Toxicity And Mechanism Of Microplastics-dechlorane Plus/Cadmium Combined Pollution To Algae

Microplastics generally refer to plastic particles or fragments less than 5 mm in diameter,and it was a new global pollutant.Microplastics pollution has become one of the environmental issues of widespread concern at home and abroad.In recent years,domestic and foreign scholars have successively carried out pollution research and toxicological research on microplastics in the ocean,and research on microplastics in freshwater environments is in the ascendant.Microplastics in freshwater environments mainly originate from land(wind,surface runoff and groundwater runoff,etc.)and sewage treatment plants.Therefore,the freshwater environment was regarded as a sink of microplastics.In addition,the water environment also contains a variety of toxic pollutants(such as heavy metals,drugs and persistent organic pollutants).Microplastics can absorb these toxic substances in water and carry them in the environment for transmission.However,there were few reported on the impact of the interaction of microplastics and pollutants on aquatic plants,and the impact of the complex interaction of microplastics and pollutants on aquatic plants is not clear.Therefore,the toxicity of polystyrene nanoplastics(PSNPs)and Bis(hexachlorocyclpentadiene)cyclooctane(dechlorane plus,DP)/cadmium(Cd)to two aquatic plants was studied in this thesis.The toxicity experiments of PSNPs and DP to Chlorella vulgaris show that: The maximum inhibition rate of PSNPs to Chlorella vulgaris was 13.28%.After exposured,the reactive oxygen species(ROS)content,superoxide dismutase(SOD)activity,and malondialdehyde(MDA)content were significantly increased in Chlorella vulgaris cells.This indicated that Chlorella vulgaris were in a state of oxidative stress.Under PSNPs stress,the photosynthetic system of Chlorella vulgaris was damaged,manifested as a significant decrease in chlorophyll content and maximum photoelectron yield.This might be related to excess ROS produced by algae cells.Metabolomics of Chlorella vulgaris showed that PSNPs could affect enzyme and protein synthesis and nitrogen metabolism pathways.Therefore,PSNPs have toxic effects on Chlorella vulgaris mainly by inducing oxidative stress and altering metabolic pathways such as protein synthesis.DP had no toxic effect on Chlorella vulgaris,and had no effect on its growth,physiology and biochemical,and at the same time,DP did not cause changes in the metabolic profile.Compared with the toxicity test of PSNPs alone,under the co-exposure of PSNPs and DP,the physiological and biochemical parameters of Chlorella vulgaris did not change significantly.However,co-exposure of the two pollutants affected more metabolic pathways of Chlorella vulgaris,so the interaction of PSNPs with DP increased the potential toxicity of algae After 24 hours of the experiment,we found that the algae in the PSNPs treated group had severe agglomeration.The SEM images of algae showed that large number of PSNPs were adsorbed on the surface of algae,while DP can exacerbate the agglomeration and adsorption effect between algae and PSNPsThe toxicity experiments of PSNPs and Cd on Ceratophyllum demersum L showed that:Cd could reduce the growth length and increased the glutathione(GSH)activity and MDA content in Ceratophyllum demersum L.Similarly,10 mg/L PSNPs also inhibited the growth of Ceratophyllum demersum L,but had no effect on GSH activity and MDA content.Under the co-exposure of Cd and PSNPs,PSNPs alleviated the toxic effect of Cd on Ceratophyllum demersum L;and the content of Cd in Ceratophyllum demersum L decreased significantly when PSNPs was added.Therefore,PSNPs alleviate the toxicity of Cd by reducing the absorption of Cd in Ceratophyllum demersum L.The SEM and TEM electron microscope pictures showed,Ceratophyllum demersum L could not absorb and transport PSNPs,under the exposure of PSNPs alone.However,under the combined effect of PSNPs and Cd,we found that a large number of PSNPs accumulated in the xylem vessels and cells,which might be that Cd can destroy the cell structure of Ceratophyllum demersum L and increased the possibility of PSNPs entering into Ceratophyllum demersum L.This thesis investigated the toxic effects of the interaction of PSNPs with two different pollutants on algae.We found that the combined effects of different pollutants and PSNPs had different toxicity to algae.Therefore,different pollutants with combined action with PSNPs would bring different poison production mechanisms to plants.This thesis was the first to evaluate the effect of the interaction between PSNPs and DP on the toxicity of Chlorella vulgaris,and explore the toxic effects of PSNPs and Cd on Ceratophyllum demersum L.This provided a reference for assessing the ecological impact of nanoplastics,dechlorane plus and cadmium in freshwater environments.