The Immobilization And Bioavailability Of SRB For Heavy Metals In Plants Rhizospheres Of The Yangtze Esturay Flat Tide

It is widely believed that tidal flat wetlands are an important "sink" of metal deposits in estuarine environment.Because of developed economy and full of industries,a large number of urban sewage treatment plants drainage and industrial wastewater discharged into the estuary area.With the existence of bacteria,the different types of metals enriched and immobilization in the sediments.Due to the tidal effect,a considerable amount of metals came into the tidal flat.With plants growth in different stages,metals accumulated and transferred to ground and underground of plant tissue.The redistribution of metals in water,sediments and plants is an important aspect of biogeochemistry and ecological self-healing.The distribution of 13 kinds of metal concentrations in different seasons,saptial,plants species were studied by ICP-MS.And the distribution of different forms of sulfur and sulfate-reducing bacteria(SRB)in rhizospheres and surface sediment,seasonal and spatial distribution in tidal flat were studied.Based on the above research,the effect of SRB on the bioavailability of metal in rhizospheres studied by correlation analysis.Finally,combined with the indoor short-term exposure experiment,it revealed that the effect of the roots of Scirpus capillaris on the immobilization and bioavailability of metallic silver observed under the participation of SRB.Based on the metal concentration analysis of 8 sampling sites in the Yangtze River estuary,it was found that the total metal concentrations in the plant root sediments was the lowest in January,the highest in April.The levels of Fe,Ti and Mn were dominated metals,which was 2-3 orders of magnitude higher than other metals.The concentration of Cd was the lowest.The metal concentrations in WSK and SDK,which close to the wastewater discharge,and CY which near Landfill wastewater discharge,showed the highest metal level among all sampling sites.The results showed that the average content of heavy metals in the roots of Scirpus triquter was the lowest,the concentration of Cu in the roots.of Phragmites australis was the highest,and the other 12.heavymetalsu were accumulated most in the the sediments of Spartina alterniflora.In addition to metal Mn,the plant tissue distribution of metal content showing:root>stem>leaves.Compared with July and Octber,Januray and April had accumulated higher concentration of metal in roots,stems and leaves of plants In general,the metal elements had a higher level in SDK and WSK of Scirpus triquter and Phragmites australis,while WSK and DH had a higher the metals concentration of different tissue of Phragmites australis.Scanning electron microscopy(SEM)characterized the morphology and size of granules in plant tissues.The results indicted that the particles adsorbed in different tissues were different in size and shape,including round,quadrilateral,long strips and granules.The particles contain metals always appeared in the form aggregates,which also shows that nanoparticles are widely present in estuarine plant environments.Based on the analysis of 8 sampling sites along Yangtze Esturay,it was found that the distribution of sulfur in the different sediments of S.triquter root system was S O42>S>acid volatile sulfur(AVS).The distribution of SRB abundance in root sedim ents was much higher than in surface sediment.Seasonal distribution showed that the concentrations of sulfur in different forms and SRB abundance had the highest level i n April.The spatial distribution indicated that the sampling sites with severe pollution,such as WSK and CY,were significantly higher than other sites.The results showed that there were significantly correlations between SRB abunrancet and the concentrations of others heavy metals except Iron,when used APS-a as the target gene quantified the SRB abunrance.However,signifant correlections was existed in SRB abunrancet and Mn,Pb when used APS-b as the target gene quantified the SRB abunrance.Both of this showed that,in some degree,SRB may effectively removed metals in rhizospheres sediments environment.The higher the abundance of SRB,the lower the SO42-content were occurred in some sampling sites,such LHK and QYK,which is likely to be the result of SRB reduction of sulfate.The SEM results of internal control experiments showed that the particles of metal sulfide was formed in the nutrient solution of AgNO3 treatment group,and the particles size increased with the exposure concentration.Both Ag+ and Ag NPs exposure treatment,the residual Ag concentration in the nutrient solution with SRB was much lower than controls.All of the treatment showed that a large amount of silver ions accumulated in the roots and stems of the plants,at the same time,the concentration of Ag accumulated in the plants increased with the durable exposure time and treatment concentrations.Among the four treatment ways,the Ag+ treated experimental group had the highest concentration of Ag in plant tissue.For Ag+treatment,the accumulated Ag concentrations in root and stem with the help of SRB were much lower than controls,conversely,occurred in Ag NPs treatment.However,the experimental results showed that the participation of SRB did not show a significant effect on the transport efficiency of Ag in Scirpus tissue.In general,the other treatment ways indicated TF values in different exposure times decreaed with increased exposure concentrations except the Ag+ and SRB treatment way.Scanning electron microscopy showed that Ag particles was attached to the roots and stems of Scirpus,but the particles contained-Ag was not found at the top of Scirpus stems.This may result of the short-term polar exposure and nano-silver had no enough time to the transmission upward.Analysis the plant tissue after digesting by SP-ICP-MS,it showed that amount of Ag NPs were accumulated in tissues and the size of particles were less than 60nm.The size results were consistent with SEM.In summary,in the case of indoor exposure tests,the SRB did play an important role in fixed Ag among the plant root environment,while the nanomagne silver did not.It may related to the experimental period,particle size,root exudates and so on.About this point necessarily and effective research should be taken to explore in the future work.