Geochemical and Molecular Mechanisms Controlling ... · Geochemical Modeling * Critical understanding of Hg flux, biogeochemical controls, and microbial determinants (Menheer, 2004)

Geochemical and Molecular MechanismsControlling Contaminant Transformation

in the Environment

ORNL ERSP Science Focus Area (SFA)

ERSP 3rd Annual PIMeeting, April 7 – 9, 2008

Managed by UT-Battellefor the Department of Energy

Strategy for understanding contaminanttransformation and environmental behavior

Microbial andgenetic controls

Fundamental rates and mechanisms

Transformation in field Speciation & mechanisms Molecular dynamics

Reaction mechanisms and kinetics at groundwater–surface water interface

Sediment-water interface

Species/ abundance

Microbial communities

Coupled microbial

and geochemical

reactions

Molecular level understanding

of contaminant association

and reaction

Molecular structureand simulations

catalytic

domain

NmerA

MerA core

N-terminus

C-terminus

CYS 11

CYS 14

CYS 136

CYS 141

CYS 558

CYS 559

Fieldbiogeochemistry

(Luther et al. 1999)

Thiol-like binding

Carboxyl bindingCarboxyl bindingCarboxyl binding

Thiol-like binding


Hg2+ + 2e- = Hg(0)

1000 1200 1400 1600 1800

Inte

ns

ity

(a

.u.)

Haitzer et al. (2003)

3 Managed by UT-Battellefor the Department of Energy

Research focus and goals

• Mercury – the net balance of methylationand demethylation

Geochemical/biological controls on Hg speciation andtransformation, and how and what Hg precursors areproduced, transported and methylated

Enzymatic mechanisms of transformation between majorHg species and methyl mercury.

• Uranium – stability in subsurface

Microbial oxidizers – Rates and mechanisms in theoxidation of U(IV) minerals

Structure and function of key heme proteins required fordirect electron transfer, microbial-mineral interface models

Y-12

ORNL

ETTP

Hg in water, sediment and biota in streams (in red)

300,000 kg of Hg lost to soil

and groundwater at Y-12

Impact UEFPC

Industrial use areasHg contaminated soil, buildings, storm

drain network, sediments, ground and

surface water

Mercury concerns at Oak Ridge Reservation

Source Areas

High mercury concentrations in biota

• High concentrations of elemental andHg(II) complexes in shallow soils nearindustrial infrastructure

• Oak Ridge environment: stronggroundwater/surface water interactions(>50” annual rainfall)

• Methyl mercury is readily accumulatedand can increase up the food chain

• Hg exceeds regulatory limits—newstandards could significantly impact Y-12operations and costs

• TN TDEC developing an East Fork PoplarCreek TMDL; focus on loading/flux, notconcentration

• TN recently lowered Hg level that triggers anadvisory

• EPA concern for ecological risks

• Modernization of facilities could result inincreased transport of Hg to streams

EFPC downstream of Y-12


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Hg

, g

/g

(fi

sh

),

g/

L (

wate

r)

Water

Fish

• Mercury bioaccumulation in fish is not proportional toconcentrations of waterborne Hg

Examples of water/ fish disconnect (see poster):Oak Ridge Sites Hg in water Hg in fish

(ng/L) (mg/kg)

White Oak Creek 60 0.5

EF Poplar Cr (upper) 400 0.8

EF Poplar Cr (lower) 100 0.8

Bear Cr 1–3 0.7

Rogers Quarry 1 1.1

Reference site 1–3 0.2

• Hg in fish correlates with methyl Hg in water, but not withtotal Hg in water. So, at contaminated sites, there is nomodel relating methyl Hg and total Hg in water

• Not possible to eliminate inorganic Hg inputs; alternativestrategies to reduce methylation may be only means to reachfish concentration targets

Basic research needs: elucidate Hg methylationprocesses at sediment-water interface and thecontrols on methyl Hg production

Source control has not lowered Hg in fish


The mercury challenge

National:

• Global pollutant readily transportedand re-emitted

• Highly toxic to human and ecologicalreceptors

Methylmercury (MeHg) is a potenthuman neurotoxin, highlybioaccumulative

• Hg found at all DOE sites; waste andenvironmental issues at many (e.g.,Savannah River, Paducah…)

• Complex chemistry /speciation/methylation–demethylationprocesses

• Hg at industrial contaminated sites

Hg methylation at sediment-water interface

Need to elucidate:

Oxidation, reduction, andspecies transformation

Dominant chemical speciesand bioavailability

Abiotic /biotic methylationand demethylation

Biochemical pathways formethylation anddemethylation

Coupled biogeochemicalreactions – sorption,complexation, precipitation,stabilization, fate andtransport

Surface catalyzed andphotochemical reactions

MeHg Hg(II ) Hg(0)Reduction

OxidationHgS(s )

HgS(HS )-

Hg(HS)2

Hg-NOM

Hg-clay/oxide


Oxidation

HgS(s)

Hg(0)

Hg-particle

Hg(OH)2

Part

icu

late

DOM

Hg(0)MeHgRedox /DOM photo/redox

Dis

solv

ed

Hg-DOM

HgCln(n -2)-

HgCl(OH )

HgS(HS )-

cell

cell

Biological demethylation

Catalyzed and photochemical demethylation

Water

Sediment


Research team

Advisory Panel

T Barkay (Microbiologist)

S Lindberg (Hg cycling)

R Mason (Hg geochemist)

A Summers (Biochemist)

R Wildung (Geochemistry)

E Phillips (DOE-ORO)

Microbial and

genetic controls

(Hg and U)

A Palumbo (ORNL)

C Gilmour

(Smithsonian)

T Phelps (ORNL)

S Brown (ORNL)

J Wall (U Missouri)

Haakrho Yi (ORISE)

Molecular scale &

simulations

(Hg and U)

L Liang (ORNL)

J Smith (UTK)

L Shi (PNNL)

D Myles (ORNL-

CSD)

New hire (TBD)

A Johs (ORISE)

Fundamental

Mechanisms

(Hg)

B Gu (ORNL)

K Kemner (ANL)

K Littrell (ORNL-

SNS)

K Nagy (UIC)

H Zhang (TN Tech)

C Miller (ORISE)

Site

Biogeochemistry

(Hg)

S Brooks (ORNL)

G Southworth

(ORNL)

G Luther (U

Delaware)

Postdoc (TBN)

BER ERSD

Program

Managers

ORNL

Liyuan Liang

(Research Manager)

Diverse expertise

Strong partnership


Integrated research approach

New science: fundamental understanding

of cont. transformation

Path forward: addressing cont. remediation

challenges

MeHg Hg(II)?

I. Field investigation & geochemical modeling*

• Site geochemistry,

species, flux, microbial

community

• Coupled reactions on

Hg speciation

II. Fundamental mechanisms*

• Speciation, DOM/POM on

methylation & demethyl.

and catalyzed reactions

Hg2+ + 2e- = Hg(0)

• MeHg bioavailable Hg species; NOM and

particulate surfaces methyl. & demethyl.

III. Microbial and genetic controls

• Community, genes, and

geochemical controls

• SRB methylation;

others demethylation?

• U oxidation

VI. Molecular structure and simulations

• Proteins complexes in electron transfers (U

and Hg), quantum/ molecular simulation

• Mercury resistance genes,

biomolecular mechanisms

* These tasks Hg only


I. Site biogeochemistryI. Site biogeochemistry

Field studies (UEFPC)

• Measurement of Hg flux

• Quantify geochemical gradients

• Benthic flux chambers

• EXAFS and XANES analysis

Microcosm Studies

• Stable Hg isotopes to facilitate analysis

• Transformation pathways

Microbial Community Structure at the

sediment-water interface

• Functional gene arrays

• Principal microbial communities

Geochemical Modeling

* Critical understanding of Hg flux,biogeochemical controls, andmicrobial determinants

(Menheer, 2004)

Flux chambers

(Luther et al., 1999)

Microelectrodes

Field measurementsField measurements

Complementary

laboratory

microcosms

Functional gene

arraysGeochemical

modeling

-20

-15

-10

-5

-5.5 -4.5 -3.5 -2.5 -1.5

log {Cl-}

log

{H

S-}

MeHgS-

(MeHg)2S

MeHgOH0 MeHgCl0


II. Fundamental mechanisms and transformations

2 4 6 8 10

0.0

1.0x10-9

2.0x10 -9

3.0x10-9

4.0x10-9

5.0x10 -9

Hg-DOM

Hg

(II)

sp

ecie

s (

M)

pH

HgCl2

Hg(OH)2

Hg(OH)CO-

3

Thiol - like binding


Thiol - like binding


Haitzer et al. (2003)

Hg(II ) speciation: H +–Cl-–CO3

2-–DOM

MeHg nitrate

Barradell et al. (1993)* Critical understanding of dominant Hg

species, its bioavailability, andbiogeochemical controls on rates andmechanisms of Hg methylation anddemethylation

Determine speciation and abiotic controls

• Rates and mechanisms, oxidation/reduction

• Single reactant to multi-component systems

• Real-time spectroscopic analysis coupled with CVAA orCVAFS analysis

Establish roles of DOM and POM in Hg

methylation, demethylation, complexation,

and stabilization of particulate Hg species

• Specific moieties and functional groups

• Labeled isotope studies; EXAFS and XANES analysis,speciation and coordination chemistry

• Species, models, and effects on bioavailability

Surface catalyzed and photochemical reactions

• Roles in methyl. and demethylation

• Sorbed species and reactions


III. Microbial and genetic controlson mercury methylation

Genome wide PCA of COGs

Hg methylators

Non-Hg

methylato

rs

Desulfovibrio cell pellet

grown with and without Hg

Elucidate the genetic determinants of methyl Hg

production and regulation

• Comparative gene expression, mutagenesis, andcomplementation

Determine the effect of geochemical factors on

gene regulatory networks for mercury methylation

• Use whole genome microarrays to examine both bioticand abiotic effects on the methylating and nonmethylatingDesulfovibrio transcriptomic profiles

Examine relationships among community

structure, geochemical conditions, and methyl Hg

production in sediments collected from Hg-

contaminated sites

• Functional gene arrays

• 16S rRNA gene clone library analysis

Desulfovibrio africanus(SEM by Dwayne Elias, U of Missouri)

*Critical understanding of the geneticbasis of the methylation and demethylationprocesses and the geochemical controlson microbial transformation.


Establish biochemical pathways in

bacterial demethylation

Obtain structure of protein/protein

and protein/DNA complexes

• Apply small angle neutron scattering toreveal structure-function relationships

Reveal enzymatic mechanisms to

understand the processes of

demethylation and reduction

• Use quantum mechanical/molecularmechanical simulations

Barkay, T., S.M. Miller, and A.O. Summers: FEMS Microbiol Rev,

2003. 27(2-3): p. 355-84.

* Critical understanding ofbiomolecular mechanisms in Hgtransformation (demethylationand methylation) by investigationof structure-functionrelationships

IV. Molecular structure and simulations


Small Angle Neutron Scattering to elucidateSmall Angle Neutron Scattering to elucidatestructure and function of molecular machinesstructure and function of molecular machines

SAXS/SANS for characterization of

proteins and protein complexes

Define protein shapes and compare

solution and crystal structures

SAXS/SANS is used to elucidate

dynamic protein functional

relationships

SANS with contrast variation provides

a method to reveal the orientation and

location of specific components in

complex biomolecular systems

Figure adapted from: Brown, N. L, et al.: The MerR family of transcriptional regulators. FEMS microbiology reviews 27:145-163

(2003)

Conformational change in ternary

MerR-DNA-RNAP complex induced

by Hg2+ binding initiates transcription

+

RNAP

MerR-DNA

16 Managed by UT-Battellefor the Department of Energy 16

Uranium focus on microbial U oxidation andsubcellular electron transfer processes

U(VI)

Fe(III)

Microbial oxidation

U(IV), U(0)

Fe(II)

Microbial oxidation• Rates and mechanisms

• Controlling factors

• Microbial communities

Additional biogeochemical

processes addressed by

other ERSP PIs and IFCs

Zachara & Fredrickson, 2004; ERSP PI

meeting

Reguera, G., et al.: Extracellular electron

transfer via microbial nanowires. Nature

435:1098-1101(2005).

U(IV)

Fe(II)

Microbial reduction

Microbial reduction

Function of cytochromes required for

dissimilatory metal reduction

• Protein purification,

crystallization

• Structure analyses by neutrons, x-ray

diffraction /scattering

• Biomimetic membrane systems

• Homology modeling

e- donor

Oxidized

e-


Roole of metal oxidizing bacteriaaffecting U speciation

Study microbial oxidation of U using site materials from Oak

Ridge IFC

• Use microcosms

Use Acidithiobacillus ferrooxidans as a model organism to

study genetic responses

• Construct whole genome microarray

• Conduct single and multi-factor experiments to investigate genetic responses tovarious geochemical conditions

Ongoing work (see Phelps Poster)

• Have obtained cultures of Acidithiobacillus ferrooxidans & testing pH tolerance inlab media

• Designing the whole genome microarray and will print and test it this FY

*Critical understanding of role ofspecific metal oxidizing bacteriaaffecting U oxidation state andthus mobility in the subsurface

Acidothiobacillus ferrooxidans growingon culture plates. The cells themselvesare colorless, the rust coloring associatedwith growing colonies results from the

microbial production of Fe(III)


Cytochrome protein structure indissimilatory metal reduction

* Critical understanding offunction of cytochromesrequired for dissimilatorymetal reduction

Elucidate structure ofcytochrome complexes andstructure functionrelationships

• Use of small angle neutronscattering (SANS) to understandmechanisms of electrontransport to minerals

Investigate membraneinsertion properties andinteraction with mineralsurfaces

• development of a biomimeticbacterial-mineral interface modelsystem for neutron reflectometrystudies

Shi et al., Journal of Bacteriology, 188:4705-4714, 2006

Weber et al., Nature Reviews Microbiology, 4(10), 752-764, 2006

Ross et al., Applied and Environmental Microbiology, 73:5797-5808, 2007

MtrAMtrA

MtrBMtrB

MtrCMtrC

OmcAOmcA

Inner Membrane

Outer Membrane

Periplasm

LPS/EPS

Menaquinones

NADH

Dehydrogenase

NADH NAD+NADH NAD+

Cytoplasm

Environment

e-

OmcAOmcA

CymACymA

StcStc e-

N

C

?

1

2

3

N

C

?

1

2

3

Hcc-like

domain


MeHg+

Time / s

0 500 1000 1500

De

flec

tion

, nm

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

Injection

Concentration, M

1e-17 1e-16 1e-15 1e-14 1e-13 1e-12 1e-11 1e-10 1e-9 1e-8 1e-7 1e-6 1e-5 1e-4

De

flec

tion

, nm

0

5

10

15

20

25

Bending of the cantilever to 1x10-6 M

of CH3Hg+ in water (three experiments)

Bending of this cantilever as

a function of the concentration of CH3Hg+

Au

S

SH

H HS

SH

S

SH

HHS

SH

S

SH

HHS

SH

= HgMe+

Directed research (short term)

High throughput methyl mercury detection using 1,6-

Hexanedithiol monolayers modified cantilevers


Expected deliverables

Improved understanding

of contaminant behavior

and biogeochemical

mechanisms and rates

Align with ERSD mission

I. Field investigations

• Critical understanding of Hg

flux, biogeochemical

controls, and microbial

determinants

Hg2+ + 2e- = Hg(0)

MeHg Hg(II)?

• Dominant Hg species, its

bioavailability, and

biogeochemical controls on

rates and mechanisms of Hg

methylation and

demethylation

III. Microbial and genetic control

• The genetic basis of the

methylation and demethylation

processes and the

geochemical controls on

microbial transformation

• Role of metal oxidizing

bacteria

IV. Molecular dynamics and simulation• Biomolecular mechanisms in Hg transformation

(demethylation and methylation) by investigation of

structure-function relationships

• Function of cytochromes

required for dissimilatory metal

reduction

II. Fundamental mechanisms


Partnerships and CollaborationKey collaborations

• ORNL task leaders and staff

Field geochemistry, Brooks, Southworth; Aqueous chemistry, Gu, Miller;Microbiology, Palumbo, Brown, Phelps; Environmental surface chemistry,Liang; Biophysics, Johs; other existing staff as needed, new hires (TBD)

• University connections-- External Science collaborators

C. Gilmour (Microbiology, Smithsonian), H. Guo, J Smith (MolecularDynamics and enzyme simulation, UTK), G. Luther (Sediment sulfidechemistry), S. Miller (Hg molecular biology, UCSF), K. Nagy (coordinationchemistry, UIC), L. Shi (protein biochemistry, PNNL), A. Summers (Hgbiochemistry, UGA), J. Wall (Microbiology, UMC), H. Zhang (Hg chemistry,TTU)

• Nat Lab and User FacilitiesT. Droubay (Materials physicist,EMSL), Ken Kemner (EXAFS,APS), K. Littrell (Neutronscattering, ORNL SNS/HFIR),D. Myles (Deuterium labeling,CSMB)

Together with

Advisory panel

Oak Ridge DOE

EM applied science programSpallation Neutron Source at ORNL



Scientific Impact and DOE Benefits

Understand key Hg precursors for microbial methylation

– Geochemical manipulation

– Role of sulfide, thiosulfate, NOM etc influencing Hg speciation

– Catalyzed and photochemical transformation of Hg

Reduce net methylation

– Change biochemistry, microbialprocesses; ecology

– Stimulate demethylation in microbialcommunity

– Use of genomics sequence data,microarray technology and advancedanalytical methods

Other products or contributions

• EM-22 Hg workshop

• Communicate to EM


OxidationHgS(s )

HgS(HS )-

Hg(HS)2

Hg-NOM

Hg-clay/oxide


Oxidation

HgS(s)

Hg(0)

Hg-particle

Hg(OH)2

Part

icu

late

DOM

Hg(0)MeHgRedox /DOM photo/redox

Dis

solv

ed

Hg-DOM

HgCln(n -2)-

HgCl(OH )

HgS(HS )-

cell

cell

Biological demethylation

Catalyzed and photochemical demethylation

Water

Sediment


LDRD and internal investment Supporting theERSP SFA

• Tracing Nanoparticle Transport in Porous Mediaby Neutron Radiography and SANS (LDRD Seedmoney fund)

• ESD –subsurface laboratory renovation

• Probing molecular interactions betweenmicrobial-cell proteins and mineral surfaces withneutrons (neutron sciences initiative)

• (Seed Money Fund)

25 Managed by UT-Battellefor the Department of Energy Presentation_name

Site Investigation

• Relationship between groundwater-surface waterinteraction and Hg concentrations at sediment-waterinterface

• Sediment-to-water column flux of Hg & MeHg in relationto water chemistry, biogeochemical gradients, andenvironmental variables (e.g., photoinduced effects)

• Biogeochemical controls on the transformations thatsustain methyl Hg concentrations in water

• Relationships among microbes, community structure,geochemistry, and Hg transformations


Hg(0), Hg(II), Hg(I)

Methylmercury

(MeHg)

mic

rob

es

Meth

yla

tio

n

?

Bioavailable

Hg species or

Precursors?

SITE BIOGEOCHEMICAL PROCESSES and MICROCOSM STUDIES

THg, MeHg flux,

geochemistry, microbial

community structure

Biogeochemical

controls and redox

couples

Relationship between


communities, Hg

transformations

Diffusive –vs– Advective Flux

Small Advective Flux >>

Diffusive

Relationship to SnCl2reactive Hg

Demethylation

Surface catalyzed rxns

Photochemical rxns

*Free radicals

*Reactive species

*Surface functional groups

and characterization

Demethylation

MeHg Hg(0) or Hg(II)

Microbial processes

*Sorbed and reactive species

(both chemical & biological

origin)

Ab

ioti

c m

eth

yla

tio

n –

ra

tes

an

d m

ec

ha

nis

ms

?

*NO

M,

*cata

lyzed

reacti

on

s,

*meth

yl

fun

cti

on

al

gro

up

s

Geochemistry – Microbial Community – Hg Transformations



Methylmercury

(MeHg)

mic

rob

es

Meth

yla

tio

n

?

?

Bioavailable

Hg species or

Precursors?

Fundamental mechanisms and transformations

Species Identification and

Controlling Processes



Geochemical controls

and redox couples*rates and mechanisms

Roles of natural organic

matter (DOM and POM) *complexation, species

*dissolution, stabilization

*methylation/demethylation

Oxidation and reduction

Hg(0) Hg2+

Precipitation, sorption,

and particulates

e.g., Hg2+ + S= HgS

Speciation and Geochemical Controls

Demethylation


Photochemical rxns

*Free radicals

*Reactive species

*Surface functional groups


Demethylation

MeHg Hg(0) or Hg(II)

Microbial processes

*Sorbed and reactive species

(both chemical & biological

origin)

Ab

ioti

c m

eth

yla

tio

n –

ra

tes

an

d m

ec

ha

nis

ms

?

*NO

M,

*cata

lyzed

reacti

on

s,

*meth

yl

fun

cti

on

al

gro

up

s


mic

rob

es


Methylmercury

(MeHg)

mic

rob

es

species

rates

Bioavailable

Hg species or

Precursors?

Microbial MeHg Production and Genetic Determinants

Demethylation

Demethylation

Demethylation –

microbial processes

• Reduction by dissimilatory

metal reduction

• Ubiquitous mercury

resistance genes (mer):

Expression of enzymes

specific for demethylation

and reduction

?

• Microbial community

structure

• Methylation strains

• Demethylation strains

• Hg Bioavailability

• Geochemical controls

• Sequence and genetic

controls

• Protein over expression


Co

ntr

ollin

g p

rocesses

Demethylation


Photochemical rxns• Free radicals

• Reactive species

• Surface functional groups


• Sorbed and reactive species

(both chem. & biol. origin)

DemethylationMeHg Hg(0) or Hg(II)

Microbial processes


Methylmercury

MeHg

Meth

yla

tio

n

?

Bioavailable

Hg species or

Precursors?

Integrated tasks



Geochemical controls

& redox couples*rates and mechanisms

Roels of Natural organic

matter (DOM and POM)*complexation and species

*dissolution and stabilization

*methylation/demethylation

Oxidation and reduction

Hg(0) Hg2+

Molecular dynamics and

simulation

Volatilization by

dissmilatory metal

reduction

Hg2+ + e- Hg0

Is a

bio

tic m

eth

yla

tio

n s

ign

ific

an

t?

Na

tura

l o

rga

nic

ma

tte

r a

nd

ca

taly

ze

d r

ea

cti

on

sN

atu

ral

org

an

ic m

att

er

an

d c

ata

lyze

d r

ea

cti

on

s

Is a

bio

tic m

eth

yla

tio

n s

ign

ific

an

t?

Na

tura

l o

rga

nic

ma

tte

r a

nd

ca

taly

ze

d r

ea

cti

on

sN

atu

ral

org

an

ic m

att

er

an

d c

ata

lyze

d r

ea

cti

on

s

Is a

bio

tic m

eth

yla

tio

n s

ign

ific

an

t?

Na

tura

l o

rga

nic

ma

tte

r a

nd

ca

taly

ze

d r

ea

cti

on

s

• Reduction by dissimilatory

metal reduction

• Ubiquitous mercury

resistance genes (mer):

Expression of enzymes

specific for demethylation

and reduction

Dem

eth

yla

tio

n

microbes

Precipitation, sorption,

particulates

e.g., Hg2+ + S= HgS

Demethylation and

reduction – mer operon

MerA: Hg2+ Hg0

MerB: HgR Hg2+ + R

MerR, MerD, MerOP, RNAP:

Transcriptional regulation

MerT, MerC – Hg2+

transport

NADPH

NADP+

Methylation

Hg2+ + ? MeHg



Methylmercury

(MeHg)

Meth

yla

tio

n

microbes

Hg

Precursors

Focus on key Hg biogeochemical processes

Task 1: Hg, MeHg flux,


community structure

Task 2: Species identification

and controlling processes

Dem

eth

yla

tio

nTask 3: Microbial processes,

genes sequence and genetic

controls

Task 4: Structure, dynamics,

and function of relevant

enzymes

HypothesesEnzymatic mechanisms

of transformation between

major Hg species and

methyl mercury

Oxidation, reduction,

and species transformation

Dominant chemical species

and bioavailability

Biological and abiotic

methylation and

demethylation

Coupled biogeochemical

reactions – sorption,

complexation, precipitation,

stabilization, fate and transport

Surface catalyzed and

photochemical reactions


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Hg

, g

/g

(fi

sh

),

g/

L (

wate

r)

Water

Fish

So far, mercury bioaccumulation not proportional to the

concentration of waterborne Hg

ORR Examples of water/fish disconnect:

Site Hg in water Hg in fish

(ng/L) (mg/kg)

White Oak Creek 60 0.5

EF Poplar Cr (upper) 400 0.8

EF Poplar Cr (lower) 100 0.8

Bear Cr 1–3 0.7

Rogers Quarry 1 1.1

Reference site 1–3 0.2

Mercury Concentrations in FishRemain Elevated

Elimination of inorganic Hg inputs not possible; alternative

strategies that reduce methylation in-situ may be the only

way to reach fish concentration targets

Basic research needs on mercury

methylation at sediment-water

interface and particularly what limits

methyl mercury production


• Ab initio shape reconstruction by DAMMIN.(D. Svergun, Biophys J. 76: 2879-2886, 1999)

Low resolution shape reconstruction fromSANS/SAXS data


Data flow and integration

Coupled processes

Microcosm

Studies

Integrated Data Analysis,

Modeling and Assessment

Field Investigation and

Improved Understanding

Geochemistry Microbiology

Fundamental Rates

and Mechanisms

Microbial Community

and Genetic Controls

Molecular Structure,

Dynamics

Species SequenceDominant microbes

ProteinElectron transfer

Determination of site

geochemistry, dominant chemical

species and microbial community

provides critical information for

controlled laboratory mechanistic

studies

Fundamental understanding of Hg

species transformation,

geochemical controls, and genetic

determinants essential for

methylation and demethylation

processes

Critical understanding of

biomolecular mechanisms in Hg

transformation (demethylation and

methylation) using structure-

functional relationships and genetic

regulation

Geochemical modeling, molecular

simulation, and data integration for

improved understanding of field

processes and remedial controls


Microbial MeHg Production

• Elucidate the genetic determinants of MeHgproduction and regulation.

Comparative gene expression, mutagenesis, andcomplementation.

• Determine the effect of geochemical factors on generegulatory networks for mercury methylation.

Use whole genome microarrays to examine both bioticand abiotic effects on the methylating andnonmethylating Desulfovibrio transcriptomic profiles.

Examine relationships among community structure,geochemical conditions, and MeHg production insediments collected from Hg-contaminated sites.

Functional gene arrays

16S rRNA gene clone library analysis

Scientific Issues Addressed

EFPC downstream of Y-12

Desulfovibrio africanus(SEM by Dwayne Elias, U of

Missouri)

Documents

Geochemical and Molecular Mechanisms Controlling ... · Geochemical Modeling * Critical understanding of Hg flux, biogeochemical controls, and microbial determinants (Menheer, 2004)