| The problem of water and soil pollution caused by the continuous release of heavy metals from a large area of historical lead-zinc slag dumps in northwest Guizhou has attracted much attention.Vegetation restoration is an important way to control the release and migration of heavy metals from lead-zinc smelting residues.Dissolved organic matter(DOM)from different sources in plant rhizosphere is a key factor affecting the migration and transformation of heavy metals in lead-zinc smelting residues.In the process of phytoremediation,plant litter and decomposition products of organic amendments were the main sources of DOM in plant rhizosphere environment,and there were interactions between DOM and microorganisms.However,the effects of DOM component-microbial coupling from different sources on the translocation and transformation of heavy metals from Pb-Zn smelting residues during phytoremediation are still unclear.In this study,a lead-zinc smelting waste residue dump in northwest Guizhou,which has been undergoing ecological restoration for 10 years,was taken as the research object.Organic improvement(Cow manure)and litter of dominant remediation plant(Robinia pseudoacacia L.)on the waste residue dump were used as two sources of DOM in the waste residue dump.To investigate the effects of DOM from different sources on bacterial community composition and heavy metal translocation and transformation of lead-zinc smelting slag,and to provide a theoretical basis for scientific ecological restoration projects in the waste slag yard.Results were as follows:(1)DOM increased the pH,EC and DOC values and decreased the Eh value in the reaction system.The fluorescent components of DOM contained humic-like substances and protein-like substances,and there were some differences in the maximum fluorescence value(Fmax)and the position of fluorescence peak between them.In the DOM treatment group,C1,C2 and C3 were in the form of a single peak.Two characteristic fluorescence peaks appeared in C2 and C3 in the DOM treatment group of cattle manure,and the fluorescence intensity of the main peak was greater than that of the secondary peak.(2)The surface morphology of waste slag changes from smooth to uneven,and it is mainly composed of holes and cracks.In the DOM treatment group,filamentous matter was easily adsorbed and fixed on the surface of waste slag with particles,which was conducive to hindering the dissolution and release of heavy metals from waste slag.The mineral composition of the waste slag mainly includes quartz,sillimanite,gypsum and magnetite.With the increase of incubation time,only the gypsum characteristic peak in the waste slag disappeared.Similar functional groups,mainly Si-O,Al-O,O-H and O=C=O,exist in the waste residue and its leachate.In general,DOM from different sources has no significant effect on the mineral composition of the waste slag in a short period of time due to the complex composition of the waste slag and the stable primary minerals.(3)In the waste residue,Cu is mainly oxidized(F3),Pb is mainly reduced(F2),and Zn and Cd are mainly acid-soluble(F1).The total and available contents of heavy metals in the waste residue were Pb>.Zn>Cu>Cd.In general,DOM increased the available states of Cu,Zn and Cd in waste slag and decreased the available states of Pb in waste slag.DOM from different sources promotes the release of heavy metals from the waste slag as a whole,and the heavy metals Cu,Pb,Zn and Cd in the waste slag mainly exist in the form of divalent,among which Cd and Zn exist in the carbonate bound state in the original ore.The shift of binding energy in the different treatments towards higher or lower indicates the coexistence of heavy metals with other forms such as PbO,Pb(OH)2 and Zn(OH)2.(4)DOM addition from different sources significantly changed the composition and structure of bacterial community,and the diversity and abundance of bacteria decreased with the increase of culture time.At the phylum level,the dominant bacterial phyla in different DOM treatment groups were consistent.They were Proteobacteria,Actinobacteriota,Chloroflexi,Firmicutes,Acidobacterta,Gemmatimonadota,and Bacteroidota,among which Proteobacteria had the highest relative abundance.Gaiella,Arthrobacter,Pseudomonas and Massilia were the dominant genera in DOM treatment groups,which were resistant to heavy metals.Metabolism-related functions such as Carbohydrate transport and metabolism gradually weaken with the depletion of DOM.(5)The diversity of bacterial communities was comprehensively regulated by various environmental factors.Among them,pH and EC were the key factors affecting the content of heavy metals and the diversity of bacterial communities,and the changes of DOM components also affected them to a certain extent.The leaching behavior of heavy metals from waste slag is mainly regulated by environmental factors.The correlation between DOM content and environmental factors is not strong,which is determined by the differences in the source and composition of DOM and the interaction of bacteria.DOM components are closely related to the changes of bacterial community.Environmental factors indirectly affect the changes of DOM components mainly by affecting bacterial diversity,which is related to bacterial functional diversity.In general,environmental factors and the interactions between DOM components and bacterial communities could affect the bioavailability of heavy metals in slag to varying degrees.In conclusion,the components of DOM from different sources are consistent,but their own attribute levels are different.DOM addition from different sources promoted the release of heavy metals from lead-zinc smelting waste slag,but the release pattern was closely related to the types of heavy metals,incubation time and DOM content.Although DOM from different sources has a certain degree of dissolution on the surface of waste slag,due to the relative stability of lead-zinc smelting slag,the release of heavy metals is limited.The main minerals in the waste slag did not change significantly under the action of DOM,only the characteristic peak of gypsum changed.With the increase of culture time,the content of DOM gradually showed a trend of depletion,and the fluorescence intensity of DOM components also changed significantly,which affected community composition and function in the waste residue.The coupling relationships among DOM,microbes,and heavy metals from different sources showed that DOM and bacterial communities had a dynamic interaction,and their coupling affected the migration and transformation of heavy metals in p B-Zn smelting slag. |
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