Biological Response Of Earthworms To Cd And Pb Contaminated Soil

As an important part of the environment,soil is a typical compound contamination system as the undertaker of about 90%pollutants.Earthworm is an important environmental bioindicator in soil.It is of great environmental significance to clarify the single and combined contamination of heavy metals on the corresponding biological characteristics of earthworm.In this paper,cadmium(Cd)and lead(Pb)were used as heavy metal elements,2 kinds of earthworms,Eisenia fetida with surface accumulation type and Pheretima guillelmi with benthic type,were used as recipient soil animals.The effects of Cd and Pb on body protein content,antioxidant enzymes(superoxide dismutase and catalase),biotransport enzymes(glutathione S-transferase),mitochondrial reactive oxygen species(ROS)production rate in earthworm and bacterial community structure of earthworm gut and soil(earthworm casts)were analyzed,and the influence characteristics of Cd and Pb contaminated soil on earthworm biology were explored.The main conclusion are as follows:(1)When Cd contamination occurred,there was a good correlation between the concentration of pollutants and the mortality of the two earthworms,and the effect of concentration of Cd was greater than that of inoculation time;Earthworms did not achieve avoidance response in either starvation or satiety state.Under Cd contamination stress,the body protein content of earthworm was inhibited.With the increase of Cd concentration,superoxide dismutase(SOD)activity was activated.The catalase(CAT)activity in Eisenia fetida increased first and then decreased,while there was a little change range in Pheretima guillelmi.The glutathione S-transferase(GST)activity in Eisenia fetida did not change much after inoculation for 7 and 14 days,but decreased after inoculation for 28 days,while the overall increase in Pheretima guillelmi was observed.In the early stage of inoculation,ROS in Eisenia fetida did not change significantly,but it was activated after inoculation for 28 days,while in the early stage of stress,ROS in Pheretima guillelmi decreased,which was activated after stress for 28 days.After earthworms swallowed Cd-contaminated soil,the diversity of bacterial community in earthworm gut increased significantly,while the abundance decreased,but it was not significant;compared with CK treatment,its structure changed greatly at both phylum level and genus level.The abundance of Firmicutes and Desulfobacterota in Eisenia fetida decreased,while the abundance of Proteobacteria increased,while the abundance in Pheretima guillelmi was opposite.Soil bacterial communities inoculated with earthworms and uninoculated with earthworms were distinguished in clustering,and the two kinds of earthworms were also obviously distinguished,and their bacterial community structure changed significantly.(2)When Pb contamination occurred,the mortality of both earthworms showed an upward trend;In starvation state,earthworms did not achieve avoidance effect,while in satiety state,when the concentration of Pb was high,the avoidance response of earthworms was significant.Under Pb contamination stress,the body protein content of earthworm decreased with the increase of inoculation time;the SOD activity in Eisenia fetida increased with the increase of Pb concentration,while the SOD activity in Pheretima guillelmi increased first and then decreased.After inoculation for 7 days and 14 days,there was a little change range in the CAT activity of two kinds of earthworms,but after inoculation for 28 days,the CAT activity in Eisenia fetida was activated.In two kinds of earthworms,GST activity was activated(El)and inhibited(E2)in the early stage of stress,which was activated on the 28th day after inoculation.ROS in Eisenia fetida did not change significantly in the early stage of inoculation,but inhibited in the later stage,while that in Pheretima guillelmi was generally inhibited.After earthworms swallowed Pb contaminated soil,the diversity of bacterial community in earthworm gut increased significantly,while its abundance decreased significantly;at the phylum level,the abundance of Firmicutes and Proteobacteria changed greatly,and the change in the two earthworms showed an opposite trend;After inoculation with two kinds of earthworms,compared with those without inoculation,the clustering of soil bacterial community was quite different,but the clustering difference between inoculated Eisenia fetida and Pheretima guillelmi was little,and the abundance of Proteobacteria and Bacteroides,which account for the most proportion,increased.(3)When combined contamination of Cd and Pb occurred,the mortality of both earthworms increased with the increase of Cd or Pb concentration;there was no obvious difference in avoidance rate of earthworms in starvation state,but the avoidance response of earthworms was obvious in satiety state.Under the combined pollution stress of Cd and Pb,the content of earthworm body protein decreased in the low concentration Cd group and increased in the high concentration Cd group;With the increase of Pb concentration,the SOD activity of most earthworms also increased.With the increase of Cd concentration,the SOD activity of most earthworms decreased;there was no obvious rule in the change of GST activity between the two earthworms,and Eisenia fetida had more activation effect,while Pheretima guillelmi had more inhibition effect;the CAT activity in Eisenia fetida did not change significantly,but the CAT activity of Pheretima guillelmi after inoculation for 28 days was significantly higher than that after inoculation for 7 days and 14 days.The ROS of earthworms in the treatment group was higher than that in the control group,and the ROS in Eisenia fetida after inoculation for 28 days and Pheretima guillelmi in all periods was more obvious.After earthworms swallowed Cd and Pb contaminated soil,the diversity and abundance of earthworm coelenteric bacteria community increased significantly,but it was not significant;at the phylum level,in terms of Proteobacteria with the largest proportion,Eisenia fetida increasesd,while Pheretima guillelmi decreased;after inoculation with earthworms,the clustering of soil bacterial community had no obvious law,and the changes of soil bacterial community were complex.