The Photochemical Behavior Of Carbon Dots,and Its Bioaccumulation Kinetics And Toxicity On Two Types Of Marine Dinoflagellates

With the ever-increasing development of nanotechnology,the environmental risks of ENMs with sizes smaller than 100nm,especially carbon-based NMs(CNPs),have received a lot of attention as a result of their unique physicochemical properties.In order to avoid the risks,information of the environmental behavior and potential environmental toxicological effects of CNPs are in urgent need.In the present study,we synthesized 14C-labeled carbon dots(CDs)by one-way microwave pyrolysis to investigate their photochemistry in marine environment.Two marine algae,Prorocentrum micans and Prorocentrum donghaiense were used as the objective organisms,and the bioaccumulation and toxicity of CDs in these two organisms were compared.The photochemical degradation of CDs was easily affected by pH and light in the sea water,while the salinity and the existence of natural organic matter did not significantly alter their photodegradation.Compared with visible light,UV irradiation greatly improved the degradation efficiency of CDs and 100%of the CDs were degraded after 6-d irradiation.By using a variety of ROS promoters and inhibitors together with different characterization methods,we concluded that the photodegradation of CDs in seawater was not caused by ROS,but by a kind of photo-induced surface oxidation behavior.Accompanying with the mass agglomeration of CDs,photo-induced degradation attenuated the particle size,ensuring the relatively good dispersity of CDs in seawater system.A series of uptake and efflux tests were conducted,it was found that active transport and passive diffusion were responsible for CDs translocation.As compared to Prorocentrum micans,Prorocentrum donghaiense had higher uptake and lower elimination.Especially at day 6,CDs were more accumulated in Prorocentrum donghaiense than in Prorocentrum micans.Considering the much longer biological half-life of CDs,they will cause very serious toxic effects.With light illumination,CDs can translocate into the cell in the form of particle or in the dissolved form(degradation products)and become toxic.Our toxicity tests showed that,CDs inhibited the growth of Prorocentrum dolghaiense more than that of Prorocentrum micans.The degradation products accounted partly for the toxicity of Prorocentrum micans while completely for the toxicity of Prorocentrum donghaiense.Our preliminary results revealed that the degradation products contained three types of substances:one was the derivatives of glucose and polyethylene glycol,one was the derivatives of phenol with polyethylene glycol,the other was the derivatives of polyethylene glycol itself.It implies that the toxicity of the degradation products was similar to the skeleton of their parent compounds,possessing the hydrophilic groups and aromatic carbon skeleton.Overall,our research shed a new light on the CNPs bioaccumulation and toxicity,establishing a new quantitative detection method,and also improved our understanding about their behavior,effects and fate in the natural aquatic environment,which further provided the theoretical supports for ecological risk assessment on CNPs.