The Molecular Mechanism Of Nanoparticles Effects On Aquatic Organisms

With the development of nanotechnology,nanomaterials are widely used in various fields such as manufacture,medicine and pharmacy,electronics and daily life.Nanomaterials would form nanoparticles,which possess the characteristics of low-dose and long-term existence,by emitted into water through point source and non-point source.The accumulation of nanoparticles in aquatic organisms,delivery in food chain and the toxic effect have been drawn more and more attention with the detection of nanopaticles in water environment.However,traditional toxic assessment methods mainly focus on end point to explore the effect on biological lethality,reproductive effects,growth disturbances and other behaviors.The concentration of nanoparticles in these studies is usually much higher than that in actual environment and therefore fail to reflect biological effects of nanoparticles in low-dose of long-term exposure conditions,especially neglecting the probable stimulating effect on the growth of aquatic life and thus can not make comprehensive and objective evaluation on the toxic effects of nanoparticles.In this study,nC₆₀0 and nano-silver were selected as model nanoparticle materials to represent the particles formed in the water environment.Scenedesmus obliquus and Daphnia similis were used as tested aquatic organisms.Omics technology including transcriptome combination metabolomics were adopted to study on the interact molecules mechanism to aquatic organisms.Study contents as follows:（1）Low-dose of nC₆₀0 was found to have a minor growth inhibitory effect on Scenedesmus obliquus.The work evaluated genes and metabolic change of Scenedesmus obliquus under low-dose and long-time nC₆₀conditions using transcriptomics and metabolomics;（2）The study evaluated the chronic physiological effects and corresponding metabolic change of AgNPs on Daphnia similis,which were exposed to two ambient concentrations（0.02 and 1μg/L）of AgNPs for 21days;（3）We wanted to investigat the metabolic changes of the growing Daphna similis with exposure to 0.02 and 1μg/L AgNPs.And this work studied the baseline changes in metabolites of a Daphnia similis through its life-cycle.The results show that:（1）The Scenedesmus obliquus cells exposed to nC₆₀0 had several significant alterations in cellular transcription and biochemical processes.During the 7-day exposure to nC₆₀,2234 and 2448unigenes were differentially expressed by 0.1mg/L and 1mg/L nC₆₀-treated groups compared with the control,including 2085 or 2247 up-regulated genes and149 or 201 down-regulated genes,respectively.We successfully identified22 metabolites,including 6 significantly changed metabolites,such as sucrose,D-glucose,and malicacid.The citrate cycle（TCA cycle）（ko00020）was the main target of both differentially expressed genes and metabolic change.However,accumulation of sucrose could have induced feedback inhibition of photosynthesis in Scenedesmus obliquus,explaining the slight growth inhibition observed.（2）It was observed that the AgNPs caused a hormetic response on Daphnia;stimulating feeding capability and a significant increment in average length/dry mass compared to control specimens.Exposure to AgNPs also led to significantly reduced fecundity and increase in the appearance of ephippia,ahallmark hormesis response in Daphnia.41metabolites were identified,including 18 significantly-changed metabolites,suggesting downregulation in energy metabolism（amino acids,such as tyrosine,leucine,tryptophan and lysine;fatty acids such as linolenic acid）and upregulation of lipid related metabolism（fatty acids,such as arachidonic acid）were key events in these responses.The results provided a renewed mechanistic understanding of low concentration chronic toxicity of AgNPs toxicity on Daphnia.（3）A dynamic kinetic pattern of the growing Daphnia’s metabolome underwent a cycle from day 0 to day 21,with the level of metabolites gradually increasing from day 0 to day 10;then the level remained steady at day 10 to day 13;declined from day 13 followed;finally falled back to the baseline level of day 0 on day 21.The significant changes in certain metabolites,such as amino acids（serine,threonine and tyrosine）,sugars（D-Allose）and fatty acids（arachidonic acid）revealed new insights into how these metabolites in Daphnia respond to chronic AgNPs stress.These significant difference genes and metabolites are useful to elucidate the underlying molecular mechanisms and find biomarkers for future studies and offer new insights into the early detectable changes with nanopaticals low-dose of long-term exposure.