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