Toxicological Effect Of Fluoranthene On Earthworm Mediated By Microplastics

Micro plastics is a new environmental pollutant which has attracted people's attention in recent years.Micro plastics have a small volume and a large specific surface area.When they enter the soil,they will affect the environmental behavior of hydrophobic organic pollutants in the soil,thus affecting soil organisms such as earthworm.Earthworm is a typical soil biota,an indicator of soil pollution and an important subject in the study of ecotoxicology.PAHs is a hydrophobic organic pollutant with heavy soil pollution in farmland.At present,there are more studies on the toxicity of PAHs on earthworm,but the study on the ecological toxicity of PAHs to organisms is less under the guidance of micro plastics.Therefore,the effects of E.fetida on earthworm toxicity and their differences were studied by simulating polluted soil with fluoranthene as the representative of PAHs.At individual level,the effects of PAHs on the acute toxicity and avoidance behavior of earthworms were studied by natural soil method under the influence of different kinds of micro plastics under the environment related concentration.At the cell level,the damage degree of pollutants to lysosomal membrane in earthworm was studied.From the beginning of adding neutral red dye to the microscope fixed field of vision,more than 50%of the cells in the body cavity were stained,which is called the neutral red retention time.The NRRT can reflect the damage of lysosome.The changes of SOD,CAT,POD and MDA content of earthworms under pollution stress were studied.The conclusions are as follows:(1)The acute toxicity test showed that the concentration of the treated group was 40mg/kg without adding micro plastic,and the earthworm death began to occur.With the addition of microplastics,the lethal effect of earthworm was significantly higher than that of the control group without micro plastic,and the toxicity of PS treatment group to the red worm was higher than that of the other treatment groups.The LC₅₀ of fluoranthene treatment group was 131 mg/kg,and the LC₅₀ of adding micro plastics PE?PS and PVC was 118mg/kg,98 mg/kg and 124 mg/kg respectively.The LC₅₀ of the treatment group was lower than that of the non treated group.The toxicity of all treatment groups to earthworm was significantly dose-effect.The results of the study showed that the high concentration of fluoranthene(>40mg/kg)inhibited earthworm activity,and the earthworm did not consume energy and the declining trend of quality is slow.(2)The results showed that when the concentration of fluoranthene reached 10 mg/kg,the avoidance behavior of earthworm began to appear,and the higher the concentration,the more obvious the avoidance trend.The avoidance behavior of earthworm was more obvious in the treatment group with the increase of fluoranthene concentration than other two kinds of micro plastics.When the concentration of fluoranthene reached 40 mg/kg,the avoidance rate reached 80%in all treatment groups,which had obvious toxic effect on earthworm.(3)The results of neutral red test showed that:when earthworm was exposed to external pollution stress,NRRT of each treatment group was lower than that of the control group,indicating that pollutants in each treatment group would damage the lysosomal membrane of earthworm coelomocytes.With the extension of exposure time,NRRT became shorter,and there was a significant time effect relationship.The treatment group had a significant concentration effect relationship on the stability of earthworm lysosomal membrane.NRRT of microplastic fluoranthene treatment group was significantly lower than that of fluoranthene treatment group and single microplastic treatment group.When fluoranthene concentration reached 40 mg/kg,the NRRT time of earthworm in PVC treatment group was the shortest,which indicated that compared with the other two kinds of microplastics,PVC had the strongest damage to the lysosomal membrane of earthworm.(4)The antioxidant defense test showed that SOD,CAT and POD activities were activated in the control group when exposed for 7 days.With the increase of concentration,the activity of SOD,CAT and POD was inhibited by high concentration fluoranthene.The enzyme activity of earthworm reached the peak when the concentration of fluoranthene was10 mg/kg in the treated group.The MDA content of earthworm exposed at 14 days was lower than that of 7 days.It indicated that earthworm itself had the repairing effect on fluoranthene pollution stress mediated by microplastics,but the repair function was limited and could not completely solve lipid peroxidation.