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Environmental Exposure Assessment Environmental Fate Processes and Exposure Modelling Michael Matthies Institute of Environmental Systems Research University.

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Presentation on theme: "Environmental Exposure Assessment Environmental Fate Processes and Exposure Modelling Michael Matthies Institute of Environmental Systems Research University."— Presentation transcript:

1 Environmental Exposure Assessment Environmental Fate Processes and Exposure Modelling Michael Matthies Institute of Environmental Systems Research University of Osnabrück, D Osnabrück USF

2 Content Introduction Basic Assumptions Environmental Fate Processes - Partitioning - Transport - Transformation Single Medium Modelling Intermedia Exchange Processes Multimedia Modelling Application and Applicability (Refined Approach)

3 Risk assessment Effects assessment Exposure assessment Risk characterisation Risk = f(Exposure,Effects,Probability) Risk management PEC PEC / PNEC 1 ? PNEC

4 Exposure Modelling An exposure model converts a mass load [kg/a] into an environmental concentration (PEC) [kg/m 3 ]. Release estimation Physico-chemical properties Environmental fate processes Exposure Model Predicted Environmental Concentration (PEC)

5 Release, Distribution and Fate Primary environmental medium Multimedia environment Water Air Soil Biota Anthropo- sphere Release Distribution Local Scale Regional to global scale Point or diffuse release

6 Environmental media can be defined in such a manner as to represent phases or mixtures of phases in a thermodynamic sense. Rules and laws of chemical equilibrium and kinetics can be applied to environmental systems. Feedback of toxic effects on organisms on the chemicals fate is neglected. No mixtures, only single compounds are considered. Interaction between components of mixtures are therefore also not regarded. Usually, only molecular-dispersively dissolved compounds and no separate phases of compounds are considered. Environmental Fate Process Modelling Basic assumptions

7 Environmental Fate Processes An environmental fate or chemodynamic process is the quantitative or qualitative change of a substance with time due to environmental factors. This can be a change of - mass, - concentration, - chemical structure, or - any substance property. Chemodynamic points out the dynamic nature of processes involved.

8 Environmental Fate Processes Partitioning - partitioning between two phases, e.g. air and water, - ad/desorption on particles, - uptake into lipid phases. Transport - mixing and dilution, - ad/convection, - diffusion, - dispersion. Transformation - photolysis and photochemical degradation, - hydrolysis, - microbial biotic degradation - metabolic transformation.

9 Partitioning Environment is divided into non-mixable phases Air, surface water, soil, sediment, ground water, plants, etc. Chemicals are partitioning into all or several phases in thermodynamic equilibrium. Partition coefficients partitioning of a substance between two phases. dependent on substance and phase properties. partition coefficient phase i and j: K OA K AW K OW Lipids (octanol) Air Water

10 Interdependence of physical-chemical properties

11 Transport and transformation processes Diffusion microscopic (molecular) isotropic random movement and mixing of molecules (Browns molecular movement) based on 2nd law of thermodynamics (entropy) property of the molecule and the surrounding medium Advection directed flow of a medium, e.g. water or air flow based on 1nd law of thermodynamics (energy conservation) e.g. a substance is transported downstream by the flowing of a river Dispersion macroscopic flow dynamic process, occurs only in moving media orders of magnitudes faster than diffusion turbulent mixing (eddy diffusion)

12 Transport and Transformation Processes diffusion/dispersionadvectiondegradation 1. order combination of all processes

13 Fate processes in water advection volatilisationdischarge deposition of particles (sedimentation) degradation

14 Fate processes in water Sorbed and dissolved fraction deposition of particles (only sorbed fraction) volatilisation (only dissolved fraction) bioconcentration (only dissolved fraction) Bioconcentration in fish regression model: no biomagnification f W = f (particle concentration, OC-content, K OC )

15 Example: Bioconcentration

16 Fate processes in water Volatilisation diffusive mass transfer between air and water two-films theory two serial resistances Sedimentation (effective) sedimentation velocity of particles diffusive mass transfer into sediment pore water sediment burial Degradation hydroloysis aquatic photolysis microbial degradation

17 Fate processes in air atmospheric discharges area sources (e.g. urban area or pesticide spraying) multi-point sources (e.g. stack or vent) gas-particle distribution sorption of gaseous compounds to particles dry and wet deposition of gaseous and particle-bound fraction Pankow-Junge equation: calculated particle-bound fraction: Benzene: 0%, DEHP: 5%, TCDD: 32%, OCDD: 99% VP L vapour pressure of sub-cooled liquid c Junge-constant (ca. 17 [Pa×cm]) s particle surface (ca. 1,5E-6 [cm²/cm³])

18 Fate processes in air concentration = input / (advection + deposition + degradation) Degradation Deposition Advection Input (Area Emission) x z y steady state!

19 Fate processes in soil Three input scenarios puls input continuous substance input contaminated upper soil layer Analytical solution homogeneous vertical soil profile average continuous water input and output (generic scenario) water flow u and hydrodynmanic D are constant u.v.a. Mathematical model z Precipitation and evaporation degradation diffusion und dispersion advection u l D Leaching

20 Plant model Above ground plant parts roots degradation and growth diffusion soil/roots Wet and dry particle deposition gaseous exchange stemleaves fruit roots

21 Plant uptake model in EUSES

22 Transport for Multimedia Pollutants Water Sediment Surface soil Air Root-zone soil Roots Leaves Deep soil Gases Particles

23 A compartment (or box) is a well-mixed component of a system. Differential mass balance: change of mass = dm/dt = Input - Output; linear differential equations 1 /dt = - k 1 m 1 + k 2 m 2 + I A multi-compartment model consisting of various different environmental media is a multimedia model. Multimedia Exposure Modelling Mass Balance Approach m1m1 m2m2 I fat (octanol) K OA K AW K OW air water

24 Equilibrium and steady state equilibrium thermodynamic equilibrium in closed system immediate equilibration in open system steady state in open systems no mass change with time: dm/dt = 0 Input = Output IO

25 Unit World generic global environment 1 km² area, 6 km height, 70% water, 30% soil Fugacity concept introduced for real gases to account for molecular interactíons; applied to all other environmental media escaping tendency of a chemical dependency of partition coefficients on fugacity (in equilibrium) concentration= fugacityfugacity capacity mol / m³= Pamol / (m³ Pa) Multi media models (Mackay,1991)

26 I II III & IV Multi media models Level I - IV Closed system: phase equilibrium (partition coefficients) Open system: same as Level I but with advective input and output and degradation in steady-state Open system: same as Level II but with interphase mass transfer non equilibrium Level III: steady-state Level IV: non steady-state

27 fish air water soil sediment plants Multi-media models Form the environment to compartments Background ubiquitous occurrence of chemicals virtually all chemicals are distributed over various media due to advection and dispersion with wind and water partitioning between phases

28 Multi media model with 4 compartments (Unit World) Water 0.7 km² 10 m = m³ Sediment 0.7 km² 3 cm = m³ Soil 0,3 km² 15 cm = m³ Air 1 km² 6 km = m³

29 Illustration of Level I and II model f = fugacity Z = fugacity capacity V = volume C = f·Z M = C·V = f·Z·V Input air water soil Z Output Level I: no input and output Level II: with input and output

30 Multi-media models Level I example calculation (Unit World)

31 Regional emission and distribution model

32 Illustration of Level III f = fugacity Z = fugacity capacity V = volume = valve (== resistance) Input air water sediment Z Output Input f V

33 European Union System for the Evaluation of Substances (EUSES) Model structure

34 Local emission and distribution pathways All stages of life-cycle

35 Model optimization Model and parameter uncertainties

36 Restricted Applicability Polar substances Super lipophilic compounds Surfactants Heavy metals Polymers Complexes Metabolites Mixtures

37 Exposure and Risk Assessment Software CemoS Chemical Exposure Model System Compilation of nine exposure models; substance data base; estimation routines mainly for educational purposes EUSES European Union System for the Evaluation of Substances Official software for the risk assessment of chemicals in the EU Based on Technical Guidance Document CalTOX 8-compartment multi-media programme; hazard and risk assessment recommended for the risk assessment of contaminated soil in California Excel-spreadsheet

38 Questions?

39 Decision support system EUSES Parameters and Connectivity

40 Literature Trapp,S., Matthies,M.: Chemodynamics and Environmental Modeling - An Introduction, Springer, Heidelberg, 1997 Trapp,S., Matthies,M.: Dynamik von Schadstoffen - Umweltmodellierung mit CemoS, Springer, Heidelberg, 1996 Thibodeaux,L.: Environmental Chemodynamics: movement of chemicals in air, water and soil (2. Aufl.), Wiley, New York, 1996 Klöpffer, W.: Verhalten und Abbau von Umweltchemikalien - Physikalisch chemische Grundlagen, ecomed, Landsberg, 1996 Mackay,D.: The Fugacity Approach - Multimedia Environmental Models, Lewis Pub., Michigan, 1991 van Leeuwen,C., Hermens,J.: Risk Assessment of Chemicals - An Introduction, Kluwer Acad. Publ., Dordrecht, 1995

41 Exposure Assessment release estimation physico-chemical properties environmental parameters Exposure Model Predicted Environmental Concentration (PEC)

42 Flow dynamic approach Based on first physical principles of mass and energy conservation and entropy changes. Flow dynamics in atmosphere, ground and surface water etc. Partial differential equations, which usually have to be solved numerically. Examples: global circulation model, groundwater transport. Mass balance approach Similar to the pharmaco-kinetic models for drugs. Same approach as in cost accounting or demographic models. Based on exchange of matter between compartments and reaction kinetics. Linear differential equations, which can be solved analytically or numerically. Examples: Multi-media models of Mackay; (bio-)reactor models. Exposure Modelling Two Approaches

43 Plant model Model assumptions roots: Gleichgewichtsverteilung mit dem Boden leaves: gewöhnliche Differentialgleichung Benötigte Daten 10 pflanzenspezifische Parameter: Blattoberfläche, Wachstumsrate, etc. 2 Konzentrationen: Bodenwasser und Luft (Gasphase) 1 substanzabhängiger Parameter (logK OW ) Transferpfade Quelle - Luft - Blätter Quelle - Boden - Wurzel Quelle - Boden - Luft (Ausgasung, Resuspension) - Blätter Alternative Modellierungsansätze Biokonzentrationsfaktoren Mehr-Kompartimentmodelle

44 Aquatic Bioconcentration model in EUSES

45 Illustration of Level I model f = fugacity Z = fugacity capacity V = volume C = f·Z m = C·V = f·Z·V V Air Water Soil Z f

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