ECOTOX PARTITIONING
VL 1 & 2
VL 1 & 2
What are partitioning coefficients and what is passive partitioning
Partitioning Coefficients: predict the distribution of a chemical between 2 different phases
-> where does it prefer to be in the environment
-> passive: it describes the affinity of chemicals, not their real behavior (as the environment is dynamic) and thus often overestimate bioaccumulation in organisms/phases
Partitioning into air vs. water - KH
- what is Kaw
- what can you estimate with KH? (with cut-offs)
- what other factors does this partitioning depend on
Kaw = dimensionless form of KH
KH: estimate the volatility of a chemical:
KH < 3x10-7: low volatility
3x10-7 < KH < 10-5: semi-volatile
KH < 10-3: significant rate of volatilization
KH > 10-3: more volatile than water/tendendy to escape in the air
-> also depends on water solubility (which also depends on molecular weight)
Partitioning to SOLIDS & ORGANIC MATTER - Kd & Koc
- what is special with soil
- what is Kd and how is it interpreted
- what chemicals are more likely to partition to organic matter
- how is Kd related to Koc
- how can you calculate how much of the chemical goes where
soil is a complex mixture: contains clay minerals & organic matter, as well as quarzt, bacteria, air, water.
Kd: depends for each chemical on the soil -> several Kd for one chemical
- low Kd = high concentration in the water
chemicals likely to partition to organic matter:
- apolar chemicals with low water solubility
- uncharged chemicals/cations
- chemicals that interact little with water
Koc: fraction in organic matter -> Kd/foc (foc = fraction of organic carbon in the soil) -> plot Kd against foc = Koc
- Koc is unique for 1 chemical
LOGKoc <1.7 very large mobility in soil/will not partition significantly to soil
> 3.7 immobile: the higher Koc, the higher the affinity for organic carbon
fw = 1/1+rsw x Kd -> fraction of chemical in water
rsw = ratio of solids & water
Define Kow and its cut-off values
Explain LFER and their limitations
Kow = distribution of a chemical between the octanol and water phase
Kow >1: prefers lipids
Kow <1: prefers water
logKOW > 4: POP (bioaccumulative)
LFER:
the goal is to determine the Koc values with known Kow values -> as Kow is easier to measure
logKoc = a x logKow + b
+ works well when used within one compound class, works well for apolar & monopolar compounds
- does not work well for bipolar/ionic compounds, as Kow cannot be used reliably to estimate partitioning to organic phases
Alternative: polyparameter LFER (ppLFER)
What effect has the charge of your chemical? (ionized vs. non-ionized)
Whan is the neutral and when the ionized form prevalent?
Explain logDow -> why do we need it? is it higher at neutral or at ionized species?
the charge of your chemical strongly influences it's environmental behavior:
ionized -> water-soluble
non-ionized/neutral -> lipid soluble; well absorbed into membranes -> higher Dow
pH > pKA: ionized form present
pKA < pH: neutral form present
Dow = pH-corrected Kow -> as Kow only applies to the neutral species of chemicals
Name the 2 most important biological phases where chemicals can partition to:
Lipids: 2 major functions (energy storage -> apolar lipids like triacylglycerol; structural components -> polar lipids like phospholipids)
Liposomes are used as laboratory surrogates for lipids to investigate membrane-water partitioning
-> apolar lipids or chemicals that have a similar structure as phospholipids tend to partition to lipids/incorporate into biological membranes
Proteins: may make up the largest part of biological tissue mass
AAS dictate the properties and thus the affinity for chemicals
Define Bioconcentration Factor and Biomagnification Factor
BCF: uptake of a chemical from the aqueous phase (net accumulation from all sources in the environment)
BCF = concentration organism/ concentration water
-> influenced by lipid, protein content, biotransformation etc.
BMF: uptake of a chemical from the diet/accumulation throughout the food chain
BMF = concentration organism/concentration diet
How can you estimate the BCF?
predict it from Kow -> logBCF = a x logKow + b (via LFER) -> a&b depend on the species you calculate it for
How can you estimate the concentration in an entire organism? (needed to calculate BCF, BMF etc)
Kbio = concentration in the organism / concentration in the exposure medium -> sum it up for all relevant phases (proteins, lipids etc)
for lipids: f x c/m (f = fraction of organism that is lipid, c/m = concentration of chemical in lipid at equilibrium with medium)
limitation: strongly simplified assumptions underlying the calculations -> there are phases we might ignore, as we measure the partition coefficients in the lab when the phases are at equilibrium. In real life, (eg plants), there is no equilibrium
Considerations for partitioning to lipids (3)
for (apolar) chemicals with logKow > 3: Kow = Klipid (approximately)
for chemicals with logKow 3-6: LFER is valid
logKOW < 3: no data, more polar compounds -> the relationship is not linear
considerations for partitioning to protein (3)
Albumin is used as a reference compound
similar for apolar, monopolar & bipolar compounds
limitation: different proteins have different affinities
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Cartes-fiches
What are partitioning coefficients and what is passive partitioning
Partitioning Coefficients: predict the distribution of a chemical between 2 different phases
-> where does it prefer to be in the environment
-> passive: it describes the affinity of chemicals, not their real behavior (as the environment is dynamic) and thus often overestimate bioaccumulation in organisms/phases
Partitioning into air vs. water - KH
- what is Kaw
- what can you estimate with KH? (with cut-offs)
- what other factors does this partitioning depend on
Kaw = dimensionless form of KH
KH: estimate the volatility of a chemical:
KH < 3x10-7: low volatility
3x10-7 < KH < 10-5: semi-volatile
KH < 10-3: significant rate of volatilization
KH > 10-3: more volatile than water/tendendy to escape in the air
-> also depends on water solubility (which also depends on molecular weight)
Partitioning to SOLIDS & ORGANIC MATTER - Kd & Koc
- what is special with soil
- what is Kd and how is it interpreted
- what chemicals are more likely to partition to organic matter
- how is Kd related to Koc
- how can you calculate how much of the chemical goes where
soil is a complex mixture: contains clay minerals & organic matter, as well as quarzt, bacteria, air, water.
Kd: depends for each chemical on the soil -> several Kd for one chemical
- low Kd = high concentration in the water
chemicals likely to partition to organic matter:
- apolar chemicals with low water solubility
- uncharged chemicals/cations
- chemicals that interact little with water
Koc: fraction in organic matter -> Kd/foc (foc = fraction of organic carbon in the soil) -> plot Kd against foc = Koc
- Koc is unique for 1 chemical
LOGKoc <1.7 very large mobility in soil/will not partition significantly to soil
> 3.7 immobile: the higher Koc, the higher the affinity for organic carbon
fw = 1/1+rsw x Kd -> fraction of chemical in water
rsw = ratio of solids & water
Define Kow and its cut-off values
Explain LFER and their limitations
Kow = distribution of a chemical between the octanol and water phase
Kow >1: prefers lipids
Kow <1: prefers water
logKOW > 4: POP (bioaccumulative)
LFER:
the goal is to determine the Koc values with known Kow values -> as Kow is easier to measure
logKoc = a x logKow + b
+ works well when used within one compound class, works well for apolar & monopolar compounds
- does not work well for bipolar/ionic compounds, as Kow cannot be used reliably to estimate partitioning to organic phases
Alternative: polyparameter LFER (ppLFER)
What effect has the charge of your chemical? (ionized vs. non-ionized)
Whan is the neutral and when the ionized form prevalent?
Explain logDow -> why do we need it? is it higher at neutral or at ionized species?
the charge of your chemical strongly influences it's environmental behavior:
ionized -> water-soluble
non-ionized/neutral -> lipid soluble; well absorbed into membranes -> higher Dow
pH > pKA: ionized form present
pKA < pH: neutral form present
Dow = pH-corrected Kow -> as Kow only applies to the neutral species of chemicals
Name the 2 most important biological phases where chemicals can partition to:
Lipids: 2 major functions (energy storage -> apolar lipids like triacylglycerol; structural components -> polar lipids like phospholipids)
Liposomes are used as laboratory surrogates for lipids to investigate membrane-water partitioning
-> apolar lipids or chemicals that have a similar structure as phospholipids tend to partition to lipids/incorporate into biological membranes
Proteins: may make up the largest part of biological tissue mass
AAS dictate the properties and thus the affinity for chemicals
Define Bioconcentration Factor and Biomagnification Factor
BCF: uptake of a chemical from the aqueous phase (net accumulation from all sources in the environment)
BCF = concentration organism/ concentration water
-> influenced by lipid, protein content, biotransformation etc.
BMF: uptake of a chemical from the diet/accumulation throughout the food chain
BMF = concentration organism/concentration diet
How can you estimate the BCF?
predict it from Kow -> logBCF = a x logKow + b (via LFER) -> a&b depend on the species you calculate it for
How can you estimate the concentration in an entire organism? (needed to calculate BCF, BMF etc)
Kbio = concentration in the organism / concentration in the exposure medium -> sum it up for all relevant phases (proteins, lipids etc)
for lipids: f x c/m (f = fraction of organism that is lipid, c/m = concentration of chemical in lipid at equilibrium with medium)
limitation: strongly simplified assumptions underlying the calculations -> there are phases we might ignore, as we measure the partition coefficients in the lab when the phases are at equilibrium. In real life, (eg plants), there is no equilibrium
Considerations for partitioning to lipids (3)
for (apolar) chemicals with logKow > 3: Kow = Klipid (approximately)
for chemicals with logKow 3-6: LFER is valid
logKOW < 3: no data, more polar compounds -> the relationship is not linear
considerations for partitioning to protein (3)
Albumin is used as a reference compound
similar for apolar, monopolar & bipolar compounds
limitation: different proteins have different affinities
