09/04/2010 USEtox short course – chemical fate modelling 1 DTU Management Engineering, Technical University of Denmark Chemical fate modelling Overview of typical mass balance concepts and introduction to transport and degradation rate calculations as well as matrix solutions Assistant professor Morten Birkved [email protected]09/04/2010 USEtox short course – chemical fate modelling 2 DTU Management Engineering, Technical University of Denmark Learning objective and outline Objectives: • To understand what fate modelling is • To understand the role of fate modelling in USEtox • To understand how fate modelling is applied in USEtox Outline 1.What is chemical fate 2.Chemical fate processes 3.What is chemical fate modelling 4.How is chemical fate modelling applied in USEtox 5.Exercise 6.Presentation of solution to exercise 7.Questions 09/04/2010 USEtox short course – chemical fate modelling 3 DTU Management Engineering, Technical University of Denmark What is chemical fate A matter of (important) details? 09/04/2010 USEtox short course – chemical fate modelling 4 DTU Management Engineering, Technical University of Denmark What is chemical fate modelling Do we need fate and exposure models in LCA? Fate and exposure models serves one purpose only in impact assessment of chemical emissions: Prediction of chemical behavior in the environment The prediction power of the chemical fate and exposure models facilitates the quantification of the marginal toxicological impacts occurring in LCIA caused by chemical emissions. 09/04/2010 USEtox short course – chemical fate modelling 5 DTU Management Engineering, Technical University of Denmark What is chemical fate A matter of chance? ? 09/04/2010 USEtox short course – chemical fate modelling 6 DTU Management Engineering, Technical University of Denmark What is chemical fate A matter of chance?
Transcript
09/04/2010USEtox short course – chemical fate modelling1 DTU Management Engineering, Technical University of Denmark
Chemical fate modellingOverview of typical mass balance concepts and introduction to transport and degradation rate calculations as well as matrix solutions
09/04/2010USEtox short course – chemical fate modelling2 DTU Management Engineering, Technical University of Denmark
Learning objective and outlineObjectives:• To understand what fate modelling is• To understand the role of fate modelling in USEtox• To understand how fate modelling is applied in USEtox
Outline1.What is chemical fate 2.Chemical fate processes3.What is chemical fate modelling4.How is chemical fate modelling applied in USEtox5.Exercise6.Presentation of solution to exercise7.Questions
09/04/2010USEtox short course – chemical fate modelling3 DTU Management Engineering, Technical University of Denmark
What is chemical fateA matter of (important) details?
09/04/2010USEtox short course – chemical fate modelling4 DTU Management Engineering, Technical University of Denmark
What is chemical fate modellingDo we need fate and exposure models in LCA?
Fate and exposure models serves one purpose only in impact assessment of chemical emissions:
Prediction of chemical behavior in the environment
The prediction power of the chemical fate and exposure models facilitates the quantification of the marginal toxicological impacts occurring in LCIA caused by chemical emissions.
09/04/2010USEtox short course – chemical fate modelling5 DTU Management Engineering, Technical University of Denmark
What is chemical fateA matter of chance?
?
09/04/2010USEtox short course – chemical fate modelling6 DTU Management Engineering, Technical University of Denmark
What is chemical fateA matter of chance?
09/04/2010USEtox short course – chemical fate modelling7 DTU Management Engineering, Technical University of Denmark
What is chemical fateSeverity of chemical emissionsa)What main fate properties determines the fate pattern of a
chemical emission - i.e. which overall properties controls the fate of a chemical emission?
1. It’s mobility (transport potential)2. Is ability to avoid degradation (persistence)
b)What factors determines the severity/impact potential of a chemical emission – i.e. which factors controls the impact potential of a chemical emission?
1. It’s toxicity (affinity for a specific receptor)2. It’s exposure pattern (availability to interact with a receptor)3. It’s fate pattern (ability to reach (i.e. mobility) and have time (i.e.
persistence) to interact with a receptor)
09/04/2010USEtox short course – chemical fate modelling8 DTU Management Engineering, Technical University of Denmark
What is chemical fateAdressing chemical behaviour in the environment in LCAAssessment resolution:”Single compound” assessment (CAS number resolution)
Impact potential
IP = Q × CF
Assessment of ecotoxicological impacts :
CF = EF × FF × XF
Assessment of human toxicologicalimpacts:
CF = EF × FF × XF = EF × IF
09/04/2010USEtox short course – chemical fate modelling9 DTU Management Engineering, Technical University of Denmark
What is chemical fateRole of fate models in LCA
Air
WaterSoil
Sediment Direct source term
Inter-media transfer factors
Degradation
Plant
+
Inhalation
Ingestion
Environmental distribution of chemical – resulting human exposure
09/04/2010USEtox short course – chemical fate modelling10 DTU Management Engineering, Technical University of Denmark
What is chemical fateRole of fate and exposure in LCIA
Emissions into compartment m
Time integrated concentration in n
Dose taken in
Risk of affectedpersons
Damage onhuman health
Chemicalfate
Humanexposure
Potency(Dose -
response)
Concentration - response
Fraction transferred to n
Severity
Speciesexposure - intake
Potentially affectedfraction of species
Intakefraction
iF
Effectfactor
Fate factor
Time and spaceintegrateddamage onecosystems
Severity
Effectfactor
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09/04/2010USEtox short course – chemical fate modelling12 DTU Management Engineering, Technical University of Denmark
Chemical fate processesMultimedia partioning of chemicals
-15
-13
-11
-9
-7
-5
-3
-1
1
3
5
-3 -1 1 3 5 7 9
Log(Kow)
log
(Kaw
)
4
6
8
waterSolid
water and solid
solid and air
water and air
air
multimedia
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Chemical fate modellingNested models
Huijbregts et al. 2010
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Chemical fate modellingModelling principles – model approaches
[A]i or j
time
Compartment i
Compartment j
Ki/j
j
ii/j
[A]
[A]K
Ki/j
Ki/j
Ki/j
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Chemical fate modellingModelling principles – model approaches
[A]i
time
Steady state 0dt
d[A]i
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Chemical fate modellingModelling principles – model approaches
Mackay (2001)
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Chemical fate modellingMass balance modelLavoisier principle of mass conservation:
« In all operations of nature, matter cannot be created/destroyed, although it may be rearranged. This implies that for any chemical process in a closed system, the mass of the reactants must equal the mass of the products »
AirIN OUT
dM/dt = In - Out
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Chemical fate modelling Basic processes for environmental mass balance modelingINPUTS
– Emission or Source, Sm [kg/hour]– Intermedia transfer rate coefficient ki,m [hour-1]
• From other compartments• From outside the system
OUTPUTS– Intermedia transfer rate coefficient km,i [hour-1]
• To other compartments• Burial processes into deep sediments• Advection out of the system
09/04/2010USEtox short course – chemical fate modelling19 DTU Management Engineering, Technical University of Denmark
Air
S k·M
IN OUT
dM/dt = 0
Emission rate: S [kg/day]
Mass in compartment: M [kg]
Removal rate coefficient: k [per day]
(fraction of mass eliminated per day)
S =
Chemical fate modelling Equilibrium and/or Steady state: IN = OUT
09/04/2010USEtox short course – chemical fate modelling20 DTU Management Engineering, Technical University of Denmark
Air
k∙M
OUT
Removal rate coefficient: k [day‐1]
(fraction of mass eliminated per day)
Half‐life: ½ [day]
(days to eliminate half of mass)
½ = ln(2)/k
Chemical fate modelling Rate Constant - Half-life Relationship
dM/dt = ‐k ∙M
Per definition: M(½ )/M(0)=0.5
dM/dt = In ‐ Out
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Chemical fate modelling Removal rate coefficients k
Air kout
ka,i
ka,deg
a,degi
ia,a,outtota, kkkk 321 R
1
R
1
R
1
R
1
Like electric resistances
Units = time 321 ½,½,½,½,
1111
tot
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= · +)( tM
k M
S
SkM ‐1 0dt
dM a
Dynamic:
Steady State:
How is chemical fate modelling applied in USEtoxMatrix Algebra Solution Dynamic and steady state solution
w
a
totwaw
wata
w
a
S
S
kk
kk
M
M1
1,
,
Source vector (kg/h)
Mass vector (kg)
Rate coefficient matrix (1/h)
Air
Water
WaterAir
Fate factor matrix
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How is chemical fate modelling applied in USEtoxExercise: Fate of TCE in a two-compart. Syst.
23
Trichloroethylene (TCE) is a colourless, somewhat toxic, volatile liquid belonging to the family of organic halogen compounds. It is a chemical widely used in industry as a solvent in dry cleaning, in degreasing of metal objects, and in extraction processes, such as removal of caffeine from coffee or of fats and waxes from cotton and wool
water
air
Water outflow = 2 · 107 m3/d
Water volume = 3 · 109 m3
TCE emissions to water = 590 kg/d
Air outflow =1.45 · 1012 m3/d
Atmospheric degradation half‐life = 15 daysAquatic degradation half life = 150 days
Air volume = 2.5 · 1011 m3
kadv,a =
kadv,w =
kdeg,w =
kdeg,a =
Air‐to‐water transfer factor, kaw = 5.57 · 10‐3 days‐1
Water‐to‐air transfer factor, kwa = 1.91 · 10‐1 days‐1
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How is chemical fate modelling applied in USEtox Fate of TCE in a two-compart. syst.
Q1) Determine the total rate coefficients in air and water?
Q2) Which is the dominant removal pathway in air and in water respectively?
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How is chemical fate modelling applied in USEtox Fate of TCE in a two-compart. syst.
25
Q3: Determine the Mass (or Concentration in air and water respectively)?
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Solutions
26
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How is chemical fate modelling applied in USEtox Fate of TCE in a two-compartment system - Q1
