Effects On Physiological Response Of Lead And Polystyrene Microplastics On Juvenile Chinese Mitten Crab Eriocheir Sinensis

With the growth of population,global needs for plastics are increasing.In our daily life,plastics products are becoming indispensable.Microplastics(MPs)are defined as plastic particles with sizes less than 5 mm,their highly hydrophobic surfaces and fugacity capacity make MPs a potential carrier of environmental pollutants like heavy metals in freshwater.Chinese mitten crab(Eriocheir sinensis)is an important economic species of crustaceans and mainly cultivated in the Yangtze River basin.Furthermore,the benthic nature of E.sinensis makes them potential candidates as bioindicators of contaminants including heavy metals and MPs.The purpose of this study is to reveal whether environmental concentrations of MP and Pb will increase the bioaccumulation in hepatopancreas and the effects of MPs on antioxidant system,energy and lipid metabolism,liver damage and cell apoptosis of Pb in E.sinensis,to provide some reference for physiological response of crustacean to environmental stress.1.Effects of Pb and polystyrene microplastics on Pb bioaccumulation,tissue morphology and liver damage in hepatopancreas of juvenile E.sinensisTo investigate the effects of microplastics(MPs)and lead(Pb)on the toxic effects of E.sinensis,under laboratory conditions,juvenile crabs were exposed to Pb(0,5 and 50 μg/L)and MPs(0 and 400 μg/L)for 7,14 and 21 days,to investigate the activities of alanine aminotransferase(GPT)and oxalacetic aminotransferase(GOT)in hepatopancreas and hemolymph,Pb bioaccumulation and histopathologic changes in hepatopancreas of E.sinensis.The results showed that:(1)MPs increased Pb bioaccumulation in hepatopancreas of E.sinensis in 14 days.(2)GPT and GOT activities showed hepatopancreas injury under combined stress of MPs and Pb.(3)MPs aggravated Pb damage to hepatopancreas tissue morphology,and this kind of damage was aggravated with the increase of exposure time,the number and volume of cytoplasmic vacuoles in columnar epithelial cells increased,and the wall of hepatic tubules became thinner and atrophic.2.Effect of Pb and polystyrene microplastics on antioxidant system and fatty acid anabolism of juvenile E.sinensis.MPs had increased Pb bioaccumulation in hepatopancreas of E.sinensis,to further figure out the effect of this phenomenon,under laboratory conditions,juvenile crabs were exposed to Pb(0,5 and 50 μg/L)and MPs(0 and 400 μg/L)for 7,14 and 21 days.To explore the expression levels of antioxidant enzymes and genes related to preliminary anabolism of fatty acids in juvenile crab: The levels of superoxide dismutase(SOD),oxidized glutathione(GSSG),glutathione peroxidase(GSH-PX),glutathione(GSH),acetyl-Co A carboxylase(ACC),malondialdehyde(MDA)in hepatopancreas of E.sinensis and relative expression of very long chain fatty acid elongase 6(elvol6),fatty acid desaturase 6b(fad6b)and acetyl-Co A carboxylase(acc)genes of hepatopancreas were determined.The results showed that:(1)Compared with the high concentration Pb treatment(50 μg/L),the low concentration Pb treatment(5 μg/L)inhibited the activity of antioxidant and fatty acid anabolism.(2)In short term exposure(14 days),the combined stress of MPs and Pb significantly inhibited the antioxidant system and lipid metabolism of E.sinensis.3.Effects of Pb and polystyrene microplastics stress and recovery period on detoxification,metabolism and apoptosis of juvenile E.sinensisTo further study the effects of MPs on Pb toxicity,under laboratory conditions,juvenile crabs were exposed to Pb(0,5 and 50 μg/L)and MPs(0 and 400 μg/L)for 14 days and followed by a 7-day recovery without toxic substances.The levels of detoxification enzyme system(glutathione S-transferase(GST),reduced glutathione(GSH)and metallothionein(MT)and the relative expression levels of heat shock protein(hsp70 and hsp90)genes),energy metabolism and lipid metabolism(lactate dehydrogenase(LDH)activity,triglyceride(TG)content and acetyl coenzyme were measured in hepatopancreas of E.sinensis.The relative expression levels of acetyl-Co A carboxylase(acc)and fatty acid synthetase enzyme(fas)genes)and cell apoptosis(relative expression levels of p53 and caspase3)genes were measured as well,the results showed that:(1)The lower concentration of Pb activated the expression of detoxication enzyme system,energy and lipid metabolism,and cell apoptosis system in hepatopancreas of juvenile crab to protect the organism,and the protective mechanism appeared week in high concentration of Pb treatment,all the measured indexes showed a downward trend.(2)MPs increased the metal toxicity of Pb,and all the indices of combined stress group increased significantly.