Toxicological Effect Of Hg Stress On Earthworm

Mercury pollution will not only affect the regular function of the soil,lead serious damage to the environment,but also threaten human health through the food chain.As the main soil fauna group,earthworms are a good indicator to the soil pollution situation.In order to reveal the effect of mercury stress on the physiology and petrochemistry of earthworms under different exposure concentrations,explore the new biomarkers for the early diagnosis of soil pollution,and provide basic toxicological data for the construction of terrestrial biological ligand model for mercury,based on the enrichment and release rule of mercury,the oxidative responce,reproductive toxicity,behavioral toxicity,and the proteome expression of Eisenia foetida under different Hg exposure concentrations were studied.The results can provide theoretical basis for the diagnosis,biological monitoring,pollution control and reparation for Hg polluted soil.The main conclusions:(1)Enrichment and release rule for HgEisenia foetida showed certain ability to enrich Hg.Under 1-8mg/kg exposure level,the bioconcentration factors(BCF)were 1.69-2.95,and the maximum concentration was 18.93mg/kg;under the condition of16-64mg/kg,the BCF were 5.21-7.62,and the maximum concentration was 476.33mg/kg.Earthworms has fast enrichment rate in the first 8 d,then the rate slowed down,and became stable after 90 d;The mercury in earthworms is mainly distributed after 25 segment of earthworms.Along with the release in clean soil,the amount of Hg in earthworms decreased in varying degrees,and become stable after 64 d.(2)Oxidative response under Hg exposureThe effects of Hg stress on superoxide dismutase(SOD)and glutathione peroxidase(GSH-PX)of earthworms were inhibited,and the content of malondialdehyde(MDA)increased,but catalase(CAT)activity was not significant.SOD and GSH-PX was inhibited by Hg,and it may be one of the causes for the increase of MDA content.The resistance enzymes of earthworms showed different stages of stress response to Hg exposure,and the peak time of stress reaction of different enzymes was different.The content of MDA has better dose-effect relationship with the exposure concentration and the Hg enrichment in earthworms.(3)Reproductive toxicity under Hg stressUnder Hg pollution,the sperm morphology of Eisenia foetida was significantly affected.4 forms of sperm aberration were observed:hook like bending in the head,the top ring,local swelling and whole sperm curled up.The rate of sperm morphological aberration showed a dose effect relationship with Hg exposure concentration.Normal spermatogenic cells of earthworm were arrayed regularly,the cell structure is complete and clear,golgi apparatus and mitochondria were normal.After 64 mg/L filter paper exposure for 24 h,a small number of cells began to rupture,organelles flowed out,the golgi apparatus began to degrade,and the morphology of mitochondria also changed abnormally.Under 128 mg/kg Hg exposure for 28d,the majority of cells rupture,organelles outflow,and found a large number of abnormal crystal structure.With the increase of exposure concentration,damage to earthworm sperm DNA increased.Higher Hg exposure concentration can lead more serious damage to earthworm sperm DNA.Under 128 mg/kg Hg stress,30%spermatozoa were mildly damaged,25%spermatozoa were moderate,7%sperm was severe and only 35%sperm Not damaged.(4)Behavioral toxicity under Hg stressThere is no obvious avoidance behavior under 64mg/kg exposure concentration,the avoidance concentration of Eisenia foetida to Hg is128mg/kg.Hg could obviously inhibit the CO₂ production of earthworms.The inhibitory effect is dose-dependent after 2d,and the effect is more serious after 7d;under 128mg/kg Hg exposure,the respiration inhibition rate was 51.3%.After 72h,excavation activity was inhibited at 32mg/kg and 128mg/kg;after 7d,excavation activity tends to stop under 8,32,128mg/kg treatment;the maximum excavation depth of earthworms was significently decreased under 128 mg/kg(24.8 cm)compared to the control group(33.4cm)(P<0.05).(5)Expression of earthworm proteome under Hg stressAfter exposed to Hg pollution soil,10 proteins of earthworm were up-regulated,4 proteins were down-regulated.In the up-regulated protein,the function of 6 proteins was not clear,3 proteins were actin for different functions,one was fibrinolytic enzyme;in the down-regulated proteins,2were actin,2 were coordination proteins in hemoglobin.Western Blot showed that the expression of PLEK in Eisenia foetida decreased and OGFRL1 was increased,which was consistent with the results of two-dimensional electrophoresis.