1. ENVIRONMENTAL FATE TOPIC 3

2. OVERVIEW – Environmental Fate Terms – Environmental Modeling – Air – Water – Multi Media – Choosing the right model – Midterm #1 Review

3. ENVIRONMENTAL FATE – Where do environmental hazards come from? – Point sources – smoke or water discharge from a factory – contamination from a Superfund site – Non-point sources – automobile exhaust – agricultural runoff – Natural sources

4. ENVIRONMENTAL FATE – How does exposure occur? – Pathways (one or more may be involved) – Air – Surface Water – Groundwater – Soil – Food – Non-food consumer products, pharmaceuticals

5. ENVIRONMENTAL FATE – Environmental Fate – ultimate destination of contaminants released into the environment – Chemodynamics= study of chemical release, distribution, degradation, and fate in the environment – Three Major Components – 1. Transport – 2. Transfer – 3. Transformation

6. ENVIRONMENTAL TRANSPORT – Physical movement of pollutants in a media / matrix – Atmosphere (air) – Hydrosphere (water) – Lithosphere (soil) – Biosphere (living organisms)

7. ENVIRONMENTAL TRANSFER – Movement of pollutants through media – Between environmental matrices (air, soil, water, and living organisms) – If you release a chemical into the environment, where does it ultimately end up?

8. ENVIRONMENTAL TRANSFORMATION – Change in the physical or chemical structure in a pollutant – Oxidation, photolysis, chemical interaction of pollutants – Example – photochemical smog; rust

9. PRIMACY OF REAL DATA – Real data takes priority in environmental fate modeling – Not always available – Cost prohibitive – Time prohibitive – Timing of study

10. MASS BALANCE – Many fate models are built on concept of mass balance – Aka. Conservation of mass – Mt = M2 + M1 – M3 – M1 = mass entering compartment – M2 = existing mass – M3 = mass exiting compartment – Mt = total mass in the compartment

11. MASS BALANCE

12. – Sources (M1) may include transfer and transport – Background levels (M2) mean the level of a pollutant / chemical present attributable to natural sources – Metals – Radiation – Sulphur dioxide

13. EPA CEAM – Models have been developed since the 1960’s – Currently in wide use in remediation planning, licensing of new chemicals and identification of emission sources – Center for Exposure Assessment Modeling (CEAM) – NIH has database of modeling studies

14. AIR MODELING CONCEPTS – Primary routes contaminants use to enter the air are evaporation or stack emissions – Begin with coordinate or “frame of reference” – Helps to identify the location and movement of pollutants – 2 Types of Systems – 1. Eulerian – 2. LaGrangian

15. EULERIAN – Fixed on the Earth’s surface – Can be thought of as a map of pollutant location – Most data is collected using this system – Best suited for: – Describing topography – Atmospheric issues – Movement of reactive pollutants from multiple sources

16. LAGRANGIAN – Fixed on a parcel (compartment of air) or puff of pollutant – Observer in this frame of reference always stays in center of the puff – Makes it easier to model certain effects, such as diffusion

17. EULERIAN VS. LAGRANGIAN

18. PARCEL MOVEMENT – Movement of the compartment of air, or parcel, is dependent on many variables – Some basic information includes: – Horizontal and vertical velocity of parcel as it exits the stack – Temperature of parcel and surrounding atmosphere – Wind speed – Terrain (buildings and hills/valleys)

19. EPA UNAMAP – Air models can be traced back to EPA’s Users Network for Applied Modeling of Air Pollution (UNAMAP) – Divided 3 Categories – 1. Near Field = transport of pollutants 0-50 km from source – 2. Intermediate Range= transport of pollutants 50-250 km from source – 3. Long Range= transport of pollutants over 250 km

20. UNCERTAINTY OF AIR TRANSPORT MODELS – Uncertainty depends heavily on the category – Uncertainty in Near Field – Channeling pollutant flow vs simple diffusion – Mechanical (as opposed to natural) turbulence – Drastic changes in wind speed and direction – Effects of varying temperatures (air heating and cooling)

21. UNCERTAINTY OF AIR TRANSPORT MODELS – Intermediate Range Models have greater uncertainty due to – Substantial travel time of pollutants – Daily variations in weather – Larger terrain effects during transport – Long Range Models – Same type of problems as intermediate range – More research devoted to long range

22. AIR DISPERSION MODELS – ROLLBACK MODELS – Originated with Clean Air Act – Simple and require few resources – Relate historical data to future air quality using linear relationships – Acceptable for screening air control strategies – More sophisticated models required after initial screening

23. AIR DISPERSION MODELS – STATISTICAL MODELS – Regression Analysis is most typical approach – Variations in spatial distribution of pollutants evaluated as a statistical task – Associations are valid for the prevailing conditions – If new sources are introduced, all the previous associations may no longer be valid

24. AIR DISPERSION MODELS – GAUSSIAN PLUME AND PUFF MODELS – Among the oldest and most preferred models – Depend on the availability of realistic physical data on wind and diffusion – Especially suitable for non-reactive pollutants – Various Gaussian Models can account for problems such as: – Turbulent diffusion – Dry deposition – Washout from rain / snow

25. GAUSSIAN PLUME MODEL

27. GAUSSIAN MODEL LIMITATIONS – Depends on availability of accurate data – Wind speed / direction variability – Velocity and amount of contaminant coming out of stack – Validity drops with stable atmospheres such as inversions – Ex. If an inversion were located just above the plume, it could interfere with upward dispersion of plume – Vulnerable to effects of complex terrain – Turbulence created by terrain interferes with assumption of even dispersion of pollutants

28. AIR DISPERSION MODELS – BOX AND MULTIBOX MODELS Top of Box= first inversion layer Bottom of Box = terrain Remaining areas are usually geographically defined areas, such as mountains

29. AIR DISPERSION MODELS – REGIONAL TRAJECTORY MODELS – Usually covers larger regions – Uses Lagrangian equation: dM/dt = -(a+b+c) x M – a, b, c = dry removal, wet removal, chemical conversion – M= mass inside moving compartment – These models have been used to study – Pollution transport across the U.S. – Transport of acid rain – Large smog episodes – Focuses on mass conservation over time – Only good for limited number of source or multiple sources treated as a single source

30. ENVIRONMENTAL FATE MODELS - RIVERS – Contaminants enter water via direct application, spills, and interphase movement – Advection= horizontal movement by currents – Advection Rate= velocity of pollutants moving downstream – Diffusion = spreading or mixing – Molecular diffusion= random thermal movements of molecules – Turbulent diffusion= mixing encouraged by turbulence – Both advection and diffusion are reduced when pollutants are adsorbed to river bottom sediments

31. ENVIRONMENTAL FATE MODELS - RIVERS – Primary conceptual basis is mass balance – Can incorporate a variety of issues: – Media Transfer= movement of pollutant to air and soil – Degradation and decay of chemical compounds – Transformation of pollutant to different chemical states – Non-Point and Point Source contributions

32. ENVIRONMENTAL FATE MODELS - RIVERS – Exposure Analysis Modeling System (ExAMS) – River is seen as a series of uniformly mixed “reaches” or large compartments – Estimated concentrations are based on uniform dilutions in each reach and assumed rates of physical / chemical removal

33. UNCERTAINTIES IN RIVER MODELS – Transport of sediments which have adsorbed pollutants – Biological transformations – Complex flow conditions, such as tidal forces – Variable rates of pollution introduced into the river

34. SERATRA – Sediment radionuclide transport – Water fate model – Accounts for sediment movement in rivers – Requires extensive data input and computer time – Cannot handle reversible flow (tidal movement)

35. ENVIRONMENTAL FATE MODELS - WATERSHEDS – Watershed = water flowing over land towards surface water – Focuses on hydrological concepts – runoff patterns – rates of evaporation – percolation – soil erosion – EPA uses Hydrological Simulation Program – Fortran (HSPF) model to simulate discharging areas to rivers or reservoirs

36. ENVIRONMENTAL FATE MODELS - GROUNDWATER – Vadose Zone (unsaturated zone)= region between ground level and saturated zone – Saturated Zone= generally an aquifer composed of sand and gravel with water saturating the pores – Movement of contaminants in vadose zone are subject to adsorption and desorption

37. ENVIRONMENTAL FATE MODELS - GROUNDWATER – Once they reach the aquifer, pollutants are measured using: – Hydraulic Conductivity= movement of pollutants in saturated zone – Hydraulic Gradient= difference in water pressure – Soil Porosity= percentage of water within total volume of aquifer

38. VLEACH – Vadose Leaching model – Screening model for organic contaminants moving through the vadose zone – Only examines vertical movement towards groundwater – Simulate – 1. Vapor phase diffusion (evaporation of pollutant) – 2. Liquid phase advection (movement with water) – 3. Solid phase sorption (attachment of pollutant to soil) – 4. Equilibrium of the above

39. FOOD CHAIN MODELS – Tracking the movement of contaminants through food chains and for estimating chemical impacts on organisms – Used to evaluate pesticides by determining the persistence, mobility, and bioaccumulation potential of a active ingredient and its major metabolites – Multi-media studies show food chain may be primary source of exposure to organic pollutants

40. MULTI – MEDIA ISSUES – Environmental health professionals are concerned with components such as air, water, food, etc. – Realize these components are interlinked but raises questions – Which media pollutions is most serious? – Which treatment method works best? – Which policies should we use? Policies usually focus on one media at a time.

41. MULTI-MEDIA TRANSFER – Mathematical modeling of pollutant movement through air, water, and soil – Partitioning between phases – Phases = solid, liquid, gaseous phases of a compound – Partitioning= ratio of concentrations between two phases

42. MULTI-MEDIA TRANSFER – Air -- Water – Volatilization: transfer from water to air – Absorption: transfer from air to water – Soil – Water – Desorption: transfer from soil to water – Adsorption: transfer from water to soil – Soil – Air – Volatilization: transfer from soil to air – Deposition: transfer from air to soil

44. HENRY’S LAW – Amount of a gas that dissolves in liquid is directly proportional to the partial pressure of that gas – P = kX – K = Henry’s Law constant (air-water partitioning coefficient for a particular gas) – X= mole fraction of a gas in liquid – P= vapor pressure of a gas – Used in Air-Water Partitioning

45. OCTANOL WATER PARTITIONING COEFFICIENT – P = Co / Cw – P = octanol-water partitioning coefficient – Co = concentration of chemical in octanol – Cw = concentration of chemical in water – Octanol is a fatty alcohol – If P is high, the chemical is more fat soluble (eg. DDT) – Water-Organic Partitioning is used in food chain models – Unitless and expressed as logP

46. ORGANIC CARBON DISTRIBUTION COEFFICIENT – Koc = Cs / Cw – Koc = organic carbon distribution coefficient – Cs = concentration of chemical attached to soil – Cw = concentration of chemical in water – Organic carbon content of soil is responsible for binding with pollutants – Organic carbon is measured by combusting a soil sample and measuring the carbon dioxide produced – useful in predicting the mobility of organic soil contaminants – Higher Koc values mean the organic contaminant is less mobile

47. CHOOSING THE RIGHT MODEL – 1. Rating Models – Based on subjective ranking of geological and pollutant factors – Good for overviews, screening, hard to find or missing data – 2. Analytical Models – Based on simple math equations – Eg. Gaussian models – 3. Numerical Models – Complex equations – Need more data

48. OVERVIEW – Environmental Fate Terms – Environmental Modeling – Air – Water – Multi Media – Choosing the right model

49. QUESTIONS?