| Plastic waste has been a major component of marine waste due to its extensive use and poor management.Microplastics(MPs)and nanoplastics(NPs),because of their small size,are easily ingested by marine organisms,thus entering different tissues and organs of marine organisms and passing through the food chain to highly nutritious marine organisms.Potential hazards to the entire marine ecosystem and human health.Marine MPs and NPs pollution has become a major environmental concern in the world,but the current research mainly focuses on the toxicity of MPs to marine life.There are few studies on the effects of NPs on marine environment and their impact on the quality of marine aquatic products.Therefore,in this experiment,the economical fish Sebastes schlegelii was used as the experimental organism,and the standard product of polystyrene MPs was used as the experimental material.The control group(filtered seawater)and a micron group(5 μm,0.23mg/L)and nano group(100 nm,0.23mg/L)were established.This experiment studies the environmental behavior of MPs and NPs under seawater conditions,and the effects of MPs and NPs on the enrichment and metabolism of different tissues,toxic effects,energy storage and nutritional quality.The results are as following:(1)Both MPs and NPs had red fluorescence,with a spherical shape and a smooth surface.The average hydraulic diameters of MPs and NPs were 6.17 ± 0.16μm and 95.21 ± 2.04 nm,respectively.Under the condition of natural seawater,there is a certain subsidence in 5 μm-PS and 100 nm-PS in the first 5 hours,but there was no significant difference in settlement.With the increase of time,the MPs and NPs reached a stable state in seawater,and the settlement of 5 μm-PS was less than 100 nm-PS,indicating that the suspension of 5 μm-PS was stronger than 100 nm-PS.This is mainly due to the isoelectric point of 5 μm-PS(p Hpzc = 9.10)more away from the p H of natural seawater(8.00),resulting in higher negative charge on the surface of 5 μm-PS particles and greater electrostatic repulsion.(2)Under the exposure of 5 μm-PS and 100 nm-PS,the accumulation amount of MPs and NPs were gastrointestinal tract > gill > liver,in which the gastrointestinal tract >90%,but no MPs and NPs were not found in the muscle.And under the same exposure concentration,the accumulation of 5 μm-PS in the gills,liver and gastrointestinal tract were more than 100 nm-PS.The 5 μm-PS and 100 nm-PS were rapidly excreted by juvenile fish Sebastes schlegelii in the purification period.Using the uptake and depuration kinetic model,it was found that the enrichment ability of MPs and NPs in different tissues of juvenile fish was gastrointestinal > gill > liver,and there were significant differences.And the enrichment capacity of the same tissue for 5μm-PS was more than 100 nm-PS.The half-life of MPs and NPs in the liver is the longest,and is significantly higher than those in the gills and intestines,which indicates that MPs and NPs have the longest retention time in the liver of juvenile fish.And there was no significant difference in half-lives between 5 μm-PS and 100 nm-PS in the same tissues of juvenile fish.(3)In the early stage of MPs and NPs exposure,the activity of SOD and CAT in the liver of Sebastes schlegelii increased,and then the activity of SOD and CAT was inhibited,and the MDA content was increased,which resulted in lipid peroxidation of cells.The content of MDA in the 100 nm-PS group was significantly higher than that in the 5 μm-PS group,which indicated that the oxidative damage caused by NPs was higher than that of MPs.The results of comet assay showed that 5 μm-PS and 100nm-PS could cause DNA damage to Sebastes schlegelii,and the DNA damage of 100nm-PS was more than 5 μm-PS.This indicates that the genotoxicity of NPs is greater than that of MPs.When exposed for 15 days,the gills in the 5 μm-PS group showed elevation of epithelial cells,most of the secondary gill filaments degeneration,increase of mucus cells and cleavage of branchial epithelial cells.The gills in the 100 nm-PS group showed secondary lamellar aggregation,degeneration and vacuolization of cartilage rod-shaped cells,increase of mucus cells,detachment and permeability of gill epithelial cells.These findings indicate that the presence of MPs and NPs can affect the respiration of Sebastes schlegelii.The changes of liver were mainly reflected in the decrease of adipocytes and fat droplets in the experimental groups of 100 nm-PS and 5μm-PS,which indicated that MPs and NPs could affect the lipid metabolism of organisms.However,the intestinal damage of juvenile fish was less severe,appeared microvilli shedding and lamina propria loose.(4)After 15 days of exposure,the growth rate and total energy of juvenile fish in 5 μm-PS and 100 nm-PS groups were significantly decreased(p<0.05).And the content of crude protein,crude fat and ash in 100 nm-PS group were significantly lower than those in control group and 5 μm-PS group(p<0.05).These results indicated that the ingestion of 5 μm-PS and 100 nm-PS significantly inhibited the growth and energy storage of fish,and the presence of 100 nm-PS affected the nutritional value of fish.The growth of young fish was recovered in the purification period,but the energy and nutritional quality of juvenile fish were also affected by 5 μm-PS and 100 nm-PS.So MPs and NPs pollution will have a negative impact on the quality of marine aquatic products.In summary,the difference in the environmental behavior of MPs and NPs in seawater may be one of the reasons that affect their accumulation in the juvenile Sebastes schlegelii.Because the suspension performance of MPs is stronger than that of NPs in seawater.The content of MPs in the water layer where the juvenile fish is greater than NPs,which increases the accumulation of MPs(5 μm-PS)in the organism.Although the accumulation of MPs in the juvenile fish of Sebastes schlegelii is greater than that of NPs,The toxic effect is that NPs are more toxic than MPs,which indicates that the size effect is the dominant factor in their toxicity to juvenile Sebastes schlegelii and its nutritional quality. |
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