1. Committed since 2002
to ensuring that Europe’s food is safe
Toxicological Relevance of pesticide
metabolites
for dietary risk assessment
ECPA – IBMA- EFSA Workshop
Parma, 26th April 2012

2. Background
Reg. 1107/2008 concerning the placing of
PPPs on the market
requires:
• identification of metabolites
• determination of their “toxicological relevance”
for in/exclusion in the residue definition

3. Background
OECD guidance document on the Definition of
Residue (Series on Pesticides, No. 31; Series
on Testing and Assessment, No. 63):
• Proposes a residue definition for risk assessment, reflecting
the actual toxicological burden consisting of active
substance and relevant metabolites
• Requires a quantitative and qualitative (toxicological)
assessment of metabolites

4. Pesticide metabolites as residues
• In contrast to active substances usually very limited or no
toxicological data available although their toxic potency
and toxicological profile might differ from the parent
compound
• Reference values of parent compounds are applied for
metabolites present in food commodities

5. Assessment tools
Conventional testing of metabolites?
• Number of metabolites
• Difficulties in synthesising sufficient amounts
• Costs
• Research capacities
• Animal welfare concerns

6. Assessment tools
Preparatory Work
• Project on Threshold of Toxicological Concern (TTC)
Concept (CRD, UK)
• Project: Impact of Metabolism on Toxicity
(AGES, Austria)
• 2 projects on (Quantitative) Structure-Activity
Relationships (Q)SAR (JRC, EC)

7. Assessment tools - TTC
Applicability of thresholds of toxicological concern
in the dietary risk assessment of metabolites,
degradation and reaction products of pesticides
(published 24 March 2010)
http://www.efsa.europa.eu/en/supporting/pub/44e.htm

8. Assessment tools - TTC
• Review on the TTC concept and survey on it’s current use
• Validation of TTC for pesticides: Comparison of 100
pesticide ADIs with TTC classification
• Case study with 79 metabolites of 15 selected pesticides
Conclusions:
• TTC appropriate for assessment of metabolites
• Exposure to metabolites considered to be covered by TTC
thresholds allocated – critical is the genotoxicity threshold
• QSARs predictions for genotoxicity considered reliable

9. Assessment tools – Impact of Metabolism
Impact of metabolic and degradation processes on
the toxicological properties of residues of pesticides
in food commodities
(published 6 May 2010)
http://www.efsa.europa.eu/en/supporting/pub/49e.htm

10. Assessment tools – Impact of Metabolism
• Review of transformation pathways (11 pesticide classes) and
comparison with toxicity data (DARs, public literature)
• Based on lack of other information analyses largely based on acute tox
studies
• 140 chemical changes identified – no clear tendency for
toxification/detoxification
Conclusions:
• Toxification/detoxification cannot be attributed to certain metabolic
steps (Conjugates not necessary less toxic due to cleavage)
• Metabolite > 10% to be considered as contributing to toxicity
• Metabolites found in livestock should be considered as present in rat
• Improvement of ADME studies (more accuracy, more information)
necessary

11. Assessment tools - QSARs
Applicability of QSAR analysis to the evaluation of
the toxicological relevance of metabolites and
degradates of pesticide active substances for
dietary risk assessment
(published 7 May 2010)
http://www.efsa.europa.eu/en/supporting/pub/50e.htm

12. Assessment tools - QSARs
• Review on the use of QSAR for regulatory purposes
• Extensive evaluation of potentially useful QSARs:
(e.g. Toxtree, Lazar, Derek, Hazard Expert, Caesar, Topkat)
using different data sets (Pesticide metabolites, EU classified
substances, CPDB) for all relevant toxicity endpoints
• Case studies focused on genotoxicity based on the outcome
of the TTC project

13. Assessment tools - QSARs
Conclusions:
• Currently limited use of QSARs for regulatory purposes
• Recommendations for the application of different models
covering all relevant toxicological endpoints
• Recommendations for further research
• Combination of models recommended to optimise
sensitivity and specificity in regard to genotoxicity

14. Assessment tools - QSARs
• Refinement of proposed assessment approach
based on chronic TTC levels for metabolites having
effects upon acute exposure
• Acute reference doses mainly triggered by
reprotoxicity, developmental effects and
neurotoxicity

15. Assessment tools - QSAR
Applicability of QSAR analysis in the evaluation of
developmental and neurotoxicity effects for the
assessment of the toxicological relevance of
metabolites and degradates of pesticide active
substances for dietary risk assessment
(published 16 June 2011)
http://www.efsa.europa.eu/en/supporting/pub/169e.htm

16. Assessment tools - QSAR
• Evaluation of QSAR models (Derek, Caesar, Topkat,
Leadscope, Hazard Expert, PASS, ADME predictor, Accord)
and read across (OECD toolbox) for assessment of
reprotoxicity , developmental effects and neurotoxicity
Conclusions:
• No appropriate QSAR models or neurotoxicity identified
• Stepwise approach for developmental effects
reprotoxicity combining read across and QSAR might be
promising

17. Draft Scientific Opinion – Residue Part
Chapters:
• Residue definition - terminology
• Comparison residue definition (EFSA vs. JMPR)
• Analytical methods
• Relevant metabolites
• Types of exposure scenarios (focus on acute and
chronic for MRL setting for case studies – limited
data on metabolites; worst case assumption of
parent/metabolite ratio to cover highest possible
risk)

18. Draft Scientific Opinion – Residue Part
Chapters:
• Estimation of metabolite levels (STMR for chronic,
HR for acute for case studies)
• Calculation of acute/chronic exposures (UK NEDI
and NESTI used for case studies)
• Conversion factors
• Decision tree for exposure assessments
• Critical issues/Uncertainties
• Appendices (Selected examples for residue definitions
and differences EU/JMPR, parent/metabolite ratio; case
studies for metabolite estimations and allocated TTC
values)

19. Draft Scientific Opinion –
Toxicology Part
Chapters:
• Projects on Impact of Metabolism, TTC and
QSARs - Evaluation of PPR Panel
• Derivation of acute exposure thresholds (TTC)
• Toxicity assessment scheme for acute and for
chronic exposure
• Testing strategy for determination of relevance
of metabolites
• Critical Issues/Uncertainties
• Appendices (Checklist for use of QSARs, data for acute
TTC)

20. Draft Scientific Opinion – Isomer Part
Extension of the mandate including assessment of
isomers (September 2011)
In order to:
• investigate if the approaches proposed for
assessment of metabolites are applicable for
isomers
• identify specific issues, suitable methodologies,
research needs for isomers

21. Draft Scientific Opinion – Isomer Part
Chapter:
• Isomer terminology
• Current approaches for assessment
• Analytical methods
• Suitability of assessment tools for isomers
• Exposure assessment for isomers
• Specific issues to be addressed
• Research needs

22. Scientific Opinion
Next steps:
• Adoption of Scientific Opinion (June 2012)
• Preparation of Guidance

23. PPR Working Group Members:
Bernadette Ossendorp, Anita Stroemberg, Claudia
Bolognesi, Alan Boobis, Rebecca Scrivens, Maria
Tasheva, Markus Mueller, Christiane Vleminckx,
Susanne Hougaard Bennekou, Karen Hirsch-Ernst
Pesticides Unit: Luc Mohimont, Istvan Sebestyen,
Manuela Tiramani, Hans Steinkellner

24. Thank you!