3.2 substance parameters - uni koblenz-landau · substance parameters degt50, dt50 time taken for a...

Substance parameters–

Degradation in soilDegradation in water/sediment

Sorption

SubstanceSubstance parametersparameters


E-Fate Parameter

• Degradation / dissipation DegT50, DT50

� derived from kinetic evaluations of soil degradation / field dissipationstudies or from water-sediment studies

• Sorption Kfoc, 1/n

� estimated from batch-equilibriumstudies

• Phys-chem data


DegT50, DT50

Time taken for a 50% decline in mass or concentration of a substance to occur from

• degradation -> DegT50

• dissipation processes -> DT50� does not distinguish between transfer or

degradation processes� summarizes diff. processes such as degradation,

volatilization, photolysis, leaching etc.

Recommendations on how to derive endpoints that can be used inenvironmental fate models were provided by the

FOCUS Working Group on Degradation Kinetics*

Recommendations regarding

• Data issues• Kinetic models• Quality criteria for kinetic fits• Procedure to derive endpoints• Recommendations on the selection of endpoints

* FOCUS (2006). “Guidance document on Estimating Persistence and Degradation Kinetics from

Environmental Fate Studies on Pesticides in EU Registration. EC Document Reference SANCO/10058,

version 2.0, June 2006.


Kinetic models

• SFO single first order model

• FOMC first order multi compartment model

• DFOP double first order in parallel model

• HS hockey stick model or Gustafson-Holden model


Single first order (SFO) kinetic model

kdDT

)2ln()(50 =

tkeCC ⋅−⋅= 0

C concentration at time t C0 concentration at time 0 (mg/kg)k degradation rate (1/d)t time


FOMC

First Order Multi Compartment Modell

HSHockey Stick Modell

DFOPDouble First Order in Parallel

DT50 (FOMC) Pseudo-SFO

DT50: DT90/3.32Two consecutive SFO DT50:

slow phase and fast phase

Two parallel SFO DT50:

slow phase and fast phase

Plots of bi-phasic and multi-compartment models


SFO

one single dissipation process

FOMC

several parallel dissipation processes

HS (bi-phasic)two consecutive dissipation processes

DFOP (bi-phasic)

two parallel dissipation processes

Concepts of different kinetic models


Assessment of thegoodness of fit by

• Chi² test• Visual assessment

Assessment of thereliability of theparameter estimate by

• t-test (significance test)


Example of a pathway fit (parent + metabolite) conducted using the KinGui tool

Tools:

• ModelMaker• KinGUI• others

Results:

• k-rates (dissipation rates),• other model parameters in case of non-SFO models

from which DegT50/DT50 values can be calculated


Normalisation of degradation rates (temperature, soil moisture)

Temperature and soil moisture have an influence on the degradation rate (warm temperature and maximum soil moisture represent optimum conditions for degradation)

Surface water and groundwater tools correct degradation rates according to the temperature profile of the scenario.� DegT50/DT50 at reference conditions are needed as model input

Reference conditions used in the groundwater and surface water models: Temperature = 20°CSoil moisture = 100% FC (field capacity)

� DT50 values from experimental data need to be normalised to these reference conditions.


Temperature correction (Arrhenius approach)

Moisture correction (Walker-equation)

10/)20(

1050)20(50CT

QDegTCDegT°−

⋅=°

7.0

Θ

Θ=

ref

f

Θ soil moisture during the experimentΘref reference soil moisture at 100% field capacity


Temperature and

moisture

normalisationequations

Q10 = 2.58 (EFSA, 2007)

Example temperature correction:

DT50 measured at 25°C: 50 dayscorrection factor: 1.61DT50 normalised to 20°C: 80.5 days

Example moisture correction:

DT50 measured: 50 daysSoil moisture during study: 17%Soil moisture at 100% FC: 30%correction factor: 0.67DT50 normalised to 100% FC: 33.5 days


Substance parameter

- Degradation in water sediment -

P-I levelone-compartment approach

�DT50 water�DT50 sediment�DegT50 total system

P-II level

two-compartment approach

�DegT50 water

�DegT50 sediment

Kinetic concepts of parent disappearance in water-sediment


M-I levelone-compartment approach

�DT50 water

�DT50 sediment�DT50/DegT50 total system

Kinetic concepts of metabolite disappearance in water-sediment

M-II levelTwo-compartment approach

Theoretically comprising

water and sediment forparent and metabolite (includingbacktransfer from sediment to water)

Not recommended by FOCUS

due to high level of complexity


Modelling endpoints vs. persistence endpoints

Modelling endpoint:SFO or Pseudo-SFO DT50 to be used in surface water (and groundwater) models

Persistence endpoint:best fit DT50 to determine whether further studies are triggered

If best fit is FOMC � use pseudo DT50 = DT90/3.32 for modellingIf best fit is DFOP � use slow phase DT50 for modelling


Recommendation for the use of modelling endpoints for

parent compounds

FOCUS (2006)


Recommendation for the use of persistence endpoints

for parent compounds

FOCUS (2006)


FOCUS (2006)


Substance parameter

- Sorption, Phys-chem data -

Sorption behaviour

• Adsorption/desorption: substance reversibly binds to soil compounds (clay, organic carbon)

• Ads/des is measured in batch equilibrium studies (OECD 106) � Kd values(distribution of a substance between the equilibrium solution (water) and soil / sediment particles)

� Sorption depends on

• Soil properties (organic carbon content, pH, texture etc.)

• Substance properties

Groundwater and surface water models generally require an organic carbon related sorption value for a substance as model input.

� Koc values


Sorption behaviour: Koc

• high Koc (eg 200 mL/g) = strong sorption to soil or sediment particles

low risk of leaching to groundwater or drainage systems

higher risk of runoff loss

• low Koc (eg 20 mL/g) = low sorption to soil or sediment

high risk of leaching to groundwater or drainage systems

low risk of runoff loss


Sorption behaviour: Freundlich exponent

The Freundlich exponent (1/n) describes the linearity of the sorptionbehaviour

• 1/n = 1 � linear sorption

• 1/n < 1 �� non-linear sorption

usually 1/n values are in a range of 0.7 to 1

Current default values used for modlling in the absence of Freundlich sorption data:

1 if only one concentration was measured

0.9 if non-linearity can be expected


OC

KK F

FOC =

OC organic carbon (-) OM organic matter

n

eqFS CKC/1

⋅=

724.1

FOC

FOM

KK =

CS concentration adsorbed (kg/kg)Ceq concentration in the solution (kg/L)

1/n Freundlich exponentKF Freundlich sorption coefficient (L/kg)

Freundlich sorption isotherm


Phys. – chem. Parameters

• Molar mass (g/mol)

• Solubility in Water (g/L)

• Henry Constant (Pa x m3 / mol)

• Vapor pressure (Pa)


Data selection

• Degradation data � geometric mean values

� default in the absence of reliable data: 1000d

• Sorption data � arithmetic mean values

� default 1/n: 0.9

1 in case of linear sorption

• Phys-chem data � as reported

� for metabolites: estimated data (EPI WIN)

parent data



PEC actual and time weighted

Regulatory Assessment Endpoints

E-Fate Parameters necessary for calculation

Study Types

PECsoil

TERs of soil organisms

- Half Lives in soil - formation fraction of metabolites - incubation conditions

- DT50/DT90 (rate studies) - aerobic soil metabolism - field dissipation - field leaching . . .

PECsw TERs of water organims

- Half in water phase - formation and dissipation rates in the water phase - dissipation rates by aqueous photolysis

- Water/Sediment - aqueous photolysis - sensitized photolysis - mesocosm . . .

PECsediment TERs of sediment organims

- formation/binding onto and dissipation rates in the sediment

- Water/Sediment Study - mesocosm . . .

PECgroundwater 0.1 µg/l level on an annual basis

see PECsoil - Sorption

see PECsoil - lysimeter - adsorption/desorption . . .

Substance parameters

- End of input parameter module -

3.2 substance parameters - uni koblenz-landau · substance parameters degt50, dt50 time taken for a...

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