Appendix 3

1. Appendix 3 Frank Wania Evaluating Persistence and Long Range Transport Potential of Organic Chemicals Using Multimedia Fate Models

2. Evaluating Persistence and Long Range Transport Potential of Organic Chemicals Using Multimedia Fate Models Frank Wania, WECC Don Mackay, Eva Webster, Trent University Andreas Beyer, Michael Matthies, Universität Osnabrück 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.

3. Evaluating Environmental Persistence overall persistence Mtot and NRtot can be calculated using a multimedia environmental fate model such as EQC multimedia partitioning, and thus t, 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

4. Overall Global Persistence DLA ·fA EA Air DAW ·fA DAE ·fA DRA ·fA DEA ·fE DWA ·fW DRE ·fE DRW ·fW Water Soil DEW ·fE EE EW DLE ·fE DLW ·fW Calculating Overall Persistence 3-compartment level III model used to estimate an overall persistence of an organic chemical in the global environment Wania, F. An integrated criterion for the persistence of organic chemicals based on model calculations. WECC Report 1/98.

5. C 3500 3000 2500 B 2000 overall persistence in hours 1500 10 1000 8 6 500 log KOW 4 A 2 0 0 -15 -13 -11 -9 -2 -7 -5 -3 -1 1 log KAW 3 5 Calculating Overall Persistence 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.

6. Calculating Overall Persistence overall persistence twater with emission into water only overall persistence tsoil with emission into soil only fair fraction of emissions into soil 0 0.25 1.0 0.5 0.75 1.0 0.75 0 fwater fraction of emissions into water 0.25 0.5 fair fraction of emissions into air 0.5 0.25 0.75 overall persistence tair with emission into air only 0 1.0 linear additivity of overall persistence t = fair·tair + fwater· twater + fsoil·tsoil

7. Calculating Long Range Transport Potential Characteristic Travel Distance CM CM0 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). CM0/e distance LM • Assumptions: • steady-state between moving phase and stationary phase • no dispersion • advective transport uni-directional van Pul et al. 1998, Bennett et al. 1998, Beyer et al. 1999

8. Calculating Long Range Transport Potential 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) facilitates use of traditional multimedia model for calculation of L Example: Air Moving Over Soil NRA characteristic travel distance in air NIn air LA = u·MA / (NRA + NAS·F) LA = u·VA·ZA / (DRA + DAS·F) where F= DRS / (DSA + DRS) (fraction of chemical retained by soil) NOut NAS NSA soil NRS 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

9. Relationship Between Characteristic Travel Distance and Overall Persistence 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 t = Mtot / NRtot LM = u·MM·t/ Mtot LM is distance a molecule travels during the environmental residence time (u·t), multiplied by the proportion of mass in the moving medium (MM / Mtot) Example: Travel Distance in Air for very volatile chemicals Mair / Mtot = 1, thus Lair = u·t (maximum possible) for less volatile chemicals Mair / Mtot is small, thus Lair is small

10. Calculating Long Range Transport Potential maximum travel distance chemical partitions only into moving phase (air) 1000000 u.tair HCB 100000 tetraCB 10000 travel ditance in air in km chlorobenzene g-HCH dieldrin heptaCB DDT 1000 decaCB benzene OCDD aldrin 100 1000000 1000 10000 10000 1 10 100 half-life in air in hours minimum travel distance chemical partitions completely onto particles and deposition is irreversible

11. Calculating Long Range Transport Potential using a multimedia model (EQC) to estimate a characteristic travel distance in air and water (Beyer et al., 1999) travel distance in water in km travel distance in air in km 1000000 10000 u.t u.t g-HCH 100000 HCB 1000 a-HCH HCB tetraCB 10000 100 chlorobenzene tetraCB km dieldrin DDE g-HCH hexaCB dieldrin biphenyl DDT 1000 DDT 10 OCDD benzene TCDD OCDD aldrin 100 1 0 1 10 100 1000 10000 100 1000 10000 overall persistence in days overall persistence in days

12. 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.

13. 14000 12000 10000 8000 overall persistence in hours 6000 4000 2000 0 1967 1977 1987 1947 1957 Overall Persistence and Global Distribution Overall persistence of a-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 a-hexachlorocyclohexane. 2. Use of a global distribution model for mass balancing, source apportionment, and trend predictions. Environ. Toxicol. Chem., in press.

14. 8 7 6 biphenyl hexachloro- biphenyl 5 4 travel distance in air in 103 km toxaphene 3 2 1 0 30 0 5 10 15 20 25 temperature in °C 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 persistence 2. partitioning shifts from air into surface media (soil, water, etc.) For chemicals with t < 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.

15. Comparative Environmental Chemistry of POPs 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 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