1. 1 FOCUS Degradation Kinetics Training course 26-27 January 2005 Regulatory use of degradation endpoints Sylvia Karlsson Swedish Chemicals Inspectorate

2. 2 What are the kinetic endpoints? Parent compounds, soil: DT 50, DT 90 or rate constant, kinetic model Metabolites, soil: DT 50, DT 90 or rate constant, kinetic model, formation fraction Parent and metabolites, water/sediment: DT 50, DT 90 or rate constant, kinetic model, (formation fraction) – for overall system, water column and sediment

3. 3 What are the kinetic endpoints used for? To compare with criteria, triggers for further studies, as provided in Annex II, III and VI of Dir. 91/414/EEC and in Guidance Documents on Aquatic and Terrestrial Ecotoxicology As input to calculations of PECsoil, PECgw, PECsw and PECsed

4. 4 What endpoints are used for different purposes (triggers/PEC)? Use against triggers (parents & metabolites): DT 50 and DT 90 derived by best-fit kinetics (unless deviation from first order kinetics can be attributed to experimental artefact!) Degradation or dissipation endpoints? - Mainly left to users to decide.

5. 5 PECgw, PECsw and PECsed – calculated e.g. by FOCUS simulation tools: DT 50 or rate constant, for metabolites also formation fraction, derived by first order kinetics (1st tier). Data from lab or field studies. Endpoints from field studies must be normalised.

6. 6 PECsoil calculated by spreadsheets or parameter estimation software: DT 50 or rate constant, for metabolites also formation fraction, Endpoints derived by best-fit kinetics. Data from lab or field studies.

7. 7 Average or representative worst-case values? For use against triggers and to calculate PECsoil: Values not averaged (normally!) To calculate PECgw, PECsw and PECsed: Averaged values (normally!)

8. 8 Geometric or arithmetic mean? Rate constants and DT 50 s: Geometric – pragmatic reason: produces equal results Other parameters (e.g., formation fractions): Arithmetic

9. 9 Finally, DT 50 and DT 90 obtained by different kinetic models can be averaged. Specific recommendations are provided for metabolite endpoints and for use of endpoints for calculation of PECgw, PECsw and PECsed when first order kinetics does not provide an adequate fit.