Time is of the essence!

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Time is of the essence! Tjalling Jager Dept. Theoretical Biology

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Time is of the essence!. Tjalling Jager Dept. Theoretical Biology. Challenges of ecotox. Some 100,000 man-made chemicals For animals alone, >1 million species described Complex dynamic exposure situations Species interact dynamically in ecosystems - PowerPoint PPT Presentation

Transcript of Time is of the essence!

Page 1: Time is of the essence!

Time is of the essence!

Tjalling Jager

Dept. Theoretical Biology

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Challenges of ecotox

Some 100,000 man-made chemicals For animals alone, >1 million species described Complex dynamic exposure situations Species interact dynamically in ecosystems

We cannot (and should not) test all permutations!

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Extrapolation

“Protection goal”

Laboratory tests

time is of the essence!

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concentrations over time and

space

environmental characteristics and emission pattern

Fate modelling

mechanisticfate model

physico-chemical properties under laboratory conditions

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Fate modelling

oil-spill modelling

pesticide fate modelling

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prediction effects in dynamic

environment

Classic ecotox

effects data over time for one (or few) set(s) of conditions

Description for:• one endpoint• one timepoint• constant exposure• one set of conditions

Description for:• one endpoint• one timepoint• constant exposure• one set of conditions

EC50NOEC

summary statistics

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proper measures of

toxicity

Learn from fate modelling

effects data over time for one (or few) set(s) of conditions

that do not depend on time or conditions

prediction effects in dynamic

environment

mechanisticmodel forspecies A

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model parameters for

species

test conditions

Data analysis

mechanisticmodel forspecies A

effects data over time for one (or few) set(s) of conditions

model parameters that do not depend on time or conditions

model parameters for

toxicant

life-history information of the species

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prediction life-history traits

over time

model parameters for

species

model parameters for

toxicant

Educated predictions

mechanisticmodel forspecies A

dynamic environment: exposure and

conditions

only for one species ... model parameters that do not depend on time or conditions

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mechanisticmodel forspecies B

model parameters

for species A

model parameters for toxicant

Community effects

mechanisticmodel for

a community

simulate community effects and recovery over time

mechanisticmodel forspecies A

dynamic environment

model parameters

for species A

model parameters for toxicant

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What individual model?

mechanisticmodel forspecies A

dynamic environment

model parameters

for species A

model parameters for toxicant

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externalconcentration

(in time)

toxico-kineticmodel

toxico-kineticmodel

TKTD modelling

internalconcentration

in time

process modelfor the organism

process modelfor the organism

effects onendpoints

in timetoxicokinetics

toxicodynamics

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externalconcentration

(in time)

toxico-kineticmodel

toxico-kineticmodel

TKTD modelling

internalconcentration

in time

toxicokinetics

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TKTD modelling

internalconcentration

in time

process modelfor the organism

process modelfor the organism

effects onendpoints

in time

toxicodynamics

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Organisms are complex …

process modelfor the organism

process modelfor the organism

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Learn from fate modellers

Make an idealisation of the system how much biological detail do we minimally need …

– to explain how an organism grows, develops and reproduces– to explain effects of stressors on life history– to predict effects for untested situations– without being species- or stressor-specific

internalconcentration

in time

process modelfor the organism

effects onendpoints

in time

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Dynamic Energy Budget

Organisms obey mass and energy conservation– find the simplest set of rules ...– over the entire life cycle ...– for all organisms (related species follow related rules)– most appropriate DEB model depends on species and question

resources

waste products

growth

maintenance

maturation

offspring

Kooijman (2010)

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The “DEBtox” concept

externalconcentration

(in time)

toxico-kinetics

toxico-kinetics internal

concentrationin time DEB

parametersin time

DEBmodel

DEBmodel

repro

growth

survival

feeding

hatching

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The “DEBtox” concept

externalconcentration

(in time)

toxico-kinetics

toxico-kinetics internal

concentrationin time DEB

parametersin time

DEBmodel

DEBmodel

Internal concentration are often not measured …

repro

growth

survival

feeding

hatching

…DEB parameter cannot be measured …

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“Standard” tests ...

mechanisticmodel forspecies A

constant exposure, ad libitum food

Many DEBtox examples, e.g.: http://www.bio.vu.nl/thb/users/tjalling

model parameters for

species

model parameters for

toxicant

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Dynamic exposure

mechanisticmodel forspecies A

dynamic exposure pattern,different food levels ...

Daphnia magna and fenvalerate– modified 21-day reproduction test– pulse exposure for 24 hours– two (more or less) constant food levels

Pieters et al (2006)

model parameters for

species

model parameters for

toxicant

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Pulse exposure

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Body length Cumulative offspring Fraction surviving

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mode of action: ‘assimilation’mode of action: ‘assimilation’

Insights• parameters independent of food• chemical effects fully reversible• reproduction rate slows down …

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mechanisticmodel forspecies B

Work needed

For the individual level– select relevant species and appropriate DEB models– adapt/develop model code, allow time-variable inputs– collect and analyse relevant existing test data

Evaluate– are DEB models useful?– what are limitations?– what are major gaps in knowledge?– what test protocol is most useful?

mechanisticmodel forspecies A

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Community level

What makes community different?– dynamic interactions between species– less or more sensitive to toxicants?

mechanisticmodel for

a community

mechanisticmodel forspecies A

mechanisticmodel forspecies B

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Community level

Food web models can become rather complex …– results depend heavily on modelling choices– difficult to parameterise– focus on furry animals …– little general insight gained– not useful for generic RA

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Canonical community

Start simple:– each species a simple DEB model– closed system (open for energy)– include nutrient recycling

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Canonical community

producer

consumer

nutrients

decomposer detritus

light

predator

Start simple:– each species a simple DEB model– closed system (open for energy)– include nutrient recycling

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consumer

predatordecomposer detritus

Using the DEB community

producernutrients light

previous project at VU-ThB (EU-MODELKEY)collaboration with SCK-CEN, Belgium (EU-STAR)

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lightproducer

Using the DEB community

consumer

predatordecomposer

nutrients

detritus

previous collaborations, e.g., Univ. Antwerp (EU-NoMiracle, EU-OSIRIS)collaboration with UFZ, Leipzig (EU-CREAM)

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detritus

consumer

lightproducer

Using the DEB community

decomposer

nutrients

collaboration with Eawag, Switzerland (EU-CREAM)collaboration with IRSN, France

predator

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detritus

consumer

lightproducer

Using the DEB community

decomposer

nutrients

previous projects at VU-ThB

predator

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Work needed

For the community level– specify interactions between the species– code a community with DEB populations– simulations for various scenarios

Evaluate– what’s different at the community level?– more or less effect?– correspondence to e.g., mesocosm?– identify major gaps in knowledge

mechanisticmodel for

a community

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Wrapping up

Time is of the essence!– an organism is a dynamic system …– that interacts dynamically with others …– in a dynamic environment …– with dynamic exposure to chemicals

NOEC, EC50 etc. are useless …

time is of the essence!

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Wrapping up

Mechanistic models essential for the individual– to extract time-independent parameters from data– to extrapolate to untested dynamic conditions– to increase efficiency of risk assessment– learn from fate and toxicokinetics modellers …

Integrate models into a simple community– study how interactions affect toxicant responses– study recovery of the community

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Wrapping up

Advantages of using DEB as basis– well-tested theory for individuals– mechanistic, dynamic, yet (relatively) simple– deals with the entire life cycle– not species- or chemical-specific– small but well-connected international DEB community

resources

waste products

growth

maintenance

maturation

offspring

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Wrapping up

This project tries to deliver “proof of concept”– can DEB serve as a general platform?– can simple mechanistic community models help RA?– how can we modify test protocols?– where are the major stumbling blocks?

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More information

on DEB: http://www.bio.vu.nl/thb

on my work: http://www.bio.vu.nl/thb/users/tjalling

time is of the essence!

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Ex.1: maintenance costs

time

cum

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tive

off

spri

ng

time

bo

dy

len

gth

TPT

Jager et al. (2004)

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Ex.2: growth costs

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bo

dy

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gth

time

cum

ula

tive

off

spri

ng Pentachlorobenzene

Alda Álvarez et al. (2006)

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Ex.3: egg costs

time

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tive

off

spri

ng

time

bo

dy

len

gth

Chlorpyrifos

Jager et al. (2007)