Toxic Effects And Mechanisms Of Polystyrene Micoplastics On Caenorhabditis Elegans

Microplastics are plastics,thin films and fibers which particle size < 5 mm,many studies have shown that the microplastics are widely distributed in marine ecosystem,freshwater ecosystems,land ecosystem,and microplastics have even been found in atmosphere and lava groundwater.The United Nations Environment Assembly has listed it as the second major scientific problem in the field of environmental and ecological research.Microplastics have been found to have multiple toxic effects on Caenorhabditis elegans(C.elegans),including reproductive and developmental toxicity and neurotoxicity,and nematode physiological changes often associated with changes in behaviour,bacteriophagous nematode’s selective feeding behavior of microorganisms affect the number,activity and community structure of microorganisms,which affects soil ecological system,but the effect of microplastics on feeding preference of nematodes has not been studied.In this study,we choose C.elegans as test subject,set up two different particle size(1 μm and 5 μm)and three different concentrations(1 mg/L,10 mg/L,and 100 mg/L),to explore the relationship between its physiological effects and feeding preference effect on nematode and its mechanism,in order to provide scientific basis for toxicity evaluation and risk assessment of microplastics,the main research results are as follows:1.The physiological toxicity and motor toxicity of C.elegans after exposure to PS microplastics with different particle size and concentration were studied.The results showed that: short-term exposure of PS microplastics affected the lifespan,reproduction,bodysize,head thrashes and pharyngeal pumping of C.elegans to a certain extent.At 100 mg/L,1 μm and 5 μm of PS could shorten the lifespan of C.elegans(P < 0.05),and there was no significant difference between control and 1 mg/L,10 mg/L group(P > 0.05),C.elegans’ average lifespan was negatively correlated with PS microplastics’ exposure concentration;Both 1 μm and 5 μm PS microplastics could inhibit C.elegans’ reproduction(P < 0.05);The toxicity effect of bodysize was related to the particle size of PS microplastics;The body length and body width of C.elegans were significantly inhibited by 1 μm,1 mg/L PS microplastics(P < 0.05),5 μm,10 mg/L and 5 μm,100 mg/L PS microplastics significantly increased the body length and body width of C.elegans(P < 0.001);The head thrashes of C.elegans was significantly inhibited by short-term exposure to 1 μm,100 mg/L and 5 μm,1mg/L PS microplastics;PS microplastics of 1 μm and 5 μm could significantly increase the pharyngeal pumping frequency of C.elegans at three concentrations of 1 mg/L,10 mg/L and100 mg/L(P < 0.001);2.The effects of different particle size and concentration of PS microplastics on the feeding preference behavior of C.elegans were studied.The results showed that: after shortterm exposure to PS microplastics of 1 μm and 5 μm,the feeding preferences for X1 and Y1 of the three exposure groups did not change.After prolonged exposure to 1 μm of PS microplastics,the feeding preferences for X1 and Y1 of the three exposure groups did not change,but long-term exposure of 5 μm of PS microplastics in 1 mg/L,10 mg/L,100 mg/L three concentrations can significantly change the C.elegans’ feeding preference on X1 and Y1,this change was significantly correlated with the concentration of PS microplastics,and the greater the PS concentration,the greater the effect on the feeding preference of C.elegans.The results showed that there was no significant correlation between the change of feeding preference of PS microplastics and the physiological toxicity.3.The mechanism of PS microplastics changing the feeding preference of C.elegans was investigated at the biochemical and molecular levels.At the biochemical level,the ROS level,SOD activity,CAT activity and ACh E activity of C.elegans after long-term exposure to PS microplastics with different particle size and concentration were studied.At the molecular level,the relative expression levels of feeding related functional genes(cat-4,egl-4,gcy-28,daf-7,dbl-1,tir-1,tol-1)were studied.Long-term exposure to 1 μm,100 mg/L and5 μm,100 mg/L PS microplastics significantly increased ROS levels in C.elegans(P < 0.01);PS microplastics of 1 μm and 5 μm had no significant effect on SOD activity in C.elegans at three concentrations of 1 mg/L,10 mg/L and 100 mg/L(P > 0.05);Long-term exposure to1 μm,100 mg/L PS microplastics significantly increased CAT activity in C.elegans(P <0.05),and long-term exposure to 5 μm,1 mg/L and 5 μm,100 mg/L PS microplastics significantly increased CAT activity in C.elegans(P < 0.05).Long-term exposure to PS microplastics with particle size of 1 μm and 5 μm and concentration of 1 mg/L and 100 mg/L significantly increased the ACh E activity in C.elegans(P < 0.001);After long-term exposure to PS microplastics with particle size of 5 μm and concentration of 1 mg/L,10 mg/L and 100mg/L,the expression levels of seven feeding related functional genes,including cat-4,egl-4,gcy-28,daf-7,dbl-1,tir-1 and tol-1,were significantly increased,which was in accordance with the phenomenon that 5 μm PS microplastics can change the feeding preference of C.elegans.These results indicated that oxidative stress and neurotoxicity induced by acetylcholine were not the direct mechanism for PS microplastics changing the feeding preference of C.elegans.PS microplastics changed the feeding preference of C.elegans mainly by regulating the expression of functional genes related to feeding preference.In summary,1 μm and 5 μm polystyrene microplastics are toxic to Caenorhabditis elegans in physiological and sports aspects after short-term exposure.However,the feeding preference of nematodes for X1 and Y1 did not change significantly after short-term exposure;Long-term exposure to 5 μm polystyrene microplastics can change the feeding preference of nematodes for X1 and Y1 by regulating functional genes related to feeding.