The Combined Toxic Effect Of Microplastic And Organic Contamitants On Aquatic Organisms

With the ever-increasing production of plastics around the world,a large number of plastic wastes were released into the ocean.Due to the difficult degrading and persistence of microplastic,its impact on the environment and aquatic organisms can not be ignored.In the natural environment,microplastic usually does not exist singly and interacts with other environmental contamintants inevitably.A lot of hydrophobic organic contaminants have been found on the surface of microplastic.However,little is known about their effects on their environmental behavior and biological toxicity.There is no conclusive evidence yet.Three of the most widely used microplastics selected in this study were polyethylene(PE),polyvinyl chloride(PVC)and polystyrene(PS).Test organisms are Scenedesmus oblignus and Daphnia magana.This paper focuses on the effects of microplastic on the toxicity and bioavailability of organic contamintants.We attempt to explain the mechanism of joint toxicity,through the adsorption of microplastic with organic contamintants,and to provide a scientific basis for assessing the potential risks of microplastic in the environment.In this paper,we mainly study the adsorption of organic compounds by microplastic,the single and combined toxic effects of microplastic and organic compounds on S.obliquus,the single and combined acute and chronic toxic effects of microplastic and organic compounds on D.magana.The results showed that the isothermal adsorption of three organic compounds by microplastic conformed to the Freundlich adsorption isotherm model and belongs to the adsorption equilibrium mode on the heterogeneous surface.The adsorption of organic contamintants to microplastics is affected by microplastic material itself,the particle size and organic matter.The adsorption properties of the microplastic with the same size range of 200-250?m are PVC>PE>PS.And the adsorption capacity of PS(5.80 ?m)to organic compounds are much larger than that of PS(200-250 ?m).The smaller of the microplastic particle size,the stronger adsorption performance.In addition,the structure of organic compounds themselves also affects the adsorption performance,so all four micro-plastics showed triclocarban(TCC)>triclosan(TCS)>methyl triclosan(MTCS).In S.obliquus experiment,single microplastic and organic compounds showed obvious dose-response relationship to S.obliquus,and the toxicity of microplastic in the micrometer range was small.In the presence of microplastic,the joint toxicity of combination is complex.The presense of microplastic may not only lead to the enrichment of organic compounds toxicity,but also reduce and attenuate the joint toxicity of microplastics and organic compounds.The adsorption can be used for simple mechanism explanation,but its fundamental toxicity mechanism needs to be further explored.Different from green algae,microplastic can be taken in by D.magana.So microplastic PS(5.80 ?m)is selected as the research object.The 48 h acute toxicity of PS(5.80 ?m)to D.magana was found to be low toxicity,TCS was highly toxic,and TCC and MTCS were extremely toxic.And the combined acute toxicity of PS and organic compounds at toxicity ratio 1:5 was antagonistic.In the chronic toxicity test,the single microplastic and organic compounds had a significant effect on the growth and reproduction of D.magana at low concentration,and effects increase with the increase of compound concentration.The combined toxicity is related to the concentration of microplastic.When the microplastic concentration is higher than 1 mg/L,the joint chronic toxicity shows enhancement.Joint chronic toxicity is different from joint acute toxicity,more comprehensive response to long-term exposure to biological growth and reproduction.As the combined chronic toxicity of microplastics and organic compounds is enhanced,the aquatic organisms face more ecological risk.