Effects Of Titanium Dioxide Nanoparticles On Freshwater Algal Arsenic Accumulation And Transformation

With the rapid advancement and wide application of nanotechnology,it is inevitable that a substantial amount of nanoparticles would release into the aquatic environment.Since titanium dioxide nanoparticles have highly activivity and large specific surface,They are more easily to absorb other environmental pollutants.Currently,many researches focused on the behavior and ecotoxicity of titanium dioxide nanoparticles.But the effects of titanium dioxide nanoparticles on other vital co-contaminants remain largely unknown.Arsenic pollution has been a ubiquitous global pollutant.It's biogeochemical cycle,toxicity and prevention is also a key scientific problems which cause extensive concern.Scenedesmus obliquus and Microcystis aeruginosa were chosen independently to examine the biological reponses caused by of the co-contaminants of titanium dioxide nanoparticles?nano-TiO₂?and arsenic?arsenite:As?,arsenate:AsV?.Specifically,exposure with short-term and long-term experiments were conducted to determine,the physical and chemical properties of nano-TiO₂ and arsenic co-contaminants,the ultrastructure of polluted algae and arsenic metabolism uptake and transformation by Scenedesmus obliquus and Microcystis aeruginosa.Inductively coupled plasma mass spectrometry?ICP-MS?and high performance liquid chromatography inductively coupled plasma mass spectrometry?HPLC-ICPMS?was employed fpr primary reseach on arsenic and arsenic species.These findings would provide scientific data to understand how nano-TiO₂ effect arsenic biogeochemistry cycle in aquatic environment.The main results were as following:?1?There were significant differences of algae grownth impacted by between As? and As?with nano-TiO₂.Low concentration of arsenic?1 ?M?could stimulate the growth of Scenedesmus obliquus,while high concentration of arsenic?10 ?M,100 ?M?inhibited the growth a little.Additionally nano-TiO₂ with As? had more toxic than nano-TiO₂ with the As V for Scenedesmus obliquus.?2?Scenedesmus obliquus could enhance As? accumulation by nano-TiO₂ in 96h,and increase with the nano-TiO₂ level.But this accumulation occurred,to some extent,a delay phenomenon caused by the competition of arsenic adsorption onto nano-TiO₂ with alage uptake.Nano-TiO₂ could promote arsenic methylation by algal.The algae accumulate arsenic mainly occur in the 24h when exposed in nano-TiO₂ with AsV.Additionally,the presence of nano-TiO₂ could inhibit the algae release of arsenate.?3?In the short term?96 h?,nano-TiO₂ inhibited algal accumulation AsV and had no obvious effects on arsenic methylation.However,they contributed to AsV accumulation in algae in the long term?30 d?.In the long term,nano-TiO₂ promoted the releaseof organic asenic from Scenedesmus obliquus into the medium.?4?Nano-TiO₂ could promote arsenic accumulation and methylation of Scenedesmus obliquus and Microcystis aeruginosa.For the organic arsenic metabolism,MMA?monomethylated arsenic?was the main form of Scenedesmus obliquus,while DMA?dimethylated arsenic?was of Microcystis aeruginosa.Additionally,nano-TiO₂ could promote gaseous arsenic produce by Microcystis aeruginosa and inhibit gaseous arsenic by Scenedesmus obliquus.This may be due to that different organisms have different toxic resistance and detoxification mechanism.