Nanoiron in the Subsurface:How far will it go and how does it change?

G. Lowry, Y. Liu, N. Saleh, T. Phenrat, B. Dufour, R. Tilton, K. Matyjaszewski

Carnegie Mellon University

T. Long and B. VeronesiNational Health and Environmental Effects Research Laboratory, US EPA

Conceptual Model

Nanoiron treatment of source or plume is possible

TCE + Fe0 HC Products + Cl- + Fe2+/Fe3+

Conceptual Model

Need to understand transport and fate of nanoironto optimize treatment and understand potential risks

Potential humanexposure

Goal:Maximize treatment, and minimize unwanted exposures

Does Nanoiron Pose a Risk?• Exposure

– What are we potentially exposed to?• What Fe phases and nanoparticle sizes?• Does nanoiron change over time?• How quickly does it change?

– How much are we exposed to?• Nanoiron transport distance?• What hydrogeochemical factors control it?

• Toxicity– Is there toxicity or ecotoxicity?

• What conditions lead to toxicity?

Types of NanoironRNIP

Fe0 coreFe3O4 shell

10 nm

Fe0 coreBorate shell Amorphous

2θ (degree)

20 30 40 50 60 70

Inte

nsity

(a.u

.) (220)(222)

(311)

(400)

(110)

(422)(511) (440)

(200)(a)

(b)

(c)

Crystalline

FeOOH Fe0 Fe0/Fe3O4

Fe2+ + BH4- Fe0/FeBx/Na2B4O7

Fe(B)

Liu et al, (2005) ES&T 39, 1338; Liu et al, (2005) Chem. Mat. 17(21); 5315-5322;Nurmi et al. (2005) ES&T 39, 1221.

Nanoiron After Reaction with TCE in Water

RNIP

+ TCE/H2O

+ TCE/H2O

Fe(B)

Fe0 Corrosion Rate (pH=8-9)RNIP

Fe(B)

Fe0/Fe3O4 + H2O

Fe3O4 + H2

Fe0/FeBx/Na2B4O7 + H2O

Fe-oxide + H2 + B4O72-

Time (days)0 2 4 6 8 10H

2 pr

oduc

ed (a

s %

of t

otal

Fe0

in p

artic

le)

0

20

40

60

80

100

Fe(B) without TCEFe(B)ox without TCEFe(B)cr without TCE

0

20

40

60

80

100

0 100 200 300 400 500

Time (days)H

2 (as

% o

f Fe0 in

par

ticle

)

Exp1Exp2MODL

~1 year

~1-2 weeks

Fe0 Corrosion Rate Depends on pH

RNIP

~2 weekspH=6.5

~1 yearpH=8.9

0

20

40

60

80

100

0 3 6 9 12 15 18Time (days)

H2 (a

s %

of F

e0 ) pH6.5 pH7.0 pH7.5pH8.0 pH8.5 pH8.9

decreasing pH

How long is Nanoiron Nano?

Concentration=1.9 mg/LStable size=~400 nmTime=15 minutes

Concentration=79 mg/LStable size=~5000 nmTime=10 minutes

Nanoiron Transport is a Filtration Problem

Particle-Media Interactions (Attachment)

Flocculation and straining (cake filtration)

Particle-DNAPL Interactions (Attachment)

Uniqueness- High particle concentrationand flow velocity

Nanoiron Aggregation Affects the Ability to Transport

1”1/2”

Monolayer of sand

Inlet

Outlet

Micro-fluidic PDMS cell

26 μm

26 μm

Time=1 min

Time=10 min

Nanoiron aggregates are filtered

Surface Modifiers Increase Transportability1. Potential Surface Coatings

PolyelectrolyteSurfactantsCellulose/polysaccharides

2. Enhanced transportCharge and steric stabilization minimize particle-particle and particle-media interactions

3. Affinity for DNAPLSurface coatings provide affinity for NAPL

Effect of Different Modifiers[Fe0]=3 g/L

Potential to select transport distance

Hydrogeochemical Effects on Nanoiron Transport

Transportability is a strong function of site hydrogeochemistry.

Systematic evaluation of hydrogeochemical effects is needed

Why suspect that ZVI causes OS?•Surface chemistry

•Reactive oxygen species•Literature-daphne, fish ….. glutathione depletion

Why the brain?• Serious consequences from damage

•Target of OS-lipid content…high energy use

Nanoiron Toxicity?

Nanoiron ToxicityMammalian brain macrophage (microglia)

Fe0 and modified-Fe0 (1-30 ppm)Whole-cell and genomic responses

OS-specific endpointsTEM, confocal microscopy

SDBS Control 24 hr

Unmodified Fe0

SDBS-Fe0 24 hr

SDBS Fe3O4 24 hr

SDBS

-

Fe0 4400x

SDBS Fe3O4 4400x

SDBS Control

HBSS Fe0 4400x

Fe0-induced Oxidative Stress in CNS Cells

Response of Microglia (BV2) and Mesencephalic Neurons (N27) to Iron Nanoparticles

(1-30 ppm)

0

20

40

60

80

100

Fe0 ATP Fe0 MTTred

Fe0OxyBurst

Fe3O4 ATP Fe3O4 MTTred

Fe3O4OxyBurst

Perc

ent o

f Ass

ays

Show

ing

Effe

ct BV2 Response

N27 Response

Future Studies:Apo E Mice and Medaka Fish

Conclusions• Potential toxicity risk warrants careful

evaluation• Fe0 fairly rapidly oxidizes to Fe-oxides

– Fe0 lifetime ranges from weeks to a year– Lifetime depends on nanoiron properties and

geochemical conditions (e.g. pH)– Unmodified nanoiron rapidly aggregates, size is

concentration dependent

Conclusions• Transport of unmodified nanoiron in porous

media is limited.• Particle surface chemistry strongly influences

transportability– function of modifier type and geochemical conditions– May be predictable from filtration/colloid transport theory– Matching surface modifications to site geochemistry

offers the potential for well-controlled placement

Acknowledgement

• U.S. Department of Energy-Environmental Management Science Program (DE-FG07-02ER63507)

• U.S. EPA-STAR (R830898)• CMU project team