1.2 Wendy van Beinum

Normalisation of field degradation data
and the inclusion of aged sorption in
DegT50 determination
Wendy van Beinum, Sabine Beulke
The Food and Environment Research Agency (Fera)
York, United Kingdom
Outline
Normalisation of field degradation
1. When to use normalisation
2. Methods for deriving normalised field DegT50
Aged sorption
1. Measuring laboratory aged sorption
2. Including aged sorption in field DegT50
When to use Normalisation
• Derivation of field DegT50 at reference temperature
and moisture conditions (usually 20°C, pF2)
• Used in models that account for temp and moisture
• Allows for averaging DegT50s lab/field
When to use Normalisation
• Persistence endpoint (DT50)
• to compare with trigger values
• dissipation (incl. photolysis, volatilisation, leaching)
• no normalisation: relevant conditions
• Degradation endpoint (DegT50_matrix)
• input for modelling (PEC calculations)
• degradation only (eliminate photolysis,
volatilisation, leaching)
• normalisation: derive DegT50 at reference
conditions (20°C, pF2)
Methods for normalisation of
field DegT50 values
FOCUS degradation kinetics guidance (2006)
• Method 1: Time step normalisation
• Method 2: Normalisation of degradation rate
Method 1: Time step normalisation
• Reducing or increasing day lengths depending on
soil temperature and moisture
Moisture correction factor:
Temperature correction factor:
.
/
10
Example:
2.58
Normalised day length:
/
0.39
0.2
0.4
.
0.24
0.62
Method 1: Time step normalisation
DAT
Avg.
temp
(°C)
fTemp
Moist
(v/v)
fMoist
DNorm
0
cumulative
DNorm
0
1
10
0.39
0.20
0.62
0.24
0.24
2
10
0.39
0.25
0.72
0.29
0.53
3
12
0.47
0.25
0.72
0.34
0.87
4
12
0.47
0.25
0.72
0.34
1.21
..
Reference conditions: Tref =20°C θpF2 = 0.4
Note fTemp = 0 at T ≤ 0°C and fMoist = 1 at θ ≥ θpF2
DNorm
%of
applied
%of
applied
3.8
95.1
102.3
8
90.5
80.4
15
66.9
70.7
24.2
65.4
50.5
31.8
52.4
51.0
49.4
28.2
31.7
66.6
25.5
22.2
Method 2: Normalisation of
degradation rate
• Modelling e.g. using ModelMaker
Pesticide
kref*fMoist*fTemp
Temp
(°C)
Moist
(v/v)
0
11.0
0.21
1
10.5
0.20
2
11.8
0.24
3
12.5
0.25
4
12.2
0.24
fTemp
fMoist
Sink
DAT
..
DegT50 = ln(2)/kref
Method 2: Normalisation of
degradation rate
DegT50matrix = 11.3 days
Soil Temperature and Moisture
• Depth relevant to bulk of pesticide mass
• Measured at high resolution (e.g. daily)
Alternative:
• Simulate daily soil temperatures and moisture content
using a leaching model (e.g. PEARL)
• Using weather data (incl. potential evapotranspiration)
and soil properties (pedo-transfer functions)
• Compare with moisture measurements
Normalisation of field
degradation – final note
• Consistency: Use same temperature and moisture
dependency parameters throughout when deriving
DegT50 and in model simulations
Outline
Normalisation of field degradation
1. When to use normalisation
2. Methods for deriving normalised field DegT50
Aged sorption
1. Measuring laboratory aged sorption
2. Including aged sorption in field DegT50
Aged sorption
• Account for increase in sorption in leaching
assessments (higher-tier option for PEC GW)
• Guidance on how aged sorption studies for pesticides
should be conducted, analysed, and used in
regulatory assessments (Proposal by Fera/CRD
2012)
• Expected EFSA Opinion in 2015
Aged sorption study
•
OECD 307 laboratory degradation study with
additional aqueous extraction step
CaCl2 extraction
→ Aqueous concentration
Solvent extraction
→ Total extractable mass
Example dataset
25
Mass (µg)
20
15
10
Aged sorption model; Chi2=1.1
5
Measurements
0
0
50
Time (d)
100
50
Time (d)
100
Concentration (µg/L)
0.25
0.2
0.15
0.1
0.05
0
0
Aged sorption model
•
•
Degradation
Increase in sorption
Aged sorption model
e.g. PearlNeq or ModelMaker
C
QEq
QNeq
equilibrium
sorption
nonequilibrium
sorption
Freundlich:
KF,EQ 1/n
kdes
fNE
Aged sorption model
C
QEq
degradation
DegT50EQ
QNeq
Example
25
Mass (µg)
20
15
10
Aged sorption model; Chi2=1.1
5
Measurements
0
0
50
Time (d)
100
Mini= 19.8 µg
DegT50EQ = 87 d
KF,EQ = 2.76 L kg-1
fNE = 0.45
kdes = 0.037 d-1
0.25
Concentration (µg/L)
optimised parameters
0.2
0.15
0.1
0.05
0
0
50
Time (d)
100
GW leaching assessment
Guidance: use results from individual soils in PECGW
modelling
PEC GW with and without aged sorption
Combining higher-tier options
for sorption and degradation
Field DegT50
Refined PECGW
calculations
Lab Aged Sorption
Refined PECGW
calculations
Combining higher-tier options
for sorption and degradation
• DegT50EQ from aged sorption studies is conceptually
different from usual DegT50
• Not possible to combine/average DegT50 values
from aged sorption and other studies
C
QEq
DegT50EQ
DegT50
QNeq
Combining higher-tier options
for sorption and degradation
Field DegT50EQ
Lab Aged Sorption
Refined PECGW
calculations
Use of metabolite and field data to generate aged
sorption parameters for regulatory leaching
assessments (ongoing project, CRD PS2254)
Deriving DegT50 from field data
using aged sorption
Step 1:
• Aged sorption study in laboratory (4 soils)
• Derive aged sorption parameters
• Calculate averages for KfOM,EQ, fNE and kdes
Step 2:
• Perform field studies and measure substance mass
decline over time
• Use aged sorption model with normalisation to derive
field DegT50EQ
Deriving DegT50 from field data
using aged sorption
• Aged Sorption model (e.g. implemented in
ModelMaker, Gurney et al. 2007)
C
QEq
QNeq
Deriving DegT50 from field data
using aged sorption
• Normalisation of degradation rate for soil moisture
and temperature (Note: No time step normalisation!)
• Optimise kref for fixed sorption parameters.
C
QEq
QNeq
kref*fMoist*fTemp
Sink
DegT50EQ = ln(2)/kref
DegT50MATRIX = 221 days
DegT50EQ = 142 days
Data: Gurney et al. (2007)
DegT50 dependent on aged
sorption parameters
• Field DegT50EQ dependent on aged sorption parameters
• Which is the real DegT50EQ?
Aged sorption parameters
Fitted field
KOC,EQ
1/n
fNE
kdes
DegT50EQ
Soil 1
104
0.858
0.574
0.064
143
Soil 2
130
0.891
0.223
0.02
182
Soil 3
122
0.868
0.494
0.032
149
Soil 4
214
0.916
0.919
0.018
115
DegT50 dependent on aged
sorption parameters
• Need to use same combination of aged sorption
and DegT50EQ in GW assessment to get the same
amount of degradation
Questions and uncertainties
• Can we use average aged sorption parameters to
derive field DegT50 values?
• Can we use average DegT50EQ from different field for
PECGW assessments?
Aged sorption
(lab)
Degradation
(field)
Lab soil 1
Field soil A
Lab soil 2
Field soil B
Lab soil 3
Field soil C
Lab soil 4
Field soil D
GW
assessment
PECGW
Ongoing work
• Evaluate the effect of combining parameters from
different soils and studies
• Can default parameters be used to derive a field
DegT50EQ?
• Implications for regulatory use (tiered approach)
Thank you!
Deriving DegT50 from field data
using aged sorption – method 2
• Using reverse modelling in PEARL (coupled with
PEST) to derive DegT50EQ
• PEARL has option to include aged sorption
• Use lab aged sorption parameters
• Optimise DegT50 to fit soil residues
PEARL-PEST optimisation procedure
Weather data
•
•
•
Rainfall
Min and max temp
Evapotranspiration
PEARL
Soil profile
•
•
Texture, OC%
Ksat, Van Genuchten
Substance
parameters
•
Parameters
•
•
Application rate
DegT50EQ
Output
Total mass in profile
Aged sorption
parameters: KOM,EQ,
fNE, kdes
PEST
Field data
•
Total mass in profile

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