Effects Of Low Dose Of Phenanthrene In Soil On The Properties Of Earthworm Casts And Its Mechanism

The soil environment,on which the human being depends,has become one of the main carriers of environmental pollutants.Therefore,it is urgent to investigate soil pollution and risk assessment.At present,soil conditions are mainly analyzed by means of traditional monitoring.Traditional chemical methods can determine the type and content of pollutants in the soil,but there are great limitations in the assessment of the toxicity of pollutants.In fact,the ecological effects of pollutants on the soil system should be concerned.Biomarkers could reflect the true environmental toxic effects at the molecular or cell level of the exposure-response relationship.It provides an effective means of biological detection for hazards caused by environmental pollution.Furthermore,the effect of contaminated soil remediation in early diagnosis and evaluation has foreseeable prospects.In addition,earthworms are one of the most important habitats for soil ecosystems.Therefore,earthworms,as one of the standard test species,are recommended by many international standards of ecotoxicology which have been widely used in biomarker research.At present,the study on the biomarkers of earthworms mainly focuses on the indicators of earthworms themselves.However,there is not enough knowledge about its excrement.Only a few studies have focused on the impact of several pesticides contamination on the output of earthworm casts.The properties of earthworm casts under contaminated conditions,such as physicochemical and biological properties,have not been studied.In theory,when the soil is contaminated,due to the feeding and digestion of earthworms,it is bound to affect earthworm excretion or excrement.Therefore,it is possible to further indicate the physiological changes of earthworms and the actual conditions of soil ecosystem through such effects.However,there are insufficient researches on earthworm excrement under contaminated conditions currently.Polycyclic aromatic hydrocarbons are the main components of soil organic pollution.To this end,this study selected phenanthrene as a representative to explore the impact of phenanthrene polluted soil on earthworm cast and physiological state of Eisenia foetida.Research indicates:1 Effect of low concentration of phenanthrene polluted soil on physical and chemical properties of earthworm1)Compared with parent soils,earthworm improved TOC,NH4+-N,TAP and K and CEC while decreased pH in casts in PHE pollution soil,which means that earthworms still have the ability to play the role of ecological engineers even in pollution soil.2)The impact intensity and direction of PHE varied with different properties,which indicates that the underlying mechanisms are complex and should be clarified in future studies;3)Sensitivity of different properties of cast to phenanthrene follow the order of NH4+-N > Olsen-P > TOC= available K = CEC.The change of NH4+-N content in casts might be potential sensitive biomarker to provide early-warning signals for soil pollution and other index might also be worthy in further studies with respect to eco-toxicology purpose;4)FTIR analysis revealed that different functional groups content in casts have also been affected by PHE.2 Effects of low concentrations of phenanthrene polluted soil on the biological properties of earthworm casts1)The cellulase has sensitive response to phenanthrene pollution in soil and earthworm casts;2)The effects of phenanthrene on urease and phosphatase might be influenced by time in soil and earthworm casts;3)Microbial biomass carbon may be indicative of soil contamination as biomarker.3 Effect of Low Concentration of Phenanthrene on Earthworm Digestive Enzymes and Antioxidant Enzymes1)Phenanthrene-contaminated soil can cause the dynamic changes of the earthworm physiological index;2)The intensity and tendency of phenanthrene to earthworm digestive enzymes and antioxidant systems vary with different properties;3)the stimuli of the pollutants on earthworm digestive enzyme activity or inhibition may be an inherent factor in the changes of earthworm casts properties.In addition,as antioxidant defense system,the earthworm's digestive enzyme system may be used as a biomarker for ecological warnings of soil pollution.