Effects Of Polystyrene Microplastics Stress On Physiological Characteristics Of Freshwater Benthic Macroinvertebrate

As a new type of environmental pollutants,microplastics have become a hot research object in the field of global ecological environment.As researchers pay more and more attention to microplastics,research on the biotoxicity of microplastics in freshwater environment is also increasing.However,comprehensive studies on the behavioral and physiological toxicity of freshwater benthic invertebrates under microplastic stress are relatively limited,and the underlying toxicity mechanisms are still unclear.In this study,typical freshwater macroinvertebrates Corbicula fluminea and Bellamya aeruginosa were selected as experimental objects,and polystyrene microspheres were used as experimental materials.Concentration gradient microplastic solutions of 0,0.01,0.10 1.0 and 10 mg L^-1 were used as exposure solutions to carry out a 42-day aquatic ecological indoor culture experiment.By detecting the macrobenthos behavioral indicators and related tissue physiological indicators,the internal impact mechanism of microplastic stress on the behavior and physiological characteristics of freshwater macroinvertebrates was explored.The main conclusions are as follows:（1）High-concentration microplastic stress inhibited the behavioral characteristics of the clam（siphoning behavior,oxygen consumption and ammonia excretion,burrowing behavior）and snail（oxygen consumption and ammonia excretion,crawling behavior）.On the 21st day and the 42st day of the formal experiment,the siphon efficiency of the clam in the 0.10,1.0 and 10 mg L^-1 groups was significantly inhibited（p<0.05）.On the 7th day,the oxygen consumption and excretion behaviors of clam and snail were significantly inhibited（p<0.05）.On the 21st and 42st days,the inhibitory effect of the clam was maintained,but the snail recovered.On the 7th day,the crawling behavior in the 0.01mg L^-1 group of snails was significantly improved,but the 10mg L^-1 group was significantly inhibited on the 21st and 42nd days（p<0.05）.First,under the exogenous stress of microplastics,the shell-closure effect of the clam reduces the frequency and amplitude of shell opening,which directly leads to a decrease in its siphon efficiency,thereby reducing the behavior of oxygen consumption and ammonia excretion.Secondly,under long-term stress,the insufficient antioxidant capacity of gill tissue leads to oxidative damage,resulting in ciliary degeneration and tissue damage in gill tissue,thereby reducing the siphon efficiency and oxygen consumption and ammonia excretion.The decline of crawling behavior of snail may be due to the decrease of nervous system inhibition and orientation recognition ability caused by high concentration of microplastic stress.The perturbation of clams and patina snails affects the migration of sediment biogenic elements and the structure of sediment microplastic community,and microplastic stress changes the behaviors of clams and patina snails,indicating that microplastics affect the ecological function of benthic animal communities in the environment.（2）The observation results of tissue sections showed that microplastic stress would cause ciliary degeneration damage in the gill tissue of the clam,and the highest concentration group was the most serious;the liver tissue of snail had abnormal shapes of enlarged tubule lumen and enlarged hemolymph space phenomenon.There was no obvious morphological abnormality in the musculature of the axe foot and the gastropod of the snail.Gill tissue is the direct target organ of exogenous stress.The accumulation of microplastics in epidermal cells causes strong oxidation in local areas,resulting in tissue damage of ciliary degeneration.Morphological abnormalities in the liver tissue of snail indicate that exposure to microplastics impairs its detoxification function.（3）Stress of microplastics significantly changed the enzyme activities in the tissues of the clam and the snail.Microplastic stress can significantly inhibit acetylcholinesterase（ACh E）in benthic tissues,and significantly increase ATPase（adenosine triphosphate,ATPase）,antioxidant enzyme activities and malondialdehyde（MDA）content in tissues（p<0.05）.With stress time going by,the inhibitory effect of ACh E enzyme activity in the soft tissue of the clam was maintained,but the tissue of the snail returned to normal;superoxide dismutase（SOD）and glutathione reductase（GR）in two animal tissues still maintained a high level.The exogenous stress of microplastics induces the body to produce excess reactive oxygen species（ROS）,thereby promoting the body to increase the activity of antioxidant enzymes（SOD,CAT and GR）to eliminate high-intensity oxidative stress,and the body’s antioxidant capacity is insufficient under long-term stress,thus leading to increased MDA content in soft tissue.（4）Transcriptomic analysis was performed on the gill tissues of the 0 mg L^-1 and10 mg L^-1 groups,and the differential gene expression was compared between the two treatments.Through differential gene enrichment pathway analysis,the results showed that the related pathways such as cell membrane components and cell apoptosis in gill tissue were significantly changed.The gene expression level revealed the reason why microplastic exposure led to ciliary degeneration in the gill tissue of the clam.