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