[Title 40 CFR B]
[Code of Federal Regulations (annual edition) - July 1, 1996 Edition]
[Title 40 - PROTECTION OF ENVIRONMENT]
[Chapter I - ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)]
[Subchapter R - TOXIC SUBSTANCES CONTROL ACT--(Continued)]
[Part 796 - CHEMICAL FATE TESTING GUIDELINES]
[Subpart B - Physical and Chemical Properties]
[From the U.S. Government Publishing Office]
40
PROTECTION OF ENVIRONMENT
18
1996-07-01
1996-07-01
false
Physical and Chemical Properties
B
Subpart B
PROTECTION OF ENVIRONMENT
ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
TOXIC SUBSTANCES CONTROL ACT--(Continued)
CHEMICAL FATE TESTING GUIDELINES
Subpart B--Physical and Chemical Properties
Sec. 796.1050 Absorption in aqueous solution: Ultraviolet/visible spectra.
(a) Introductory information--(1) Guidance information. (i)
Molecular formula.
(ii) Structural formula.
(2) Standard documents. The spectrophotometric method is based on
national standards and consensus methods which are applied to measure
the absorption spectra.
(b) Method--(1)(i) Introduction, purpose, scope, relevance,
application and limits of test. (A) The primary environmental purpose in
determining the ultraviolet-visible (UV-VIS) absorption spectrum of a
chemical compound is to have some indication of the wavelengths at which
the compounds may be susceptible to photochemical degradation. Since
photochemical degradation is likely to occur in both the atmosphere and
the aquatic environment, spectra appropriate to these media will be
informative concerning the need for further persistence testing.
(B) Degradation will depend upon the total energy absorbed in
specific wavelength regions. Such energy absorption is characterized by
both molar absorption coefficient (molar extinction coefficient) and
band width. However, the absence of measurable absorption does not
preclude the possibility of photodegradation.
(ii) Definitions and units. The UV-VIS absorption spectrum of a
solution is a function of the concentration, c1, expressed in mol/
L, of all absorbing species present; the path length, d, of the
spectrophotometer cell, expressed in cm; and the molar absorption
(extinction) coefficient, i, of each species. The
absorbance (optical density) A of the solution is then given by:
A=d ici
i
For a resolvable absorbance peak, the band width is the
wavelength range, expressed in nm=10-9 m, of the peak at half the
absorbance maximum.
(iii) Reference substances. (A) The reference substances need not be
employed in all cases when investigating a new substance. They are
provided primarily so that calibration of the method may be performed
from time to time and to offer the chance to compare the results when
another method is applied.
(B) Reference compounds appropriate for the calibration of the
system are:
(1) Potassium dichromate (in 0.005 mol/L, H2SO4 solution)
from J.A.A. Ketelaar, paragraph (d)(2) of this section:
log ............................... 3.56 3.63 3.16 3.50
in nm............................. 235 257 313 350
(2) Fluoranthene (in methanol) from C.R.C. Atlas of Spectral Data,
paragraph (d)(3) of this section:
log ........................ 4.75 4.18 4.73 3.91 3.92
in nm...................... 237 236 288 339 357
(3) 4-nitrophenol (in methanol) from C.R.C. Atlas of Spectral Data,
paragraph (d)(3) of this section:
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log ........................................... 3.88 4.04
in nm......................................... 288 311
See also paragraph (d)(1) of this section.
(iv) Principle of the test method. This method utilizes a double-
beam spectrophotometer which records only the absorption differences
between the blank and test solutions to give the spectrum of the
chemical being tested.
(v) Quality criteria--Reproducibility and sensitivity. (A)
Reproducibility and sensitivity, need not be measured directly. Instead,
the accuracy of the system in measuring the spectra of reference
compounds will be defined so as to assure appropriate reproducibility
and sensitivity. It is preferable to use a recording double-beam
spectrophotometer to obtain the UV-VIS spectrum of the test compound.
Such an instrument should have a photometric accuracy of
0.02 units over the absorbance range of 0 to 2 units. It
should be capable of recording absorbances at wavelengths of 200 to 750
nanometers nm with a wavelength accuracy of 0.5 nm. The
cells employed with the instrument must necessarily be transparent over
this wavelength range and must have a path length determined to within 1
percent. To ensure that the instrument is performing satisfactorily,
spectra for test solutions of K2Cr2O7 (for absorbance
accuracy) and holmium glass (for wavelength accuracy) should be run
periodically.
(B) In the event that a recording double-beam instrument is not
available, it will be necessary to determine the absorbance of the test
solution in a single-beam instrument at 5-nm intervals over the entire
wavelength range and at 1-nm intervals where there are indicated
absorbance maxima. Wavelength and absorbance tests should be done as
with the double-beam instrument.
(2) Description of the test procedure--(i) Preparation--(A)
Preparation of test solutions. (1) Solutions should be prepared by
accurately weighing an appropriate amount of the purest form of the test
substance available. This should be made up in a concentration which
will result in at least one absorbance maximum in the range 0.5 to 1.5
units.
(2) The absorption of a compound is due to its particular chemical
form. It is often the case that different forms are present, depending
on whether the medium is acidic, basic, or neutral. Consequently,
spectra under all three conditions are required where solubility and
concentration allow. Where it is not possible to obtain sufficient
concentrations in any of the aqueous media, a suitable organic solvent
should be used (methanol preferred).
(3) The acid medium should have a pH of less than 2, and the basic
medium should be at least pH 10. The solvent for the neutral solution,
and for preparing the acidic and basic ones, should be distilled water,
transparent to ultraviolet radiation down to 200 nm. If methanol must be
used, acidic and basic solutions can be prepared by adding 10 percent by
volume of HCl or NaOH in aqueous solution ([HCl], [NaOH]=1 mol/L).
(4) In theory, all chemical species other than that being tested are
present in both beams and would therefore not appear in the recorded
spectrum of a double-beam instrument. In practice, because the solvent
is usually present in great excess, there is a threshold value of
wavelength below which it is not possible to record the spectrum of the
test chemical. Such a wavelength will be a property of the solvent or of
the test medium. In general, distilled water is useful from 200 nm
(dissolved ions will often increase this), methanol from 210 nm, hexane
from 210 nm, acetonitrile from 215 nm and dichloromethane from 235 nm.
(B) Blank solutions. A blank must be prepared which contains the
solvent and all chemical species other than the test chemical. The
absorption spectrum of this solution should be recorded in a manner
identical to that of the test solution and preferably on the same chart.
This ``baseline'' spectrum should never record an absorbance reading
varying more than 0.05 from the nominal zero value.
(C) Cells. Cell pathlengths are usually between 0.1 cm and 10 cm.
Cell lengths should be selected to permit recording of at least one
maximum in the absorbance range of 0.5 to 1.5 units. Which set of cells
should be used will be governed by the concentration and the absorbance
of the test solution as indicated by the Beer-Lambert Law. The cells
should be transparent over
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the range of the spectrum being recorded, and the path-lengths should be
known to an accuracy of at least 1 per cent. Cells should be thoroughly
cleaned in an appropriate manner (chromic acid is useful for quartz
cells) and rinsed several times with the test or blank solutions.
(ii) Performance of the test. Both cells to be employed should be
rinsed with the blank solution and then filled with same. The instrument
should be set to scan at a rate appropriate for the required wavelength
resolution and the spectrum of the blank recorded. The sample cell
should then be rinsed and filled with the test solution and the scanning
repeated, preferably on the same spectrum chart, to display the
baseline. The test should be carried out at 25 deg. C.
(c) Data and reporting--(1) Treatment of results. (i) The molar
absorption coefficient should be calculated for all absorbance
maxima of the test substance. The formula for this calculation is:
A
= ----------- ,
c,i x d
where the quantities are as defined above (see Definitions and units).
(ii) For each peak which is capable of being resolved, either as
recorded or by extrapolated symmetrical peaks, the bandwidth should be
recorded.
(2) Test report. (i) The report should contain a copy of each of the
three spectra (3 pH conditions). If neither water nor methanol solutions
are feasible, there will be only one spectrum. Spectra should include a
readable wave-length scale. Each spectrum should be clearly marked with
the test conditions.
(ii) For each maximum in each spectrum, the value and
bandwidth (when applicable) should be calculated and reported, along
with the wavelength of the maximum. This should be presented in tabular
form.
(iii) The various test conditions should be included, such as scan
speed, the name and model of the spectrophotom-eter, the slit width
(where available), cell type and path length, the concentrations of the
test substance, and the nature and acidity of the solvent medium. A
recent test spectrum on appropriate reference materials for photometric
and wavelength accuracy should also be submitted (see Reproducibility
and sensitivity).
(d) Literature references. For additional background information on
this test guideline, the following references should be consulted:
(1) Milazzo, G., Caroli, S., Palumbo-Doretti, M., Violante, N.,
Analytical Chemistry, 49: 711 (1977).
(2) Katelaar, J.A.A., Photoelectric Spectrometry Group Bulletin, 8,
(Cambridge, 1955).
(3) Chemical Rubber Company, Atlas of Spectral Data, (Cliffland,
Ohio).
[50 FR 39472, Sept. 27, 1985]
Sec. 796.1950 Vapor pressure.
(a) Introduction--(1) Background and purpose. (i) Volatilization,
the evaporative loss of a chemical, depends upon the vapor pressure of
chemical and on environmental conditions which influence diffusion from
a surface. Volatilization is an important source of material for
airborne transport and may lead to the distribution of a chemical over
wide areas and into bodies of water far from the site of release. Vapor
pressure values provide indications of the tendency of pure substances
to vaporize in an unperturbed situation, and thus provide a method for
ranking the relative volatilities of chemicals. Vapor pressure data
combined with water solubility data permit the calculation of Henry's
law constant, a parameter essential to the calculation of volatility
from water.
(ii) Chemicals with relatively low vapor pressures, high
adsorptivity onto solids, or high solubility in water are less likely to
vaporize and become airborne than chemicals with high vapor pressures or
with low water solubility or low adsorptivity to solids and sediments.
In addition, chemicals that are likely to be gases at ambient
temperatures and which have low water solubility and low adsorptive
tendencies are less likely to transport and persist in soils and water.
Such chemicals are less likely to biodegrade or hydrolyze and are prime
candidates for atmospheric oxidation and photolysis (e.g., smog
formation or stratospheric alterations). On the other hand, nonvolatile
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chemicals are less frequently involved in atmosphere transport, so that
concerns regarding them should focus on soils and water.
(iii) Vapor pressure data are an important consideration in the
design of other chemical fate and effects tests; for example, in
preventing or accounting for the loss of violatile chemicals during the
course of the test.
(2) Definitions and units. (i) ``Desorption efficiency'' of a
particular compound applied to a sorbent and subsequently extracted with
a solvent is the weight of the compound which can be recovered from the
sorbent divided by the weight of the compound originally sorbed.
(ii) ``Pascal'' (Pa) is the standard international unit of vapor
pressure and is defined as newtons per square meter (N/m2). A
newton is the force necessary to give acceleration of one meter per
second squared to one kilogram of mass.
(iii) The ``torr'' is a unit of pressure which equals 133.3 pascals
or 1 mm Hg at 0 deg.C.
(iv) ``Vapor pressure'' is the pressure at which a liquid or solid
is in equilibrium with its vapor at a given temperature.
(v) ``Volatilization'' is the loss of a substance to the air from a
surface or from solution by evaporation.
(3) Principle of the test methods. (i) The isoteniscope procedure
uses a standardized technique [ASTM 1978] that was developed to measure
the vapor pressure of certain liquid hydrocarbons. The sample is
purified within the equipment by removing dissolved and entrained gases
until the measured vapor pressure is constant, a process called
``degassing.'' Impurities more volatile than the sample will tend to
increase the observed vapor pressure and thus must be minimized or
removed. Results are subject to only slight error for samples containing
nonvolatile impurities.
(ii) Gas saturation (or transpiration) procedures use a current of
inert gas passed through or over the test material slowly enough to
ensure saturation and subsequent analysis of either the loss of material
or the amount (and sometimes kind) of vapor generated. Gas saturation
procedures have been described by Spencer and Cliath (1969) under
paragraph (d)(2) of this section. Results are easy to obtain and can be
quite precise. The same procedures also can be used to study
volatilization from laboratory scale environmental simulations. Vapor
pressure is computed on the assumption that the total pressure of a
mixture of gases is equal to the sum of the pressures of the separate or
component gases and that the ideal gas law is obeyed. The partial
pressure of the vapor under study can be calculated from the total gas
volume and the weight of the material vaporized. If v is the volume
which contains w grams of the vaporized material having a molecular
weight M, and if p is the pressure of the vapor in equilibrium at
temperature T (K), then the vapor pressure, p, of the sample is
calculated by
p=(w/M)(RT/v),
where R is the gas constant (8.31 Pa m2mol-1 K-1) when
the pressure is in pascals (Pa) and the volume is in cubic meters. As
noted by Spencer and Cliath (1970) under paragraph (d)(3) of this
section, direct vapor pressure measurements by gas saturation techniques
are more directly related to the volatilization of chemicals than are
other techniques.
(iii) In an effort to improve upon the procedure described by
Spencer and Cliath (1969) under paragraph (d)(2) of this section, and to
determine the applicability of the gas saturation method to a wide
variety of chemical types and structures, EPA has sponsored research and
development work at SRI International (EPA 1982) under paragraph (d)(1)
of this section. The procedures described in this Test Guideline are
those developed under that contract and have been evaluated with a wide
variety of chemicals of differing structure and vapor pressures.
(4) Applicability and specificity. (i) A procedure for measuring the
vapor pressure of materials released to the environment ideally would
cover a wide range of vapor pressure values, at ambient temperatures. No
single procedure can cover this range, so two different procedures are
described in this section, each suited for a different part
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of the range. The isoteniscope procedure is for pure liquids with vapor
pressures from 0.1 to 100 kPa. For vapor pressures of 10-5 to 10
3 Pa, a gas saturation procedure is to be used.
(ii) With respect to the isoteniscope method, if compounds that boil
close to or form azeotropes with the test material are present, it is
necessary to remove the interfering compounds and use pure test
material. Impurities more volatile than the sample will tend to increase
the observed vapor pressure above its true value but the purification
steps will tend to remove these impurities. Soluble, nonvolatile
impurities will decrease the apparent vapor pressure. However, because
the isoteniscope procedure is a static, fixed-volume method in which an
insignificant fraction of the liquid sample is vaporized, it is subject
to only slight error for samples containing nonvolatile impurities. That
is, the nonvolatile impurities will not be concentrated due to
vaporization of the sample.
(iii) The gas saturation method is applicable to solid or liquid
chemicals. Since the vapor pressure measurements are made at ambient
temperatures, the need to extrapolate data from high temperatures is not
necessary and high temperature extrapolation, which can often cause
serious errors, is avoided. The method is most reliable for vapor
pressures below 10 3 Pa. Above this limit, the vapor pressures are
generally overestimated, probably due to aerosol formation. Finally, the
gas saturation method is applicable to the determination of the vapor
pressure of impure materials.
(b) Test Procedures--(1) Test conditions. (i) The apparatus in the
isoteniscope method is described in paragraph (b)(2)(i) of this section.
(ii) The apparatus used in the gas saturation method is described in
paragraph (b)(2)(ii) of this section.
(2) Performance of the tests--(i) Isoteniscope Procedure. The
isoteniscope procedure described as ANSI/ASTM Method D 2879-86 is
applicable for the measurement of vapor pressures of liquids with vapor
pressures of 0.1 to 100 kilopascals (kPa) (0.75 to 750 torr). ASTM D
2879-86 is available for inspection at the Office of the Federal
Register, 800 North Capitol Street, NW., suite 700, Washington, DC. This
incorporation by reference was approved by the Director of the Office of
the Federal Register. This material is incorporated as it exists on the
date of approval and a notice of any change in this material will be
published in the Federal Register. Copies of the incorporated material
may be obtained from the Non-Confidential Information Center (NCIC)
(7407), Office of Pollution Prevention and Toxics, U.S. Environmental
Protection Agency, Room B-607 NEM, 401 M St., SW., Washington, DC 20460,
between the hours of 12 p.m. and 4 p.m. weekdays excluding legal
holidays, or from the American Society for Testing and Materials (ASTM),
1916 Race Street, Philadelphia, PA 19103. The isoteniscope method
involves placing liquid sample in a thermostated bulb (the isoteniscope)
connected to a manometer and a vacuum pump. Dissolved and entrained
gases are removed from the sample in the isoteniscope by degassing the
sample at reduced presssure. The vapor pressure of the sample at
selected temperatures is determined by balancing the pressure due to the
vapor of the sample against a known pressure of an inert gas. The vapor
pressure of the test compound is determined in triplicate at
250.5 deg.C and at any other suitable temperatures
(0.5 deg.). It is important that additional vapor pressure
measurements be made at other temperatures, as necessary, to assure that
there is no need for further degassing, as described in the ASTM method.
(ii) Gas saturation procedure. (A) The test procedures require the
use of a constant-temperature box as depicted in the following Figure 1.
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[GRAPHIC] [TIFF OMITTED] TC01AP92.036
Figure 1--Schematic Diagram of Vapor Saturation Apparatus
The insulated box, containing sample holders, may be of any suitable
size and shape. The sketch in Figure 1 shows a box containing three
solid sample holders and three liquid sample holders, which allows for
the triplicate analysis of either a solid or liquid sample. The
temperature within the box is controlled to 0.5 deg. or
better. Nitrogen gas, split into six streams and controlled by fine
needle valves (approximately 0.79 mm orifice), flows into the box via
3.8 mm (0.125 in.) i.d. copper tubing. After temperature equilibration,
the gas flows through the sample and the sorbent trap and exits from the
box. The flow rate of the effluent carrier gas is measured at room
temperature with a bubble flow meter or other suitable device. The flow
rate is checked frequently during the experiment to assure that there is
an accurate value for the total volume of carrier gas. The flow rate is
used to calculate the total volume (at room temperature) of gas that has
passed through the sample and sorbent [(vol/time) x time = volume].
The vapor pressure of the test substance can be calculated from the
total gas volume and the mass of sample vaporized. If v is the volume of
gas that transported mass w of the vaporized test material having a
molecular weight M, and if p is the equilibrium vapor pressure of the
sample at temperature T, then p is calculated by the equation
p=(w/M)(RT/v).
In this equation, R is the gas constant (8.31 Pa m3mol-1
K-1). The pressure is expressed in pascals (Pa), the volume in
cubic meters (m3), mass in grams and T in kelvins (K). T=273.15+t,
if t is measured in degrees Celsius ( deg.C).
(B) Solid samples are loaded into 5 mm i.d. glass tubing between
glass wool plugs. The following Figure 2 depicts a drawing of a sample
holder and absorber system.
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[GRAPHIC] [TIFF OMITTED] TC01AP92.037
Figure 2--Solid Compound Sampling System
(C) Liquid samples are contained in a holder as shown in the
following Figure 3.
[GRAPHIC] [TIFF OMITTED] TC01AP92.038
Figure 3--Liquid Compound Sampling System
The most reproducible method for measuring the vapor pressure of liquids
is to coat the liquid on glass beads and to pack the holder in the
designated place with these beads.
(D) At very low vapor pressures and sorbent loadings, adsorption of
the chemical on the glass wool separating the sample and the sorbent and
on the glass surfaces may be a serious problem. Therefore, very low
loadings should be avoided whenever possible. Incoming nitrogen gas
(containing no interfering impurities) passes through a coarse frit and
bubbles through a 38 cm column of liquid sample. The stream passes
through a glass wool column to trap aerosols and then through a sorbent
tube, as described above. The pressure drop across the glass wool column
and the sorbent tube are negligible.
(E) With both solid and liquid samples, at the end of the sampling
time, the front and backup sorbent sections are analyzed separately. The
compound on each section is desorbed by adding the sorbent from that
section to 1.0 ml of desorption solvent in a small vial and allowing the
mixture to stand at a suitable temperature until no more test compound
desorbs. It is extremely important that the desorption solvent contain
no impurities which would interfere with the analytical method of
choice. The resulting solutions are analyzed quantitatively by a
suitable analytical method to determine the weight of sample desorbed
from each section. The choice of the analytical method, sorbent, and
desorption solvent is dictated by the nature of the test material.
Commonly used sorbents include charcoal, Tenax GC, and XAD-2. Describe
in detail the sorbent, desorption solvent, and analytical methods
employed.
(F) Measure the desorption efficiency for every combination of
sample, sorbent, and solvent used. The desorption efficiency is
determined by injecting a known mass of sample onto a sorbent and later
desorbing it and analyzing for the mass recovered. For each combination
of sample, sorbent, and solvent used, carry out the determination in
triplicate at each of three concentrations. Desorption efficiency may
vary with the concentration of the actual sample and it is important to
measure the efficiency at or near the concentration of sample under gas
saturation test procedure conditions.
(G) To assure that the gas is indeed saturated with test compound
vapor,
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sample each compound at three differing gas flow rates. Appropriate flow
rates will depend on the test compound and test temperature. If the
calculated vapor pressure shows no dependence on flow rate, then the gas
is assumed to be saturated.
(c) Data and reporting. (1) Report the triplicate calculated vapor
pressures for the test material at each temperature, the average
calculated vapor pressure at each temperature, and the standard
deviation.
(2) Provide a description of analytical methods used to analyze for
the test material and all analytical results.
(3) For the isoteniscope procedure, include the plot of p vs. the
reciprocal of the temperature in K, developed during the degasing step
and showing linearity in the region of 298.15 K (25 deg.C) and any
other required test temperatures.
(4) For the gas saturation procedure, include the data on the
calculation of vapor pressure at three or more gas flow rates at each
test temperature, showing no dependence on flow rate. Include a
description of sorbents and solvents employed and the desorption
efficiency calculations.
(5) Provide a description of any difficulties experienced or any
other pertinent information.
(d) References. For additional background information on this test
guideline the following references should be consulted:
(1) U.S. Environmental Protection Agency. Evaluation of Gas
Saturation Methods to Measure Vapor Pressures: Final Report, EPA
Contract No. 68-01-5117 with SRI International, Menlo Park, California
(1982).
(2) Spencer, W.F. and Cliath, M.M. ``Vapor Density of Dieldrin,''
Journal of Agricultural and Food Chemistry, 3:664-670 (1969).
(3) Spencer, W.F. and Cliath, M.M. ``Vapor Density and Apparent
Vapor Pressure of Lindane,'' Journal of Agricultural and Food Chemistry,
18:529-530 (1970).
[50 FR 39252, Sept. 27, 1985, as amended at 53 FR 12525, Apr. 15, 1988;
53 FR 21641, June 9, 1988; 60 FR 34466, July 3, 1995]