ENVIRONMENTAL FATE

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CHAPTER 4

• ENVIRONMENTAL FATE

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Introduction
This chapter serves as a basis to identify the
hazards associated with different substances used
and produced in the chemical process, including
raw materials, products and or byproducts.
It would then be possible to do follow up with an
exposure assessment and a dose-response
assessment which are needed to perform risk
characterization
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Substance Classification Tree
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Chemical Properties Used to Perform Environmental
Risk Screenings
Environmental Process
Relevant Properties
Dispersion and Fate
Volatility, density, melting point, water
solubility, effectiveness of waste, water
treatment.
Persistence in the Environment
Atmospheric oxidation rate, aqueous hydrolysis
rate, photolysis rate, rate of microbial
degradation, and adsorption.
Continued on the following slide
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Chemical Properties Used to Perform Environmental
Risk Screenings
Environmental Process
Relevant Properties
Uptake by Organisms
Volatility, Lipophilicity, Molecular Size,
Degradation Rate in Organism.
Human Uptake
Transport Across Dermal Layers, Transport Rates
Across Lung Membrane, Degradation Rates within
the Human Body.
Toxicity and other Health Effects
Dose-Response Relationships.
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Boiling Point

• Distinguishes gas and liquid partitioning
• Using the substances structure, it can be
  estimated by
• Where
• Tb normal boiling point (at 1 atm) (K)
• ni number of groups of type i in the molecule,
• gi contribution of each functional group to the
  boiling point
• Corrected using

Tb 198.2 S nigi (4.1)
Tb (corrected) Tb 94.84 0.5577Tb
0.0007705(Tb)2 (Tb ? 700K) (4.2) Tb
(corrected) Tb 282.7 0.5209Tb
(Tb gt 700K) (4.3)
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Example Boiling Point Estimation
Estimate the Normal Boiling Point for diethyl
ether.
Diethyl ether has the molecular structure
CH3-CH2-O-CH2-CH3
Solving
Group -O- 2(-CH3) 2(-CH2)
gi contribution 25.16 2(21.98) 2(24.22)
The actual boiling point for diethyl ether is
307.65 K
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Example Boiling Point Estimation (Continued)

• Using equation 4.1
• Tb (K) 198.2 S nigi
• Tb (K) 198.2 2(21.98) 2(24.22) 25.16
• Tb 315.76
• b) Using equation 4.2
• Tb (corrected) Tb 94.84 0.5577Tb -
  0.0007705(Tb)2
• Tb (corr) 315.76 94.84 0.5577(315.76) -
  0.0007705(315.76)2
• Tb (corrected) 320.2 K

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Melting Point

• Distinguishes solid and liquid partitioning.
• Can be estimated using the substances boiling
  point
• Where
• Tm Melting Point in Kelvins.
• Tb Boiling Point in Kelvins.

(4.4)
Tm (K) 0.5839 Tb (K)
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Example Melting Point Estimation
Estimate the Melting Point for diethyl
ether. Solving Using equation 4.4 to
calculate the Tm Tm (K) 0.5839 Tb (K)
Tm (K) 0.5839 307.65 K Tm 179.634 K
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Vapor Pressure

• Higher Vapor Pressure Higher Air
  Concentrations
• Can be estimated using the following equations
• ln Pvp A B/(T - C) (4.5)
• Where T Tb at 1 atm
• ln(1 atm) 0 A B/(Tb C) (4.6)
• ln Pvp(atm) A(Tb C)2 / 0.97RTb1/(Tb
  C)-1/(T C)
• (4.7)
• the parameters A and C can be estimated using
• C -18 0.19 Tb (4.7a)
• A KF(8.75 R ln Tb) (4.7b)

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Vapor Pressure (continued)
For solids ln P -(4.4 lnTb)
1.803(Tb/T)- 1) - 0.803ln (Tb/T)
- 6.8(Tm/T-1) (4.8)
Where Pvp vaporization pressure (atm). T
absolute temperature and Tb is the boiling point
at 1 atm. A and C are empirical constants. B a
parameter related to the heat of vaporization. KF
a correction factor. R gas constant 1.987
L-atm K-1 mol-1 Tm melting point (K).
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Example Vapor Pressure Estimation
Estimate the Vapor Pressure for diethyl ether
Using the predicted value of 315.76 K
C -18 0.19Tb -18 0.19(320.2) 41.9944 A
Kf (8.75 R ln Tb) 1.06 8.75 1.987
ln(320.2) 21.3962
(4.7.a)
(4.7.b)
ln Pvp A(Tb C)2 / 0.97RTb1/(Tb C)
- 1/(T C) 21.39(315.76-41.99)2
/ 0.97(1.987)(315.76)1/(273.76)
1/(256) Ln Pvp -0.6677 Pvp 0.5128 atm
389.79 mm Hg.
(4.7)
Repeating the calculation for the experimental
boiling point leads to a vapor pressure estimated
of Pvp 0.6974 atm 530.06 mm Hg.
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Octanol-Water Partition Coefficient

• Describes partition between an aqueous phase and
  its suspended organic phases.
• Can be estimated using the substances structure
  

log Kow 0.229 S nifi (4.9) log Kow
(corrected) 0.229 S nifi S njcj
(4.10)
Where Kow Octanol-Water Partition
Coefficient. ni number of groups i in the
compound. fi factor associated with the group i
nj number of groups j in the compound that
have correction factors. cj
correction factor for each group j
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Example Octanol-Water Partition Coefficient
Estimation
Estimate the Octanol-Water Partition Coefficient
for diethyl ether. Solving Using equation
4.9 log Kow 0.229 S nifi log Kow 0.229
2(0.5473) 2(0.4911) (1.2566) log Kow
1.0492 1.05 therefore Kow 11.2
Group -O- 2(-CH3) 2(-CH2)
fi contribution -1.2566 2(0.5473) 2(0.4911)
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Bioconcentration Factor

• Describes partitioning between aqueous and lipid
  phases in living organisms.
• Higher bioconcentration factors higher
  quantity of bioaccumulation in living organisms
• Can be calculated using

log BCF 0.79(log Kow) 0.40
(4.11) log BCF 0.77(log Kow) 0.70 S jj
(4.12)
Where BCF Bioconcentration Factor. Kow
octanol-water partition coefficient. jj
correction factor for each group.
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Example Bioconcentration Factor (BCF) Estimation
Estimate the Bioconcentration Factor for diethyl
ether. Solving Using equation 4.9 we obtain
log Kow log Kow 0.229 S nifi log Kow
1.0492 1.05 Using equation 4.11 we can
calculate BCF log BCF 0.79(log Kow)
0.40 log BCF 0.79 (1.05) 0.40
log BCF 0.4295 therfore BCF 2.6884

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Water Solubility

• Used to assess concentrations in water
• Can be calculated using

Log S 0.342 1.0374 logKow 0.0108 (Tm 25)
Shj (4.13) Log S
0.796 0.854 logKow 0.00728 (MW) Shj
(4.14) Log S
0.693 0.96 los Kow 0.0092 (Tm 25) 0.00314
(MW) Shj (4.15)
Where S water solubility (mol/L). Kow
octanol-water partition coefficient. Tm melting
point (ªC). MW s the molecular weight of the
substance. hj is the correction factor for each
functional group j.
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Example Water Solubility Estimation
Estimate the Water Solubility for diethyl
ether. Solving Equation 4.9 gives the log
Kow 1.05 Using equation 4.14 we can calculate
the S Log S 0.796 0.854 logKow 0.00728
(MW) Shj Log S
0.796 0.854(1.05) 0.00728(74.12) 0.0 Log S
-0.6403 Therfore S 0.2289 mol/L. 16.966
g/L 16,966.068 mg/ L
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Henrys Law Constant

• Describes the affinity for air over water.
• Can be determined using

-log H log (air-water partition coeff) S nihi
S njcj (4.19)
Where H dimensionless Henrys Law
Constant. ni number of bonds of type i in the
compound. hi bond contribution to the air-water
partition coefficient. nj number of groups of
type j in the molecule. cj correction factor
for each group.
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Example Henrys Law Constant Estimation
Estimate the Henrys Law Constant for diethyl
ether.
H H H H H-C-C-O-C-C-H H H
H H
Expressed as a collection of bonds, diethyl ether
consists of 10 C-H, 2 C-C bonds, and 2 C-O bonds.
The uncorrected value of log (air to water
partition constant) is given by
-log H log (air-water partition coefficient)
10(-0.1197) 2(0.1163) 2(1.0855)
1.2066 log H-1 1.2066
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Soil Sorption Coefficient

• Used to describe the Soil-Water Partitioning.
• Can be estimated by

log Koc 0.544 (log Kow) 1.377
(4.16) log Koc -0.55 (log S) 3.64
(4.17) log Koc 0.53 1? 0.62 S njPj
(4.18)
Where Koc Soil Sorption Coefficient (µg/g of
organic carbon (to µg/mL of liquid)). Kow
Octanol-Water Partition Coefficient. S Water
Solubility. 1? first order Molecular
Connectivity Index (from literature-appendix
). nj number of groups of type j in the
compound. Pj correction factor for each group j.
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Molecular Connectivity Index Calculations
The first step in calculating 1? is to draw the
bond structure of the molecule. For example,
isopentane would be drawn as
CH3 H3C-CH-CH2-CH3
The second step is to count the number of carbon
atoms to which each carbon is attached. Each C-C
bond is given a value of 1 and di, is the
parameter that defines the quantity of carbon
atoms connected to a carbon atom i. The diagram
below gives the di, values for the different
carbon atoms.
(1)
CH3 H3C-CH-CH2-CH3
(1)
(1)
(3)
(2)
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Molecular Connectivity Index Calculations
(continued)
The third step is to identify the connectedness
of the carbons connected by the bond (di , dj).
For isopentane, these pairs are
(1,3)
CH3 H3C-CH-CH2-CH3
(2,1)
(1,3)
(3,2)
The value of 1? can then be calculated using the
equation 1? S(di dj)-0.5 (4.19) For
isopentane, 1?
(1/v3) (1/v3) (1/v6) (1/v2) 2.68
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Example Soil Sorption Coefficient Estimation
Estimate the Soil Sorption Coefficient for
diethyl ether. Solution The molecular
structure for diethyl ether is CH3-CH2-O-CH2-
CH3 Using previously calculated values for log
Kow (estimated at 1.0492) and log S (estimated
at -0.6384) we can estimate the soil sorption
coefficients using equations 4.16 and 4.17
log Koc 0.544 (log Kow) 1.377 1.9482
log Koc -0.55 (log S) 3.64 3.99
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Example Soil Sorption Coefficient Estimation
Using the molecular connectivity we can also
estimate the soil sorption coefficient First
the molecular connectivity index is calculated
using eq. 4.19 CH3-CH2-O-CH2-CH3 (molecular
structure) 2(C-C), 2(C-O), 2(1, 2) , 2(2,
2) (connection pairs) therefore 1? 2(1/v2)
2(1/v4) 2.414 Using equation 4.18 to calculate
the soil sorption coefficient log Koc 0.53
1? 0.62 S njPj log Koc 0.53 1? 0.62 S
njPj 0.53(2.414) 0.62 (-1.264) log Koc
0.63542 therefore Koc 4.32
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Where to look up this information...
http//www.chem.duke.edu/chemlib/properties.
html http//www.library.vanderbilt.edu/science/pr
operty.htm http//www.library.yale.edu/science/he
lp/chemphys.html
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What do the different Properties mean?
Adapted from the Green Engineering Textbook
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Estimating Environmental Persistence and
Ecosystem Risks

• To be discussed
• Atmospheric Lifetimes
• Aquatic Lifetimes
• Overall Biodegradability
• Ecosystems

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Estimating Atmospheric Lifetimes

• One way to estimate the atmospheric lifetime of a
  compound is to analyze the rate of oxidation of
  the substance, specifically the hydroxyl radical
  reaction rate.
• Group contributions is again one of the
  approaches that can be taken to estimate this
  property.
• Using examples, we will show how to estimate
  reaction rates and half lives while using the
  appropriate correction factors.

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Example Atmospheric Lifetime Estimation
Dimethylsulfide (DMS, CH3SCH3) produced by
phytoplankton degredation is thought to be the
major source of the sulfate and methanesulfonate
aerosol found in the marine boundary layer.
The primary objective of this research effort is
to determine the detailed mechanism of, and final
product yields from, the OH initiated gas phase
oxidation of DMS.
At the low NOx levels that are characteristic of
the remote marine boundary layer, reaction with
OH is the initial step in DMS oxidation.
OH CH3SCH3 ? Products
(1)
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The OH initiated oxidation of DMS proceeds via a
complex, two channel, mechanism involving
abstraction (1a) and reversible addition (1b,
-1b). This can be described by the reaction
sequence
CH3SCH3 OH ? CH3SCH2 H2O
(1a) CH3SCH3 OH M ? CH3S(OH)CH3
M (1b, -1b) CH3S(OH)CH3 O2 ?
Products
(3)
Because of this complex mechanism the effective
rate coefficients for reaction (1) and its
deuterated analog, reaction (2) depend on the
partial pressure of O2 at any total pressure.
OH CD3SCD3 ? Products
(2)
The two channel reaction mechanism implies that
in the absence of O2 we measure k1a, the
abstraction rate. As we add O2 the effective rate
increases until we measure a limiting rate (k1a
k1b).
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(No Transcript)
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Estimating Aquatic Lifetimes

• One way to estimate the aquatic lifetime of a
  compound is to analyze the rate of hydrolysis of
  the substance.
• The rate of hydrolysis can be estimated by

log (hydrolysis rate) log (hydrolysis rate of a
reference compound) Constant s
Therefore log (hydrolysis rate) A Bs
(4.20)
Where A is rxn and compound class
specific(depends on the reference rxn chosen) B
is rxn and compound class specific (depends on
type of rxn considered) s is a structural
parameter commonly used in linear free energy
relationship.
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Estimating Overall Biodegradability

• It is difficult to do an overall biodegradability
  analysis.
• It can be estimated using
• Where
• an is the contribution of the functional group
  (see table ).
• fn is the number of different functional group.
• MW is the molecular weight.
• I is an indicator of aerobic biodegradation rate.
• Different Values (of I) represent different life
  times

I 3.199 a1f1 a2f2 a3f3 ... anfn
amMW (4.21)
I value 5 4 3 2 1
Expected degradation rate Hours Days Weeks Months Years
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Example Overall Biodegradability Estimation
Estimate the Biodegradation Index for diethyl
ether. Solution Molecular weight of diethyl
ether MW 74.12 g/mol Using equation 4.21,
the index can be calculated I 3.199 a1f1
a2f2 a3f3 ... anfn amMW I 3.199 (-
0.0087) - 0.00221(74.12) 3.0267 Therefor a
lifetime of WEEKS
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Estimating Ecosystem Risks
Compare the Fish, Guppy and Daphnids mortalities
for an acrylate with log Kow 1.22 (e.g. ethyl
acrylate).
Guppies
log (1/LC50) 0.871 log Kow 4.87
(4.22) log (1/LC50)
0.871(1.22) 4.87 -3.80738 LC50 6417.74
µmol/L.
Daphnids
log LC50 0.00886 0.51136 log Kow

(4.23) log LC50 0.00886 0.51136(1.22)
-0.6149992 LC50 0.242 millimoles/L 242 µmol/L.
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Estimating Ecosystem Risks Continued
Fish
log LC50 -1.46 0.18 log Kow

(4.24) log LC50 -1.46 0.18(1.22)
-1.6796 LC50 0.021 millimoles/L 21 µmol/L.
The concentrations yielding 50 mortality
are Guppies (14 day) 6417.74
µmol/L. Daphnids (48 hour) 0.242 millimoles/L
242 µmol/L. Fish (96 hour) 0.021
millimoles/L 21 µmol/L.
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Environmental Fate and Exposures
Example If chemicals are released into a river
upstream of a water treament plant, what factors
need to be taken into account to estimate the
potential danger to the community. What fraction
of the chemicals are - Absorbed by river
sediments. - Volatilized into the air. - Taken
up by living organisms. - Biodegraded. -
Reacted with other compounds. - Removed in the
treatment process.
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Classification of Substances Based on Risk
By examining the table XX, we can use the
calculated properties to qualitatively quantify
the risk associated with the different
substances Three main criteria are normally
considered in the classification of the
substances persistence, bioaccumultion and
toxicity. There do not exist a given set of
regulations or guidelines on quantifying risk,
but the above parameters are used in the process.
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Available Ressources
EPA (persistent, bioaccumulating and toxic
substances) http//www.epa.gov/pbt/aboutpbt.htm
http//www.epa.gov/opptintr/pbt/ Pollution
Prevention, Waste Minimization and PBT Chemical
Reduction http//yosemite.epa.gov/R10/OWCM.NSF/
0d511e619f047e0d88256500005bec99/6ad9c10eb8a06bc28
8256506007def78?opendocument Environment canada
(existing substances evaluation)
http//www.ec.gc.ca/substances/ese/eng/psap/psap_
2.cfm