Guidance on aged sorption studies for higher-tier PEC groundwater assessments

Transcription

1 Guidance on aged sorption studies for higher-tier PEC groundwater assessments Wendy van Beinum, Sabine Beulke The Food and Environment Research Agency (Fera) York, United Kingdom

2 Background CRD commissioned the development of guidance on how aged sorption studies for pesticides should be conducted, analysed and used in higher tier pesticide leaching assessments o o o o o Experimental protocol Data requirements Fitting of a model to the experimental data Goodness of fit and acceptability of parameters Use of aged sorption parameters in regulatory leaching assessments Presented at a workshop in 21 agreed that it would be useful to test the guidance against real datasets 2

3 Background Ian Hardy, Battelle, commissioned by ECPA, fitted 127 datasets Recommendations for revisions of the guidance based on the results Fera peer review funded by CRD Revision of guidance after discussion with CRD, Battelle, ECPA and Jos Boesten, Alterra 3

4 Mass (microg) Concentration (microg/l Experimental protocol OECD 37 laboratory degradation study with additional aqueous extraction step (24 hours) Total mass.3.2 Aqueous concentration

5 Two-site model (PearlNeq) Freundlich K F,EQ 1/n equilibrium sorption Transformation DegT5 Freundlich K F,NEQ 1/n nonequilibrium sorption f NE = Ratio K F Neq :K F Eq Desorption Rate Constant: k des Model fitted to total mass and concentration in aqueous extract Optimisation of 5 parameters (1/n from independent experiment): DegT5 = degradation half-life M p,ini = initial mass of pesticide K OM,EQ = equilibrium sorption coefficient K F,EQ normalised to organic matter f NE = ratio non-equilibrium:equilibrium sorption = desorption rate constant k des

6 Data requirements New studies o Aqueous extraction 24 hours o At least 2 replicates per time point o Samples <2 days after application must be excluded from fitting o First sampling must be between 2 and 3 days after application o Elimination of data < limit of quantification o At least 6 sampling times remaining o At least 1% sorption o Soil-specific Freundlich sorption exponent 1/n

7 Data requirements Legacy studies o Extraction times 8-48 hours acceptable o At least 5 sampling times o First sampling can be later than 3 days after application o Freundlich sorption exponent 1/n can be from other soils

8 Kd (ml/g) Rel. residuals Kd Concentration (µg/l) Rel. residuals conc. Mass (µg) Rel. residuals mass Goodness of fit Aged sorption model; Chi2=1.1 5 Measurements Plot mass and concentration 2. Plot apparent Kd Plot relative residuals (P-O)/O Aged sorption model; Chi2=2.2 Measurements Calculate chi 2 errors 5. Plot sorbed mass in Eq and Neq domain

9 Kd (ml/g) Rel. residuals Kd Concentration (µg/l) Rel. residuals conc. Mass (µg) Rel. residuals mass Goodness of fit Aged sorption model; Chi2=1.1 Measurements Does the model fit mass, conc. and Kd app well? Residuals mass, conc. and Kd app small? No systematic deviations? Aged sorption model; Chi2=2.2 Measurements Chi 2 error for mass and concentration <15%?

10 Kd (ml/g) Rel. residuals Kd (ml/g) Kd Rel. residuals Kd Concentration (µg/l) Rel. Concentration residuals conc. (µg/l) Rel. residuals conc. Mass (µg) Rel. residuals Mass mass (µg) Rel. residuals mass Evidence for aged sorption Aged sorption model; Chi2=1.1 Measurements Equilibrium sorption 5 model; Chi2= Measurements (d) Time (d) Aged sorption model; Chi2=2.2 Measurements Equilibrium sorption 5 model; Chi2= Measurements (d).4.2 Chi 2 error Kd app for aged sorption model -.2 < equilibrium model?

11 Acceptability of the parameters Relative standard error must be.4 (measure of uncertainty in parameter estimate) Corresponds to a 95% confidence interval with a width of ±8% RSE =.4

12 Acceptability of the parameters fne must be <1 k des must be <.5 The fitted K OM,EQ value must not differ from the initial measured K OM,EQ by more than 2%

13 3 possible outcomes for modelling Data requirements pass Goodness of fit pass Evidence of aged sorption pass RSE values.4 pass Acceptable values for Kfeq, fne and kdes pass fail fail fail fail fail Zero aged sorption fne =, kdes = Default parameters fne =.3, kdes =.1 Fitted parameters 13

14 Analysis of ECPA datasets 127 datasets analysed by Battelle 78 datasets did not comply with data requirements (e.g. no replicate measurements, first measurement later than day 3, <6 sampling points, less than 1% sorption) Model fitting on remaining 49 datasets No. of datasets that pass this criterion No. of datasets that fail this criterion Chi 2 error Chi 2 error neq < eq

15 Analysis of ECPA datasets No. of datasets that pass this criterion No. of datasets that fail this criterion This is the only criterion failed in x datasets RSE Mini.4 4 RSE DT5.4 4 RSE Kom.4 4 RSE fne RSE kdes fne < kdes <.5 4 deviation Kfeq ±2%

16 Analysis of ECPA datasets Reason for failing Data requirements, goodness of fit Zero aged sorption 9 and/or evidence for neq sorption RSE, Kfeq or parameter ranges Defaults 13 None Fitted parameters 27 16

17 Higher tier leaching assessment Were 4 or more aged sorption experiments with contrasting soils conducted? yes Did the decision making procedure in Decision Tree 1 result in at least two datasets for which default parameters or fitted parameters can be used? no no Exposure assessment with consideration of aged sorption sorption not possible. yes

18 Higher tier leaching assessment Calculate the 8 th percentile PEC GW with each of the individual parameter sets (fitted, default or zero aged sorption) Calculate the median of the 8 th percentile PEC GW values Calculate the 8 th percentile PEC GW using mean/geomean parameters Report the 8 th percentile PEC GW for each simulation. For information only, not to be used in decision making Compare the larger of the two PEC GW with regulatory trigger value

19 Unanswered questions Is it possible to derive robust aged sorption parameters for metabolites? Is it possible to derive robust aged sorption parameters in field studies? Can we use field degradation parameters in combination with aged sorption? Need for testing reliability of parameter derivation Need for protocol, specific requirements and quality criteria 19

20 Current status PEARLNEQ 5.1 for aged sorption released by Alterra Aged sorption guidance and project report forwarded to EFSA for consideration by PPR panel Guidance will be made available on CRD website but for information only, not for use in regulatory submissions (Discuss with appropriate authority before use) Aged sorption as higher-tier option in draft GW guidance (under consideration by PPR panel at the moment) but recommendations differ and are less comprehensive