Electron shuttles such cysteine play an important role in Fe cycle and its availability in soils,while the roles of pH and organic ligands in this process are poorly understood.Herein,the reductive dissolution process...Electron shuttles such cysteine play an important role in Fe cycle and its availability in soils,while the roles of pH and organic ligands in this process are poorly understood.Herein,the reductive dissolution process of goethite by cysteine were explored in the presence of organic ligands.Our results showed that cysteine exhibited a strong reactivity towards goethite-a typical iron minerals in paddy soils with a rate constant ranging from 0.01 to0.1 hr^(-1).However,a large portion of Fe(Ⅱ)appeared to be"structural species"retained on the surface.The decline of pH was favorable to generate more Fe(Ⅱ)ions and enhancing tendency of Fe(Ⅱ)release to solution.The decline of generation of Fe(Ⅱ)by increasing pH was likely to be caused by a lower redox potential and the nature of cysteine pH-dependent adsorption towards goethite.Interestingly,the co-existence of oxalate and citrate ligands also enhanced the rate constant of Fe(Ⅱ)release from 0.09 to 0.15 hr-1;nevertheless,they negligibly affected the overall generation of Fe(Ⅱ)in opposition to the pH effect.Further spectroscopic evidence demonstrated that two molecules of cysteine could form disulfide bonds(S-S)to generate cystine through oxidative dehydration,and subsequently,inducing electron transfer from cysteine to the structural Fe(Ⅲ)on goethite;meanwhile,those organic ligands act as Fe(Ⅱ)"strippers".The findings of this work provide new insights into the understanding of the different roles of pH and organic ligands on the generation and release of Fe induced by electron shuttles in soils.展开更多
The hydro-geochemistry and isotopic variations in groundwater,coupled with sediment geochemistry,were investigated in the Middle Gangetic Plain,India,to better understand the aquifer dynamics that influence the arseni...The hydro-geochemistry and isotopic variations in groundwater,coupled with sediment geochemistry,were investigated in the Middle Gangetic Plain,India,to better understand the aquifer dynamics that influence the arsenic(As)evolution and mobilization.Eighty-four groundwater samples,thirteen River water samples,and two sediment cores(33 mbgl)were studied.The samples were analyzed for major ions and trace metals,including As and stable isotopic variability(δ^(2)H,δ^(18)O,andδ^(13)C).The study area was categorized into older and younger alluvium based on existing geomorphological differences.Younger alluvium exhibits higher As enrichment in sediment and groundwater,ranging of 2.59–31.52 mg/kg and bdl to 0.62 mg/L.Groundwater samples were thermodynamically more stable with As(OH)_(3)species ranging from 88.5%to 91.4%and FeOOH from 69%to 81%,respectively.PHREEQC and mineralogical analysis suggested goethite and siderite act as a source and sink for As.However,statistical analysis suggested reductive dissolution as the primary mechanism for As mobilization in the study area.Spatio-temporal analysis revealed elevated concentrations of As in the central and northeastern regions of the study area.Stable isotope(δ^(2)H andδ^(18)O)analysis inferred active recharge conditions primarily driven by precipitation.The depleted d-excess value and enrichedδ^(18)O in the groundwater of younger alluvium indicate the effect of groundwater recharge with significant evaporation enrichment.Groundwater recharge potentially decreased the quantity of arsenic in groundwater,whereas evaporation enrichment increased it.Rainwater infiltration during recharge introduces oxygenated water into the aquifer,leading to changes in the redox conditions and facilitating biogeochemical reactions.The carbon isotope(δ^(13)C)results suggest that high microbial activity in younger alluvium promotes As leaching from sediment into the groundwater.展开更多
基金supported by the National Natural Science Foundation of China(Nos.42077301,21876161)the National Key Research and Development Project of China(No.2020YFC1808702)Guangdong Academy of Sciences’Project(No.2019GDASYL-0102006).
文摘Electron shuttles such cysteine play an important role in Fe cycle and its availability in soils,while the roles of pH and organic ligands in this process are poorly understood.Herein,the reductive dissolution process of goethite by cysteine were explored in the presence of organic ligands.Our results showed that cysteine exhibited a strong reactivity towards goethite-a typical iron minerals in paddy soils with a rate constant ranging from 0.01 to0.1 hr^(-1).However,a large portion of Fe(Ⅱ)appeared to be"structural species"retained on the surface.The decline of pH was favorable to generate more Fe(Ⅱ)ions and enhancing tendency of Fe(Ⅱ)release to solution.The decline of generation of Fe(Ⅱ)by increasing pH was likely to be caused by a lower redox potential and the nature of cysteine pH-dependent adsorption towards goethite.Interestingly,the co-existence of oxalate and citrate ligands also enhanced the rate constant of Fe(Ⅱ)release from 0.09 to 0.15 hr-1;nevertheless,they negligibly affected the overall generation of Fe(Ⅱ)in opposition to the pH effect.Further spectroscopic evidence demonstrated that two molecules of cysteine could form disulfide bonds(S-S)to generate cystine through oxidative dehydration,and subsequently,inducing electron transfer from cysteine to the structural Fe(Ⅲ)on goethite;meanwhile,those organic ligands act as Fe(Ⅱ)"strippers".The findings of this work provide new insights into the understanding of the different roles of pH and organic ligands on the generation and release of Fe induced by electron shuttles in soils.
基金funded by the Ministry of Earth Sciences(MoES)under the Geochronology project[MoES/P.O.(Seismic)8(09)-Geochron/2012]。
文摘The hydro-geochemistry and isotopic variations in groundwater,coupled with sediment geochemistry,were investigated in the Middle Gangetic Plain,India,to better understand the aquifer dynamics that influence the arsenic(As)evolution and mobilization.Eighty-four groundwater samples,thirteen River water samples,and two sediment cores(33 mbgl)were studied.The samples were analyzed for major ions and trace metals,including As and stable isotopic variability(δ^(2)H,δ^(18)O,andδ^(13)C).The study area was categorized into older and younger alluvium based on existing geomorphological differences.Younger alluvium exhibits higher As enrichment in sediment and groundwater,ranging of 2.59–31.52 mg/kg and bdl to 0.62 mg/L.Groundwater samples were thermodynamically more stable with As(OH)_(3)species ranging from 88.5%to 91.4%and FeOOH from 69%to 81%,respectively.PHREEQC and mineralogical analysis suggested goethite and siderite act as a source and sink for As.However,statistical analysis suggested reductive dissolution as the primary mechanism for As mobilization in the study area.Spatio-temporal analysis revealed elevated concentrations of As in the central and northeastern regions of the study area.Stable isotope(δ^(2)H andδ^(18)O)analysis inferred active recharge conditions primarily driven by precipitation.The depleted d-excess value and enrichedδ^(18)O in the groundwater of younger alluvium indicate the effect of groundwater recharge with significant evaporation enrichment.Groundwater recharge potentially decreased the quantity of arsenic in groundwater,whereas evaporation enrichment increased it.Rainwater infiltration during recharge introduces oxygenated water into the aquifer,leading to changes in the redox conditions and facilitating biogeochemical reactions.The carbon isotope(δ^(13)C)results suggest that high microbial activity in younger alluvium promotes As leaching from sediment into the groundwater.
