modelling the plant uptake of organic chemicalsplant uptake of organic chemicals chris collins rsc,...

© University of Reading 2008 www.reading.ac.uk

Dept Soil Science

October 11, 2010

Modelling the plant uptake of organic chemicalsChris Collins

RSC, Contaminated Land Meeting, 2010

Aim

• To give an overview of where we are, recent developments.

• Current models and their problems.

• The way forward.

• I am at the junction between modelling and experimentation– Jack of all trades master of none– We need the continuum

2


Current State

3


Uptake pathways

4

Volatilisation from soil

Suspension of soil particles by wind and rain

Dry and wet deposition of particles followed by desorption into leaf

Transport in the transpiration stream within the xylem

Evaporation and volatilisation from leaf

Gaseous deposition to leaf via cuticle and stomata

Desorption from soil followed by root uptake from soil solution

Volatilisation from soil

Suspension of soil particles by wind and rain

Dry and wet deposition of particles followed by desorption into leaf

Transport in the transpiration stream within the xylem

Evaporation and volatilisation from leaf

Gaseous deposition to leaf via cuticle and stomata

Desorption from soil followed by root uptake from soil solution


Plant uptake of organic pollutants

• We need to understand to model –– crop uptake of pollutants and pesticides

• We need to understand to remediate – plant uptake can be most important component of exposure.

• Many current models based on old research e.g. Briggs-Ryan (1983). These do not always provide the best prediction of the experimental data.


Briggs and Bromilow relationships

Roots Shoots

6

0

50

100

150

200

250

0 1 2 3 4 5 6

log KOW

Ro

ot

con

cen

trat

ion

fac

tor

0.0

0.2

0.4

0.6

0.8

1.0

-3 -1 1 3 5 7

log KowT

SC

F

Burken and Schnoor Briggs et al Hsu et al

N.B. Solution culture experiments, limited number of chemicals, limited range of experiments.


Briggs-Ryan raltionships - soil properties

Root Shoot

7

0

1

2

3

4

5

0 2 4 6 8

log Kow

Ro

ot

con

cen

trat

ion

fac

tor

(foc = 0.01) (foc = 0.025) (foc = 0.06)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-2 0 2 4 6

log Kow

Sh

oo

t co

nce

ntr

atio

n f

acto

r

(foc = 0.01) (foc = 0.025) (foc = 0.06)


Hydrophobicity and polarity

8


Aerial deposition – background source

9

KOA = KOW

KAW


Predominant pathways

10


Predominant uptake pathways

11

Blue coloring indicates PAH spiked solution.A: Bare roots in spiked solution; AACTIVE – shoot removed at start of the experimental period, ADEAD root killed by acid treatment.B: Plants grown in spiked solution with different PAH concentrations. C: Plants grown in spiked solution, plant shoots in the light CLIGHT and half darkness CDARK. D: Half plants grown in clean solution DCLEAN; others have half of their roots in spiked solution and half in clean solution DPOLL; all the plants sharing the same air conditions. E: Half plants grown in spiked EPOLL and half in clean ECLEAN solution; all the plants sharing the same air conditions.


Significant pathways

Passive uptake by the root

Transport in the transpiration stream- Dependent on water solubility

Deposition following volatilisation

Transport in the phloem

We should focus research onthe root pathway for PAH. N.B. Different for other chemicals


Recent findings

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New work TSCF

14

Dettenmaier study 100s of measurements and much wider range of chemicals, others 4-8


Two photon excitation microscopy

Root uptake Calculated degradation

15


Combined root uptake and soil volatilisation model

Total uptake Fractional uptake

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4 5 6 7 8 9 10 11 12 13 14

Log KOA

-7

-6

-5

-4

-3

-2

-1

0

Lo

g K

AW

Log mass deposited to the shoot (mg)

-2 -2.5 -3 -3.5 -4 -4.5 -5 -5.5

4 5 6 7 8 9 10 11 12 13 14

Log KOA

-7

-6

-5

-4

-3

-2

-1

0

Lo

g K

AW

Log fraction of chemicaldeposited to shoot

-0.5 -1 -1.5 -2 -2.5 -3 -3.5 -4 -4.5

HCB


Modelling

17


Model types

• Simple regression e.g. Travis and Arms

• Mechanistic models e.g. Trapp and Matthies– Growth dilution– Metabolism– Transpiration

• Fugacity models e.g. Hung and Mackay– Suite of partition coefficients between different environmental

media and plant components.

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)log578.0(588.1log owv KB −=


Model types

• A note about ionisable compounds – not my area of expertise.

• Separate compounds into neutral and ionic free fractions – e.g. Henderson-Hasselbach equation

• Subsequent uptake following soil to root partition and movement into stem via the transpiration stream as previously discussed.

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Plant uptake modelling – modelinter-comparison

DCB from sludge HCB from sludge


Plant uptake modelling – modelinter-comparison

TCB sludge - aged TCB spiked - fresh


Model Intercomparison

22

Shoot vegetables

Root vegetable

sTravis and Arms 2.2 Trapp and Matthies 1.6Ryan et al. 1.9 Ryan et al. 1.1Topp et al 0.9 Hung and Mackay 0.9Hung and Mackay 0.7 Chiou et al 0.6Chiou et al 0.6 Topp et al 0.6Trapp and Matthies 0.5


Data variability

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Data variability


Plants Experimental variability -1


Plants experimental variability– species

Eudicots

Monocots

Asterid

Rosid

PoalesLiliales

RanunculalesCarophyllales

Ericales

Solanales

ApialesAsteralesDipscales

CucurbitalesFabales

Lamiales

Brassicales

Myrtales

Rosid 1

Rosid 2

Asterid 1

Asterid 20.10 b

0.42 a

0.06 b

0.07b

0.42 a

0.34 a0.19 ab

0.05 c

0.44 a

0.19 abc

0.34 ab

0.01 c

0.7 c

0.02 bc

0.06 c

0.07 c

0.10 c

0.02 bc

0.14 bc 0.06 c

0.07 bc

0.06 c 0.02 bc

0.17 bc

0.03 c

0.10 c

0.01 bc

0.34 ab 0.18 ab

0.44 a

0.05 bc

CLASS GROUP SUPERORDER ORDER


Do we have the data we need?

ChemicalPlant

componentRange Mean Data

Most sensitive

parameters (% of

variation)DCB Leaf 2.1 x 1-5 –1.51 x 1-3

2.0 x 10-4 1.3 bL2 (84)

Root 0.04 – 1.1 0.15 0.1 (core)

0.1 (peel)

bR2 (53)

f.o.c. (22)

TCB Leaf 2.6 x 1-6

– 1.92 x 1-42.0 x 10-5 8.3 bL (81)

Root 0.06 – 2.40 0.30 2.8 (core)

5.5 (peel)

bR (54)

f.o.c. (23)

HCB Leaf 2.1 x 1-6

– 1.51 x 1-41.8 x 10-5 4.4 bL (80.6)

Root 4.6 x 1-5

– 2.2 x 1-21.2 x 10-3 0.08 (core)

9.5 (peel)

bR (91.3)

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Models do not account for differences between core and peel


The way forward

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Crop specific models

29



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OC = organic carbon content of soil KOC = soil water to organic carbon partition coefficientρwet = soil wet density ρdry = soil dry densityKAW = air to water partition coefficient PA = volume fraction soil airPW = volume fraction soil water



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Cstem = conc. in stem CXy = conc. in xylem Q = annual transpiration Μ = mass of woody stemKWood = water to wood partition coefficient KE = metabolic rateKG = growth rate



32

QF = fruit annual transpiration Cfruit = conc. in fruit Cstem = conc. in stem KWood = water to wood partition coefficientCSoil = conc. in soil



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No genuine sensitivity analysisPattern same as T and AComparison with one data set


What next?

• Focus on important pathways for chemical of interest.

• Emphasise law of parsimony

• Validation, validation, validation

• Good experimental protocols required to allow modellers to use all results.– Rapid measures of bioavailable fraction – SPME, silicone– Background air concentrations– Soil properties

modelling the plant uptake of organic chemicalsplant uptake of organic chemicals chris collins rsc,...

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