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

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FOCUS Degradation KineticsTraining course 26-27
January 2005Regulatory 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!)Degradat
  ion 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
  PECsoilValues not averaged (normally!)
• To calculate PECgw, PECsw and PECsedAveraged
  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.