Understanding Organic Chemical Processes in Aquatic Environments

1. Organic Chemical Model Summary of Process Equations and Model Input Data WASP7 Course

2. Aquatic Transport, Speciation and Transformation Processes

3. TOXI Organic Chemical Processes • Equilibrium Processes • Sorption • Ionization • Kinetic Processes • Volatilization • Photolysis • Hydrolysis • Bacterial Degradation • Oxidation • Reduction

4. Sorption - Desorption • Reaction • Movement of chemical between the dissolved phase and particulate or solid phase. The chemical may be physically associated or chemically bound to functional groups on the solid. • Linear Partitioning Equation • Data • Partition coefficient (Kp, Koc, or Kow), Lw/kgS • Solids concentration, mg/L • Solids organic fraction

5. Ionization • Reaction • Dissociation of neutral parent molecule into ionic species • Weak acid − Weak base • Equilibrium Equations • Data • pKai, negative log of Kai • pKbi, negative log of Kbi • pH, negative log of [H+]

6. Volatilization • Data • Atmospheric concentration, g/m3 • Depth (surface area/volume), m • Henry’s Law constant, atm/molar • Water temperature, kelvin • Conductivity, kv, m/day • Function of depth, current velocity and wind speed, m/sec • Reaction • Movement of dissolved chemical between water and air • Kinetic Equation

7. Photolysis • Reaction • Degradation of dissolved chemical by sunlight • Data • Surface photolytic rate constant, kps, day-1 • Latitude and reference latitude, degrees • Light intensity at surface • Depth (surface area/volume), m • Light extinction coefficient, m-1 • Measured, or function of chl a, DOC, S • Kinetic Equation

8. Hydrolysis • Reaction • Kinetic Equation • Data • pH • kH or kHn, day-1 • kHa, molar-1day-1 • kHb, molar-1day-1

9. Bacterial Degradation • Reaction • Kinetic Equation • Data • kBW or kBS, day-1 • kB, (cells/mL)-1day-1 • bacterial population density, bac, (cells/mL)

10. Oxidation • Reaction • Kinetic Equation • Data • kOX, day-1 • kO, (moles/L)-1day-1 • oxidant concentration, oxrad, (moles/L)

11. Reduction • Reaction • Kinetic Equation • Data • kEX, day-1 • kE, (moles/L)-1day-1 • reductant concentration, exrad, (moles/L)

12. Organic Toxicant Time Functions • Water temperature (4) (degrees C) • Water velocity (4) (m/sec) • pH of water column & benthic segments • Normalized light intensity (photolysis option 2) • Wind speed at 10 meters (m/sec) • Bacteria population (Water & Benthos) • Air temperature (degrees C) • Reaeration rate constant (day-1) • Chlorophyll-a (mg/L)

13. Organic Toxicant Segment Parameters • Water velocity time function pointer • Water temperature (time function pointer and multiplier) • Wind speed multiplier • Reaeration rate multiplier • Dissolved organic carbon, DOC (mg/L) • Fraction organic carbon for solids 1, 2, 3 (fraction) • Chlorophyll a concentration (mg/L) • pH • Light extinction coefficient (meter-1) • Bacteria Population (cells/100 mL) • Oxidative radical concentration (moles/L) • Extra environmental property (e.g., reductant, moles/L) • Overall decay rate constant for chemicals 1, 2, 3 (day-1)

14. Constants Groups Solids Ionization Sorption Volatilization Hydrolysis Photolysis Biodegradation Oxidation Reduction Notes on Listing Constants are listed by group for Non-Ionic Toxicant module In the general Organic Toxicant Module, these constants are repeated for each of 5 ionic species Chemical 1 constants are shown; these are repeated for chemicals 2 and 3 Organic Toxicant Constants

15. Sorption Constants

16. Volatilization Constants

17. Hydrolysis Constants

18. Hydrolysis Constants, cont’d

19. Photolysis Constants

20. Biodegradation Constants

21. Oxidation Constants

22. Reduction Constants

23. Ionization Constants

24. Additional Oxidation Constants for Ionic Chemical