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/m 3 Concentration in water Cw = 2 mol/m 3 Kow = Co/Cw = 5,000 Partitioning of DDT Oil Water

Concentration in oil: Co = mol/m 3 Concentration in water: Cw = 10,000 mol/m 3 Kow = Co/Cw = Partitioning of NaCl Oil Water

K 12 = C 1 /C 2 = S 1 /S 2 K 12 : Chemical Partition Coefficient between media 1 and 2 (unitless) C 1 : Concentration in medium 1 (mol/m 3 ) C 2 : Concentration in medium 2 (mol/m 3 ) S 1 : Solubility of chemical in medium 1 (mol/m 3 ) S 2 : Solubility of chemical in medium 2 (mol/m 3 )

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 f i,A = f i,B K 12 = C 1 /C 2 = S 1 /S 2  i,A : Chemical potential of chemical i in medium A  i,B : Chemical potential of chemical i in medium B f i,A : Fugacity of chemical in medium A (Pa) f i,B : Fugacity of chemical in medium B (Pa)

What is an “evaluative” environment?

Mass Balance Total Mass =  M i =  (C i.V i ) Total Mass = C W.V W + C A.V A + C AE.V AE + C BS.V BS + C SS.V SS + C S.V S + C AB.V AB + C TB.V TB M : Mass (moles) C : Concentration (moles/m 3 ) V : Volume (m 3 ) K : Partition Coefficient Subscripts: W : WaterAB : Aquatic Biota AE : AerosolBS : Bottom Sediments S : SoilSS : Suspended Sediments A : AirTB : Terrestrial Biota

K AW = C A /C W K AEW = C AE /C W K BSW = C BS /C W K SSW = C SS /C W K SW = C S /C W K ABW = C AB /C W K TBW = C TB /C W Substitute the partition coefficients in the Mass Balance Equation

Total Mass = C W. V W + K AW. C W. V A + K AEW. C W. V AE + K BSW. C W. V BS + K SSW. C W. V SS + K SW. C W. V S + K ABW. C W. V AB + K TBW. C W. V TB Total Mass = C W.(V W + K AW.V A + K AEW.V AE + K BSW.V BS + K SSW.V SS + K SW.V S + K ABW.V AB + K TBW.V TB ) UNKNOWN Total Mass = C W.V W + C A.V A + C AE.V AE + C BS.V BS + C SS.V SS + C S.V S + C AB.V AB + C TB.V TB

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? P air P water Equilibrium: P air = P water f air = f water P air : Pressure of water in air P water : Pressure of water in liquid water f air : Fugacity of water in air f water : Fugacity of water in liquid water

What is fugacity? P air P water Equilibrium: P air = P water f air = f water P air : Pressure of benzene in air P water : Pressure of benzene in liquid water f air : Fugacity ofbenzene in air f water : Fugacity of benzene in liquid water

a f m f Measuring fugacity

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/m 3 ) f : fugacity (Pa) Z : fugacity Capacity (mol/Pa.m 3 )

What is Z? Z is the number of moles of a substance that you can add to 1m 3 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.

K AW = C A /C W f A.Z A /f W.Z W = Z A /Z W Since f A = f Z

ANALOGY : Fugacity Capacity(mol/m 3.Pa) amount of substance (in moles) that you can add to 1m 3 of a phase or medium in order to raise the fugacity of the chemical in that phase by 1 Pa. Heat Capacity (J/m 3.K) amount of heat (in Joules) that you can add to 1m 3 of a phase or medium in order to raise the temperature of the medium by 1 degree Kelvin.

Mass Balance Total Mass = Sum (C i.V i ) Total Mass = Sum (f i.Z i.V i ) At Equilibrium : f i are equal Total Mass = M = f.Sum(Z i.V i ) f = M/Sum (Z i.V i ) C : Concentration (mol/m 3 ) f : fugacity (Pa) Z : fugacity Capacity (mol/Pa.m 3 )

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: f W = f A C W /Z W = C A /Z A Z W = C W.Z A /C A Z W = C W /R.T.C A Z W = 1/K AW R.T H = K AW R.T Z W = 1/H

Recipes for Z Particulate: f W = f S Phases, i.e.C W /Z W = C S /Z S Soil,Z S = C S.Z W /C W SedimentZ S = K SW.Z W Susp. Sed.Z S = K SW /H Z S = K* SW.d S /H Z S = f OC.K OC.d S /H Z S = f OC.0.41.K OW.d S /H

Recipes for Z Biological f W = f B PhasesC W /Z W = C B /Z B Z B = C B.Z W /C W Z B = K BW.Z W Z B = K BW /H Z B = K* BW.d B /H Z B = L B.K OW.d B /H