Lecture notes 445

1
(No Transcript)
2
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.
3
Environmental Partitioning
What is Partitioning?
4
Partitioning of DDT
Concentration in oil Co 10,000 mol/m3
Oil
Concentration in water Cw 2 mol/m3
Water
Kow Co/Cw 5,000
5
Partitioning of NaCl
Concentration in oil Co 0.001 mol/m3
Oil
Concentration in water Cw 10,000 mol/m3
Water
Kow Co/Cw 0.0000001
6
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)
7

• Equilibrium
• End result of a partitioning process.
• Concentrations in media reflect the chemicals
  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)
8
What is an evaluative environment?
9
(No Transcript)
10
Mass Balance Total Mass S Mi S
(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
11
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
12
Total Mass CW.VW CA.VA CAE.VAE CBS.VBS
CSS.VSS CS.VS CAB.VAB CTB.VTB
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
UNKNOWN
Total Mass CW.(VW KAW.VA KAEW.VAE
KBSW.VBS KSSW.VSS KSW.VS KABW.VAB
KTBW.VTB)
13
Application
14
What are the merits limitations of the
Environmental Partitioning Approach for
Evaluative Environments?
15

• 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

16

• 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

17

• 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

18
What is fugacity?
19
What is fugacity?
then
Glass of Water
20
What is fugacity?
Glass of Water
21
What is fugacity?
Glass of Water
Glass of Water
22
What is fugacity?
Equilibrium Pair Pwater fair fwater
Pair
Pwater
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
23
What is fugacity?
Equilibrium Pair Pwater fair fwater
Pair
Pwater
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
24
Measuring fugacity

25

26

• 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

27
What is the Relationship between? Fugacity
Concentration
28
Relationship between Fugacity Concentration C
f.Z C Concentration (mol/m3) f fugacity
(Pa) Z fugacity Capacity (mol/Pa.m3)
29

• 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 chemicals partition
  coefficient K.

30
KAW CA/CW fA.ZA/fW.ZW ZA/ZW Since
fA fZ
31
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.
32
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)
33
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
34
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
35
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 KSW.dS/H ZS
fOC.KOC.dS/H ZS fOC.0.41.KOW.dS/H
36
Recipes for Z Biological fW fB Phases CW/ZW
CB/ZB ZB CB.ZW /CW ZB KBW.ZW ZB
KBW/H ZB KBW.dB/H ZB LB.KOW.dB/H