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Chemical concentration, activity, fugacity, and toxicity. Don Mackay and Jon Arnot Trent University. McKim Conference Duluth, MN September, 2007. Outline. A refresher of some physical chemistry Four chemicals, log K OW = 2, 4, 6, 8 Two organisms, fish and mammal
Don Mackay and Jon Arnot
Raoult P = x PSL (ideal)
Raoult P = x PSL (non-ideal)
Dalton P = y PT
so P = x PSL =y PT
f = x fR = y PT
P = x PSL =y PT
when f = P, fR = PSL , = 1
f and P are “escaping pressures” Pa
2Two immiscible liquids and a gas phase in equilibrium, liquid solute.
P f = x11PSL =x22PSL = yPT
x11=x22= yPT / PSL= P / PSL = activity
Saturation or solubility occurs when activity=1.0
Solubility is a measure of the activity coeff.
P or f or activity
Partition coefficients KA1, KA2, K12
can be expressed using x1, x2,y or C1, C2, CA g/m3
e.g., KAW, KOW, KOA
Depend on 1, 2 and PSL
Can give ratios of 1/ 2
Relate C to f using C = Zf, Z is a “fugacity capacity”
Useful if solvent is complex, e.g., fish Z = 1/(PSL)
CAIR=ZAIR f C1= Z1 f C2 = Z2 f K12=Z1/Z2
The solute is in the liquid state and “thinks” it is a liquid so it behaves according to PSL
We must “correct” using F for solids
For gases we lump PSL as H, Henry’s Law constant
Melting point is high i.e., >> 25oC
F is low, e.g., 0.1 to 0.001
PSS << PSL SSS << SSL
F = PSS / PSL = SSS / SSL
Solubility xS can be used to estimate
Liquids xS = 1 Solids xS = F
Be wary of reported PS and SS of solids!
QSARs and retention time methods give PSL andSSL
log KOW = 2, 4, 6, 8
Define MW, melting point, octanol , vapor pressure
Deduce water, solubility, KAW, KOAfor both liquid and solid states
100 g fish, 10% lipid
100 g mammal, 10% lipid
Respiration and feeding rates
lipid = octanol
No metabolic biotransformation
Respiratory exchange; k1and k2
Growth dilution; kG
Fecal egestion; kE
Dietary intake; kD
Two organisms – same properties and processes
NLOM equivalent to 3.5% lipid
CWater = 1 g.m-3 of each chemical
air is in equilibrium, so
CAir = 0.009 to 0.003g.m-3 depending on KAW
Hamelink, Neely, Veith, Mackay
Assume toxic effect at 3 mmol.kg-1 or 3 mol.m-3
What are the water and air concentrations required to cause toxicity?
Essentially a “backward” bioconcentration experiment
Concentrations and fugacities vary by about six orders of magnitude
Activities vary relatively little (factor of 3)
The system is striving for equi-fugacity, externally and internally.
Toxicity depends on:
as well as KOW
Is a general QSAR for toxicity attempting too much? Categories?
Perhaps a set of QSARs yielding parameters that can be combined using a model?