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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
‘aged sorption’‘time-dependent sorption’‘kinetic sorption’‘non-equilibrium sorption’
Not a new concept
‘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
Defra project PS2244
Fera, Battelle and ECPA
Testing the draft guidance with industry
datasets. Requirements for revision
highlighted and discussed with CRD
2008-2010
Defra project PS2235
Fera and Alterra
Development of guidance on the
implementation of aged soil sorption studies
into regulatory exposure assessments
2007-2008
Defra project PS2228
Central Science Laboratory (Fera)
Characterisation and modelling of time-
dependent sorption of pesticides
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
Defra project PS2244
Fera, Battelle and ECPA
Testing the draft guidance with industry
datasets. Requirements for revision
highlighted and discussed with CRD
2008-2010
Defra project PS2235
Fera and Alterra
Development of guidance on the
implementation of aged soil sorption studies
into regulatory exposure assessments
2007-2008
Defra project PS2228
Central Science Laboratory (Fera)
Characterisation and modelling of time-
dependent sorption of pesticides
History of guidance development
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
Defra project PS2244
Fera, Battelle and ECPA
Testing the draft guidance with industry
datasets. Requirements for revision
highlighted and discussed with CRD
2008-2010
Defra project PS2235
Fera and Alterra
Development of guidance on the
implementation of aged soil sorption studies
into regulatory exposure assessments
2007-2008
Defra project PS2228
Central Science Laboratory (Fera)
Characterisation and modelling of time-
dependent sorption of pesticides
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
Defra project PS2244
Fera, Battelle and ECPA
Testing the draft guidance with industry
datasets. Requirements for revision
highlighted and discussed with CRD
2008-2010
Defra project PS2235
Fera and Alterra
Development of guidance on the
implementation of aged soil sorption studies
into regulatory exposure assessments
2007-2008
Defra project PS2228
Central Science Laboratory (Fera)
Characterisation and modelling of time-
dependent sorption of pesticides
History of guidance development
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.
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
Defra project PS2244
Fera, Battelle and ECPA
Testing the draft guidance with industry
datasets. Requirements for revision
highlighted and discussed with CRD
2008-2010
Defra project PS2235
Fera and Alterra
Development of guidance on the
implementation of aged soil sorption studies
into regulatory exposure assessments
2007-2008
Defra project PS2228
Central Science Laboratory (Fera)
Characterisation and modelling of time-
dependent sorption of pesticides
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
Defra project PS2244
Fera, Battelle and ECPA
Testing the draft guidance with industry
datasets. Requirements for revision
highlighted and discussed with CRD
2008-2010
Defra project PS2235
Fera and Alterra
Development of guidance on the
implementation of aged soil sorption studies
into regulatory exposure assessments
2007-2008
Defra project PS2228
Central Science Laboratory (Fera)
Characterisation and modelling of time-
dependent sorption of pesticides
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
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
Overview of Guidance
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
equilibrium sorption
long-term sorption
soil solution
equilibrium sorption
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
equilibrium sorption
long-term sorption
soil solution
Aged Sorption model
29
equilibrium sorption
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
Overview of Guidance
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
▪ Good visual and statistical model fit
▪ Reliable parameters
▪ Evidence of aged sorption
2 = 1.9
Acceptance criteria
▪ Good visual and statistical model fit
▪ Reliable parameters
▪ Evidence of aged sorptionRelative Standard Error ≤ 40%
(confidence interval ± 80%)
Acceptance criteria
▪ Good visual and statistical model fit
▪ Reliable parameters
▪ Evidence of aged sorption
Evidence of Aged Sorption
Acceptance criteria
▪ Good visual and statistical model fit
▪ Reliable parameters
▪ Evidence of aged sorption
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
Overview of Guidance
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
G3 Clay loam 122 0.858
G4 Sandy loam 183 0.845
Geometric mean 138
Arithmetic mean 0.882
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
G3 Clay loam 122 0.858
G4 Sandy loam 183 0.845
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
Groundwater assessment
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
Aged sorption strategies:
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
Aged sorption strategies:
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:
w: fera.co.uk/aged-sorption
w: enviresearch.com/aged-sorption