| Polybrominated biphenyl ether(PBDEs)and heavy metals have a high detection rate in the e-waste dismantling site.Among the homologs of PBDEs,2,2',4,4'-tetrabrominated biphenyl ether(BDE-47)which has higher toxicity to organisms and humans has the highest detection rate and content.Cu also has a high content in e-waste dismantling site White-rot fungi can secrete non-specific functional enzymes,which can efficiently degrade organic pollutants.Therefore,white rot fungi are widely used in the removal of persistent organic pollutants.In this study,Pycnoporus sanguineus was selected as the tested strain to study its removal mechanism of BDE-47/Cu2+and its response to pollutant stress.The main research results are as follows:(1)When the pH value of the culture solution was varied between 2-7,the removal rate of BDE-47 was increased firstly then decreased with the increase of the pH,the highest removal rate(61.2%)was obtained when the pH value was 5.The removal rate of Cu2+increased with the increase of pH,When the pH value continues to increase,the Cu2+removal rate tends to be stable.Therefore,the pH of the system was set at 5.When the inoculation amount of.sanguineus spore fluid was 0.5%,1.5%,2.5%,3.5%and 5%,the removal rate of 0.5mg/L BDE-47 was 30.5%,43.325%,51.0%,51.9%and 52.1%,respectively,and that of 2 mg/L Cu2+was 32.3%,52.1%,66.0%,66.6%and 66.7%,respectively.Accordingly,the inoculation amount of the experimental system.sanguineus spore liquid was set at 2.5%.(2)The maximum removal rate of BDE-47 by intracellular enzyme was 27.9%when the fungi have been cultured for four days and the degradation peak of BDE-47 by extracellular enzyme was 27.7%when the fungi have been cultured for three days.In the presence of P450 enzyme inhibitor(piperomyl butoxide,PB),the removal rate of BDE-47 was lower than that of the control group,this result indicated that intracellular P450 enzyme was involved in the removal of BDE-47.The biodegradation of BDE-47 by extracellular enzymes was positively correlated with the activity of LiP and MnP in the first 3 days,then although the activities of the two enzymes decreased,the biodegradation rate of BDE-47 remained stable,this could be due to the increase of the Lac activity,so it can be concluded that LiP,MnP and Lac play a certain role in the process of biodegradation of BDE-47 by P.sanguineus.(3)6 metabolites were detected during the degradation of BDE-47 by P.sanguineus,namely 6'-hydroxy-2,2',4,4'-tetrabromodiphenyl ether(6'-OH-BDE-47),5'-hydroxy-2,2',4,4'-tetrabromodiphenyl ether(5'-OH-BDE-47),2'-hydroxy-2,4,4'-tribromodiphenyl ether(2'-OH-BDE-28),4'-hydroxy-2,2',4-tribromodiphenyl ether(4'-OH-BDE-17),2,4-dibromophenol(2,4-DBP)and 4-bromophenol(4-BP).Combined experimental results along with previous research findings,possible pathways of BDE-47 degradation by P.sanguineus were proposed as follows:(?)under the catalysis of functional enztmes,the ether bond between two benzene rings was broken,forming 2,4-DBP and 4-BP.(?)BDE-47 was converted directly into hydroxylated intermediates through substitution reaction between OH-and Br-,and transformed further into bromophenols.(?)Lower bromine diphenyl ethers like 2,2',4-tribromodiphenyl ether(BDE-17)and 2,4,4'-tribromodiphenyl ether(BDE-28)were formed from BDE-47,which were then hydroxylated into 4'-OH-BDE-17 and 2'-OH-BDE-28;the cleavage of ether bond further decomposed the hydroxylated metabolites into bromophenols.(4)Low concentration of Cu2+(?2 mg/L)promotes the removal of BDE-47 and Cu2+by promoting the secretion of proteins and organic acids of the fungi,while high concentration of Cu2+(? 5 mg/L)has adverse effects,thereby reducing the ability to remove pollutants. |
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