FOCUS Degradation Kinetics Training course 26-27 January 2005 Regulatory use of degradation endpoints

1 Sylvia Karlsson Swedish Chemicals Inspectorate

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 2

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 3

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.

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• 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.

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• 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.

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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!) 7

Geometric or arithmetic mean?

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

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.

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