Toxic Effect Of Cow Dung Biochar On Earthworm

Biochar has a wide application prospect in many fields.Earthworms,as"soil engineers",have complex interactions with the biochar applied to the soil.Earthworms are used as indicator organisms to reflect the ecological safety of biochar.It provides an important basis for the rational use of biochar.In this study,Eisenia foetida was used as an experimental animal to explore the toxic effects of cow dung biochar prepared at 350?,550?and750?from biological,cellular,hysiological and biochemical levels on earthworms,and modify the potential harmful factors of cow dung biochar and compare the difference on the individual levels before and after modification.The effects of three kinds of cow dung biochar on the acute toxicity and avoidance behavior of Eisenia foetida,the activities of peroxidase?POD?,catalase?CAT?,superoxide dismutase?SOD?,the content of malondialdehyde?MDA?and the damage of lysosomal membrane of coelomic cells were studied by natural soil test method.The specific research results are as follows:?1?The results of acute toxic effects of cow dung biochar on earthworms showed that three kinds of cow dung biochar had toxic effects on earthworm.With the increase of the proportion of biochar,the mortality of earthworm in each treatment group also increased.The LC₅₀0 of 350?,550?and 750?cow dung biochar charcoal was 5.56%,5.84%and 4.96%respectively,when earthworms exposed to three kinds of cow dung biochar charcoal for 14 days.The toxicity of 750?cow dung biochar to Eisenia foetida was higher than that of other two temperatures.?2?The results of earthworms'avoidance behavior showed that the avoidance rate of 350?cow dung biochar treatment groups to earthworm was 100%,which had a significant toxic effect on earthworm.The impact of550?cow dung biochar on earthworm avoidance behavior is relatively weak.?3?The effects of 350?,550?and 750?cow dung biochar on antioxidant enzyme activity and MDA content in earthworm were studied.The results showed that the time-effect of POD activity rwas not significant,the time-effect and dose-effect of CAT activity were significant,and the time-effect of SOD activity was significant.The activation of antioxidant enzymes of earthworm exposed to 550?cow dung biochar was stronger than that at other two temperatures,and the MDA content of three kinds of cow dung biochar had the same change trend:MDA content increased with the increase of the concentration of biochar,there was obvious time-effect and dose-effect relationship.?4?Exposed to 350?,550?and 750?cow dung biochar,the lysosomal membrane of Eisenia foetida was damaged,the Neutral Red Retention Time?NRRT?was shortened,and there was an obvious time-effect relationship between NRRT and exposure time.Except for the treatment group exposed for 2 days,there was also a dose-effect relationship between NRRT and exposure concentration.?5?The toxic effects of 750?cow dung biochar on Eisenia foetida were compared at the individual level after PAHs removal.The result showed that the mortality rate of Eisenia foetida in the low and medium concentration treatment group decreased significantly under the exposure of the modified biochar,which indicated that PAHs was a harmful factor to Eisenia foetida.