Appendix 3 Frank Wania Evaluating Persistence and Long Range Transport Potential of Organic Chemicals Using Multimedia Fate Models
Appendix 3
Frank Wania
Evaluating Persistence and Long Range Transport Potential of Organic Chemicals
Using Multimedia Fate Models
What?
development of techiques that incorporate multimedia fate models in the process of evaluating candidate POPs for
persistence and long range transport potential.
Why?
because the multimedia distribution of a chemical profoundly affects its environmental persistence and potential for long
range transport.
Evaluating Persistence and Long Range Transport Potential of Organic Chemicals Using Multimedia Fate Models
Frank Wania, WECCDon Mackay, Eva Webster, Trent University
Andreas Beyer, Michael Matthies, Universität Osnabrück
M
N
f V Z
f Dtot
Rtot
i i Bii
i Rii
overall persistence
multimedia partitioning, and thus , is governed by:
physical-chemical properties
mode of emission
environmental characteristics
Webster, E., Mackay, D., Wania, F. Evaluating Environmental Persistence. Environ. Toxicol. Chem. 1998, 17, 2148-2158
Mtot and NRtot can be calculated using a multimedia environmental fate model such as EQC
Evaluating Environmental Persistence
3-compartment level III model used to estimate an overall persistence of an organic chemical in the global environment
M
N N
f V Z
f D Dtot
Rtot Ltot
i i Bii
i Ri Lii
( )
Overall Global Persistence
Calculating Overall Persistence
EA
DRE ·fE
Air
Soil Water
EE EW
DRW ·fW
DRA ·fA
DLW ·fWDLE ·fE
DLA ·fA
DAW ·fADAE ·fA
DEW ·fE
DEA ·fE DWA ·fW
Wania, F. An integrated criterion for the persistence of organic chemicals based on model calculations. WECC Report 1/98.
dependence of overall persistence on physical chemical properties as expressed by log KAW and log KOW.
Assumptions: Equal fraction of emissions into air, water and soil. Half-lifes 48 h in air, 1460 h in water and 4380 in soil. Level III.
Calculating Overall Persistence
-15
-13
-11
-9 -7 -5 -3 -1 1 3 5
-2
0
24
68
10
0
500
1000
1500
2000
2500
3000
3500
ove
rall
per
sist
ence
in h
ou
rs
log KOWA
B
C
log KAW
Calculating Overall Persistence
0.5
0
1.0
0.5
0
1.0
water fraction of emissions
into water
air fraction of emissions
into soil
0.50
1.0
0.250.75
0.25
0.75
0.250.75
overall persistence water
with emission into water onlyoverall persistence soil
with emission into soil only
overall persistence air
with emission into air only
air fraction of emissions
into air
linear additivity of overall persistence= air·air + water· water + soil·soil
Calculating Long Range Transport Potential
Assumptions:• steady-state between moving phase and stationary phase
• no dispersion• advective transport uni-directional
CM0CM
CM0/e
distanceLM
Characteristic Travel Distance
distance it takes for the concentration in the moving
phase (e.g. air) to fall to e-1 or 37 % of its initial value due to
degradation in the moving phase (e.g. air) and net transfer
to the stationary phase (e.g. soil, water).
van Pul et al. 1998, Bennett et al. 1998, Beyer et al. 1999
Reformulation for Well-Mixed (or Box) Systems the distance in well-mixed system over which the concentration in the moving phase falls to half its input value. Then the rate of advective loss equals the
total loss by reaction: 0.5 NIn = NOut = (NRM + NRS)
air
Calculating Long Range Transport Potential
soil
NIn
NOut
NRA
NRS
Example: Air Moving Over Soil
NAS NSA
LA = u·MA / (NRA + NAS·F)
LA = u·VA·ZA / (DRA + DAS·F)
where F = DRS / (DSA + DRS)
(fraction of chemical retained by soil)
characteristic travel distance in air
facilitates use of traditional multimedia model for calculation of L
Beyer, A., Mackay, D., Matthies, M., Wania, F., Webster, E. 1999. An evaluation of the role of mass balance models for assessing the long range transport potential of organic
chemicals. Report 99:01, Environmental Modelling Centre, Trent University, Peterborough
Relationship Between Characteristic Travel Distance and Overall Persistence
LM = u·MM· / Mtot
LM is distance a molecule travels during the environmental residence time (u·), multiplied by the proportion of mass in
the moving medium (MM / Mtot)
Example: Travel Distance in Airfor very volatile chemicals Mair / Mtot = 1, thus Lair = u·(maximum possible)for less volatile chemicals Mair / Mtot is small, thus Lair is small
It can be shown that the general formulation for the travel distance in moving phase M is LM = u·MM / NRtot
whereas overall persistence was defined as = Mtot / NRtot
half-life in air in hours
tra
vel d
itan
ce in
air
in k
m
OCDD
aldrin
benzene
HCB
tetraCB
heptaCBdecaCB
dieldrin
chlorobenzene
DDT
100
1000
10000
100000
1000000
1 10 100 1000 10000 10000 1000000
-HCH
u.air
maximum travel distancechemical partitions only into moving phase (air)
minimum travel distancechemical partitions completely onto particles
and deposition is irreversible
Calculating Long Range Transport Potential
travel distance in air in km
-HCH
TCDD
DDT
DDE
HCB
tetraCBhexaCB
dieldrin
OCDD
1
10
100
1000
10000
100 1000 10000
km
overall persistence in days
aldrin
dieldrin-HCH
biphenyl
chlorobenzene
HCB
OCDD
DDTbenzene
tetraCB
100
1000
10000
100000
1000000
0 1 10 100 1000 10000
u.
travel distance in water in km
Calculating Long Range Transport Potential
using a multimedia model (EQC) to estimate a characteristic travel distance in air and water (Beyer et al., 1999)
u.-HCH
overall persistence in days
Limitations of These Techniques
1. for many candidate substances, not even the most basic physical-chemical properties are available.
2. overall persistence and travel distance are dependent on environmental characteristics, e.g. temperature.
3. these techniques provide a scale to rank chemicals according to the persistence and LRT potential, but not cut-off criteria, for what constitutes persistence/ non-persistence, and LRT potential/no LRT potential.
0
2000
4000
6000
8000
10000
12000
14000
1947 1957 1967 1977 1987
ove
rall
per
sist
ence
in h
ou
rs
Overall Persistence and Global Distribution
Overall persistence of -HCH as calculated by a global distribution model during the time period 1947-1996.
persistence is not fixed value, but dependent on climate and thus on the zonal distribution of a chemical
Wania, F., and D. Mackay 1999. Global chemical fate of -hexachlorocyclohexane. 2. Use of a global distribution model for mass balancing, source apportionment, and trend predictions.
Environ. Toxicol. Chem., in press.
Effect of Temperature on Travel Distance in Air
A drop in temperature causes two opposing effects:1. reaction half-lifes increase, resulting in an increase in persistence2. partitioning shifts from air into surface media (soil, water, etc.)
0
1
2
3
4
5
6
7
8
0 5 10 15 20 25 30
temperature in °C
trav
el d
ista
nce
in a
ir in
103
km
biphenyl
toxaphene
hexachloro-biphenyl
For chemicals with < 550 days, Lair always increases with decreasing temperature.
If degradation in environment is fast, a short Lair is determined by a short persistence and not by small partitioning into air. If T drops, the persistence of such substances will increase severely and Lair will also rise.
There is a need to investigate the influence of zonal ecosystem characteristics (climate, vegetation, soils, etc.) on
the multimedia fate of organic chemicals
Objective: Comparing various ecosystems with respect to their potential to cause high exposure of POPs to organisms
Comparative Environmental Chemistry of POPs
fate process ecosystem characteristic
degradation - clearance potential by degradation
partitioning - dilution potential
intermedia transfer - clearance potential by export / retention potential
- focussing potential within ecosystem
bioaccumulation - focussing potential within ecosystem