Normalisation of field degradation data and the inclusion of aged sorption in DegT50 determination

Transcription

1 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

2 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

3 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

4 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)

5 Methods for normalisation of field DegT50 values FOCUS degradation kinetics guidance (2006) Method 1: Time step normalisation Method 2: Normalisation of degradation rate

6 Method 1: Time step normalisation Reducing or increasing day lengths depending on soil temperature and moisture Temperature correction factor: 10 / Moisture correction factor:. Example: 2.58 / Normalised day length: 0.24

7 Method 1: Time step normalisation DAT Avg. temp ( C) f Temp Moist (v/v) f Moist D Norm cumulative D Norm Reference conditions: T ref =20 C θ pf2 = 0.4 Note f Temp = 0 at T 0 C and f Moist = 1 at θ θ pf2

8 D Norm %of applied %of applied

9 Method 2: Normalisation of degradation rate Modelling e.g. using ModelMaker k ref *f Moist *f Temp Pesticide Sink f Temp f Moist DAT Temp ( C) Moist (v/v) DegT50 = ln(2)/k ref

10 Method 2: Normalisation of degradation rate DegT50 matrix = 11.3 days

11 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

12 Normalisation of field degradation final note Consistency: Use same temperature and moisture dependency parameters throughout when deriving DegT50 and in model simulations

13 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

14 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

15 Aged sorption study OECD 307 laboratory degradation study with additional aqueous extraction step CaCl 2 extraction Solvent extraction Aqueous concentration Total extractable mass

16 Example dataset Mass (µg) Concentration (µg/l) Aged sorption model; Chi2=1.1 5 Measurements Time (d) Aged sorption model Degradation Increase in sorption Time (d)

17 Aged sorption model e.g. PearlNeq or ModelMaker C Q Eq Q Neq equilibrium sorption nonequilibrium sorption Freundlich: K F,EQ 1/n k des f NE

18 Aged sorption model C Q Eq Q Neq degradation DegT50 EQ

19 Example Mass (µg) Concentration (µg/l) Aged sorption model; Chi2=1.1 5 Measurements Time (d) optimised parameters M ini = 19.8 µg DegT50 EQ = 87 d K F,EQ = 2.76 L kg -1 f NE = 0.45 k des = d Time (d)

20 GW leaching assessment Guidance: use results from individual soils in PEC GW modelling PEC GW with and without aged sorption

21 Combining higher-tier options for sorption and degradation Field DegT50 Lab Aged Sorption Refined PEC GW calculations Refined PEC GW calculations

22 Combining higher-tier options for sorption and degradation DegT50 EQ from aged sorption studies is conceptually different from usual DegT50 Not possible to combine/average DegT50 values from aged sorption and other studies C Q Eq Q Neq DegT50 EQ DegT50

23 Combining higher-tier options for sorption and degradation Field DegT50 EQ Lab Aged Sorption Refined PEC GW calculations Use of metabolite and field data to generate aged sorption parameters for regulatory leaching assessments (ongoing project, CRD PS2254)

24 Deriving DegT50 from field data using aged sorption Step 1: Aged sorption study in laboratory (4 soils) Derive aged sorption parameters Calculate averages for Kf OM,EQ, f NE and k des Step 2: Perform field studies and measure substance mass decline over time Use aged sorption model with normalisation to derive field DegT50 EQ

25 Deriving DegT50 from field data using aged sorption Aged Sorption model (e.g. implemented in ModelMaker, Gurney et al. 2007) C Q Eq Q Neq

26 Deriving DegT50 from field data using aged sorption Normalisation of degradation rate for soil moisture and temperature (Note: No time step normalisation!) Optimise k ref for fixed sorption parameters. C Q Eq Q Neq k ref *f Moist *f Temp Sink DegT50 EQ = ln(2)/k ref

27 DegT50 MATRIX = 221 days DegT50 EQ = 142 days Data: Gurney et al. (2007)

28 DegT50 dependent on aged sorption parameters Field DegT50 EQ dependent on aged sorption parameters Which is the real DegT50 EQ? Aged sorption parameters Fitted field K OC,EQ 1/n f NE k des DegT50 EQ Soil Soil Soil Soil

29 DegT50 dependent on aged sorption parameters Need to use same combination of aged sorption and DegT50 EQ in GW assessment to get the same amount of degradation

30 Questions and uncertainties Can we use average aged sorption parameters to derive field DegT50 values? Can we use average DegT50 EQ from different field for PEC GW assessments? Aged sorption (lab) Lab soil 1 Lab soil 2 Lab soil 3 Lab soil 4 Degradation (field) Field soil A Field soil B Field soil C Field soil D GW assessment PEC GW

31 Ongoing work Evaluate the effect of combining parameters from different soils and studies Can default parameters be used to derive a field DegT50 EQ? Implications for regulatory use (tiered approach) Thank you!

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33 Deriving DegT50 from field data using aged sorption method 2 Using reverse modelling in PEARL (coupled with PEST) to derive DegT50 EQ PEARL has option to include aged sorption Use lab aged sorption parameters Optimise DegT50 to fit soil residues

34 PEARL-PEST optimisation procedure Weather data Rainfall Min and max temp Evapotranspiration Soil profile Texture, OC% Ksat, Van Genuchten Substance parameters Aged sorption parameters: K OM,EQ, f NE, k des PEARL Parameters Application rate DegT50 EQ PEST Output Total mass in profile Field data Total mass in profile