Transport of nanoparticles with groundwater affected by soil- and dissolved organic matter

Fritjof Fagerlund, Maryeh Hedayati, Jean-Marc Mayotte and

Prabhakar Sharma

Department of Earth Sciences, Uppsala University

Contact: fritjof.fagerlund@geo.uu.se

1

Contents

Background

Nanoparticles, transport

Objectives

Laboratory experiments

Results

Discussion

Conclusions

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Source: http://nano.cancer.gov/learn/understanding/

nanoparticle sand colloid

Nanoparticles

Nanoparticles have

enormous surface-to-

weight ratio

Many nanomaterials

have special properties

that differ from the parent

bulk material

TiO2 nanoparticles (NPs) are widely used in many applications

and products including cosmetics and paints

Sunblock lotions

New applications: Perfluorosilane-coated TiO2 NPs are

used in oil-resistant, self-cleaning paint (Lu et al., Science

347(6226), March 2015)

TiO2 NPs typically don’t penetrate the skin but may cause

damage if inhaled or ingested

May interact with other contaminants. E.g. enhanced uptake of

arsenic (As(V)) was found in carp fish in the presence of TiO2

NPs (Sun et al., 2007)

TiO2 nanoparticles

Nanoparticle transport

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potential energy

EDL Repulsion

van der Waals

Attraction

energy

barrier

energy

minimum

distance

Dissolved organic matter (DOM)

Soil organic matter (SOM)

Both DOM and SOM are often present –

One example is the artificial recharge of groundwater for the

water supply of Uppsala

The objective of this study was to investigate the effects of DOM

and SOM on TiO2 nanoparticle transport in groundwater

Applications to nanoparticles, pathogens, particle-mediated

contaminant transport

Organic matter & Objectives

Particle – organic matter – soil

interactions

affect particle transport

Artificial groundwater recharge basin for the water

supply of Uppsala, Sweden

Soil with high organic

matter content was

sampled from infiltration

basins

The same soil was acid

cleaned for comparison

The river water used for

infiltration containing DOM

was also sampled

8 combinations:

Soil Water Ionic

strength

SOM DOM Low

Clean Clean High

Transport scenarios

Main Solution

(Phase 1)

DI water

(Phase 3)

Background solution

(Phase 2)Sand

Column

Pump

Spectrophotometer Fraction

Collector

Sand column (10 cm)

Switch from background water

to water with TiO2 nanoparticles

(10 mg/L)

Both TiO2 and DOM

concentrations measured using

a spectrophotometer

Transport & retention of TiO2

was studied

Experimental setup

Effects of DOM in water

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0.8

1

1.2

0 2 4 6

Re

lati

ve

co

nce

ntr

ati

on

C/C

0

Pore volumes

Clean soil with no SOM

Tracer

E2, natural water, Low IS

E4, natural water, high IS

E6, clean water, Low IS

E8, clean water, high IS

Tracer is fully mobile

At low ionic strength

in clean water, TiO2 are

highly mobile

High ionic strength

immobilizes TiO2 in

clean water

With DOM in water

TiO2 has intermediate

mobility both at low and

high ionic strength

Increasing trends

may be due to DOM

attachment to soil DOM ensures that some mobility exists &

reduces the effect of ionic strength

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1

1.2

0 2 4 6

Re

lati

ve c

on

cen

trat

ion

C/C

0

Pore volumes

Natural soil with SOM

Tracer

E1, natural water, Low IS

E3, natural water, high IS

E5, clean water, low IS

E7, clean water, high IS

With both SOM and

DOM present, TiO2 are

highly mobile

This is regardless of

high or low ionic

strength

For TiO2 in clean water

at low IS SOM reduces

the mobility compared to

clean soil

For clean water at

high IS SOM increases

TiO2 mobility

Effects of SOM in soil

Combination of SOM & DOM means high TiO2

mobility regardless of IS

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Z-p

ote

nti

al (

mV

)

Clean soil, Low IS

Clean Soil, High IS

SOM in soil, Low IS

SOM in soil, High IS

soil Z-

potential

TiO2 particles

Z-potential

DOM in

water

Clean

water

Inflow Outflow

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Z-potential of soil and TiO2 NPs

z-potential strongly

negative in soil

- less with SOM & high IS

DOM reduces neg.

z-potential in TiO2 NPs

z-pot. reduced between

inflow and outflow

- This occurs both in

clean soil & with SOM

0

500

1000

1500

2000

2500

Agg

rega

te s

ize

(n

m)

Clean soil, Low IS

Clean soil, High IS

SOM in soil, Low IS

SOM in soil, High IS

DOM in

water Clean water

Inflow Outflow

A correlation between z-

potential and aggregate

size exists

DOM => Average

aggregate size > 1µm

DOM => aggregation

High IS => Large

aggregate size (expected)

For low IS, aggregate

size increases between

inflow and outflow

- This occurs both in

clean soil & with SOM

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. 0

500

1000

1500

2000

2500

-40 -30 -20 -10 0

Agg

rega

te s

ize

(n

m)

Z-potential (mV)

Average aggregate size of TiO2 NPs

DOM SOM

very

high

mobility

Increase

mobility

at high IS

Red.

mobility

at low IS Red.

mobility

at low IS

Increase

mobility

at high IS

Red.

z-pot. of

TiO2 NPs

Larger

aggreg.

size

slight red.

z-pot. of

soil Produce

DOM

Effect of DOM & SOM on transport

DOM and SOM may

reduce the interaction

between TiO2 NPs and

solid medium

Attachment appears

to be blocked in the

presence of DOM and

SOM

Change in the

dominant retention

mechanism

Very high particle

mobility when both

SOM & DOM present

Summary & Conclusions (1)

Influence of soil organic matter (SOM) and dissolved organic matter

(DOM) on the transport and retention of TiO2 nanoparticles was studied

in flow-through column experiments.

For clean soil, DOM in the water increased TiO2 NP mobility at high

ionic strength (IS), but decreased it at low IS.

DOM thus decreased the sensitivity to IS and ensured some NP

mobility even at high IS.

Similarly, when clean water was used, SOM increased TiO2 NP

mobility at high IS and decreased it at low IS, thus reducing sensitivity

to IS and ensuring some mobility.

When both SOM and DOM were present very high TiO2 NP mobility

was observed regardless of whether the IS was low or high.

The presence of DOM and SOM influences particle-particle and

particle-grain interactions.

Reduction in z-potentials can explain increased aggregation and

reduced particle mobility at low ionic strengths.

However, DLVO interactions alone cannot explain the increased

particle mobility when both DOM and SOM are present

It appears SOM and DOM cause blocking of particle attachment to

the medium by attraction forces, favouring particle mobility & transport.

However, the exact mechanism is not yet clear and subject to further

research

To conclude: the mobility of nanoscale particles may be significatly

enhanced in aquifers which contain organic matter => these aquifers

are more vulnerable to unwanted particle transport.

Summary & Conclusions (2)

Ion C (mM)

Li+ 0.0014

Na+ 0.5269

K+ 0.0815

Ca2+ 2.1062

Mg2+ 0.3044

F- 0.0303

Cl- 0.7754

NO2- 0.0095

Br- 0.0015

NO3- 0.0695

PO43- 0

SO42- 0.9423

C2O42- 5.12E-05

Water chemistry

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Ab

sorb

an

ce

Relative concentration

DOM calibration curve

Presence of 10mg/l TiO2

Absence of

TiO2

00.10.20.30.40.50.60.70.8

0 10 20 30 40

Ab

sorb

an

ce

Concentration (mg/l)

TiO2 calibration curve

Presence of DOM

Absence of DOM

Spectrophotometer adsorbance

Additional data

Experiment Soil Water phase

NaCl (mM)

TiO2 Particle Diam. (nm)

Z-Potential (mV)

E1 SOM DOM 7.5* 1003 -15.8 E2 Clean DOM 7.5* 1907 -17.4 E3 SOM DOM 31.5** 1149 -15.1 E4 Clean DOM 31.5** 1195-1509 -16.1 - -17 E5 SOM Clean 7.5 263-659 -21.3 - -35.8 E6 Clean Clean 7.5 283-1000 -11.4 - -28.1 E7 SOM Clean 31.5 370-879 -22.2 - -33.3 E8 Clean Clean 31.5 865-919 -11.3 - -29.5

Column experiment scenarios & measured ranges for particle

size & z-potentials

* Equivalent NaCl concentration, ** Adjusted, equivalent NaCl conc.

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