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TOX 715: Environmental Toxicology
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  1. TOX 715: Environmental Toxicology Environmental Transport

  2. Transport and Fate of Toxicants in the Environment Transport and fate model Environmental factors that may modify exposure Exposure-Response Model Toxicant Source(s) Toxicant Exposure Toxicant Effects

  3. Environmental Compartments

  4. Environmental Chemodynamics

  5. Fugacity • “Tendency of a compound to escape from one environmental compartment into another one”

  6. Fugacity Basics • Fugacity is to mass diffusion what temperature is to heat transfer. • Fugacity is linearly proportional to concentration. • Chemicals move from compartments in which they have high fugacities to those of low fugacity.

  7. Fugacity Basics • When the fugacities of a compound in two adjacent phases are equal, the system is in equilibrium. • Fugacity is expressed in units of pressure.

  8. C1 C0 Fugacity

  9. Partitioning

  10. Partitioning

  11. Solvent Partitioning

  12. Other Partition Coefficients: • Kow • Koc, Kb and Kpw

  13. Partitioning Theory and the Environment • Partitioning can be used to model the distribution of an organic compound in the environment. • Examples: • Sorption • Bioconcentration.

  14. Bioaccumulation • Bioaccumulation • general term used to describe a series of processes by which chemicals found in the environment are accumulated and concentrated in living organisms • Bioconcentration • Biomagnification

  15. Bioconcentration Factors

  16. Calculating BCFs • log BCF = 0.76 log Kow – 0.23 • log BCF = log Kow – 1.32 • log BCF = 0.50 log kow – 3.457

  17. Bioavailability

  18. Vapor Pressure • The pressure that the vapor of a substance exerts on its own liquid or solid state at equilibrium • 1 atm = 760 mmHg = 760 torr = 1.013 x 105 Pa.

  19. Measuring Vapor Pressures • PV = nRT • P = nRT/V = 244.4 (n/V) atm • n/V = vapor density in moles/L • R = universal gas constant = 0.082 L atm/°K/mole • T = temperature in the generating column in °K

  20. Henry’s Law • At equilibrium and at a determined temperature a constant relationship exists between the concentration of a chemical in air and water. • Henry’s Law Constant

  21. Estimating Volatilization Rates from H’

  22. Adsorption

  23. General Characteristics • Physico-chemical properties of the sorbent and the adsorptive • Area of the sorbent • The lower the aqueous solubility of the adsorptive (solute) the higher the binding potential • Heat has the potential to reduce adsorption

  24. Dissipation

  25. Environmental Transport

  26. Advection • Refers to the passive movement of a chemical as part of its presence in a medium that is in movement itself. • It can happen in the same compartment or between different compartments.

  27. Homogeneous Advection • Example, consider water in a stream flowing at 1000 m3/h and carrying a chemical at 0.5 μg/m3. The chemical is being advected in water at a rate of 500 μg/h.

  28. Heterogeneous Advection • Refers to the case where there is a secondary phase present inside the main advective medium. • Examples: particulate matter present in advecting river water, particles carried by wind.

  29. Diffusion • Random movement of chemical molecules due to the presence of a state of disequilibrium. • It will transport chemicals from one place to the other one within the same compartment as well as between compartments until equilibrium is reached.

  30. Intraphase Diffusion • Two types of diffusional intraphase transport: molecular and turbulent diffusion. • Molecular diffusion: movement of particles because of a concentration gradient. • Turbulent diffusion: happens because of the turbulent mixing of the bulk medium.

  31. Intraphase Diffusion • Fick’s law:

  32. Interphase Diffusion • Diffusion between two phases can be described using the following formula:

  33. Transport in Solution • Advection • Molecular diffusion • Turbulent diffusion • Dispersion

  34. Transport in Solution • Advection • Molecular diffusion • Turbulent diffusion • Dispersion

  35. Water-Air Transport

  36. Transport between Water-Air

  37. Transport through Soil • Vadose zone • Saturated zone • Aquaclude (basal rock)

  38. Transport in the Vadose Zone • Chemicals are able to migrate through the vadose zone by three main mechanisms: • dissolved in solution • as gases (vapor) • adsorbed to particles

  39. Transport through Groundwater

  40. Atmospheric Transport • Volatilization • Advection • Deposition

  41. Advective Transport

  42. Deposition

  43. Deposition