Interaction Effects And Mechanism Of BDE209-Pb Compound Pollution And Soil Microorganisms In The Presence Of Earthworms

With the development of electronic technology,electronic waste has become a global environmental problem.The refractory pollutants included in electronic waste,such as polybrominated diphenyl ethers(PBDEs)and heavy metals,will cause serious damage to the ecological system and human health while the soil is polluted.This study selected decabromodiphenyl ether(BDE209)and lead(Pb)as the representatives of polybrominated diphenyl ethers and heavy metals to study the bioremediation of BDE209-Pb co-contaminated soil with the help of earthworms(Eisenia fetida),and the toxic effects of BDE209-Pb on soil microorganisms and earthworms..The main results were as follows:(1)Compared with the control,earthworms significantly promoted the removal of BDE209 and Pb in the soil(p<0.05),and the removal rate of BDE209 in CS1 and CS5 were 14.12%and 14.93%,while the removal rate of Pb in CS2 and CS3 were 23.96%and 25.71%,respectively(28 d).In the early stage of pollution(2 d),Pb was mainly in the forms of CAR-Pb and FeMnOX-Pb,and the Pb risk levels were very high(LV4 and LV5).Under the action of microorganisms,Pb was transformed to FeMnOX-Pb and OMB-Pb,after 28 days the soil Pb risk levels dropped to medium even low level(LV2 and LV3).However,the presence of earthworms increased the contents of EXCH-Pb and CAR-Pb.(2)The soil had strong adsorption to Pb,and the adsorption characteristics completely conformed to the Langmuir and Freundlich isothermal adsorption equation(R2 were 0.994 and 0.978,respectively).Factors such as pH,soil redox potential and humus had influence on Pb forms,higher pH,lower Eh,and higher content of soil humus especially humic acid would lower the Pb availability,and do less harm to the environment.In addition,soil microorganisms also had adsorption to Pb,it’s possibly related with O-H,C-H,C=O,O=C=O,N-H,C-O,C-O-C and other groups.(3)BDE209 and Pb could inhibit the growth of microorganisms,resulting in the inhibition of microbial biomass and soil respiration intensity,which showed significant dose effect relationships(p<0.05 or 0.01).Compared with the control,the soil respiration intensity of S1,S2,S3,S4 and S5 were decreased by 5.41%,14.19%,32.43%,39.19%and 39.86%,respectively(28 d).While in the presence of earthworms,this species could improve soil environment,promote the growth and breeding of microbial,leading to the increase of microbial biomass and soil respiration intensity.After 2 days the soil respiration intensity of CS1 was 28.3 mg CO2 kg-1 d-1,which was twice as much as S1(p<0.01).Additionally,a good dose-response relationship between EXCH-Pb content and respiration intensity might provide a basis for ecological risk assessment(R2 of two two systems were 0.949 and 0.988,respectively).(4)BDE209 and Pb could also cause acute toxic effects to the earthworms,in line with the dose and time effects(R2 of 72-h exposure were 0.933 and 0.940,respectively),and the Pb toxicity to earthworms was higher than BDE209.After 28-d exposure,the low concentration pollution could induce the SOD activity(p<0.01),and the high concentration pollution could damage earthworm cells,inhibiting the SOD and CAT activities(p<0.05 or 0.01).What’s more,BDE209 and Pb could also cause damage to the lysosome membrane,and the higher concentration of pollutions,the greater the damage(p<0.01).