Toxic Effects And Mechanisms Of Microplastic Particles On Caenorhabditis Elegans And Danio Rerio

Microplastics?MP?are plastic fragments with sizes<5mm.Due to small size and large surface area,MPs are generally considered to have greater environmental harm than large plastics,thus has become an important environmental problem of global concerns.In recent years,toxicology studies on MP have increased;however,previous studies are mainly focused on one type of MP.Little is known about toxicity differences between multiple types or sizes of MP.In addition,studies have shown that MP can induce physical damages,even lead to adverse effects,such as inflammation and stress.However,the mechanisms of MP have not yet been fully clarified.In the present thesis,polyamide?PA?,polyethylene?PE?,polypropylene?PP?,and polyvinyl chloride?PVC?with nearly same diameter of⁷0?m,and polystyrene?PS?particles with different sizes of 0.05,0.1,0.5,1.0,2.0,and 5.0?m were selected as representative MPs.Soil organism Caenorhabditis elegans?C.elegans?and freshwater vertebrate Danio rerio?D.rerio?were used as model organisms.Nematodes in the stage of L1 or L2 were exposed in the concentrations of0.5-10.0mg·m^-2 or 1mg·L^-1 microplastics suspensions for 2 or 3d.Zebrafish were exposed to 0.001-10mg·L^-11 microplastics suspentions for 10d.The aim of this study is to systematically compare and analyze toxic effects of multiple types of MP including growth and development toxicity,intestinal damages,oxidative stress and motor chronic neurotoxicity.In addition,basing on multiple types of fluorescence-labeled transgenic nematodes,effects of PS exposure on the expression of specific proteins involved with calcium,acidity in intestine and glutathione S-transferase in nematodes were fully investigated at molecular and genetic levels.The main results are as follows:?1?Chronic exposure to multiple types of MP at the concentrations of0.5-10.0mg·m^-22 including PA,PE,PP,PVC?⁷0?m?or PS?1.0 and 5.0?m?increased mortality in C.elegans.5mg·m^-22 MP with different types and sizes inhibited body length,and reduced embryo numbers and brood sizes of worms.Moreover,1mg·L^-11 PS-MP with sizes of 0.1-5.0?m can significantly shorten lifespan in nematodes.Among these sizes,1.0?m PS-MP had the greatest impact on survival,body length,reproduction,and longevity to nematodes.?2?Exposure to 1mg·L^-11 PA,PE,PP,and PVC-MP with diameter of⁷0?m resulted in significantly damages in intestine of D.rerio,characterized with cracking of villi and splitting of enterocytes.PS-MP with sizes of 0.05-1.0?m at the concentratin of 1mg·L^-11 caused similar damages in intestine of nmatodess,including abnormal morphology and fracture of epithelial cells in intestine.Furthermore,1mg·L^-11 PS-MP with sizes of 0.05-1.0?m decreased the expression of GCaMP related to calcium level and increased the expression of acidity-related genes vha-6,opt-2,and nhx-2 in C.elegans.?3?Exposure to 5mg·m^-22 PA,PE,PP,PVC,and PS-MP upregulated the expression of glutathione S-transferase 4 enzyme?GST-4?in nematodes.MP's joint exposure to curcumin,oligometric proanthocyanidins?OPC?or oxytetracycline?OTC?in the concentration of 200?mol·L^-11 can effectively reverse the elevated expression of GST-4 induced by 1mg·L^-11 PS-MP?0.1-5.0?m?in C.elegans.?4?Chronic exposure to 1mg·L^-11 PS-MP with sizes of 0.1-0.5?m increased the frequency of head threashes and body bends.In addition,crawling speed,bending angle and the frequency of mid-body bending of worms presented special changes after exposure to PS-MP.Moreover,PS-MP(1mg·L^-1,0.1-0.5?m)caused downgeneration and damage characteristics of cholinergic and GABAergic neurons on nematodes,but didn't influence dopaminergic neurons.The above results indicate that:?1?The growth and development toxicity on C.elegans induced by MP is closely related to particle size,instead of its polymer type.?2?Intestine is one of the main targets of MP toxicity,causing intestinal damages in C.elegans and D.rerio by interacting with the intestinal surface physically.?3?Abnormaly expression of calcium-related proteins,acidity-related genes in intestine and oxidative stress in nematodes are the important mechanisms of MP toxicity.?4?MP can exert chronic neurotoxicity and cause damages of motor behavior,via the means of degeneration of motor-related neurons partially in nematodes.In summary,the present thesis systematically compared the toxicity differences among multiple types and sizes of MP in nematodes and zebrafish,and revealed the size-dependent toxicity of MP.Furthermore,the studies about histopathological research on intestine in nematodes and zebrafish,expression changes of calcium and acidity-related genes,and oxidative stress provide new view and evidence for the pathways and mechanisms of MP toxicity.In addition,the paper revealed the chronic neurotoxicity of MP.These results offer an important scientific basis for revealing the environmental health risks of MP.