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Environmental Exposure Assessment Environmental Fate Processes and Exposure
Modelling
Michael Matthies
Institute of Environmental Systems Research
University of Osnabrück, D-49069 Osnabrück
E-mail: matthies@uos.de
USF
Content
Introduction Basic Assumptions Environmental Fate Processes
- Partitioning- Transport- Transformation
Single Medium Modelling Intermedia Exchange Processes Multimedia Modelling Application and Applicability (Refined Approach)
Risk assessment
Effects assessmentExposure assessment
Risk characterisationRisk = f(Exposure,Effects,Probability)
Risk management
PEC
PEC / PNEC 1 ?
PNEC
Exposure ModellingAn exposure model converts a mass load [kg/a] into an
environmental concentration (PEC) [kg/m3].
Release estimation
Physico-chemical properties
Environmental fate processes
Exposure Model
Predicted Environmental Concentration (PEC)
Release, Distribution and Fate
Primary environmental
medium
Multimedia environment
Water
Air
Soil
Biota
Anthropo-sphere
Release Distribution
Local Scale Regional to global scale
Point or diffuse release
Environmental media can be defined in such a manner as to represent phases or mixtures of phases in a thermodynamic sense.
Rules and laws of chemical equilibrium and kinetics can be applied to environmental systems.
Feedback of toxic effects on organisms on the chemicals’ fate is neglected.
No mixtures, only single compounds are considered. Interaction between components of mixtures are therefore also not regarded.
Usually, only molecular-dispersively dissolved compounds and no separate phases of compounds are considered.
Environmental Fate Process ModellingBasic assumptions
Environmental Fate Processes
An environmental fate or chemodynamic process is the quantitative or qualitative change of a substance with time due to environmental factors. This can be a change of- mass,- concentration, - chemical structure, or- any substance property.
Chemodynamic points out the dynamic nature of processes involved.
Environmental Fate Processes
Partitioning- partitioning between two phases, e.g. air and water,- ad/desorption on particles,- uptake into lipid phases.
Transport- mixing and dilution,- ad/convection, - diffusion,- dispersion.
Transformation- photolysis and photochemical degradation,- hydrolysis,- microbial biotic degradation- metabolic transformation.
Partitioning
Environment is divided into non-mixable phases— Air, surface water, soil, sediment, ground water, plants, etc.
— Chemicals are partitioning into all or several phases in thermodynamic equilibrium.
Partition coefficients— partitioning of a substance between two phases.
— dependent on substance and phase properties.
— partition coefficient phase i and j:
j
iij C
CK
KOAKAW
KOW
Lipids (octanol)
Air
Water
Interdependence of physical-chemical properties
m olar m assM
m elting pointM P
air-waterpartition ing
K AW
octanol-waterpartition ing
K OW
watersolubility
W S
vapourpressure
VP
org. C -waterpartition ing
K OC
TRWS
MVP
TR
HenryKAW
1
KKmolJlmg
molgPa111
1 1
Transport and transformation processes
Diffusion— microscopic (molecular) isotropic random movement and mixing of
molecules (Brown’s molecular movement)
— based on 2nd law of thermodynamics (entropy)
— property of the molecule and the surrounding medium
Advection— directed flow of a medium, e.g. water or air flow
— based on 1nd law of thermodynamics (energy conservation)
— e.g. a substance is transported downstream by the flowing of a river
Dispersion— macroscopic flow dynamic process, occurs only in moving media
— orders of magnitudes faster than diffusion
— turbulent mixing (eddy diffusion)
Transport and Transformation Processes
diffusion/dispersion2
2
2
2
)(x
CDD
x
CD
t
CDispDiff
advectionx
Cu
t
C
degradation 1. orderCt
C
combinationof all processesC
x
Cu
x
CD
t
C
2
2
Fate processes in water
advection
volatilisationdischarge
deposition of particles (sedimentation)
degradation
Fate processes in water
Sorbed and dissolved fraction— deposition of particles (only sorbed fraction)
— volatilisation (only dissolved fraction)
— bioconcentration (only dissolved fraction)
Bioconcentration in fish— regression model:
— no biomagnification
fW = f (particle concentration, OC-content, KOC)
10log672,4log74,2log20,0
6log170,0log85,0log
2OWOWOW
OWOW
KKK
KKBCF
BCFCC WasserFisch
Example: Bioconcentration
Mass Distribution in the System Fish - Water
1,6
98,4
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350 400
time (h)
KFW = 60____ k1 = 0.0001 1/h___ k2 = 0.006 1/h
--- k1 = 0.001 1/h--- k2 = 0.06 1/h
Water
Fish
Fate processes in water
Volatilisation— diffusive mass transfer between air and water
— two-films theory
— two serial resistances
Sedimentation— (effective) sedimentation velocity of particles
— diffusive mass transfer into sediment pore water
— sediment burial
Degradation— hydroloysis
— aquatic photolysis
— microbial degradation
Fate processes in air
atmospheric discharges— area sources (e.g. urban area or pesticide spraying)
— multi-point sources (e.g. stack or vent)
gas-particle distribution— sorption of gaseous compounds to particles
— dry and wet deposition of gaseous and particle-bound fraction
— Pankow-Junge equation:
— calculated particle-bound fraction:
Benzene: 0%, DEHP: 5%, TCDD: 32%, OCDD: 99%
VPL vapour pressure of sub-cooled liquidc Junge-‘constant‘ (ca. 17 [Pacm])s particle surface (ca. 1,5E-6 [cm²/cm³])scVP
scf
LPa
Fate processes in air
xyzxyvyzu
IC
dep
concentration = input / (advection + deposition + degradation)
Degradation
Deposition
Advection
Input (Area Emission)
x
z
y
stea
dy st
ate!
Fate processes in soil
Three input scenarios— puls input
— continuous substance input
— contaminated upper soil layer
Analytical solution— homogeneous vertical soil profile
— average continuous water input and output (generic scenario)
— water flow u and hydrodynmanic D are constant
— u.v.a.
Mathematical model
Cz
CD
z
Cu
t
C
2
2
z
Precipitation and evaporation
degradation
diffusion unddispersion
advectionu
D
Leaching
Plant model
Above ground plant parts
roots
degradation and growth
diffusion soil/roots
Wet and dry particle deposition
gaseous exchange
stem leaves
fruit
roots
Plant uptake model in EUSES
Cl8
Cl7
Cl4
Cl6 Cl5
Cl6
Cl6
28
180
52
153
101
1,E-10
1,E-09
1,E-08
1,E-07
1,E-06
1,E-05
1,E-04
1,E-03
1,E-10 1,E-09 1,E-08 1,E-07 1,E-06 1,E-05 1,E-04 1,E-03
Predicted conc. [mg/kg]
Me
asur
ed
conc
. [m
g/k
g]
TC D D -H xC D D
PC B 28-52PC B 101-180
H pC D DO C D D
med
ian
max
min
Transport for Multimedia Pollutants
Water
Sediment
Surface soil
Air
Root-zone soil
Roots
Leaves
Deep soil
Gases
Particles
— A compartment (or box) is a well-mixed component of a system.
— Differential mass balance: change of mass = dm/dt = Input - Output;
— linear differential equations e.g. dm1/dt = - k1m1 + k2m2 + I
— A multi-compartment model consisting of various different environmental media is a multimedia model.
Multimedia Exposure ModellingMass Balance Approach
m1 m2I
fat(octanol)
KOAKAW
KOW
air
water
Equilibrium and steady state
equilibrium— thermodynamic equilibrium in closed system
— immediate equilibration in open system
steady state in open systems— no mass change with time: dm/dt = 0
— Input = Output
I O
Unit World— generic global environment
— 1 km² area, 6 km height, 70% water, 30% soil
Fugacity concept— introduced for real gases to account for molecular interactíons; applied to all
other environmental media
— escaping tendency of a chemical
— dependency of partition coefficients on fugacity
(in equilibrium)j
i
jj
ii
j
iij Z
Z
Zf
Zf
C
CK
concentration = fugacity • fugacity capacitymol / m³ = Pa • mol / (m³ Pa)ZfC
Multi media models (Mackay,1991)
I
II
III & IV
Multi media models Level I - IV
Closed system:phase equilibrium (partition coefficients)
Open system:same as Level I but with advective input and output and degradation in steady-state
Open system:same as Level II but with interphasemass transfer non equilibriumLevel III: steady-stateLevel IV: non steady-state
fish
air
water
soil
sediment
plants
Multi-media models Form the environment to compartments
Background— ubiquitous occurrence of chemicals
— virtually all chemicals are distributed over various media due to advection and dispersion with wind and water partitioning between phases
Multi media modelwith 4 compartments (Unit World)
Water0.7 km² • 10 m= 7 • 106 m³
Sediment0.7 km² • 3 cm= 2.1 • 104 m³
Soil0,3 km² • 15 cm= 4.5 • 104 m³
Air1 km² • 6 km= 6 • 109 m³
Illustration of Level I and II model
f = fugacityZ = fugacity capacityV = volume
C = f·ZM = C·V = f·Z·V
Input
air water soil
Z
Output
Level I: no input and outputLevel II: with input and output
Multi-media modelsLevel I example calculation (Unit World)
2,3,7,8 - TCDD LAS BENZENE
MW [g/mol] 322 348 78
logK OW [-] 6,8 2,0 2,1
VP [Pa] (25°C) 2,0E-07 0 12.700
WS [mg/l] (25°C) 1,9E-05 1.100 1.760
results [%]
Sediment Soil Water Air
run off
diffusionemission degradation
Natural soil
Air
Agricultural soil Industrial soil
Sediment
Water
Regional scale
Continental scale
indirect emissions (STP sludge)
dry and wet deposition
leaching
adsorption/volatilisation
air flow
water flow
advection
adsorption/desorption
burial
sedimentation/resuspensation
Regional emission and distribution model
Illustration of Level III
f = fugacityZ = fugacity capacityV = volume
= valve (== resistance)
Input
air
water
sediment
Z
Output
Output
Input
f
V
Input
European Union System for the Evaluation of Substances (EUSES)
Model structure
STP m odel
Level IIIM ulti-m edia
m odel
locald istribution
hum ans
worm /fish
R eleaseestim ation
Environm ental distribution Indirect exposure
Local emission and distribution pathways
All stagesoflife-cycle
Model optimizationModel and parameter uncertainties
level of detail / com plexity
error due touncerta inty
structura lerror
tota l error
Restricted Applicability
Polar substances Super lipophilic compounds Surfactants Heavy metals Polymers Complexes Metabolites Mixtures
Exposure and Risk Assessment Software
CemoS— „Chemical Exposure Model System“
— Compilation of nine exposure models; substance data base; estimation routines
— mainly for educational purposes
EUSES— „European Union System for the Evaluation of Substances“
— Official software for the risk assessment of chemicals in the EU
— Based on Technical Guidance Document
CalTOX— 8-compartment multi-media programme; hazard and risk assessment
— recommended for the risk assessment of contaminated soil in California
— Excel-spreadsheet
Questions?
Decision support system EUSESParameters and Connectivity
D T 50b io water
C loca lairC std air
D ILU T IO N
k Plant
D E P T H i
Food chain I: Secondary poisoning
C inh
Q Prod
F c prod
V room
I inh
n
T contact
Ioral
C der
C oral
C prod
U to t
V prod
D
A der
V appl
T H der
A R E A der
U der,pot
W der
A m igr,der
F c m igr
F oral
T H art
A R E A art
C artC der,ann
C inh,ann
C oral,ann
a rt2
a rt2
a rt2
m ed .
a rt1
m ed .
a rt1
a rt2
a rt1
a rt2
m ed .
m ed.: substance con ta ined in a m ed iumart1 : non-vo la tile substance m igra ting from an a rtic leart2 : substance m igra ting from an a rtic le in to food o r d rink
Consum er Exposure
T em iss ion
R E LE A S E reg production,am ount used
R E LE A S E contprivate use,rest
kdeg stp
C loca leff
Sim ple Treat
T O N N A G E k
T O N N A G E reg
P R O D V O Lreg
P R O D V O Lcont
F m ainsource ii: p roduction , fo rm u la tion , p rocess ing ,
p riva te use , recove ry
F connec tstp
K air-water
khydrwater
kpho to water
D T 50hydrwater
kdeg water
kb io water
kab io soil
D T 50b io -aersed
Sim pleBox
K p RS
K p PS
K p A
K p SLS
H E IG H T air
R A IN R A T E
R E LE A S E contproduction,j
j: a ir, water, ind, agric, surf,to ta l
F production, j
j: a ir,water,ind,agric,surf
F form ulation, j
j: a ir,water,ind,agric,surf
F processing, j
j: a ir,water,ind,agric,surf
F private use, j
j: a ir,water,ind,agric,surf
F recovery, j
j: a ir,water,ind,agric,surf
R E LE A S E cont form ulation,jj: a ir, water, ind, agric,
surf,to ta l,rest
R E LE A S E contprocessing,jj: a ir, water, ind, agric,
surf,to ta l,rest
R E LE A S E contprivate use,j
j: a ir, water, ind, agric, surf,to ta l
R E LE A S E cont recovery,j
j: a ir, water, ind, agric, surf,to ta l
R E LE A S E contproduction,am ount used
A -T ab les
B -T ab les
F LO W water*
P E C oral,wormi=agric
R E LE A S E reg private use,rest
B IO T A water
K oc
K plant-water
F a irplant
F lip id plant
F w ate rplant
b
F oc soil g plant
R H O plan t
A R E A plant
Q transp
V leafK leaf-a ir
T S C F
F ass aer
C leaf;C grass
i=grassland; agric
C root
B C F Fish
C fish
IC grass
IC soil
C O N V grass
IC dw tgrass
IC dw tsoil
C drwF pur
D O S E drw,fish,leaf
,
root,m eat,m ilk
B A F m eatB A F m ilk
H E N R Y
K ow
V P
S O L
T E M P bo il
T E M P m elt
kb io stp
kab io stp
E stp air
C sludge
P E C stp
E stp -reg air
E stp -reg water
E stp -reg agric
E stp -con tair
E stp -con twater
E stp -con tagric
H R T PS
D E P T H PS
R H O RS
S O LID S
B O D
C A S
D E P T H A
R H O PS
R H O A
C O X
G
D E P T H SLS
R H O SLS
H R T SLS
Q stp
N *
k SLR
T E M P stp air
T E M P stp water
M
W IN D S P E E D
P R O D V O L
T O N N A G EE X P O R T
IM P O R T
F tonnage k
F prodvo l reg
T O N N A G E cont
T O N N A G E reg form
F chem form
E loca l i,ji: p roduction , fo rm u la tion , p rocess ing , p riva te use ,
recove ryj: a ir, w a te r
T em iss ion ii: p roduction , fo rm u la tion , p rocess ing ,
p riva te use , recove ry
E cont jj: a ir, ind
R ho Soil
R ho water
R ho Air
R ho Solid
F so lid soil
F w ate rsoil
F a irsoil
R ho Sed
R ho Susp
F so lid susp
F so lid sed
F w ate rsusp
F w ate rsedC O N V sed
C O N V soil
C O N junge
S U R F aer
V P L
T E M P
R
K p susp
K p Sed
K p Soil
F oc susp
F oc sed
K soil-water
K susp-water
K sed-water
k O H kdeg air
D T 50photo water
O H C O N C air
D T 50b io soil kb io soil
kdeg soil
kb io -aersed
kdeg sed
F aerSed
kb io -anaersed
kab io sed
F Resp
IH air
IH drw
IH fish
IH leaf
IH root
IH m eat
IH m ilk
B W
B IO inh
B IO oral
P E C contwater,to t
P E C contwater
P E C contair
P E C contagric
P E C contagric,porew
P E C contnatura l
P E C cont ind
P E C contsed
P E C reg water, to t
P E C reg air
P E C reg agric
P E C reg agric, porew
P E C reg natura l
P E C reg ind
P E C reg sed
A R E A *
D E P R A T E aer
C O LLE F F aer
F water *
D E P T H water *
F flow out reg
S U S P water *
D E P T H sed
S E T T LR A Tsusp
S U S P P R O Dwater
S U S P eff
F ind *
F runo ffsoil
F agric *
E R O S IO N
F in fsoil
F natura l *
kas lsoila ir
kas lsoilwater
kw s water
kaw air
kaw water
kw s sed
C m eat;C m ilk
i=grassland
B IO der
D O S E air D O S E to t
C loca l in fE F F LU E N T loca lstpN loca l
F s tp air
F stp -reg air
F stp -reg water
F stp -reg agric
F stp -con tair
F stp -con twater
F stp -con tagric
H P V C
IN D C A T
U S E C A T
M A IN C A T
E contwater
E contdirect-water
j:surf,water
E reg water(j: water)
R E LE A S E reg production,j
j: a ir, water, ind, agric, surf,to ta l
R E LE A S E reg form ulation,jj: a ir, water, ind, agric,
surf,to ta l,rest
R E LE A S E reg processing,jj: a ir, water, ind, agric,
surf,to ta l,rest
R E LE A S E reg private use,j
j: a ir, water, ind, agric, surf,to ta l
R E LE A S E reg recovery,j
j: a ir, water, ind, surf,to ta l
E reg j
j: a ir,ind
E reg direct-water
j:surf,water
E loca lwater
F oc RS
F oc PS
F oc A
F oc SLS
W IN D S P E E D T A U air *
R A IN D IR E C T *
R U N O F F *
T A U water *
N E T sedra te *
E F F LU E N T stp *
P E C reg water
B C F biota
E loca lair
C loca lair,ann
P E C loca lair,ann
D E P to ta l D E P to ta lann
F A S S aer
D E P std aer
C loca lwater C loca lwater,ann
F LO W
P E C loca lwater,ann
P E C loca lwater
P E C loca lsed
k volat i
kas lair
k leach i
k i
D air i
C dep10 i
C sludge1 iA P P Ls ludge i
F acc i
C sludge10 i
C loca l10 i
C loca l i
T i
P E C loca l i P E C loca l i, porew
F st-s t i
C in f i
P E C loca lgrwi=agric
P E C oral,fish
K worm -porew B C F worm
T A B III-6
T A B III-7
T A B III-7
C inh, worker, vapourT E M P w ork
C 1 inh, worker, vapour
U der,pot,workerW der, workerA R E A der, worker
W orkplace Exposure
kgrow th plant
ke lim plant
km etab plant IC drw
IC air
Food Chain II: Indirect exposure of hum ans via the environm ent
i=so il; agric; grassland Local environm ental d istribution
Em ission part
M O LW
D T 50b io stp
n worker
EASE
D E P std gas
F LO W air*
D R Y D E P aerosol
W A S H O U T
S C A V ra tio
W A S T E W *
G A S A B S w ater
G A S A B S so il
V O LA T w ater *
F d iss lvd water *
V O LA T so il
A D S O R B sed *
D E S O R B sed *
G R O S S sedra te *
R E S U S P ra te *
S E D R A T E *
LE A C H so il
C reg natura l
C reg agric
C reg ind
C reg air
C reg water
C reg sed
Literature
Trapp,S., Matthies,M.: Chemodynamics and Environmental Modeling - An Introduction, Springer, Heidelberg, 1997
Trapp,S., Matthies,M.: Dynamik von Schadstoffen - Umweltmodellierung mit CemoS, Springer, Heidelberg, 1996
Thibodeaux,L.: Environmental Chemodynamics: movement of chemicals in air, water and soil (2. Aufl.), Wiley, New York, 1996
Klöpffer, W.: Verhalten und Abbau von Umweltchemikalien - Physikalisch chemische Grundlagen, ecomed, Landsberg, 1996
Mackay,D.: The Fugacity Approach - Multimedia Environmental Models, Lewis Pub., Michigan, 1991
van Leeuwen,C., Hermens,J.: Risk Assessment of Chemicals - An Introduction, Kluwer Acad. Publ., Dordrecht, 1995
Exposure Assessment
release estimation
physico-chemical properties
environmentalparameters
Exposure Model
Predicted Environmental Concentration (PEC)
Flow dynamic approach— Based on first physical principles of mass and energy conservation and
entropy changes.
— Flow dynamics in atmosphere, ground and surface water etc.
— Partial differential equations, which usually have to be solved numerically.
— Examples: global circulation model, groundwater transport.
Mass balance approach— Similar to the pharmaco-kinetic models for drugs.
— Same approach as in cost accounting or demographic models.
— Based on exchange of matter between compartments and reaction kinetics.
— Linear differential equations, which can be solved analytically or numerically.
— Examples: Multi-media models of Mackay; (bio-)reactor models.
Exposure ModellingTwo Approaches
Plant model
Model assumptions— roots: Gleichgewichtsverteilung mit dem Boden
— leaves: gewöhnliche Differentialgleichung
Benötigte Daten— 10 pflanzenspezifische Parameter: Blattoberfläche, Wachstumsrate, etc.
— 2 Konzentrationen: Bodenwasser und Luft (Gasphase)
— 1 substanzabhängiger Parameter (logKOW)
Transferpfade— Quelle - Luft - Blätter
— Quelle - Boden - Wurzel
— Quelle - Boden - Luft (Ausgasung, Resuspension) - Blätter
Alternative Modellierungsansätze— Biokonzentrationsfaktoren
— Mehr-Kompartimentmodelle
Aquatic Bioconcentration model in EUSES
1,E-04
1,E-03
1,E-02
1,E-01
1,E+00
1,E+01
1,E+02
1,E-04 1,E-03 1,E-02 1,E-01 1,E+00 1,E+01 1,E+02
Predicted conc. [mg/kg]
Me
asur
ed
conc
. [m
g/k
g]
m ax
m in
uncerta inty analysism edian
DEHP
PCB
101-180 (eel)28-52 (eel)101-18028-52
Illustration of Level I model
f = fugacityZ = fugacity capacityV = volume
C = f·Zm = C·V = f·Z·V
V
Air Water Soil
Z
f