Toxicological Study On Response Of Different Biological Level Characteristics Of Collembolan(Collembola) To Heavy Metals In Farmland And Antibiotics Pollution

Collembolan are regarded as important receptors of soil ecological risk assessment because of their main ecological status and functions in soil and their high sensitivity and tolerance to environmental change.The existing risk assessment of heavy metal pollution in the field is mostly based on the study of the whole soil fauna community and the traditional community structure and population characteristics,lacks the screening of specific indicator species.On the other hand,fluoroquinolone antibiotics?FQs?,a new class of pollutant,hardly degradeable and can accumulate continuously in soil,but their effects in soil have not been clearly understood and evaluated.Moreover,under natural conditions,the phenomenon of heavy metals and antibiotics combined pollution is widespread,which may produce more complex new pollutants.Therefore,this paper adopted the method of combining field research with laboratory experiments.To study the effects of heavy metals?cadmium,lead,zinc?,antibiotics?norfloxacin?and combined pollution of heavy metals and antibiotics on differentbiologicallevelcharacteristics?communitystructure,population characteristics,physiological and biochemical characteristics,gut microecosystem?of collembolans and their response to pollution.Therefore,taking the farmland around Lanping Lead?Pb?-Zinc?Zn?mine in Yunnan Province as the research object,this paper explores the community structure of collembolan and the change characteristics of specific species in heavy metal-polluted farmland in the mining area and the response law of collembolans to heavy metal pollution.Taking norfloxacin?NFC?in FQs as an example,Systematic toxicological tests were carried out on the classical toxicological receptor F.candida,to explore the response of F.candida to it at population level,physiological biochemical level and gut microecosystem level.The response of F.candida to the combined pollution of NFC and Cadmium?Cd?was preliminarily explored.The results are as follows:Investigation of farmland around Lanping Pb-Zn mine,A total of 1445individuals were acquired,belongs to 2 orders,6 families and 15 genera,totaling 26species.The average density was 12042 individuals/m².The characteristics of field soil Collembola community with obvious dominant groups and relatively deficient groups were reflected.The farther the sample points were from mine or river,the lower the concentration of Cd,Pb and Zn in soil were,and the species richness,richness index,abundance of collembolans and heavy metal content in collembolan body increased,especially the species richness and heavy metal content of collembolans.Onychiurus sp.was negatively correlated with the available Pb The three species of Isotoma were negatively correlated with both the total and available Cd.Isotoma sp.3 of them was also negatively correlated with the total and available Zn.Lepidocyrtus sp.was positively correlated with the total of Cd?Pb?Zn.These species could be screened as indicators of heavy metal pollution assessment.On the other hand,some species?including those mentioned above?are closely related to soil physicochemical properties:Onychiurus sp.and Onychiurus folsomi were positively correlated with soil organic matter content.Isotoma sp.1 was positively correlated with soil pH and soil bulk density.These species could be screened as indicators of soil quality.In the classical toxicity test,in the soil system?with yeast?,F.candida was not affected in the range of experimental concentration.EC₁₀>1000 mg/kg.In the soil system?without yeast?,the number of reproduction and adult body length decreased by 34.38%and 9%respectively under 1000 mg/kg NFC treatment compared with the control.EC₁₀=165.27 mg/kg.There was no significant difference in the number of adults,reproductive numbers and adult length in the dish system,but the juveniles length decreased by 22.22%under 1000 mg/kg NFC treatment compared with the control.The results showed that NFC produced toxicity to F.candida mainly through oral exposure.In the compound pollution experiment,Cd and NFC showed antagonistic effect.Whether Cd is 10 or 100 mg/kg,with the increase of NFC concentration,the concentration of Cd in adults and juveniles increases gradually,indicating that NFC can accelerate the accumulation of Cd in F.candida.In the study of antioxidant enzymes and lipid peroxides,there was no significant difference in body length between the treatment and the control.However,the body weight decreased significantly at NFC 80,320,1280 mg/kg.Peroxidase?POD?was induced on the 7th day,and the POD activity of all NFC treatments increased significantly.Catalase?CAT?was also induced on the 7th day.At lower NFC concentration,CAT activity was induced to peak value,while at higher NFC concentration,CAT activity was inhibited.On the 14th day,superoxide dismutase?SOD?activity increased with the increase of NFC concentration and reached the peak at 80 mg/kg.Malondialdehyde?MDA?content also increased with the increase of NFC concentration at 14th day,and MDA content reached the highest at 1280 mg/kg.The results of Two-way ANOVA analysis showed that the dose-effect relationship between the activity of CAT,SOD and NFC concentration will change with the exposure time,the dose-effect relationship between MDA and NFC didn't change with exposure time,the dose-effect relationship is relatively stable.In the study of response characteristics of gut microbiota to NFC in F.candida,diversity analysis showed that soil microbiota had greater community diversity and abundance than gut microbiota.The abundance and diversity of gut microbial community were not affected by NFC,while the abundance and diversity of soil microbial community were decreased by NFC.Species composition analysis showed that OTU of gut microbiota decreased significantly under the influence of NFC,but the OTU of soil microbiota did not change significantly under the influence of NFC.The species composition of gut microbiota and soil microbiota was significantly different.proportion of Wolbachia decreased significantly and Methylophilaceae increased significantly at 80 mg/kg NFC.They have potential as indicator groups of FQs.Soil microbiota varied greatly in different treatments.Except Actinobacteria and Ktedonobacteria,the other classes were significantly affected by NFC.