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Objectives:
to formalize the relationship between the properties of the chemical and its environmental behaviour.
to apply these relationship to develop tools for the assessment of the fate of the chemical in the environment.
What is Partitioning?
Environmental Partitioning
Concentration in oil:
Co = 10,000 mol/m3
Concentration in water
Cw = 2 mol/m3
Kow = Co/Cw = 5,000
Partitioning of DDT
Oil
Water
Concentration in oil:
Co = 0.001 mol/m3
Concentration in water:
Cw = 10,000 mol/m3
Kow = Co/Cw = 0.0000001
Partitioning of NaCl
Oil
Water
Partitioning
Partitioning is the phenomenon where a chemicalsubstance distributes itself based on its ability todissolve in the media involved.
K12 = C1/C2 = S1/S2
K12 : Chemical Partition Coefficient between media 1 and 2 (unitless)
C1 : Concentration in medium 1 (mol/m3)
C2 : Concentration in medium 2 (mol/m3)
S1 : Solubility of chemical in medium 1 (mol/m3)
S2 : Solubility of chemical in medium 2 (mol/m3)
Equilibrium•End result of a partitioning process.
•Concentrations in media reflect the chemical’s solubilities of the chemical substance in the media involved
•A situation where the concentrations in the two media do no longer change with time.
i,A = i,B
•fi,A = fi,B
•K12 = C1/C2 = S1/S2
i,A : Chemical potential of chemical i in medium A
i,B : Chemical potential of chemical i in medium B
fi,A : Fugacity of chemical in medium A (Pa)
fi,B : Fugacity of chemical in medium B (Pa)
What is an “evaluative” environment?
Mass Balance
Total Mass = Mi = (Ci.Vi)
Total Mass = CW.VW + CA.VA + CAE.VAE + CBS.VBS +
CSS.VSS + CS.VS + CAB.VAB + CTB.VTB
M : Mass (moles)
C : Concentration (moles/m3)
V : Volume (m3)
K : Partition Coefficient
Subscripts:
W : Water AB : Aquatic Biota
AE : Aerosol BS : Bottom Sediments
S : Soil SS : Suspended Sediments
A : Air TB : Terrestrial Biota
KAW = CA/CW
KAEW = CAE/CW
KBSW = CBS/CW
KSSW = CSS/CW
KSW = CS/CW
KABW = CAB/CW
KTBW = CTB/CW
Substitute the partition coefficients in the Mass Balance Equation
Total Mass = CW. VW + KAW. CW. VA + KAEW. CW. VAE + KBSW. CW. VBS + KSSW. CW. VSS + KSW. CW. VS + KABW. CW. VAB + KTBW. CW. VTB
Total Mass = CW.(VW + KAW.VA + KAEW.VAE + KBSW.VBS
+ KSSW.VSS + KSW.VS + KABW.VAB + KTBW.VTB)
UNKNOWN
Total Mass = CW.VW + CA.VA + CAE.VAE + CBS.VBS +
CSS.VSS + CS.VS + CAB.VAB + CTB.VTB
Chemical Name: dioxinAmount (moles): 1Temperature (C): 25Molecular Weight (g/mol): 322Water Solubility (g/m3): 1.93E-05Vapor Pressure (Pa): 2.00E-07log Kow (no units): 6.8
Concentration C (mol/m3) = f.Z 1.15E-05 2.29E-05 4.47E-05 2.29E-05 1.48E-10 1.99E-13Mass (moles) = C.V 0.515514 0.481146 0.000313 0.000802 0.001033 0.001192 1% Mass 0.515514 0.481146 0.000313 0.000802 0.001033 0.001192
Soil Sediment Biota S.Sedim. Water Air Total
Application
What are the merits & limitations of the Environmental Partitioning Approach for Evaluative Environments?
Environmental Partitioning in Evaluative Environments
Merits:
•Provides assessments of the environmental distribution of chemicals based on chemical properties
•Can be used for comparing/ranking chemicals
Environmental Partitioning in Evaluative Environments
Limitations:
•Closed System
•Describes an end-situation, achieved after a long time when equilibrium is reached.
•Absolute values of concentrations are irrelevant
•Well mixed environment
•Assumes chemical losses (through transformation and transport) do not occur
Environmental Partitioning in Evaluative Environments
Limitations:
•Closed System
•Describes an end-situation, achieved after a long time when equilibrium is reached.
•Absolute values of concentrations are irrelevant
•Well mixed environment
•Assumes chemical losses (through transformation and transport) do not occur
What is fugacity?
Glass of Water
What is fugacity?
then
Glass of Water
What is fugacity?
Glass of Water
What is fugacity?
Glass of Water
What is fugacity?
Pair
Pwater
Equilibrium:
Pair = Pwater
fair = fwater
Pair : Pressure of water in air Pwater : Pressure of water in liquid water
fair : Fugacity of water in air fwater : Fugacity of water in liquid water
What is fugacity?
Pair
Pwater
Equilibrium:
Pair = Pwater
fair = fwater
Pair : Pressure of benzene in air Pwater : Pressure of benzene in liquid water
fair : Fugacity ofbenzene in air fwater : Fugacity of benzene in liquid water
af
mf
Measuring fugacity
af
mf
mf
efPOG cylinder (68 mm o.d., 64 mm i.d., 70 mm tall)coated with EVA solution
5/16 “ steel support rod
eight, 3/16 “ air circulation holes
gap between upper and lowerstainless steel bowls to promote aircirculation
Fugacity
•Escaping Tendency of the chemical
•The partial pressure that the chemical substance exerts
•Referred to as f
•Measured in units of pressure (Pa)
•Applies to all media
•Expresses chemical potential or activity in a measurable quantity
What is the Relationship between?
Fugacity
&
Concentration
Relationship between
Fugacity & Concentration:
C = f.Z
C : Concentration (mol/m3)
f : fugacity (Pa)
Z : fugacity Capacity (mol/Pa.m3)
What is Z?
•Z is the number of moles of a substance that you can add to 1m3 of a phase or medium in order to raise the fugacity of the chemical in that phase by 1 Pa.
•Expresses the ability of a medium to “dissolve” a chemical substance
•The ratio of Z values for a chemical substance is equivalent to the chemical’s partition coefficient K.
KAW = CA/CW
fA.ZA/fW.ZW =
ZA/ZW
Since fA = fZ
ANALOGY :
Fugacity Capacity(mol/m3.Pa)
amount of substance (in moles) that you can add to 1m3 of a phase or medium in order to raise the fugacity of the chemical in that phase by 1 Pa.
Heat Capacity (J/m3.K)
amount of heat (in Joules) that you can add to 1m3 of a phase or medium in order to raise the temperature of the medium by 1 degree Kelvin.
Mass Balance
Total Mass = Sum (Ci.Vi)
Total Mass = Sum (fi.Zi.Vi)
At Equilibrium : fi are equal
Total Mass = M = f.Sum(Zi.Vi)
f = M/Sum (Zi.Vi)
C : Concentration (mol/m3)
f : fugacity (Pa)
Z : fugacity Capacity (mol/Pa.m3)
Recipes for Z
Air:
Ideal Gas Law : p.V = n.R.T
p = (n/V).R.T
p = C.R.T
f = C.R.T.
C/f = 1/RT
Z = (C/f) = 1/RT
Recipes for Z
Water: fW= fA
CW/ZW = CA/ZA
ZW = CW.ZA /CA
ZW = CW/R.T.CA
ZW = 1/KAWR.T
H = KAW R.T
ZW = 1/H
Recipes for Z
Particulate: fW= fS
Phases, i.e. CW/ZW = CS/ZS
Soil, ZS = CS.ZW /CW
Sediment ZS = KSW.ZW
Susp. Sed. ZS = KSW/H
ZS = K*SW.dS/H
ZS = fOC.KOC.dS/H
ZS = fOC.0.41.KOW.dS/H
Recipes for Z
Biological fW= fB
Phases CW/ZW = CB/ZB
ZB = CB.ZW /CW
ZB = KBW.ZW
ZB = KBW/H
ZB = K*BW.dB/H
ZB = LB.KOW.dB/H