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FOCUS Degradation KineticsTraining course 26-27 January 2005

Regulatory use of degradation endpoints

Sylvia Karlsson Swedish Chemicals Inspectorate

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What are the kinetic endpoints?

• Parent compounds, soil: DT50, DT90 or rate constant, kinetic model

• Metabolites, soil: DT50, DT90 or rate constant, kinetic model, formation fraction

• Parent and metabolites, water/sediment: DT50, DT90 or rate constant, kinetic model, (formation fraction) – for overall system, water column and sediment

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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

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What endpoints are used for different purposes (triggers/PEC)?

• Use against triggers (parents & metabolites): DT50 and DT90 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:

DT50 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:

DT50 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!)

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Geometric or arithmetic mean?

• Rate constants and DT50s: Geometric – pragmatic reason: produces equal results

• Other parameters (e.g., formation fractions): Arithmetic

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Finally,

• DT50 and DT90 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.