Table Of ContentMontgomery, John H. "Frontmatter"
Groundwater Chemicals Desk Reference
Boca Raton: CRC Press LLC,2000
Preface
The proliferation of research publications and continuing public awareness dealing with
the fate, transport, and remediation of hazardous substances in the environment has
stimulated this third edition of the Groundwater Chemicals Desk Reference.
Since the publication of the second edition, additional data have been critically reviewed.
New data included in this edition are bioconcentration factors, aquatic mammalian toxicity
values, degradation rates, corresponding half-lives in various environmental compartments,
ionization potentials, aqueous solubility of miscellaneous compounds, and biological,
chemical, and theoretical oxygen demand values for various organic compounds. The
following data field fields have been added to each chemical profile: sources of
contamination, entropy of fusion, and Merck reference citation. New tables include
quantitative and qualitative nature of various petroleum fuels, Henry’s law constants, soil
adsorption constants, and toxicity data for a wide variety of chemicals. These data should
prove useful to the environmental regulating community and environmental consultants,
especially for conducting risk-based contamination assessments.
The Registry of Toxic Effects of Chemical Substances (RTECS) Number Index was deleted
for three reasons. First, the Chemical Abstract Service (CAS) Registry Number Index is
commonly used to search the documented literature for the compound of interest. Second,
the CAS Number Index can be used to obtain the RTECS Number for a particular substance.
Third, the RTECS Number Index was deleted to conserve space.
The presentation of data remains unchanged in this edition to make it easy for the reader
to locate information. The Environmental Fate section has been expanded significantly. This
section is subdivided into the following categories: Biological, Soil, Plant, Surface Water,
Groundwater, Photolytic, and Chemical/Physical. When available, photolytic, hydrolysis,
biodegradation, and volatilization half-lives of chemicals in various media are included. To
conserve space, references are no longer given at the end of each chemical profile. All
references now appear at the end of the main text, before the tables.
The book is based on more than 2,600 references. Most of the citations reviewed from the
documented literature and included in this book pertain to the fate and transport of chemicals
in the subsurface environment and toxicity data for mammals and aquatic species
(approximately 700 new references). Every effort has been made to select accurate
information and present it in a clear, consistent format. The publisher and author would
appreciate hearing from readers regarding corrections and suggestions for material that might
be included for use in future editions.
The author is grateful to the staff of CRC Press, in particular Arline Massey, Carol
Whitehead, and Christine Andreasen, for their invaluable contributions and suggestions
during the preparation of this book. The author also extends thanks to the many anonymous
reviewers for their comments and suggestions on draft proofs.
John H. Montgomery
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Introduction
The compounds profiled in this book include solvents, herbicides, insecticides,
fumigants, and other hazardous substances most commonly found in the groundwater
environment; the organic Priority Pollutants promulgated by the U.S. Environmental
Protection Agency (U.S. EPA) under the Clean Water Act of 1977 (40 Code of Federal
Regulations (CFR) 136, 1977); and compounds most commonly found in the workplace.
The compound headings are those commonly used by the U.S. EPA and many
agricultural organizations. Positional and/or structural prefixes set in italic type are not
integral parts of the chemical names and hence are disregarded in alphabetizing. These
include asym-, sym-, n-, sec-, cis-, trans-, "-, $-, (-, o-, m-, p-, N-, S-, etc.
Synonyms: These are listed alphabetically following the convention used for the compound
headings. Compounds in boldface type are the Chemical Abstracts Service (CAS) names
listed in the eighth or ninth Collective Index. If no synonym appears in boldface type, then
the compound heading is the CAS assigned name. Synonyms include chemical names,
common or generic names, trade names, registered trademarks, government codes and
acronyms. All synonyms found in the literature are listed.
Synonyms were retrieved from several references, primarily from the Registry of Toxic
Effects of Chemical Substances (RTECS, 1985).
Beneath the synonyms is the structural formula, a graphic representation of atoms or
group(s) of atoms relative to one other. This is given for every compound regardless of its
complexity. The limitation of structural formulas is that they depict these relationships in two
dimensions.
Chemical Abstracts Service (CAS) Registry Number: This unique identifier is assigned by
the American Chemical Society to chemicals recorded in the CAS Registry System. This
number is used to access various chemical databases including the Hazardous Substances
Data Bank (HSDB), CAS Online, Chemical Substances Information Network, and many
others. This entry is also useful to conclusively identify a substance regardless of the
assigned name.
Department of Transportation (DOT) designation: This is a four-digit number assigned by
the U.S. Department of Transportation (DOT) to hazardous materials and is identical to the
United Nations identification number (which is preceded by the letters UN). This number is
required on shipping papers, on placards or orange panels on tanks and on a label or
package containing the material. These numbers are widely used by personnel responding to
emergency situations, e.g., overturned tractor trailers, to identify transported material quickly
and easily. The DOT designations and appropriate responses to each chemical or
compounds are cross-referenced in the Emergency Response Guidebook. Additional
information is provided in this book, which may be obtained from the U.S. Department of
Transportation, Research and Special Programs Administration, Materials Transportation
Bureau, Washington, D.C. 20590.
DOT label: This label is the hazard classification assigned by the U.S. Department of
Transportation. Federal regulations require it on all containers shipped.
Molecular formula: This is arranged by carbon, hydrogen, and remaining elements in
alphabetical order in accordance with the system developed by Hill (1900). Molecular
formulas are useful for identifying isomers (i.e., compounds with identical molecular
formulas) and are required to calculate the formula weight of a substance.
Formula weight: This is calculated to the nearest hundredth using the empirical formula and
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the 1981 Table of Standard Atomic Weights as reported in Weast (1986). Formula weights are
required for many calculations, such as converting weight/volume units, e.g., mg/L or g/L, to
molar units (mol/L); with density for calculating molar volumes; and estimating Henry’s law
constants.
Registry of Toxic Effects of Chemical Substances (RTECS) number: Many compounds are
assigned a unique accession number consisting of two letters followed by seven numerals.
This number is needed to quickly and easily locate additional toxicity and health-based data
that are cross-referenced in the RTECS (1985). For additional information, contact NIOSH,
U.S. Department of Health and Human Services, Mail Stop C-13, 4676 Columbia Parkway,
Cincinnati, OH 45226-1998 (toll free: 1-800-35-NIOSH; fax: 513-533-8573).
Merck Reference: The two sets of numbers refer to the edition and monograph number as
found in the 10th edition of “The Merck Index” (Windholz et al., 1983). For example, the entry
10, 1063 refers to an entry in the 10th edition as monograph number 1063.
Physical state, color, and odor: The appearance, including the color and physical state
(solid, liquid, or gas) of a chemical at room temperature (20-25 °C) is provided. If the
compound can be detected by the olfactory sense, the odor is noted. Unless noted
otherwise, the information provided in this category is for the pure substance and was
obtained from many sources (CHRIS, 1984; HSDB, 1989; Hawley, 1981; Keith and Walters,
1992; Sax, 1984; Sax and Lewis, 1987; Toxic and Hazardous Industrial Chemicals Safety
Manual for Handling and Disposal with Toxicity and Hazard Data, 1986; Sittig, 1985;
Verschueren, 1983; Windholz et al., 1983). If available, odor thresholds in air and/or taste
thresholds in water are given. The odor threshold is the lowest compound concentration in
air that can be detected by the olfactory sense and it is usually reported as parts per billion
(ppb) as micrograms per cubic meter (µg/m3). Sometimes the odor threshold in water is given
and is reported as µg/kg. Taste thresholds in water are usually given in mass per unit volume
(e.g. µg/L).
Boiling point: This is defined as the temperature at which the vapor pressure of a liquid
equals the atmospheric pressure. Unless otherwise noted, all boiling points are reported at
1.0 atmosphere pressure (760 mmHg). Although not used in environmental assessments,
boiling points for aromatic compounds have been found to be linearly correlated with
aqueous solubility (Almgren et al., 1979). Boiling points are also useful for assessing entry of
toxic substances into the body. Body contact with high-boiling liquids is the most common
means of entry of toxic substances into the body. Inhalation is the most common means of
entry into the body for low-boiling liquids (Shafer, 1987).
Diffusivity in water: Molecular diffusion is defined as the transport of molecules (e.g.,
organic compounds) in either liquid or gaseous states. Typically, molecular diffusion is not a
major factor under most environmental conditions. However, in saturated aquifers with low
pore water velocities (i.e., <0.002 cm/sec), diffusion can be a contributing factor in the
transport of organic compounds.
Very few experimentally determined diffusivities of organic substances in water are
available. If experimentally determined diffusivity values are not available, Hayduk and
Laudie (1974) recommend the following equation for estimating this parameter:
D = (1.326 x 10-4)/01.14V0.589) [1]
where D is the diffusivity of the substance in water (cm2/sec), 0 is the viscosity of water
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(centipoise, cps), and V is the molar volume of the solute (cm3/mol). The molar volume is
easily determined if the liquid density of the solute is available. Molar volume may also be
determined using the LeBas incremental method as described in Lyman et al. (1982). The
latter method is required to determine molar volumes of substances that are solids at ordinary
temperatures. More recent methods for estimating molar volume using molecular group
contributions are described by Baum (1998).
Diffusivity values are reported in a modified exponential form. For example, the
experimentally determined diffusivity of benzene in water is 1.09 x 10-5 cm2/sec, but this value
is reported as 1.09 (x 10-5 cm2/sec).
Dissociation constant: In an aqueous solution, an acid (HA) will dissociate into the car-
boxylate anion (A-) and hydrogen ion (H+) and may be represented by the general equation:
HA H+ + A- [2]
(aq)
At equilibrium, the ratio of the products (ions) to the reactant (non-ionized electrolyte) is
related by the equation:
K = ([H+] [A-]/[HA]) [3]
a
where K is the dissociation constant. This expression shows that K increases if there is
a a
increased ionization and vice versa. A strong acid (weak base) such as hydrochloric acid
ionizes readily and has a large K , whereas a weak acid (or stronger base) such as benzoic
a
acid ionizes to a lesser extent and has a lower K . The dissociation constants for weak acids
a
are sometimes expressed as K , the dissociation constant for the base, and both are related to
b
the dissociation constant for water by the expression:
K = K + K [4]
w a b
where K is the dissociation constant for water (10-14 at 25 °C), K is the acid dissociation
w a
constant, and K is the base dissociation constant.
b
The dissociation constant is usually expressed as pK = -log K . Equation [4] becomes:
a 10 a
pK = pK + pK [5]
w a b
When the pH of the solution and the pK are equal, 50% of the acid will have dissociated
a
into ions. The percent dissociation of an acid or base can be calculated if the pH of the
solution and the pK of the compound are known (Guswa et al., 1984):
a
For organic acids: " = [100/(1 + 10(pH-pKa))] [6]
a
For organic bases: " = [100/(1 + 10(pKw-pKb-pH))] [7]
b
where " is the percent of the organic acid that is nondissociated, " is the percent of the
a b
organic base that is nondissociated, pK is the -log dissociation constant for an acid, pK
a 10 w
is the -log dissociation constant for water (14.00 at 25 °C), pK is the -log dissociation
10 b 10
constant for base (pK = pK -pK), and pH is the -log hydrogen ion activity (concentration)
b w a 10
of the solution.
Because ions tend to remain in solution, the degree of dissociation will affect processes
such as volatilization, photolysis, adsorption, and bioconcentration (Howard, 1989).
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Heat of fusion: This value, normally reported in kcal/mol, is also referred to as the heat of
melting. For solids, the heat of fusion is required to estimate the solubility of the solute to
account for crystal lattice interactions. The theoretical basis for introducing this value into
the estimation of aqueous solubility of organic solids is explained by Irmann (1965) and
Yalkowsky and Valvani (1979). Heat of fusion data is available in many texts including Dean
(1987), Weast (1986), and CHRIS (1984).
Henry’s law constant: Sometimes referred to as the air-water partition coefficient, the
Henry’s law constant is defined as the ratio of the partial pressure of a compound in air to
the concentration of the compound in water at a given temperature under equilibrium
conditions. If the vapor pressure and solubility of a compound are known, this parameter can
be calculated at 1.0 atm (760 mmHg) as follows:
K = Pfw/760S [8]
H
where K is Henry’s law constant (atm m3/mol), P is the vapor pressure (mmHg), S is the
H
solubility in water (mg/L), and fw is the formula weight (g/mol).
Henry’s law constant can also be expressed in dimensionless form and may be
calculated using one of the following equations:
K = K /RK
H H
or K = S /S [9]
H a
where K is Henry’s law constant (dimensionless), R is the ideal gas constant (8.20575 x 10-5
H
atm m3/mol K), K is the temperature of water (degrees Kelvin), S is the solute
a
concentration in air (mol/L), and S is the aqueous solute concentration (mol/L). Many papers
present Henry’s law constants as H (M/atm) representing the solubility of the chemical. The
relationship between K and H is:
H
K = 1/(H x 1000) [10]
H
In addition, Henry’s law constants may be expressed as a mole fraction ratio between the
air and aqueous phases (Leighton and Calo, 1981):
K = y/x [11]
AW
where y is the mole fraction of the chemical in air and x is the mole fraction of the chemical in
water. The partition coefficients K and K are related by the expression:
H AW
K = K V /V [12]
H AW w a
where V is the molar volume of water (m3/mol) and V is the molar volume of air (m3/mol). At
w a
standard temperature (25 °C) and pressure (1 atm), V and V are 1.81 x 10-5 and 2.45 x 10-2
w a
m3/mol, respectively.
It should be noted that estimating Henry’s law constant assumes the gas obeys the ideal
gas law and the aqueous solution behaves as an ideally dilute solution. The solubility and
vapor pressure data inputted into the equations are valid only for the pure compound and
must be in the same standard state at the same temperature.
The major drawback in estimating Henry’s law constant is that both the solubility and
the vapor pressure of the compound are needed in equation [8]. If one or both parameters are
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unknown, an empirical equation based on quantitative structure-activity relationships
(QSAR) may be used to estimate Henry’s law constants (Nirmalakhandan and Speece, 1988).
In this QSAR model, only the structure of the compound is needed. From this, connectivity
indexes (based on molecular topology), polarizability (based on atomic contributions) and
the propensity of the compound to form hydrogen bonds can easily be determined. These
parameters, when regressed against known Henry’s law constants for 180 organic
compounds, yielded an empirical equation that explained more than 98% of the variance in
the data set having an average standard error of only 0.262 logarithm units.
Henry’s law constant may also be estimated using the bond or group contribution
method developed by Hine and Mookerjee (1975). The constants for the bond and group
contributions were determined using experimentally determined Henry’s law constants for
292 compounds. The authors found that those estimated values significantly deviating from
observed values (particularly for compounds containing halogen, nitrogen, oxygen and
sulfur substituents) could be explained by “distant polar interactions,” i.e., interactions
between polar bonds or structural groups.
A more recent study for estimating Henry’s law constants using the bond contribution
method was provided by Meylan and Howard (1991). In this study, the authors updated and
revised the method developed by Hine and Mookerjee (1975) based on new experimental
data that have become available since 1975. Bond contribution values were determined for 59
chemical bonds based on known Henry’s law constants for 345 organic compounds. A good
statistical fit [correlation coefficient (r2) = 0.94] was obtained when the bond contribution
values were regressed against known Henry’s law constants for all compounds. For selected
chemicals classes, r2 increased slightly to 0.97.
Russell et al. (1992) conducted a similar study using the same data set from Hine and
Mookerjee (1975). They developed a computer-assisted model based on five molecular
descrip-tors which was related to the compound’s bulk, lipophilicity, and polarity. They
found that 63 molecular structures were highly correlative with the log of Henry’s law
constants (r2 = 0.96).
Henry’s law constants provided an indication of the relative volatility of a substance.
According to Lyman et al. (1982), if K <10-7 atm m3/mol, the substance has a low volatility.
H
If K is >10-7 but <10-5 atm m3/mol, the substance will volatilize slowly. Volatilization
H
becomes an important transfer mechanism in the range 10-5< H <10-3 atm m3/mol. Values of
K >10-3 atm m3/mol indicate volatilization will proceed rapidly.
H
The rate of volatilization will also increase with an increase in temperature. ten Hulscher
et al. (1992) studied the temperature dependence of Henry’s law constants for three
chlorobenzenes, three chlorinated biphenyls, and six polynuclear aromatic hydrocarbons.
They observed that over the temperature range of 10 to 55 °C, Henry’s law constant was
doubled for every 10 °C increase in temperature. This temperature relationship should be
considered when assessing the role of chemical volatilization from large surface water bodies
whose temperatures are generally higher than those typically observed in groundwater.
Henry’s law constants are reported in a modified exponential form. For example, the
experimentally determined Henry’s law constant of benzene is 5.48 x 10-3 atm m3/mol;
however, this value is reported as 5.48 (x 103 atm m3/mol).
Interfacial tension with water: With few exceptions, most organic compounds entering the
aqueous environment are non-miscible liquids. The interfacial tension between the
compound and water (i.e., groundwater, surface water bodies, etc.) is numerically equivalent
to the free surface energy that is formed at the interface. Compounds with high interfacial
tension values relative to water are easy to separate after mixing and are not likely to form
emulsions (Lyman et al., 1982). The interfacial tension of organic compounds can be used to
calculate the spreading coefficient to determine whether it forms a lens or macromolecular
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film with water (Demond and Lindner, 1993):
s = ( -( -( [13]
OW W(O) O(W) OW
where s is the spreading coefficient of the organic liquid at the air-water interface, ( is
OW W(O)
the surface tension of water saturated with the organic liquid, ( is the surface tension of
O(W)
the organic liquid saturated with water and ( is the interfacial tension between organic
OW
liquid and water. Organic liquids with spreading coefficients greater than zero form a thin
layer on the water surface. Conversely, the organic liquid forms a lens if the spreading
coefficient is negative.
The units of interfacial tension are identical for surface tension, i.e., dyn/cm. Interfacial
tension values of organic compounds range from zero for completely miscible liquids (e.g.,
acetone, methanol, ethanol) up to the surface tension of water at 25 °C which is 72 dyn/cm
(Lyman et al., 1982). Interfacial tension values may be affected by pH, surface-active agents,
and dissolved gases (Schowalter, 1979). Most of the interfacial tension values reported in
this book were obtained from Dean (1987), Demond and Lindner (1993), CHRIS (1984), and
references cited therein.
Ionization potential: The ionization potential of a compound is defined as the energy
required to remove a given electron from the molecule’s atomic orbit (outermost shell) and is
expressed in electron volts (eV). One electron volt is equivalent to 23,053 cal/mol.
Knowing the ionization potential of a contaminant is required to determine the
appropriate photoionization lamp for detecting that contaminant or family of contaminants in
air. Photo-ionization instruments are equipped with a radiation source (UV lamp), pump,
ionization chamber, an amplifier (detector), and a recorder (either digital or meter). Generally,
compounds with ionization potentials less than the radiation source (UV lamp rating) being
used will readily ionize and will be detected by the instrument. Conversely, compounds with
ionization potentials more than the lamp rating will not ionize and will not be detected by the
instrument.
Bioconcentration factor, log BCF: The bioconcentration factor is defined as the steady-state
concentration of the chemical in an organism (kg of chemical/kg of organism) to the
concentra-tion of the chemical in the organism’s environment (kg of chemical/kg of medium
or kg of chemical/m3 of medium). Bioconcentration factors have also been determined for
volatile organic compounds in vegetation. The bioconcentration factors were determined by
measuring the concentration of the compound in leaves (mass/unit volume) to the
concentration of the compound in air (mass/unit volume) (Hiatt, 1998). Generally, high
bioconcentration factors tend to be associated with very lipophilic (low aqueous solubility)
compounds. Conversely, low bioconcentration factors are associated with compounds
having high aqueous solubilities.
Logarithmic bioconcentration factors have been shown to be correlated with the
logarith-mic octanol/water partition coefficient in aquatic organisms (Davies and Dobbs,
1984; de Wolf et al., 1992; Isnard and Lambert, 1988) and fish (Davies and Dobbs, 1984;
Kenaga, 1980; Isnard and Lambert, 1988; Neely et al., 1974; Ogata et al., 1984; Oliver and
Niimi, 1985). In addition, bioconcentration factors are well correlated by a linear solvation
energy relationship (commonly known as LSER) that includes the intrinsic solute molecular
volume and solvatochromic parameters that measure hydrogen bond acceptor basicity and
donor acidity of the compound (Park and Cho, 1993).
Soil sorption coefficient, log K : The soil/sediment partition or sorption coefficient is
oc
defined as the ratio of adsorbed chemical per unit weight of organic carbon to the aqueous
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solute concentration. This value provides an indication of the tendency of a chemical to
partition between particles containing organic carbon and water. Compounds that bind
strongly to organic carbon have characteristically low solubilities, whereas compounds with
low tendencies to adsorb onto organic particles have high solubilities.
Nonionizable chemicals (e.g. hydrocarbons, ethers, alcohold) that sorb onto organic
materials in an aquifer (i.e., organic carbon) are retarded in their movement in groundwater.
The sorbing solute travels at linear velocity that is lower than the groundwater flow velocity
by a factor of R , the retardation factor. If the K of a compound is known, the retardation
d oc
factor may be calculated using the following equation from Freeze and Cherry (1974) for
uncon-solidated sediments:
R = V /V = [1 + (BK /n )] [14]
d w c d e
where R is the retardation factor (unitless), V is the average linear velocity of groundwater
d w
(e.g., ft/day), V is the average linear velocity of contaminant (e.g., ft/day), B is the average
c
soil bulk density (g/cm3), n is the effective porosity (unitless), K is the distribution
e d
(sorption) coefficient (cm3/g).
By definition, K is defined as the ratio of the concentration of the solute on the solid to
d
the concentration of the solute in solution. This can be represented by the Freundlich
equation:
K (or K ) = VM /MM = C /C n [15]
F d S L S L
where V is the volume of the solution (cm3), M is the mass of the sorbed solute (g), M is the
S
mass of the porous medium (g), M is mass of the solute in solution (g), C is the
L S
concentration of the sorbed solute (g/cm3), C is the concentration of the solute in the
L
solution (g/cm3), and n is a constant.
Values of n are normally between 0.7 and 1.1 although values of 1.6 have been reported
(Lyman et al., 1982). If n is unknown, it is assumed to be unity and a plot of C versus C will
S L
be linear. The distribution coefficient is related to K by the equation:
oc
K = K /f [16]
oc d oc
where f is the fraction of naturally occurring organic carbon in soil.
oc
Sometimes K is expressed on a naturally occurring organic-matter basis and is defined
d
as:
K = K /f [17]
om d om
where f is the fraction of naturally occurring organic matter in soil. The relationship
om
between K and K is defined as:
oc om
K = 0.58K [18]
om oc
where the constant 0.58 is assumed to represent the fraction of carbon present in the soil or
sediment organic matter (Allison, 1965).
For fractured rock aquifers in which the porosity of the solid mass between fractures is
insignificant, Freeze and Cherry (1974) report the retardation equation as:
R = V /V = [1 + (2K /b)] [19]
d w c A
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where K is the distribution coefficient (cm) and b is the aperture of fracture (cm).
A
To calculate the retardation factors for ionizable compounds such as acids and bases,
the fraction of un-ionized acid (") or base (") needs to be determined (see Dissociation
a b
constant). According to Guswa et al. (1984), if it is assumed only the un-ionized portion of
the acid is adsorbed onto the soil, the retardation factor for the acid becomes:
R = [1 + ("BK /n )] [20]
a a d e
However, for a base they assume that the ionized portion is exchanged with a
monovalent ion and the un-ionized portion of the base is adsorbed hydrophobically.
Therefore, the retardation factor for the base is:
R = {1 + [("BK )/n ] + [CECB(1-")]/(100 -z+n )} [21]
b b d e b e
where CEC is the cation exchange capacity of the soil (cm3/g) and -z+ is the sum of all
positively charged particles in the soil (milliequivalents/cm3). Guswa et al. (1984) report that
the term -z+ is approximately 0.001 for most agricultural soils.
Correlations between K and bioconcentration factors in fish and beef have shown a
oc
log-log linear relationship (Kenaga, 1980) as well as solubility of organic compounds in water
(Abdul et al., 1987; Means et al., 1980). Moreover, the log K has been shown to be related
oc
to molecular connectivity indices (Govers et al., 1984; Gerstl and Helling, 1987; Koch, 1983;
Meylan et al., 1992; Sablji(cid:131) and Proti(cid:131), 1982; Sablji(cid:131), 1984, 1987), solvatochromic parameters
(Cho and Park, 1995), and high performance liquid chromatography (HPLC) capacity factors
(Haky and Young, 1984; Hodson and Williams, 1988; Szabo et al., 1990, 1990a).
In instances where experimentally determined K values are not available, they can be
oc
estimated using recommended regression equations as cited in Lyman et al. (1982) or Meylan
et al. (1992). All the K estimations are based on regression equations in which the aqueous
oc
solubility or the K of the substance is known.
ow
Various classes of compounds are not represented in recommended regression
equations for estimating K values because experimentally determined K values are not
oc oc
available. These classes of compounds include, but are not limited to, alcohols, aldehydes,
esters, ether, saturated hydrocarbons, and ketones. Generally, these types of compounds are
very soluble in water (i.e., mg/L or greater) and low K values suggesting its adsorption to
ow
soil will be nominal. Nevertheless, these compounds will adsorb to some degree on activated
carbon. Removal of these compounds and other hazardous substances from water by
adsorption on powdered or granular activated carbon is commonly used as a primary or
secondary remedial alternative.
Adsorption isotherms of compounds onto activated carbon or other materials are
usually approximated by the Freundlich equation:
log x/m = log K + (1/n) log C [22]
F
where x/m is the amount of solute adsorbed (e.g., mg/g of carbon), C is the equilibrium
concentration (e.g., mg/L), and K and 1/n are empirical constants characteristic of the
F
compound and adsorption material. When n is unity, the adsorption isotherm is linear.
Freundlich constants (K ) for a variety of organic compounds are summarized in Table 12.
F
Octanol/water partition coefficient, log K : The K of a substance is the n-octanol/water
ow ow
partition coefficient and is defined as the ratio of the solute concentration in the water-
saturated n-octanol phase to the solute concentration in the n-octanol-saturated water
phase. Values of K are therefore unitless.
ow
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