1. Biology-Based Modelling Tjalling Jager Bas Kooijman Dept. Theoretical Biology

2. Contents  Current procedures in (eco)tox  Biology-based methods  A glimpse into the future?  Workshop announcement

3. “RISK” Risk assessment EXPOSURE EFFECTS Available dataAssessment factor Three LC50s1000 One NOEC100 Two NOECs50 Three NOECs10

4. Integrated model for system Integrated model for system Process parameters at env. conditions Process parameters at env. conditions PEC Lab. experiments Exposure assessment Extrapolation to e.g.: different compartment sizes different temperature time-varying emissions

5. Effects assessment PNEC Lab. experiments

6. Contr. Analysing test data NOEC Response log concentration * 1. Statistical testing

7. Analysing test data EC50 Response log concentration 1. Statistical testing 2. Regression

8. Limitations Practical problems as summary statistic –NOEC has received serious criticism –ECx and NOEC change with exposure time

9. EC10 changes in time survival body length cumul. reproduction body length cumul. reproduction 05101520 0 0.5 1 1.5 2 2.5 carbendazim time (days) 0246810121416 0 20 40 60 80 100 120 140 pentachlorobenzene time (days) Alda Alvarez et al., 2006 (ES&T)

10. Limitations Practical problems as summary statistic –NOEC has received serious criticism –ECx and NOEC change with exposure time Not all data are used –only data at last time point –test protocols prescribe more time points –in some cases, more endpoints available

11. Survival dichlorobutene 0 5 10 15 20 0.010.11 concentration (mM/L) survival 1-3 days 4 days Data from Geiger et al., 1985

12. Reproduction phenol 9-20 days 21 days 0 20 40 60 80 100 120 0.010.1110 concentration (mg/L) total eggs/female Further available - survival data - possibly body weight Data from OECD ring test

13. Limitations Practical problems as summary statistic –NOEC has received serious criticism –ECx and NOEC change with exposure time Not all data are used –only data at last time point –test protocols prescribe more time points –in some cases, more endpoints available No biological mechanism –selected curve for ECx is descriptive –limits analysis of non-standard data (e.g. degradation) –limits extrapolation to other scenarios …

14. process parameters? integrated model? Effects assessment Assessment factor Regression or statistical test Regression or statistical test Lab. experiments Available data Assessment factor Three LC50s1000 One NOEC100 Two NOECs50 Three NOECs10 Extrapolation to e.g.: different body sizes? different temperature? time-varying exposure? populations? PNEC

15. Biology-based modelling

16. Biology based methods OECD recommendations (1996) –NOEC is inappropriate and should be phased out –incorporate exposure time in data analysis –favour mechanistic models if they fit the data ISO and OECD guidances (2006) –statistical analysis of ecotoxicity data –biology-based methods included next to standard methods

17. Biology based methods exposure concentration effects in time toxicokinetics internal concentration toxicodynamics calculated by fate models e.g. one-comp. model or PBPK e.g. DEB model

18. Dynamic Energy Budgets (DEB) growth reproduction assimilation maintenance DEB provides simple rules for resource acquisition and allocation

19. Effect of toxicants in DEB blank value internal concentration DEB parameter NEC Potential targets probability to die maintenance costs assimilation costs for growth costs for reproduction death of embryos

20. DEBtox  Currently only method with general applicability –combines toxicokinetics and -dynamics –analysis of all regular ecotox endpoints –data from standard OECD protocols  Large body of literature over last 10+ years  Windows software –version 1.0 in 1996, version 2.0.1 in 2004 –freely downloadable

21. Windows version Only for standard tests –acute survival –Daphnia reproduction –fish growth –algal population growth

22. Example: Hexachlorobutadiene Fitting 4 parameters for entire data set No-effect concentration: NEC = 0.13 (0.091-0.16) Data from Geiger et al., 1985

23. Example: Hexachlorobutadiene 020406080100 0 0.2 0.4 0.6 0.8 1 external concentration (mol/L) time (hours) LC0 LC10 LC25 LC50 NEC iso-effect lines

24. Example: Phenol Fitting 4 parameters for entire data set MoA: ‘costs for growth’ NEC = 0.82 (0.52-0.91) Data from OECD ring test

25. Example: Phenol 5101520 time (days) 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 external concentration (mg/L) EC0 EC10 EC25 EC50 NEC iso-effect lines

26. Advantages  Make efficient use of all data points in time –more accurate parameter estimates –reduce number of test animals  Extract more information from same data –kinetic information on toxicity (e.g., ECx at any time point) –physiological mode of action (for population response)  Yield a more robust summary statistic –time-independent NEC may replace NOEC and ECx Using standard test data …

27. Advantages  Fit non-standard data –loss of compound from test system –limited tests (single dose, no control, one indiv. per dose) –no need to discard existing test data  Simultaneous fit on multiple data sets –more endpoints (life-cycle toxicity) –different compounds: mixture toxicity  Educated extrapolations –intermittent exposure, food limitation, population etc. –between compounds (QSARs), between species … Furthermore …

28. A glimpse into the future?

29. Characterisation of impacts? PEC/PNEC EXPOSURE EFFECTS EXPOSURE EFFECTS “IMPACTS”

30. Example  Daphnia magna exposed to Cd  Test based on OECD repro test –15 days –survival and offspring daily –body weight at end of test Data from Heugens et al., 2006 (ET&C) Analysis in Jager et al., 2006 (Ecotox)

31. 0246810121416 0 0.2 0.4 0.6 0.8 1 survival 051015 0 20 40 60 80 100 120 reproduction body size Mode of action Cd decreases assimilation Mode of action Cd decreases assimilation Simultaneous fits

32. Extrapolations 00.050.10.150.2 0 0.1 0.2 0.3 0.4 concentration population growth rate (1/day) PEC impact NEC ecologically relevant time independent integrates endpoints

33. Extrapolations 00.050.10.150.2 0 0.1 0.2 0.3 0.4 concentration population growth rate (1/day) NEC impact PEC impact ecologically relevant time independent integrates endpoints compare chemicals PEC

34. Extrapolations 00.050.10.150.2 0 0.1 0.2 0.3 0.4 concentration population growth rate (1/day) 90% food 80% food

35. Matching release scenario time exposure time survival time emission

36. Announcing a workshop  There is potential for improvement of RA with biology-based methods  Biology-based methods are available and described by ISO and OECD http://www.bio.vu.nl/thb/deb Workshop organised by ECB –introduce these methods to regulatory community –discuss potential for implementation –planned for 2 days in week of 4-8 June 2007