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Aged Sorption

2nd April 2020

Dr Wendy van Beinum (Enviresearch)

Dr Chris Sinclair (Fera)

Outline▪ Introduction

▪ What is aged sorption?

▪ History of guidance development

▪ Overview of Guidance

▪ Laboratory study requirements

▪ Model theory and mechanism

▪ Parameter fitting

▪ Groundwater assessment

▪ Considerations

▪ Advantage/disadvantage considerations

▪ Future developments

▪ Aged sorption testing strategies

Introduction

aged sorption

What is aged sorption?

‘aged sorption’‘time-dependent sorption’‘kinetic sorption’‘non-equilibrium sorption’

Not a new concept

History of guidance development

2003-2004

Defra project PS2206

Warwick HRI

Systematic study on time-dependent

sorption in the laboratory

2009

FOCUS Groundwater Workgroup

Tiered approach for groundwater and aged

sorption was described in detail as an option

for refinement at Tier 2a and providing

guidance on how to derive aged sorption

parameters from aged sorption studies using

model fitting.

2010

Aged sorption Stakeholder Workshop

(York)

Presentation of guidance to European

regulatory authorities, academia, consultancies

and industry and agreement for ECPA to supply

industry datasets for independent testing

2010-2012


Fera, Battelle and ECPA

Testing the draft guidance with industry

datasets. Requirements for revision

highlighted and discussed with CRD

2008-2010


Fera and Alterra

Development of guidance on the

implementation of aged soil sorption studies

into regulatory exposure assessments

2007-2008


Central Science Laboratory (Fera)

Characterisation and modelling of time-

dependent sorption of pesticides


2003-2004


Warwick HRI



2009







model fitting.

2010


(York)





2010-2012






2008-2010


Fera and Alterra




2007-2008






The specific objectives were

1. To review model concepts and experimental techniques to characterise aged sorption;

2. To measure aged sorption in laboratory studies for a range of soils and pesticides using various experimental techniques;

3. To derive model input parameters from the experimental data and evaluate the effect of the experimental methodology, data handling and parameter estimation techniques on the results;

4. To assess whether aged sorption parameters derived in laboratory studies are suitable to describe pesticide behaviour in undisturbed lysimeters; and

5. To develop and disseminate guidance on how aged sorption studies should be conducted, analysed and used in regulatory assessments.


2003-2004


Warwick HRI



2009







model fitting.

2010


(York)





2010-2012






2008-2010


Fera and Alterra




2007-2008





Guidance updates and approval

2012CRD publish draft

guidance & submitted to EFSA

PPR panel for review

2015EFSA PPR panel

provide statement on guidance

proposal

2017Revised draft

guidance proposal submitted to EFSA

PPR panel

2018EFSA provide

opinion about the guidance for aged

sorption

2019Finalised guidance submitted to EC for

approval

Overview of Guidance

Experimental procedures

Model fitting to

derive parameters

Use in regulatory risk assessment

(FOCUS groundwater modelling)

Overview of guidance


Experimental procedures

Laboratory study requirements

Soils

▪ Minimum 4 soils with contrasting properties should show evidence of aged sorption

▪ Same soils (from the same batch) for aged and batch equilibrium sorption

▪ Soils handled according to OECD307

▪ Batch equilibrium sorption experiment according to OECD 106 to derive Freundlich exponent (1/n)

▪ Performed on same soils (from same batch)

▪ Also important in confirming experimental design for aged sorption study

▪ Determination of time to adsorption equilibrium

▪ Determination of the soil:solution ratio

Batch equilibrium sorption

▪ Duplication with sacrificial sampling

▪ In the dark, 20±2 oC, moisture between pF 2 and 2.5

▪ Timepoints set to follow pattern of decline

▪ First sample (day 0) after application is required

▪ Minimum six timepoints remain after elimination during data analysis

Aged sorption experiment

Aged sorption experiment

▪ Two extractions required either in serial on the same sample or parallel on subsamples

▪ 0.01M CaCl2 extraction

▪ Solvent extraction (same for all soils)

▪ Followed by centrifugation and determination of parent concentration in the supernatant

▪ Non-extractable residues determined by combustion

Extraction with solvent

Extraction with 0.01 M CaCl2


Model theory and mechanism

Aged Sorption model

25

equilibrium sorption

long-term sorption

soil solution

Aged Sorption model

26

Freundlich sorption:

Kom,eq and 1/n


long-term sorption

soil solution


long-term sorption

soil solution

Aged Sorption model

27

Freundlich sorption:

Kom,neq and 1/n

ratio:

fNE = Kom,neq /Kom,eq

rate constant:

kdes (d-1)

Aged Sorption model

DegT50EQ


long-term sorption

soil solution

Aged Sorption model

29


long-term sorption

Kom,eq

soil solution

ratio

fNE = Kom,neq / Kom,eq

rate constant

kdes (day-1)

DegT50EQ

Use 1/n from batch sorption study on same soil


Parameter fitting

PEARLNEQ 5.1

https://www.pesticidemodels.eu/pearl/

pearl-pearl-based-applications

https://www.pesticidemodels.eu/pearl/

pearl-pearl-based-applications

PEARLNEQ 5.1

Model fitting

Data provided by ECPA EFSA Journal 2018;16(8):5382

ECPA soil 6A

ECPA soil 6B

ECPA soil 6C

ECPA soil 6D

SoilDegT50EQ

(days)

kdes

(day-1)

fNE

(-)

Kom,eq

(mL/g)

6A 108 0.0394 0.706 199

6B 91.4 0.0253 0.576 161

6C 176 0.0456 0.598 224

6D 78.7 0.0278 0.668 185

Acceptance criteria

▪ Good visual and statistical model fit

▪ Reliable parameters

▪ Evidence of aged sorption

Acceptance criteria




2 = 1.9

Acceptance criteria



▪ Evidence of aged sorptionRelative Standard Error ≤ 40%

(confidence interval ± 80%)

Acceptance criteria




Evidence of Aged Sorption

Acceptance criteria




Aged sorption endpoints

SoilDegT50EQ

(days)

kdes

(day-1)

fNE

(-)

Kom,eq#

(mL/g)

6A 108 0.0394 0.706 199

6B 91.4 0.0253 0.576 161

6C 176 0.0456 0.598 224

6D 78.7 0.0278 0.668 185

Geometric mean: 0.0335 0.635

# Fitted Kom,eq values not used in groundwater assessment


Groundwater assessment


▪ New sorption and degradation data ..to be combined with existing substance data

SoilTexture

(USDA)

Kom,eq

(mL/g)1/n

6A Sandy loam 168 0.895

6C Loam 131 0.974

6D Silt loam 122 0.908

6G Loamy sand 238 0.948

6H Clay loam 154 0.875

G1 Clay loam 71 0.799

G2 Sandy loam 120 0.838



Geometric mean 138

Arithmetic mean 0.882


▪ New sorption and degradation data ..to be combined with existing substance data

SoilTexture

(USDA)

Kom,eq

(mL/g)1/n

6A Sandy loam 168 0.895

6C Loam 131 0.974

6D Silt loam 122 0.908

6G Loamy sand 238 0.948

6H Clay loam 154 0.875





Geometric mean 138

Arithmetic mean 0.882

Soil DegT50 DegT50EQ

6A 162 108

6B 128 91.4

6C 239 176

6D 115 78.7

6E 279 163

6F 318 235

G1 120 67.1

G2 384 207

G3 445 236

G4 556 281

Geomean 238 147

Parameter Value

Kom,eq (mL/g) 138

1/n 0.882

kdes (day-1) 0.0335

fNE (-) 0.635

DegT50EQ (d) 147


Aged sorption can lead to a six fold reduction in PECGW

0

0.1

0.2

0.3

0.4

Chat Hamb Joki Krem Okeh Piac Port Sevi Thiv

Lower tier

Aged sorption

Substance ‘ECPA06’

EFSA Journal 2018;16(8):5382

g/L

Aged sorption considerations

Considerations

▪ Will it work?

▪ Cost and effort versus chances of success

▪ Preliminary calculation

▪ Precautions: e.g. extra soils

When to use aged sorption

▪ Aged sorption of metabolites

▪ Aged sorption study in the field

▪ Combining lab aged sorption with field DegT50

Further developments

▪ Improve procedure for using field DegT50EQ

▪ Complete tool for aged sorption – kinetic modelling, checking against criteria, selecting endpoints for groundwater modelling

Aged sorption strategies

Aged sorption strategies:

No existing data

▪ Combined soil degradation and aged sorption study

▪ Soil selection (4 or more)

▪ Timepoints (6 or more)

▪ Batch equilibrium study (OECD 106) with same soils

▪ Modeller expertise and input during experimental phases

▪ Modelling reports

▪ Aged sorption modelling report

▪ Degradation kinetic modelling report


Lower tier data available

▪ Review of existing information

▪ Scoping assessment

▪ Experimental studies (inc. modeller support)

▪ Batch equilibrium study

▪ Aged sorption study

▪ Modelling reports

▪ Aged sorption modelling report

▪ Degradation kinetic modelling report


Additional

▪ Preliminary experiments (rate of degradation and/or soil selection)

▪ Metabolites studies

▪ Application of the EFSA OECD 106 checklist

▪ Refined groundwater modelling

Summary▪ Introduced aged sorption

▪ Overview of available guidance

▪ Considerations

We are here to help with your aged sorption requirements

Questions & Answers

Please use the chat feature to ask your questions

Thank you for your time

For more information please email or visit:

e: [email protected]

w: fera.co.uk/aged-sorption

w: enviresearch.com/aged-sorption

mailto:[email protected]

https://www.fera.co.uk/aged-sorption

https://www.enviresearch.com/aged-sorption

aged sorption - info.fera.co.ukinfo.fera.co.uk/.../aged-sorption-full-slide-deck.pdf · defra...

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