Study On The Impact Of Simulated CO₂ Leakage From Geological Storage On Earthworms

CO₂ capture and storage?CCS?is currently recognized as an effective measure to reduce carbon dioxide emissions in the world.However,the CO₂ stored underground has the risk of leakage because of various unstable factors,posing a threat to the soil environment and soil ecosystem.In this study,Eisenia fetida was selected as the research object.The effect on the morphology and physiological changes of earthworms were researched by simulating the leakage of high concentration of CO₂ from CCS,the toxic effects of high concentration of CO₂on the earthworms caused by CCS leakage were explored.Meanwhile,the effects of oxidative stress produced by soil CO₂ concentration changes were evaluated by measuring the activity of biomarker enzyme activities in earthworms.The effects of CO₂ leakage from geological storage on earthworms?a typical soil animal?were identified,and the sensitivity indexes were selected,so as to provide references for the risk assessment of CCS project and the identification of leakage.The conclusions of this study are as follows:?1?The CO₂ leakage of CCS,whether slow leakage with small flow or rapid leakage,can improve the concentration of CO₂ in the topsoil.After slowly leaking at a low flow rate?0.2L/min?for 10 hours,the CO₂ concentration in the soil surface layer can reach 0.15%;when CO₂ is introduced at 0.3mpa pressure for rapid leakage,the CO₂ concentration at-5cm from the surface can reach 12%.At this time,due to the increase of soil CO₂ concentration,it will affect the surface-type earthworms Eisenia fetida.?2?High concentrations of CO₂ in soil can have toxic effects on earthworms.The high concentration of CO₂ in the soil caused earthworms to have external morphological changes such as clitellum swelling,tail beading and tail breaking;skin and setae were damaged and epidermis was wrinkled.With the increase of CO₂ concentration and the extension of exposure time,the mortality rate of earthworms increased continuously.The median lethal concentrations of 7 d and 14 d for high concentration CO₂ soil were 26.39%and 17.78%,respectively,and the lysosomal membrane neutral red retention time?NRRT?of granulocytes decreased.?3?Under different CO₂ concentration and exposure time in soil,the ecotoxicity effect on earthworm will be produced.When CO₂ concentration in soil changes,the protein content in earthworm is not simply linear with CO₂ concentration and exposure time,and there is no obvious correlation.Under different exposure time,SOD activity was activated to the maximum when CO₂ concentration was 2%,and the GST activity augment first and then reduce with the increase of CO₂ concentration.When the exposure time was the same,POD activity basically increased first and then decreased and as the increase of CO₂ concentration MDA content basically decreased first and then increased.The CAT activity of earthworm in the treatment group with higher CO₂ concentration?4%,6%and 8%?was the same as that in the control group,showing a trend of rising first and then falling.?4?According to the analysis,earthworms are expected to be used as indicators of CO₂ leakage and the lysosome NRRT can be used as an early warning indicator to indicate that the CO₂leakage of geological storage has an adverse effect on the earthworm population;SOD and GST are more sensitive to the changes in the external environment and respond faster,especially SOD can show a significant difference in a short time.Therefore,this study gives two earthworm ecotoxicological biomarkers,lysosomal NRRT and biological enzyme SOD,which provides technical references for identifying CO₂ leakage in CCS projects in the future and lays the foundation for the impact study of CCS projects.