzyme activity kit,16 S r RNA gene sequencing were used to determine the microbial biomass carbon,dehydrogenase and urease activities,and the bacterial community structure in the sediment,respectively.The existence of MWCNTs in sediment increased the adsorption capacity of the sediment mixture for 2,4-DCP,which further affected the microbial biomass carbon,enzyme activity,and bacterial community structure in the sediment,especially for the sediment with MWCNTs at a level of 0.5%(w/w).When the content of MWCNTs in sediment was extremely high(5%,w/w),the MWCNTs themselves had a greater impact on the microbial community in sediment.Bacteroidetes,Planctomycetes,and Nitrospirae were feature bacterial phylums in the sediment,which could be used to reflect the effects of MWCNTs and 2,4-DCP on the bacterial community in sediment.The 4th section describes the study about the effect of MWCNTs on the metabolic function of microbial communities in the riverine sediment contaminated with phenanthrene.The Biolog ECO microplate was used to study the effects of different dosages of MWCNTs on the carbon metabolic activity and Shannon-Wiener diversity index of microbial communities in the sediment.MWCNTs at a content of0.5% to 2.0%(w/w)could significantly affect the carbon metabolism function of microbial community in the sediment.The phenanthrene-contaminated sediment showed the highest microbial metabolic activity and Shannon-Wiener diversity index after the addition of 0.5%(w/w)MWCNTs.The results of clustering the microbial communities in different treatment groups on the trained self-organized maps showed that the effect of phenanthrene on the carbon metabolism of microbial communities in the sediment was greater than that causes by MWCNTs.The 5th section presents the further study about the effects of differently functionalized MWCNTs on the metabolic function of microbial communities in riverine sediment based on the studies in the 3rd and 4th section.The Biolog ECO microplate was used to investigate the effects of relatively high concentration of MWCNTs and their functionalization on the sediment microbial community.Hydroxylated,carboxylated,and aminated MWCNTs had a negative impact on the metabolic function of microbial communities in riverine sediment.At the dosage of0.5%(w/w),the aminated MWCNTs significantly reduced the metabolic activity and diversity of the microbial community in sediment,while all types of the MWCNTs showed an inhibitory effect on the metabolic function of microbial communities at the dosage of 2.0%(w/w).The sediment microbial community preferred polymers and amino acids on the microplate,and the dose of MWCNTs used in this study had a greater impact on microbial metabolism than the functionalization.In this paper,the effects of MWCNTs on the transport and ecotoxicity of organic pollutants in riverine sediments were systematically studied,and the results provide a lot of valuable information for assessing the risks of MWCNTs and coexisting pollutants in the aquatic environments,which may be helpful for the safety management and engineering applications of carbon nanotubes.