combining measurements and models to understand emissions ... · to understand emissions, fate,...
TRANSCRIPT
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Combining measurements and models to understand emissions, fate, exposure
and pharmacokinetics of POPs
Matthew MacLeod
Stockholm University
Department of Applied Environmental Science
Stockholm, Sweden
University of Birmingham, UK – May 9 2014
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Acknowledgments • Global fate and transport modeling
– Harald von Waldow, Lara Lamon, Henry Wöhrnschimmel
• Urban diffuse source characterization
– Bojan Gasic, Claudia Moeckel, Zhanyun Wang, Christian Bogdal, Andreas Buser, Amelie Kierkegaard
• Population PK modeling
– Roland Ritter, Fiona Wong, Qingwei Bu
• Concepts and collaboration
– Martin Scheringer, Konrad Hungerbuhler, Tom McKone, Ian Cousins, Jochen Mueller, Kevin Jones
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Combining measurements and models to understand emissions, fate, exposure and
pharmacokinetics of POPs
1. Why model?
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Why model?
• Because we cannot help it!
– Everyone is an implicit modeler
• It is valuable to make models explicit
– Assumptions are defined
– Sensitivity and scenario analysis is possible
– Others can replicate your results
Epstein, J. M. Journal of Artificial Societies and Social Simulation, 11(4), 12, 2008.
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Models of open systems can never be verified
• Models are limited conceptualizations of the real system
• Models are limited in the empirical accuracy of their governing equations
• Models are limited with respect to input parameterization
Oreskes, N. 2003. “The role of quantitative models in science,” in Models in Ecosystem Science, Princeton University Press, pp. 13-31.
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The ground rules for model development…
• Epstein:
– “You must make models”
• Oreskes:
– “Your models will always be wrong”
• These two rules are unbreakable, and are not in conflict
• We should not fixate on modeling as a tool to make predictions
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16 reasons other than prediction to build models
(Epstein, Journal of Artificial Societies and Social Simulation 11(4), 2008)
1. Explain (very distinct from predict)
2. Guide data collection
3. Illuminate core dynamics
4. Suggest dynamical analogies
5. Discover new questions
6. Promote a scientific habit of mind
7. Bound (bracket) outcomes to plausible ranges
8. Illuminate core uncertainties.
9. Offer crisis options in near-real time
10. Demonstrate tradeoffs / suggest efficiencies
11. Challenge the robustness of prevailing theory through perturbations
12. Expose prevailing wisdom as incompatible with available data
13. Train practitioners
14. Discipline the policy dialogue
15. Educate the general public
16. Reveal the apparently simple (complex) to be complex (simple)
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16 reasons other than prediction to build models
(Epstein, Journal of Artificial Societies and Social Simulation 11(4), 2008)
1. Explain (very distinct from predict)
2. Guide data collection
3. Illuminate core dynamics
4. Suggest dynamical analogies
5. Discover new questions
6. Promote a scientific habit of mind
7. Bound (bracket) outcomes to plausible ranges
8. Illuminate core uncertainties.
9. Offer crisis options in near-real time
10. Demonstrate tradeoffs / suggest efficiencies
11. Challenge the robustness of prevailing theory through perturbations
12. Expose prevailing wisdom as incompatible with available data
13. Train practitioners
14. Discipline the policy dialogue
15. Educate the general public
16. Reveal the apparently simple (complex) to be complex (simple)
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Combining measurements and models to understand emissions, fate, exposure and
pharmacokinetics of POPs
2. The global mass budget of POPs
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A very simple model…
E (mol/h) k (/h)
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A very simple model… Sources: E Sinks: M×k
E (mol/h) k (/h) M (mol)
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E (mol/h) k (/h) M (mol)
• The rate of emissions of chemicals to the environment often contributes most to uncertainty in exposure concentrations used in risk assessments (Arnot et al. 2006)
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Emission estimates can be made with a “bottom-up” approach…
ACCIDENTAL
RELEASES
(A)
DISPOSAL (D)
USAGE (U)
Landfills (l)
Soils (s) Open Burning (o)
Waste incin.(w)
Destruction (d)
Dis
po
sa
l (d
f)
Open (1)
Small capacitors (2)
Nominally closed (3)
Accid
en
tal (a
f)
Life
tim
es (
k)
CONSUMPTION (C)
Usage factors ()
Closed (4)
Fires (f)
Emission factors (ef)
EMISSIONS (E)
Emission estimation
methodology for PCBs,
courtesy of Knut Breivik
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Breivik’s “bottom-up” PCB emission estimates
0.1
1.0
10.0
100.0
1000.0
10000.0
100000.0
1930 1940 1950 1960 1970 1980 1990 2000
Tonn
es
0.1
1.0
10.0
100.0
1000.0
10000.0
100000.0
Tonn
es
Production
Emissions
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Ground-truthing Breivik’s estimates…
Small World® - A global-scale fugacity model - Level I and Level III solutionsDeveloped at the Swiss Federal Institute of Technology, Zurich & Stockholm University, Sweden
Input Parameters
Calculated Values
Air
OK 8.61961
100
Fugacity 6.5E-10 Pa
808298 mol
18.86% 63.9275
2.6E-13 mol/m3
18.0892 262.47
Soil Water
OK 13.5882 1.29725 OK 239.519
0 0
Fugacity 5.11E-10 Pa Fugacity 6E-10 Pa
2561662 mol 915120 mol
59.78% 21.36%
1.7E-07 mol/m3 2.5E-11 mol/m3
2.02652 1.17722 17.0097 7.23948
Emission Advection
Degradation Transfer
hours years
42851 4.89
58545 6.68
159852 18.25
Overall persistence (Pov)
Overall advective time (Aov)
Inventory
Distribution
Distribution
Inventory
Concentration
Concentration Concentration
Overall residence time (Tov)
Distribution
Inventory
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Ground-truthing with SmallWorld…
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Ground-truthing with SmallWorld…
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More detailed models agree…
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So… Uncertainties in bottom-up emission estimates can bounded and reduced by evaluation them against observations with mass-
balance models…
What about industrial chemicals where bottom-up estimates have
not been made?
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Short term (hourly) variability of concentrations in air could be used to
estimate emission rates
Time
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Diel (24-hour) cycles that may affect concentrations of SVOCs in air
• Temperature
• Hydroxyl radical concentration
• Boundary layer height and stability
• Wind speed
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Zurich in summer time as a microcosm for Europe…
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Model structure to investigate diel pollutant dynamics
Residual Layer
Nocturnal Boundary Layer
MacLeod et al. Environmental Science & Technology, 41(9), 3249 - 3253, 2007.
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Zurich field campaigns 2007, 2009 & 2011
• Two sampling sites:
– City site: Zurich ~450 m
– Hill site, background: Uetliberg ~850m
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Gasic et al. Environmental Science & Technology, 43(3), 769 - 776, 2009.
PCBs Uetliberg City site
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• We estimate that the city of Zurich emits 15
kg/y* of PCBs to the atmosphere.
* ± factor 2
• Consistent with Breivik’s ‘max’ emission
scenario
• Consistent with urban-rural concentration
gradients in cities in North America and
western Europe
Gasic et al. Environmental Science & Technology, 43(3), 769 - 776, 2009.
Bogdal et al. Environmental Science & Technology, 48(1), 482-490, 2014.
Cities are sources of POPs
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Cities are sources of POPs
• Brominated flame retardants (Moeckel et al. 2010)
– Zurich emits ~10 kg/y of four congeners of PBDEs to the atmosphere
• Perfluorinated substances (Wang et al. 2011)
– 8:2 FTOH (23 kg/y) 10:2 FTOH (7 kg/y)
– MeFOSA (0.7 kg/y) EtFOSA (0.4 kg/y)
• Siloxanes (Buser et al. 2013)
– Zurich emits 44 000 kg/y of D5 and 5 000 kg/y D6
• Other applications…
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Combining measurements and models to understand emissions, fate, exposure and
pharmacokinetics of POPs
3. Population-level exposure and pharamacokinetics
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A very simple model…
I (mol/h) k (/h)
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A very simple model… Intake: I Clearance: M×k
I (mol/h) k (/h) M
(mol)
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I (mol/h) k (/h) M
(mol)
• Rates of intake (I) and whole-body clearance (k) are often highly uncertain, but in some cases we have good measurements of body burdens (M) from biomonitoring.
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Ritter et al. 2011. Environmental Health Perspectives 119 (2) 225.
Case Study 1: PCBs in the UK population
• Biomonitoring
– Cross-sectional data from the entire population for 1990 & 2003
• Exposure
– Results from 9 total diet studies between 1970 & 2002
• Elimination
– Estimated elimination half-lives for different PCBs from weeks to years
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PCB153 Exposure Studies
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PCB153 Biomonitoring
data
Biomonitoring and
exposure data for
PCB 153 can be fit
simultaneously
Human elimination half life:
13 years Similar story for 8
other PCB congeners
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Ritter et al. 2011. Environmental Health Perspectives 119 (2) 225.
PCBs in the UK population
• Yes!
– Good model fits to intake estimates and biomonitoring data for 9 PCB congeners
– Model-fitted human elimination half-lives between 3 and 16 years for different PCB congeners
Is our empirical understanding of exposure,
body concentration and elimination self-
consistent?
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PCBs in the Australian Population
Bu et al. Environment International (in revision).
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PCBs in the Australian Population
• Human elimination half-lives for PCBs are similar in the UK and Australia, but perhaps a bit longer in Australians
• Peak intake of PCBs in Australia was 7-20 times lower than peak intake in the UK, and 60 times lower for PCB 180
• Intake follows a similar temporal trend in the UK and Australia
Bu et al. Environment International (in revision).
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Combining measurements and models to understand emissions, fate, exposure and
pharmacokinetics of POPs
Trivia Challenge:
Which POP is most abundant in the bodies of Europeans?
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Norwegians
PFOS (Perfluorooctane sulfonate)
Most abundant POPs measured in humans
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Case Study 2: PFOS in US population
0
10
20
30
0 20 40 60 80 100
Age
GM of PFOS in five NHANES sampling years: 1999, 2003, 05, 07, 09
men
women
se
rum
co
nce
ntr
ati
on
ng
/m
L
Men > Women
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Research Question:
PFOS is known to bind to serum blood
proteins…
Is there enhanced elimination of PFOS by
menstruating women?
What is the elimination rate of PFOS for:
• Men
• Women (menstruating and non-
menstruating)
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Model Results
20 40 60 80
10
20
30
40
50
20 40 60 80 20 40 60 80 20 40 60 80 20 40 60 80
1999 2003 2005 2007 2009
Age
PF
OS
- S
eru
m
ng/m
L
Men, empirical US NHANES
Women, empirical US NHANES
Men, modeled – HL 5.5 years
Women (non-menstruating), modeled – HL 4.3 years
Women (menstruating), modeled – HL 4.9 years
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4 5 6 PFOS Half-life in US population
Model Results
Men (intrinsic)
5.5 yrs
Non-menstruating women (intrinsic + other processes)
4.3 yrs
Menstruating women (intrinsic)
4.9 yrs
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Elimination HL of
PFOS in women is
shorter than in men
by 25%
Yes, but…
Menstruation only accounts for
12% of the 25% difference.
The remaining difference
between men and women may
be due to:
• Sex-specific elimination route
(renal?)
• Model uncertainty
Research Question:
Is there enhanced elimination of PFOS by
menstruating women?
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Reasons other than prediction to build models
(Epstein, Journal of Artificial Societies and Social Simulation 11(4), 2008)
1. Explain (very distinct from predict)
2. Guide data collection
3. Illuminate core dynamics
5. Discover new questions
6. Promote a scientific habit of mind
7. Bound (bracket) outcomes to plausible ranges
8. Illuminate core uncertainties.
Combining measurements and models to understand emissions, fate, exposure and
pharmacokinetics of POPs
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Acknowledgments
• Swiss Federal Agency for the Environment (BAFU)
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