EPA-650/2-74-124
DECEMBER 1974
Environmental Protection Technology Series
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These series are:
1. ENVIRONMENTAL HEALTH EFFECTS RESEARCH
2 . ENVIRONMENTAL PROTECTION TECHNOLOGY
3. ECOLOGICAL RESEARCH
4. ENVIRONMENTAL MONITORING
5. SOCIOECONOMIC ENVIRONMENTAL STUDIES
6. SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
9. MISCELLANEOUS
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to
develop and demonstrate instrumentation, equipment and methodology
to repair or prevent environmental degradation from point and non-
point sources of pollution. This work provides the new or improved
technology required for the control and treatment of pollution sources
to meet environmental quality standards.
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EPA-650/2-74-124
DEVELOPMENT
OF SAMPLING METHOD
FOR TOTAL ATMOSPHERIC SELENIUM
by
William J. Barrett and Herbert C. Miller
Engineering and Applied Sciences Department
Southern Research Institute
2000 Ninth Avenue South
Birmingham, Alabama 35205
Contract No. 68-02-1220
ROAP No. 26ACX, Task 19
Program Element No. 1AA010
EPA Project Officer: Eva Wittgenstein
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
December 1974
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EPA REVIEW NOTICE
This report has been reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development.
EPA, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
11
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PREFACE
Experimental work on this project began in July 1973 and was
completed in June 1974.
M. Patricia Alewine, Associate Chemist, and Michael Rooks,
Assistant Chemist, assisted in performing the work described
in this report.
Discussions with members of the staff of the National
Environmental Research Center at Research Triangle Park and
with Dr. William Fulkerson and his associates at Oak Ridge
National Laboratory were helpful in planning this work and
in interpreting the results.
111
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TABLE OF CONTENTS
Page
Preface iii
List of Tables vi
Sections
I Introduction 1
II Summary 3
III Conclusions 4
IV Recommendations 6
V Methods for the Determination of Selenium 8
VI Laboratory Generation of Selenium Vapors and 14
Aerosols
VII Laboratory Evaluation of Methods of Sampling 21
for Selenium in Air
VIII Selenium Sampling of the Ambient Atmosphere 28
and Investigation of the Chemical Forms of
Atmospheric Selenium
IX Conclusions Concerning the Nature of Atmospheric 35
Selenium
References 38
Technical Report Data (EPA Form 2220-1) 42
v
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LIST OF TABLES
Pag
No. 2
1 Recovery of Selenium from Filters with Analysis
by the Methylene Blue Method
2 Nebulization-Generator Output •*-
3 Selenium Analyses of Generator Effluent at 74 °C 17
4 Selenium Analyses of Generator Effluent at 27°C 18
5 Particle-Size Distribution of Selenium Aerosol 19
Generator Effluent
6 Selenium Retention of Treated Filters for Sam- 24
pling the Dry-SeO2 Generator Effluent
(Preliminary Results)
7 Collection Efficiencies of Bubbler Solutions for 26
(CH3)2Se Vapor
8 Retention of Selenium from the Dry-Se02 Genera- 27
tor by Various Bubbler Solutions
9 Selenium Content of Ambient Atmospheric Samples 30
10 Andersen Cascade Impactor Sampling of the 31
Ambient Atmosphere
11 Effect of Digestion Treatment on the Determina- 33
tion of Selenium by the DAN Method
VI
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SECTION I
INTRODUCTION
This report describes the experimentation undertaken and the
results obtained in connection with a project to develop sam-
pling and analytical methods for total atmospheric selenium.
The primary purposes of this contract were to develop a col-
lection technique for the quantitative collection of total
atmospheric selenium and to characterize the forms in which
selenium occurs in the atmosphere. A secondary, but essen-
tial, requirement was that an analytical method be selected
and demonstrated to be suitable for the routine laboratory
determination of the selenium in field-collected samples.
Although little is known about the occurrence, distribution,
and concentration of selenium in the atmosphere, the element
and its compounds may be as significant with regard to health
as some others that have been more thoroughly investigated.
Selenium compounds are known to be toxic, although their pre-
cise role in human biochemistry is not fully understood. A
threshold limit value (TLV) of 0.2 mg/m3 has been established
for selenium compounds (as Se) by the American Conference of
Governmental Industrial Hygienists.1 Recognition of the pos-
sibility of increasing exposure of the populace to selenium
from combustion and incineration processes demands that more
attention be given to the methodology of sampling and charac-
terization of atmospheric selenium.
Selenium is widely distributed in nature and occurs only in
very small concentrations, most often in association with sul-
fide minerals. It is concentrated from soils in some areas
by certain types of plants. Even in these more concentrated
natural forms, however, the proportion of selenium is very low.
The average concentration of selenium in the earth's crust
has been estimated to be only about 0.09 yg/g (parts per
million).
Major sources of atmospheric selenium include nonferrous
metallurgical operations, glass-melting furnaces, the combus-
tion of fossil fuels, and the incineration of solid wastes,
especially paper.2'3 It has been estimated that in 1969 the
commercial consumption of selenium in the United States was
660 kkg (728 tons). Emissions to the atmosphere were esti-
mated to total 900 kkg (986 tons); of this amount, 65% was
derived from the burning of coal, 21% from glass-manufacturing
processes, 9% from the production of nonferrous metals, and
7% from the burning of fuel oils.1*
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Th^re appears to be no firm information in the literature
the chemical species in which selenium occurs in tne amDJ
atmosphere. This lack of information may be attri ^
the difficulties arising from the extremely low total con e
tration levels of selenium and to the fact that the selenium
compounds that may be present can constitute no more tnan
small fraction of the total atmospheric contaminants in any
given sample.
The approach undertaken relative to the sampling problem was
based on the use of retentive filters for the collection of
particulate material containing selenium and evaluations of
chemically treated filters for retention of selenium that may
occur in the gaseous or vapor form. In the initial phase of
the investigation, laboratory aerosol generators were set up
for evaluations of filter materials, and some effort was
expended in establishing the 2,3-diaminonaphthalene (DAN)
fluorometric method as the primary analytical technique for
selenium. Later, samples of atmospheric particulate material
were analyzed for selenium and procedures were investigated
for determining the relative amounts of selenium present in
different oxidation states in the particulate material. Also,
additional selenium aerosol and vapor generators were set up,
characterized, and used in evaluations of other candidate sam-
pling devices.
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SECTION II
SUMMARY
The primary purposes of this contract were to develop a tech-
nique for the quantitative collection of total atmospheric
selenium and to characterize the forms in which selenium
occurs in the atmosphere.
The approach undertaken relative to the sampling problem was
based on the use of retentive filters for the collection of
particulate material containing selenium and evaluations of
chemically treated filters for the retention of selenium that
may occur in the gaseous or vapor form. In the initial
stages of the investigation, laboratory aerosol generators
were set up for evaluations of filter materials and, on the
basis of comparison with other methods, the 2,3-diamino-
naphthalene (DAN) fluorometric method was selected as the
primary analytical technique for selenium. Later, samples of
atmospheric particulate matter were analyzed for selenium and
procedures were investigated for determining the relative
amounts of selenium present in different oxidation states in
the particulate material. Also, additional selenium aerosol
and vapor generators were set up, characterized, and used in
evaluations of other candidate sampling devices.
It appeared that the selenium present in the ambient atmo-
sphere exists predominantly as, or in association with, par-
ticulate matter, and that little or no loss of selenium by
vaporization occurred during continuous sampling with filters,
Thus, it was tentatively established that conventional partic-
ulate sampling was sufficient for collecting the bulk of atmo-
spheric selenium. Vapor forms of selenium are believed to
make a negligible contribution to total atmospheric selenium.
The most probable chemical forms in which atmospheric sele-
nium exists were determined to be the element and the dioxide
(or selenite).
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SECTION III
CONCLUSIONS
On the basis of the experimental results presented in this
report—primarily the results of laboratory experiments with
a dry-selenium dioxide aerosol generator and the analyses of
atmospheric particulate samples—the following conclusions
were reached.
• Selenium occurs in the atmosphere primarily as
selenium dioxide and elemental selenium, in
roughly equal proportions. Selenium in the +6
oxidation state does not occur in the atmosphere.
Efforts to establish the presence or absence of
organic selenium were not conclusive.
• Selenium occurs in the atmosphere primarily in
particulate form or in association with particu-
late material. The contribution of vapor forms
to total atmospheric selenium is believed to be
negligible.
• Little or no selenium is lost by vaporization dur-
ing continuous sampling with filters.
• Selenium in the atmosphere is not primarily asso-
ciated with the smaller size fractions, as it has
been shown to be in stack emissions, but is most
abundant in the particle sizes near the mass mean
diameter.
• Conventional high-volume particulate sampling is
adequate for the collection of atmospheric sele-
nium.
• Of the reagent-impregnated filters evaluated for
collecting vapor forms of selenium, none were
demonstrated to be applicable to atmospheric sam-
pling, and, moreover, they were not shown to be
effective in laboratory experiments.
• Analyses of particulate samples collected at an
urban site of heavy industrial pollution and
samples collected at a site of only moderate
pollution suggested that the selenium concentra-
tions in the air at the two sites were the same —
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essentially at a uniform background level—and
that the sources in the heavily polluted area
were not significant emitters of selenium.
• Errors can occur in the estimation of selenium
concentrations by the DAN-fluorometric method if
samples are subjected to a strong oxidative treat-
ment without a subsequent reduction step to con-
vert Se(VI) to Se(IV).
• Cyclohexane was found to be superior to toluene
or hexane as the extracting solvent for a piaz-
selenole, primarily because of the much lower
blank fluorescence observed with cyclohexane.
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SECTION IV
RECOMMENDATIONS
As a result of this investigation, several recommendations^
for future research can be made. First, additional labora-
tory studies should be conducted to evaluate treated filter
materials for the retention of elemental selenium vapor.
Studies such as these take on added significance in view of
recent reports that selenium emissions from coal-fired power
plants initially exist as elemental selenium vapor. It is
reported that the sulfur dioxide present in the stack efflu-
ent is sufficient to insure the reduction of any selenium
dioxide to the element. Also, the importance of these studies
is underscored by the fact that coal burning represents the
single most significant source of atmospheric selenium. To
facilitate the experimental work, heated selenium metal
(possibly in an inert atmosphere) should serve as a conve-
nient source of the metallic vapor in a laboratory generator.
Some effort should also be expended to answer several ques-
tions concerning the nature of the elemental selenium vapor:
what is the allotropic form of the metal in the vapor phase?;
what is the stability of the metal vapor with respect to
oxidation or reduction in the atmosphere?; and does the
selenium metal vapor tend to condense rapidly to form an
aerosol? After these questions concerning the laboratory
investigation are satisfactorily answered, sampling for sele-
nium in the vicinity of a coal-fired power plant should be
conducted.
Secondly, additional methods for sampling the volatile organic
selenide—dimethyl selenide—should be considered. Sorption
on an activated carbon surface with subsequent desorption,
oxidation, and analysis is a potential avenue for future
investigation. If this volatile selenide could be success-
fully sampled, its possible presence in the ambient atmosphere
could then be investigated.
Finally, additional methods of selenium analysis which may
offer increased sensitivity and specificity should be evalu-
ated in greater depth. For example, the gas chromatographic
methods briefly studied in this investigation should be
reconsidered. These methods are based on the gas chromato-
graphic separation of a piazselenole with subsequent detec-
tion by electron capture. An additional recently described
gas chromatographic method which shows the promise of
increased sensitivity and specificity involves the detection
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of a piazselenole by microwave emission spectrometry (MES).
Because the MES detector response is not a function of the
organic moiety comprising the piazselenole but a function of
the selenium atom itself, the method appears to offer a
significant improvement over conventional electron capture
detection of the piazselenole. For these reasons the GC-MES
technique should also be considered for selenium determina-
tion in atmospheric samples.
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SECTION V
METHODS FOR THE DETERMINATION OF SELENIUM
Because of the importance of establishing a convenient and
reliable analytical method for selenium, three of the several
methods presented in the literature were evaluated for their
suitablity in the routine analysis of atmospheric samples.
The three methods which appeared to be the most adaptable for
the purposes of this study were the fluorometric procedure
using DAN, a gas chromatographic method using DAN or either
4-chloro-o-phenylenediamine or 4-nitro-o-phenylenediamine,
and a catalytic method based on the reduction of methylene
blue. Although neutron activation analysis, atomic absorption
spectrophotometry, and spark source mass spectrometry have
seen a considerable amount of use recently for the determina-
tion of elements in atmospheric particulate material, they
were not deemed especially suitable for the purposes of this
project. However, a new, highly sensitive technique worthy
of future consideration has been developed at the Oak Ridge
National Laboratory.5 This method for the determination of
selenium is based on the gas chromatographic separation of a
piazselenole with microwave emission spectrometric (MES)
detection. The method appears to offer even more sensitivity
than the methods considered in this study.
THE METHYLENE BLUE METHOD
The catalytic methylene blue method developed by West is a
simple procedure involving no instrumentation and few
reagents.6 It is useful over a range of 0.1 to 1.0 yg of
selenium. It has been used by West to determine selenium in
smoke from trash burning,7 and in cigarette papers, other
papers, and tobacco.8
The method is based on the catalytic effect of trace amounts
of selenium in the reduction of methylene blue by sodium sul-
fide. Ethylenediaminetetraacetic acid (EDTA) is used as a
general masking agent, and formaldehyde, which suppresses the
reducing power of sodium sulfide, is used to stabilize the
blank. By taking advantage of the inducing effect of Fe(Ill),
the limit of detection can be made as low as 0.1 yg of sele-
nium.6 Calibration data are obtained by measuring the time
required for complete decolorization of methylene blue after
mixing the reagents in the presence of known quantities of
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selenium. A linear calibration curve is obtained by plotting
the reciprocal of the time (min~1) versus micrograms over the
range of 0.1 to 1.0 yg of selenium.
In our evaluations of the methylene blue method, typical
results were those obtained in an experiment involving the
recovery of selenium from spiked glass-fiber filters by
extraction with water. These results are presented in
Table 1. This exercise demonstrated the uncertainty in the
methylene blue method of analysis for amounts of selenium
less than about 0.25 yg. Below this level, reproducibility
suffered from the visual uncertainty in the color change at
the end point. On the other hand, simultaneous determinations
of selenium in identical samples by the DAN-fluorometric
method resulted in selenium recoveries in excess of 90% of the
theoretical (spiked) amount. Thus, the low recovery of sele-
nium in the case of the methylene blue method suggested that
the filters may contain a surface material that inhibits the
catalytic effect of selenium on the reduction of methylene
blue by sulfide. For these reasons, and specifically for the
reason of limited sensitivity, the methylene blue method was
not selected as the primary method of analysis for atmospheric
selenium.
Table 1. RECOVERY OF SELENIUM FROM FILTERS WITH
ANALYSIS BY THE METHYLENE BLUE METHOD
Amount of Se
added, yg
0.0
0.05
0.10
0.25
0.50
0.75
1.0
Amount of
recovered,
0.09
0.19
0.19
0.23
0.35
0.52
0.67
Se
yg
THE GAS CHROMATOGRAPHIC METHOD
The gas chromatographic method is relatively new. It was
introduced by Nakashima and T6ei.9 The compound 4-chloro-p_-
phenylenediamine reacts with selenious acid (Se(IV)) to form
the 5-chloropiazselenole which is detectable by electron-
capture gas chromatography. Later, Shimoishi and Toei used
4-nitro-o-phenylenediamine to form 5-nitropiazselenole, which
is more Sensitive to electron-capture than the chloro
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compound.10 Shimoishi has used the gas n sea
method to determine selenium in pure tellurium and in sea
water12. As little as 2 ng of selenium was detected by this
method.
More recently an article by Young and Christian13 further
pointed out the utility of the gas chromatographic method of
selenium analysis. In this example, selenium (IV) reacted
with 2,3-diaminonaphthalene at pH 2 to form the well
established piazselenole, which was then extracted witn
hexane. An aliquot of the hexane layer was analyzed gas chro-
matographically with an electron-capture detector. As little
as 0.5 ng of selenium could be detected; 10 ng of selenium
could be determined in a sample by extracting into 0.1 ml of
hexane and injecting a 5-yl aliquot of the extract. The
method was applied to the determination of physiological
amounts of selenium in human blood and urine. River water
samples were also analyzed.
In our brief evaluation of the gas chromatographic methods,
known selenium samples were analyzed by the methods of Young
and Christian13 and Shimoishi and T6ei.l° In a slight modifi-
cation of their procedures, cyclohexane was used as the
extractant for the piazselenole rather than the hexane or
toluene used by Young and Christian and Shimoishi and Toei,
respectively. From studies of the DAN-fluorometrie method to
be described later in this report, we found cyclohexane to be
superior to hexane or toluene as the extracting solvent for a
piazselenole, primarily because of the much lower blank
observed with cyclohexane.
The minimum amount of selenium that could be detected in this
evaluation of the GC methods was about 0.5 ng (per 5 yl injec-
tion) . The method of Shimoishi,12 in which 4-nitro-o-
phenylenediamine is used as the reagent to form the piazsele-
nole, was found to be somewhat more sensitive than the method
using the DAN complex. Because Young and Christian13 pointed
out that the DAN complex was as sensitive to electron-capture
detection as the 4,5-dichloropiazselenole of Nakashima and
Toei,9 the present results suggest that the 5-nitropiazsele-
nole is the most sensitive of the piazselenoles investigated
thus far to electron-capture detection.
Although the 5-nitropiazselenole offered the most sensitivity,
an effluent fraction that was observed in the blank produced
a peak that overlapped the piazselenole peak and interfered
with the measurement of peak area. A similar observation was
made by Shimoishi12 who removed the overlapping peak by wash-
ing the extract with hydrochloric acid solution. The possi-
bility of back-extraction of the 5-nitropiazselenole into the
10
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washing solution appeared to be no problem. It is conceiv-
able that such a washing step would have removed the overlap-
ping peak observed in our evaluation of the method.
THE DAN-FLUOROMETRIC METHOD
From the beginning of this project, we had planned to use the
DAN-fluorometric method as the primary method for the deter-
mination of selenium. This selection was based principally
on the fact that the DAN method had been chosen as a tentative
standard method by the Intersociety Committee on Methods for
Ambient Air Sampling and Analysis.14 The essentials of this
method were introduced in 1962 by Parker and Harvey.15 The
DAN method was shown to provide more sensitivity and conve-
nience than the previously used 3,3'-diaminobenzidine method.
Since that time, the DAN method has been used for the deter-
mination of selenium in many kinds of materials. The experi-
mental procedure is straightforward, and the sensitivity
limit has been variously reported to be 2 to 20 ng of sele-
nium.
Because the DAN-fluorometric method was the primary method of
selenium analysis used in this laboratory, the method will be
given in some detail, incorporating the modifications devel-
oped during our experimentation.
Routine atmospheric samples were collected on 20.3-
by 25.4-cm (8- by 10-in.) glass-fiber filters in
high-volume samplers. A 13- by 25-cm2 section of
the filter (cut into 6-cm2 pieces) was cautiously
extracted with 30 to 50 ml of a 10:1 mixture of
concentrated nitric and perchloric acids. After
boiling to reduce the volume to about 5 ml, the
solution was diluted to approximately 50 ml with
distilled water and the solution volume again
reduced by boiling. The second digestion was then
conducted with 5 to 10 ml of concentrated hydro-
chloric acid and the total volume reduced again.
After appropriate treatment to dissolve the sample
containing 0 to 1 yg of selenium, the solution was
adjusted to pH 2 with successive additions of 10 N,
1 N, and 0.1 N NaOH. The resulting solution was
then passed through a 25-ml buret filled to the
10-ml mark with regenerated Dowex 50 WX-8, 50- to
100-mesh cationic exchange resin at a flow rate of
approximately 0.5 ml/min. The effluent was col-
lected along with any remaining traces of selenium
washed from the column with 25- or 30-ml of
distilled water. To this solution was added 0.5 ml
11
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of 0.1 M EDTA, 0.5 ml of 0.1 M NaF, and 5 ml of
0.1% DAN solution. (The DAN was dissolved in u.i i_
HC1 to give a 0.1% solution that was stable under
refrigeration for about 3 days.) The solution con
taining the selenium was then readjusted to PH^,
and an additional 5 ml of 0.1% DAN was added after
which the solution was allowed to stand for £ nr.
The solution was then transferred to a separatory
funnel and the piazselenole was extracted into
exactly 10 ml of cyclohexane by shaking for 0.5 mm.
After the separation of the aqueous and organic
phases, the cyclohexane layer was filtered into a
cuvette through a filter paper plug placed in the
stem of the separatory funnel to remove droplets of
water.
The fluorescence intensity of the sample was then
measured at an exciting wavelength of 380 nm and a
fluorescence wavelength of 525 nm. A solution con-
taining 1.0 yg of selenium was used as the refer-
ence standard. When a filter fluorometer was
employed, a Corning No. 5970 primary (uv) filter
was used in conjunction with a Corning No. 4010
(maximum transmission at 525 nm) secondary filter.
A linear calibration curve was observed over the
range of 0 to 1 yg of selenium in 10 ml of cyclo-
hexane .
In the procedure outlined above, the HClCK/HNOs digestion was
used to leach the selenium from the particulate material and
to oxidize any selenium present as the element to Se(IV). It
was determined that the +4 oxidation state, in solution as
selenite (SeOs"2), was the only form of selenium appropriate
for reaction with DAN to produce the fluorescent piazselenole.
The HC1 digestion ensured the reduction back to Se(IV) of any
selenium present as Se(VI) or any that had been inadvertently
oxidized to Se(VI). Experiments demonstrating the utility of
the hydrochloric acid digestion are presented in Section VII
of this report.
The dilution and rebelling of the solution after the initial
HNOa/HClOi, digestion served to expel the dissolved oxides of
nitrogen and thus prevented nitrite ion interference. The
EDTA and NaF solutions were used as masking agents to reduce
the possibility of metal ion interferences. Also, it was
found that the results were not significantly affected by
allowing the solutions to stand in a well-lighted laboratory
for the prescribed 2-hr period.
12
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By using cyclohexane as the extracting solvent rather than
toluene as suggested in the Intersociety Committee method, we
were able to lower the blank markedly and to increase repro-
ducibility considerably. After correction for the blank
value, samples containing as little as 0.01 yg of Se were
analyzed. This detection limit represented almost an order
of magnitude reduction due to the lower blank value in cyclo-
hexane. The detection limit offered by this modification of
the DAN-fluorometrie method was as good as, or better than,
the limits offered by the other methods of selenium analysis
evaluated in this study.
As a further evaluation of the DAN-fluorometric method, a
National Bureau of Standards Standard Reference Material was
analyzed for selenium. This standard, "Trace Mercury in Coal"
(SRM 1630), is not certified for selenium, but a value for
selenium content of 2.1 yg/g (as Se) is included in the certi-
ficate as "information only". Our method of analysis of this
coal sample was the usual DAN method with aqueous samples
prepared by the Schoniger oxygen combustion-flask technique.
The powdered coal samples were supported in the flask in
quartz wool contained in a platinum mesh boat. The absorbing
solution used in the Schoniger flask was 0.5 M HN03. Our
analysis yielded a value for selenium content of 1.6 ± 0.4
yg/g. This value was not only lower than the reported value
of 2.1 yg/g but the precision was not as high as was desired.
Incomplete combustion of the samples could, in part, explain
the low results and lack of precision because some samples
were observed to have an insoluble tar-like residue remaining
in the flask after removal of the absorbing liquid.
13
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SECTION VI
LABORATORY GENERATION OF SELENIUM VAPORS AND AEROSOLS
From the outset it was recognized that assembling and estab-
lishing the performance of laboratory aerosol and vapor gener-
ators were of prime importance in the evaluation of candidate
sampling devices. Thus, during the course of the investiga_
tion, we constructed and evaluated several selenium generating
devices for use in the laboratory.
NEBULIZATION AEROSOL GENERATOR
The first device tested was a selenium aerosol generator based
on a DeVilbiss No. 841 nebulizer. In this relatively simple
system, the nebulizer was used to spray a solution prepared
by dissolving elemental selenium in a small amount of nitric
acid and diluting with water or a sodium or ammonium chloride
solution to a known selenium concentration. This nebulizer
was designed for inhalation therapy and is intended to produce
particles in the size range from 1 to 10 ym when dilute aque-
ous solutions are dispersed from its 500-ml solution reser-
voir. Filtered and humidified air from the laboratory
compressed air system was passed through the nebulizer at
2.5 1/min. The output of the nebulizer was diluted with clean
compressed air at various dilution ratios. The relative
humidity of the dilution air was controlled by mixing two
dilution airstreams, one humidified and the other dried. The
dilution chamber consisted of a 5.1-cm i.d. glass tube 51 cm
long, with three sampling ports located at intervals along
the tube. The dilution chamber was vented to a hood.
Table 2 shows some preliminary results obtained for the
measured generator output at two selenium solution concentra-
tions. The nebulizer solution was prepared for these tests
by dissolving elemental selenium in dilute nitric acid and
diluting with water. The aerosol was sampled for 2 hr at
2 1/min through a glass-fiber filter followed by a bubbler
containing water. The glass-fiber filter was extracted with
water and the selenium was determined by the methylene blue
method. No selenium could be detected in the bubbler solu-
tion, indicating that most of it was collected on the filter
in particulate form. The results of these analyses suggested
that reasonably satisfactory performance of the generator
system could be expected at an output concentration level of
about 1 ng/1. With this technique, the concentration of
14
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Table 2. NEBULIZATION-GENERATOR OUTPUT
Concn of Se
in nebulizer
solution, mg/1
100
1
Flow rate
of dilution
air, 1/min
2.0
6.0
10.0
6.0
6.0
Dilution3
factor
0.8
2.4
4.0
2.4
2.4
Concn of Se
in generator
output, ng/1
140
110
40
0.6
0.8
The flow rate of air through the nebulizer was 2.5 1/min.
aerosol produced approached the practical limit that could be
measured by the analytical method within a reasonable sampling
time.
Although it was possible to evaluate field sample-collection
devices at the 1 ng/1 concentration level, it was desirable
to work at lower levels more nearly approaching those that
are expected to occur in the atmosphere. We therefore con-
ducted some preliminary experiments with nebulizer solutions
containing a relatively high ratio of a soluble salt to dis-
solved selenium. The principle was based on the assumption
that the ratio of the salt to selenium would be the same in
the aerosol particles as in the nebulizer solution, and that
determination of the concentration of the salt in the aerosol
would permit a valid estimation of the concentration of sele-
nium when the selenium was too low to be measured by the most
sensitive analytical method. To test this principle, we
nebulized a solution containing 1 mg/1 of selenium and 10 g/1
of ammonium chloride. The aerosol was diluted and sampled on
a glass-fiber filter, as in previous experiments. The
selenium content of the filter was determined by the methylene
blue method and the ammonium content was determined by the
ammonia electrode method. The calculated weight ratio of
ammonia (NH3) to selenium (Se) in the nebulizer solution was
3.4 x 103, and the ratio found by analysis of the generator
output was 4.3 x 103. In a similar experiment in which
sodium chloride was used instead of ammonium chloride and the
chloride content of the aerosol was determined, much poorer
agreement was obtained.
In additional experiments we substituted ammonium sulfate for
ammonium chloride in the nebulizer solution since the sulfate
is a widely occurring constituent of atmospheric aerosols.
The nebulizer solutions were prepared to contain 0.01% of
selenium (as Se) and 1.0% of NH3 added as ammonium sulfate, a
15
-------
ratio of NH3 to Se of 100 to 1. Analyses of the aerosol
collected on a glass-fiber filter gave ratios_of NH3 to be
averaging about 50 to 1. In one set of experiments, f^ers
were extracted with a measured volume of water and aliquot^
were taken for determinations of ammonia by the Nessler method
and for determinations of selenium by both the DAN-
fluorometric and methylene blue methods. The two methods for
selenium gave approximately the same average value tor tne
concentration of selenium in the aerosol, about 140 ng/1, but
the precision of the measurements was poor. Some or tne
variability of the results could have been attributable_to
instability of the aerosol generation or to variations in
efficiency of sampling.
Results from further experiments on this principle of low-
level selenium estimation in laboratory-generated aerosols
proved to be inconsistent and widely variable. Also, the
ratios of NH3 to Se found in the aerosol seldom agreed with
the known ratios in the nebulizer solution. At this point
this technique was tentatively abandoned in favor of conduct-
ing sampling evaluations at selenium aerosol concentration
levels sufficient for direct determination by existing tech-
niques .
DRY-SELENIUM DIOXIDE AEROSOL GENERATOR
One form in which selenium is likely to occur in the atmo-
sphere is selenium dioxide. Selenium dioxide could occur as
solid particles or as the vapor, or in an adsorbed state in
association with other particulate matter. It is possible,
also, that selenium present in source emissions as the dioxide
might be converted in the atmosphere to selenious acid or to
another chemical form.
Thus, we set out to determine if dry selenium dioxide could
be used as a laboratory source of selenium vapor or particu-
late material. As a starting point, it was of interest to
estimate the volatility of selenium dioxide at ambient temper-
atures. From published data on the vapor pressure at several
temperatures,16 it was calculated that the volatility at 25°C
is about 105 ng/m3. This value is several orders of magni-
tude higher than any reported atmospheric concentration of
selenium, and it suggested that dry selenium dioxide might be
a convenient source of selenium in the vapor form.
In a preliminary experiment to examine the practical signifi-
cance of the volatility, we placed 100 mg of selenium dioxide
between two glass-fiber filters and passed air at room temper-
ature through the filters at 2.0 1/min, collecting samples of
the effluent air in bubblers containing water. From the
16
-------
volatility data, as much as 2 yg of selenium dioxide was
expected in a 20-liter sample. However, no selenium could be
detected in the bubbler solutions by the methylene blue
method.
In later experiments a more elaborate set-up was constructed
to employ dry selenium dioxide as a laboratory source of sele-
nium. The dry-selenium dioxide generator was prepared by mix-
ing an aqueous solution of selenium dioxide and an inert
solid support, Chromosorb W, and evaporating the resulting
mixture to dryness. The dry charge of Se02/Chromosorb W was
then placed in a suitable glass column and enclosed by glass-
wool plugs. Provisions for temperature control were made by
wrapping the column with an insulated heating tape connected
to a variable voltage source. For generation of selenium a
dry airstream was passed through the packed column at a fixed
rate and the effluent was sampled directly to determine its
selenium concentration.
In an effort to characterize the form in which the selenium
existed and its concentration in the effluent of the genera-
tor described above, several combinations of untreated glass-
fiber filters and midget impinger bubblers containing dis-
tilled water were used for sampling. Typical results of the
selenium analyses for the various sampling configurations are
presented in Tables 3 and 4. The results are given in terms
of the amount of selenium in nanograms removed by a given
sampling device per liter of generator effluent sampled.
Table 3 contains data obtained with a generator effluent tem-
perature of 74°C as measured at the glass-wool plug in the
end of the packed column. Table 4 contains data for an
effluent temperature of 27°C (room temperature).
Table 3. SELENIUM ANALYSES OF GENERATOR EFFLUENT AT 74°C
Sampling medium
Se collected
per liter of
effluent sampled,
ng
Glass-fiber filter
Second filter in tandem filters
Impinger bubbler (water)
Second bubbler in tandem bubblers
Filter following two bubblers
Bubbler following a single filter
17
33
1
10
5
1
0.5
-------
Table 4. SELENIUM ANALYSES OF GENERATOR EFFLUENT AT 27°C
Sampling medium
Se collected
per liter of
effluent sampled,
Glass-fiber filter
Second filter in tandem filters
Impinger bubbler (water)
Filter following a single bubbler
1.2
0.05
0.7
0.02
The results with two glass-fiber filters in series indicated
that the single untreated glass-fiber filter removed the sele-
nium from the generator effluent with more than 90% efficiency,
However, the impinger bubbler containing distilled water
operated with only about 30 to 60% efficiency, depending upon
the effluent temperature. One anomalous result was the
unexpected low values for selenium retained on filters follow-
ing bubblers. The filters were expected to retain the sele-
nium passed by the bubblers, since a low efficiency had been
found for the bubblers and a high efficiency for the filters.
It may have been that losses occurred in the sampling train
between the bubblers and the filters due to the large increase
in the humidity of the sample airstream after passage through
the bubblers.
From the results of preliminary experiments conducted with
this type of selenium generator, it was concluded that the
selenium did not exist primarily as a vapor of selenium diox-
ide or selenious acid, as expected from vapor pressure data,
but as a particulate aerosol. Additionally, it was determined
that the total selenium concentration of the generator aerosol
was only about 2% of the selenium concentration expected in
the gas phase as calculated from equilibrium vapor pressure
data.
To further characterize the generator effluent, an Andersen
"Mini Personnel" cascade impactor was employed for the pur-
pose of approximate sizing of the particulate aerosol. This
particular Andersen impactor provided four impaction stages
and a final filter. To utilize the impactor, the generator
effluent was routed to a large glass jug which provided the
sampling environment and served as an enclosure for the impac-
tion device. Several samples were taken from the generator
operating at both room temperature and 74°C under conditions
similar to those described earlier. With the generator
18
-------
operating at room temperature, the initial sample volume of
approximately 2 m3 surprisingly yielded negligible amounts of
selenium, ^.e^, less than 20 ng. Results from previous
experiments" Tn which the effluent was sampled with filters
and bubblers directly from the generator at room temperature
suggested that a 2-m3 sample should yield a total of selenium
in excess of 2 yg. However, with the generator operating at
74°C, higher concentrations were obtained although these
results were lower than expected in view of earlier experi-
ments involving sampling directly from the heated generator.
Average results of the particle-size distribution for the
effluent aerosol generated at 74°C are given in Table 5 for
sample volumes of 2 to 8 m3. The analyses for selenium on
the impactor stages were done by the DAN-fluorometrie method
with the Turner filter fluorometer.
Table 5. PARTICLE-SIZE DISTRIBUTION OF
SELENIUM AEROSOL GENERATOR EFFLUENT
Impactor stage
First
Second
Third
Fourth
Final filter
Particle size,a
ym
>3.2
3.2 to 2.3
2.3 to 1.4
1.4 to 0.43
<0.43
Se,b %
18
10
9
6
57
These size cuts were based on an assumed
, particle density of 3 g/cm3.
These average percentages of Se per stage
were based on sample volumes of 2 to 8 m3
with an average total Se concentration of
1.7 yg/m3.
Because of the negligible amount of selenium collected with
the generator operating at room temperature and the reduced
amount collected with the generator heated to 74°C, it was
suspected that a significant amount of selenium was lost in
the tubing connections between the generator output and the
enclosure for the impactor. However, the results of the
particle-size analysis appeared to substantiate the results
of analyses involving the sampling devices described previ-
ously. Efficiencies of distilled-water bubblers for removing
selenium from the generator effluent were found to be 30 to
60% while untreated glass-fiber filters provided efficiencies
in excess of 90%. In view of the significant percentage
(>50%) of aerosol particles found to be smaller than 0.5 ym,
it is reasonable to assume that most of these small particles
19
-------
were not retained in the midget impinger bubblers and, hence,
the analyses of the bubbler solutions could be expected to be
low. However, glass-fiber filters appeared to collect tne
small particles efficiently and, thus, as the results indi-
cated, yielded efficiencies in excess of 90%. In addition,
the apparent dependence of bubbler efficiency on generator
temperature pointed out in previous experiments can be ratio-
nalized on the basis of these results. If it is assumed that
heating the generator gave rise to enrichment of the smaller
particles, J^.e. , less than 0.5 to 1.0 ym, then bubbler effi-
ciencies would be expected to decrease with this small parti-
cle enrichment; this assumption concurred with experimental
observation.
The usual cumulative distribution plots of percent accumula-
tion in the size cuts versus logarithm of the aerodynamic
particle size were made for the data from the impactor analy-
ses. The curve shapes suggested the possibility of a bimodal
distribution. Although data are lacking for the large
percentage of particles below 0.4 ym, the particle distribu-
tion appeared to have two maxima (MMD), one below 0.4 ym and
one above 2 ym.
DIMETHYL SELENIDE VAPOR GENERATOR
For the evaluation of treated filter materials for their sele-
nium retention properties, a known source of selenium vapor
(with no particulate selenium) was required. For this purpose
the diluted vapor of a liquid organic compound, dimethyl
selenide, was used. This particular organic selenium compound
was chosen not only for its volatility (bp = 58.2°C) and sta-
bility, but also for its biological significance. The expira-
tion of dimethyl selenide into the atmosphere can result from
plant and animal metabolism of ingested selenium compounds.17'11
The source of the dimethyl selenide vapor was a 100-liter
Mylar bag to which a small volume (25 yl) of a dilute solution
(1.38 mg/ml) of dimethyl selenide in methanol was added during
the process of filling the bag with air. The resulting con-
centration of selenium (as Se) in the bag was 250 ng/1.
Various candidate sampling devices were subsequently evaluated
by sampling the contents of the Mylar bag directly.
20
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SECTION VII
LABORATORY EVALUATION OF METHODS OF SAMPLING
FOR SELENIUM IN AIR
In evaluating candidate sampling materials for their selenium
retention properties, the approach was based on the use of
retentive filters for the collection of selenium occurring in
particulate form and chemically treated filters for the col-
lection of selenium occurring in gaseous or vapor form.
Although several reagent solutions were evaluated for use in
impinger bubblers, the conception of the most appropriate
sampling device for field use was a single reagent-impregnated
fibrous filter for collection of total atmospheric selenium.
EVALUATION OF TREATED AND UNTREATED FILTERS
In the initial phases of the study, we investigated the effi-
ciency of extraction of small amounts of selenium from Gelman
Type A glass-fiber filters to which had been added known
quantities of a standard selenium dioxide solution. On
extraction of the filters with either water or a mixture of
nitric and perchloric acids, an amount in excess of about 80%
of the added selenium was routinely recovered. The solutions
were analyzed by the DAN-fluorometric method as outlined pre-
viously. In one set of analyses, the nitric-perchloric acid
extracts were passed through the ion-exchange column as
suggested in the Intersociety Committee Method. Initially,
losses of selenium in the column were found to be as large as
25%, but further experimentation with more efficient column
washing demonstrated the losses to be usually no larger than
10%. Also, it was determined that the filter material itself
was not a source of interference in the selenium determina-
tions. That is, any contribution of selenium from the glass-
fiber material was negligible or below the detectable limit.
Subsequently, several experiments were conducted to determine
the selenium collection efficiency of glass-fiber filters,
cellulose-fiber filters, membrane filters, and glass-fiber
filters impregnated with one of three reagents. The reagents
included lead acetate and two reducing agents—sodium sulfite
and ascorbic acid—that are known to reduce Se(IV) to elemen-
tal selenium.
These particular experiments were conducted with the selenium
aerosol generator, described previously, that was based on
the nebulization of selenium dioxide solutions. It was
21
-------
assumed that the aerosol particles formed consisted initially
of selenious acid, with more or less associated water and a
small proportion of excess nitric acid (the selenium dioxide
in the nebulizer was in dilute nitric acid solution). Ifc wa^
also assumed that after evaporation of the solvent, the parti-
cles were relatively small, perhaps mostly submicron in size,
although the size distribution for this aerosol generator was
not determined.
Thus, glass-fiber filters (Gelman Type A) and Millipore fil-
ters (0.8-ym pore size) were compared for their retention of
aerosol particles from the selenium aerosol generator. The
nebulizer solution containing 0.01% selenium (as Se) was
prepared by dissolving elemental selenium in dilute nitric
acid. First, it was shown that known amounts of standard
selenious acid solutions added to either type of filter were
essentially completely recovered (80%, or more) by extraction
with either water or a nitric-perchloric acid mixture. The
output of the aerosol generator was sampled on 2.54-cm diam-
eter filters at 2 1/min for 10 min. The filters were
extracted with the acid mixture and analyzed by the DAN-
fluorometric method. The glass-fiber filters appeared to be
about twice as effective as the Millipore filters in retaining
the aerosol particles. The significance of this result was
uncertain since the particle-size distribution of the
nebulizer aerosol was not established; however, it did suggest
that a sizable proportion of the aerosol particles were sub-
micron in size, as had been previously assumed.
Cellulose-fiber filters (Whatman No. 42) were also compared
with glass-fiber filters for sampling the output of the gener-
ator. Concentration values (0.03 yg/1) calculated from deter-
mination of selenium collected on the cellulose-fiber filters
were only about 25% of the concentration values found with
glass-fiber filters (0.12 yg/1). Both types of filters were
extracted with dilute nitric acid. The reason for this
unexpected large difference was not clear. However, the
results of these determinations, unlike most of the results
that follow for the impregnated filters, were consistent and
reproducible.
The experiments with impregnated filters were generally less
than satisfactory because of the lack of reproducibility of
the results. The poor reproducibility seemed to be most
likely caused by difficulties in controlling the output of
the nebulizer. There were, however, indications that the
reducing agents, sodium sulfite and ascorbic acid, may have
brought about some reduction of selenious acid to elemental
selenium. The amounts of selenium found on these filters bv
extraction with water and determination by the DAN-
fluorometric method were consistently lower than the amounts
22
-------
found on unimpregnated glass-fiber filters, indicating that
some of the selenium was in a water-insoluble form. However,
the results calculated as concentration of selenium in the
generator output were not reproducible.
There was evidence, also, that lead acetate in the filters
may have reacted with the selenious acid (or selenium dioxide)
in the generator output to form a water-insoluble product.
Concentration values calculated from analyses of the filters
were in some instances lower for lead acetate-impregnated
filters extracted with water than for filters extracted with
dilute nitric acid. This result suggested that an acid-
soluble but water-insoluble product may have been formed.
Also, a small amount of selenious acid added directly to a
lead acetate-impregnated filter was not recovered by subse-
quent extraction with water.
Treated filters were evaluated also by sampling the effluent
of the dry-SeOa generator that was described earlier in this
report. Glass-fiber filters were treated with special solu-
tions of silver nitrate in one case and lead acetate in
another. The treatment solutions were essentially those
described by Natusch et a_l. 19 for treatment of filter mate-
rials for the collection of hydrogen sulfide. All treated
filters were used as back-up filters in tandem arrangements
with untreated glass-fiber filters. The results of the pre-
liminary experiments were somewhat encouraging; these results
are shown in Table 6. The data indicated that the first
untreated filter consistently removed the selenium present in
particulate form, and that the untreated and lead acetate-
treated back-up filters essentially collected no additional
selenium. However, the AgNO3-treated back-up filter appeared
to collect an amount of selenium in excess of the amount in
particulate form retained on the first filter. This tentative
result for the silver nitrate-treated filter suggested that
such a treated filter might be useful for retention of sele-
nium present in the ambient atmosphere in the vapor form.
Also, these data suggested that the dry-selenium dioxide
generator was producing an effluent consisting of selenium
dioxide in both the vapor and particulate forms, contrary to
other indications that the selenium dioxide was essentially
all particulate (see p. 17).
However, after additional experiments of a more diagnostic
nature were conducted, the favorable results first obtained
with the silver nitrate-treated filters were found to be sub-
ject to much uncertainty. The fluorescence readings obtained
for blank silver nitrate-treated filters proved to be highly
variable. Indeed, results obtained with silver nitrate-
treated filters using the dry-selenium dioxide generator as
the source of selenium yielded efficiencies from less than
23
-------
Table 6. SELENIUM RETENTION OF TREATED FILTERS FOR
SAMPLING THE DRY-Se02 GENERATOR EFFLUENT
(PRELIMINARY RESULTS)
Glass-fiber filter treatment
First untreated filter
Second untreated filter
First untreated filter
Second Pb(OAc)a filter
First untreated filter
Second AgNO3 filter
Se retention
(ng/1 of generator effluent)
1.25
<0.1
1.25
<0.1
1.25
1.45
10% to about 70% for selenium retention relative to the first
untreated filter in a tandem arrangement. After several such
analyses, it was concluded that the silver nitrate-treated
filters possessed little, if any, reproducible selenium-
retention capability. A similar result was obtained for
silver nitrate-treated filters used in sampling a dilute
vapor of the organic selenium compound, dimethyl selenide.
The 250-ng/l vapor source of selenium used in these evalua-
tions was the Mylar dilution bag described earlier. The
resulting retention efficiencies of the treated and untreated
filters for dimethyl selenide vapor were essentially the same
and typically less than 5%.
In view of the latter results, it appeared that the initial
conclusions concerning the nature of the effluent from the
dry-selenium dioxide generator were appropriate. That is, no
definitive evidence was found to suggest that the selenium
present in the generator effluent was in any form other than
particulate.
EVALUATION OF ACTIVATED CARBON
Sorbent tubes containing activated carbon were also used in
an effort to collect dimethyl selenide vapor from the Mylar
dilution bag. (The activated carbon was obtained from Mine
Safety Appliances Company and was the product approved by the
National Institute for Occupational Safety and Health for
sampling organic vapors.) However, DAN analyses of samples
obtained in this manner indicated selenium retention effi-
ciencies typically less than 5%. In these experiments, dis-
tilled water was used to desorb the dimethyl selenide from
the carbon. The low result did not necessarily mean that the
24
-------
dimethyl selenide vapor was collected on the carbon with low
efficiency, but it may have been that the overall recovery
process of desorbing and analyzing the selenide had a low
efficiency. This conclusion was supported in part by the
work of Lewis et al.2° on the collection of volatile selenium
compounds expired from plants. These authors demonstrated by
using Se75 in radiotracer experiments that activated carbon
was^effective in retaining volatile selenium compounds. In
addition they found distilled water and 50% aqueous ethanol
to be greater than 90% effective in desorbing the volatile
selenium compound from the carbon. In light of the fact that
our sampling efficiencies were very low with essentially the
same sampling technique, it is probable that after desorption
the selenide was not efficiently oxidized to the +4 oxidation
state that is necessary for reaction with the DAN in the
analytical procedure. The results were essentially the same,
very low, even when the samples were digested in the mixture
of oxidizing acids, nitric and perchloric. However, uncer-
tainties in the digestion treatment included possible losses
of dimethyl selenide by volatilization.
EVALUATION OF BUBBLERS
Because experiments using treated filters, untreated filters,
and activated carbon for sampling the vapor of dimethyl sele-
nide were essentially unsuccessful, subsequent experiments
employed bubblers containing water, dilute nitric acid, or
lead acetate solution for trapping the vapor. These experi-
ments were essentially no more successful than earlier experi-
ments; however, a few meaningful conclusions were drawn from
these experiments with bubblers.
As the data in Table 7 demonstrate, the bubbler solutions
that were digested with an oxidizing acid mixture consistently
had higher values for selenium collection efficiency compared
to the undigested samples, even though all efficiencies were
low. The percent efficiencies were based on a 5-min sample
at a 1 1/min flow rate from a selenium source of 250 ng/1 or
a total theoretical sample of 1.25 yg of selenium. The solu-
tions from the bubblers were analyzed by the usual DAN method
and, although the differences in the percent efficiencies of
the digested and undigested samples appeared small, the dif-
ferences were experimentally significant.
These data suggested that, although the results with the dif-
ferent bubbler solutions were similar, a bubbler could possi-
bly be used for sampling dimethyl selenide with subsequent
digestion with an oxidizing acid and analysis by the DAN
method. The low yields in these experiments were also
25
-------
Table 7. COLLECTION EFFICIENCIES OF BUBBLER
SOLUTIONS FOR (CH3)2Se VAPOR
Bubbler solution
H20
1 N HN03
2% Pb(OAc)2
H20
1 N HNO3
2% Pb(OAc) 2
Digestion step
HNOs/HClOi,
HNOa/HClO^
HNOs/HClO^
None
None
None
Efficiency, %
8
8
8
2
3
1
probably due to losses of dimethyl selenide through its vola-
tility and the inefficient oxidation of dimethyl selenide to
the +4 oxidation state necessary for DAN analysis.
These results also paralleled those of Lewis et aJ.2° in
their radiotracer evaluations of bubbler solutions for sam-
pling volatile selenium compounds. They were not able to
retain significant amounts of selenium in a variety of liquid
media: aqueous solutions of EDTA, KOH, NH^OH, lead acetate,
and KMn04-KOH; sodium ethylate in ethanol; the organic solvent
benzene; and diaminobenzidine (DAB) in hydrochloric acid solu-'
tion.
The choice of the appropriate oxidizing conditions to effect
the necessary oxidation of selenide to selenite on a filter
or in a bubbler is not a straightforward matter. However
such an oxidation would be necessary for the analysis of a
volatile selenide by the DAN method. Dimethyl selenide is
oxidized to dimethyl selenoxide by the common strong oxidiz-
ing agents and to dimethyl selenide dihalide by active halogen
oxidizing agents. Neither of these compounds is likely to
react in significant yields with DAN in the fluorometric
method of analysis. The yield of the reaction of these com-
pounds , or dimethyl selenide itself, with the oxidizing diges-
tion acids to give Se(IV) would also be expected to be low!
Thus, the efficient reaction of dimethyl selenide on a
reagent-impregnated filter surface to give Se(IV) for DAN
analysis does not appear feasible. However, the trapping of
a volatile selenium compound on a solid sorbent with oxidation
and analysis at a later time appears to be an avenue for fur-
ther investigation.
In conjunction with the evaluation of bubbler solutions for
the retention of dimethyl selenide vapor, bubbler solutions
were also tested for retention of selenium in particulate
form. Using the effluent of the dry-selenium dioxide
26
-------
generator, evaluations were conducted on aqueous bubbler solu-
tions containing 10% lead acetate (suggested by the work of
Pillay et al.2:) , 2% AgNO3, 0 .1 M HNO3, or distilled water.
The results of the selenium analyses conducted on these
bubbler solutions after exposure to the generator effluent
are presented in Table 8. The most significant result
appeared to be the high efficiency of the dilute nitric acid
bubbler relative to the others. Also, it was significant
that the lead acetate bubbler performed poorly. These results
suggested that a dilute acid solution would be most appropri-
ate for use in a back-up bubbler for the sampling of ambient
atmosphere for selenium.
Table 8. RETENTION OF SELENIUM FROM THE DRY-Se02
GENERATOR BY VARIOUS BUBBLER SOLUTIONS
Bubbler solution
Concn of Se in generator effluent,
as indicated by analysis of the
bubbler solutions, ng/1
Distilled H20
0.1 M HNO 3
2% AgNO3
10% Pb(OAc)2
3.8
5.6
1.2
<0.2
27
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SECTION VIII
SELENIUM SAMPLING OF THE AMBIENT ATMOSPHERE
AND INVESTIGATION OF THE CHEMICAL FORMS
OF ATMOSPHERIC SELENIUM
In a preliminary evaluation of the Intersociety Committee DAN
procedure for analysis of atmospheric particulate material,
25-hr samples were collected on glass-fiber filters in a high-
volume sampler and were briefly digested with nitric and
perchloric acids and analyzed. Values for selenium concentra-
tions of 4.6, 5.1, 3.9, and 6.8 ng/m3 were obtained at various
times. These results were similar to those reported in the
literature for selenium concentrations found in other parts
of the country. Pillay, for example, found concentrations of
total selenium in the range of 3 to 9 ng/m3.21 Others have
found similar small concentrations.22"26
WATER-SOLUBLE AND WATER-INSOLUBLE SELENIUM IN PARTICULATE
MATERIAL
The analysis of atmospheric particulate samples was explored
further on other occasions. Samples from the ambient atmo-
sphere outside the laboratory were collected on 20.3- by
25.4-cm (8- by 10-in.) glass-fiber filters with a high-volume
sampler. One sample was cut into several squares of known
area. Individual squares were extracted with either water or
a mixture of nitric and perchloric acids. Prior to analysis
by the DAN-fluorometric method, some of the extracts were
passed through an ion-exchange column to remove impurities
and others were not. Water extracts analyzed directly without
the ion-exchange treatment showed strong effects of interfer-
ences and did not give the normal fluorescence spectrum of
the DAN piazselenole. Water extracts treated by ion-exchange
gave more nearly normal spectra, showing the effects of remov-
ing interfering substances. A blank portion of the filter
extracted with water gave a normal low relative fluorescence
intensity, indicating that the interfering substances were
present in the atmospheric particulate material and not in
the filter material. The atmospheric concentration of sele-
nium estimated from these results for this particular sample
was 0.36 ng/m3.
Acid extracts analyzed directly without the ion-exchange
treatment gave more nearly normal spectra than the water
extracts and an estimated selenium concentration value of
28
-------
0.93 ng/m3. With the ion-exchange treatment, a concentration
value of 0.65 ng/m3 was obtained. Previous results with stan-
dard solutions of selenious acid indicated that as much as
25% of the selenium could be lost in the ion-exchange treat-
ment if extreme care were not exercised.
The results of these experiments indicated that a portion of
the selenium in the atmospheric particulate material was solu-
ble in water and that acid treatment was required for the
dissolution of a substantial additional portion. Thus, the
selenium apparently occurred in at least two different states
of chemical combination. These forms of particulate selenium
were most probably selenium dioxide (or selenious acid depend-
ing on the amount of moisture present) and elemental selenium.
The selenium dioxide (or selenious acid) would have been
readily soluble in water yielding Se(IV) in solution, but
elemental selenium would have required acid dissolution to
give Se(IV) in solution for reaction with DAN. If it is
assumed that the element and the dioxide were the only chemi-
cal forms of particulate selenium, as the data indicate, then
it can be tentatively concluded from the analyses that each
contributed approximately equally to the total selenium
associated with the particulate material.
ATMOSPHERIC SAMPLING WITH FILTERS AND BUBBLERS
In additional experiments, untreated glass-fiber filters and
distilled-water bubblers of the gas-dispersion type were
employed for collecting ambient air samples. The samples
were taken over a 6-day period within a laboratory open to a
continuous flow of ambient air. During this period the aver-
age total particulate concentration was determined to be
approximately 60 yg/m3. The sample volumes ranged from 43 to
51 m3. All samples were treated with a moderate HNOa/HClCH
(10:1) digestion step prior to routine analysis. Results of
the DAN-fluorometric analyses for the selenium content of
these atmospheric samples are presented in Table 9. These
results, in general, paralleled those obtained with the dry-
SeOa generator; however, the high value for selenium retained
on glass-fiber filters following the distilled-water bubblers
was unexpected. It could be that the conditions of high
humidity following the bubblers contributed to the increased
efficiency of the glass-fiber filters for removal of atmo-
spheric selenium. Consequently, this particular result was
in contrast to results of similar experiments conducted with
the dry-selenium dioxide generator. In those experiments
filters following bubblers retained relatively small amounts
of selenium even though the bubbler efficiency was low.
29
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Table 9. SELENIUM CONTENT OF
AMBIENT ATMOSPHERIC SAMPLES
Sampling medium
Glass-fiber filter
Second filter in tandem filters
Distilled water bubbler
Filter following a bubbler
Second filter in tandem filters
Se found,
ng/m3
1.2
0.2a
0.7
2.3
0.7
This value is uncertain because of its proxim-
ity to the blank.
SELENIUM ANALYSIS OF SIZED ATMOSPHERIC PARTICULATE MATERIAL
From the data in Table 9, the total atmospheric selenium con-
centration during this particular sampling period was esti-
mated to be 3 ng/m3. The selenium content of the particulate
matter was estimated by analysis to be 20 yg/g. These results
agree favorably with similar analyses reported in the litera-
ture. In particular, a recent publication by Natusch et al.27
suggested that several toxic elements, including selenlumT"
were preferentially concentrated into the smallest airborne
particles of fly ash derived from coal-fired power plants.
Natusch's selenium analyses by atomic absorption spectrometry
ranged from 11 to 59 yg/g for airborne fly-ash particle sizes
from 11.3 to 1.1 ym, respectively.
A similar experiment was conducted in this laboratory to
determine whether or not such a preferential concentration of
selenium in small particles exists for ambient atmospheric
particulate matter. To facilitate this study we employed an
Andersen cascade impactor which provided nine size cuts
(eight stages and a final filter) over a particle-size range
of 0.4 to 10 ym. The particulate matter on each stage was
weighed and analyzed for selenium in the usual manner.
Table 10 shows the results of the measurements. During the
sampling period the average total particulate concentration
was approximately 41 yg/m3 for a sample volume of 700 m3
The particle-size distribution was found to be log-normal
with a mass median diameter (MMD) of approximately 1 ym.
Although the results of the selenium analyses appeared some-
what uncertain because of the low value for the 0.95-to-1.8 ym
size cut, one can conclude that this experiment was not posi-
tive evidence for the phenomenon of preferential concentration
of selenium into the smaller particles (<0.5 ym) of the
30
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Table 10. ANDERSEN CASCADE IMPACTOR SAMPLING
OF THE AMBIENT ATMOSPHERE
_ Stage
0
1
2
3
4
5
6
7
Filter
Size,a ym
>10
6.4 to 10
4.3 to 6.4
2.9 to 4.3
1.8 to 2.9
0.95 to 1.8
0.57 to 0.95
0.38 to 0.57
<0.38
Particulate
weight per stage
(% of total)
10.5
7.2
6.5
7.2
9.2
11.2
11.8
19.7
16.5
Se content
per stage
(% of total)
<5
<5
<5
<5
35
<5b
40
7
<5
flow rate was 25 1/min at 25°C for these size cuts.
This result is uncertain.
ambient atmospheric aerosol. In contrast to the preferential
concentration phenomenon as cited by Natusch,27 the present
results tentatively suggest that the selenium in a multisource
atmospheric aerosol may be most abundant in particle sizes
close to the MMD.
BACKGROUND LEVEL OF ATMOSPHERIC SELENIUM
Other analyses of high-volume atmospheric samples revealed a
significant difference between the selenium content of the
particulate material in a heavy industry area and that in a
less polluted area. An air sample taken in an area of moder-
ate particulate concentration (on the Institute premises) was
found to have a selenium content corresponding to 2.0 ng/m3.
The average total particulate concentration of this sample
was 44 yg/m3. From these figures the selenium content of the
particulate matter was calculated to be 47 yg/g. However,
analysis of a sample taken in an area of heavy industry (North
Birmingham) gave a result of 2.6 ng/m3 for selenium concentra-
tion when the average particulate concentration was 350 yg/m3.
These figures suggested an average selenium content of
7.4 yg/g in the ambient particulate matter in this area.
Thus, it appears that the industry in this area of high par-
ticulate pollution is not a source of atmospheric selenium.
It is probable that the selenium content of the ambient atmo-
sphere in this area is simply the background amount that is
present in the urban Birmingham atmosphere.
31
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DETERMINATIONS OF Se(VI) WITH DAN
In further efforts to characterize the chemical forms in
which selenium occurs in the ambient atmosphere, a question
arose concerning the applicability of the DAN-fluorescence
method of selenium analysis to the determination of selenium
in the +6 oxidation state. Because the necessary oxidation
state for DAN analysis is + 4, it was considered important to
determine if the method described by the Intersociety Commit-
tee for the selenium analysis of atmospheric particulate
matter would account for any selenium present as selenate.
Thus, experiments were conducted in our laboratories with
known Se(VI) solutions (weighed as Na2Se04) treated with the
usual HN03/HC104 (10:1) digestion step, and subsequently ana-
lyzed by the DAN method. The results of these experiments
are presented in Table 11. These results demonstrated that
known Se(VI) solutions analyzed in the conventional manner
gave essentially no indication of any selenium content; how-
ever, a known solution of Se(IV) analyzed simultaneously gave
the expected result. Therefore, the results of a selenium
analysis of a particulate sample containing selenate would
have been expected to be low by the DAN method as it existed
at that time. Consequently, additional experiments were
directed toward finding a suitable reducing agent to incorpo-
rate in the DAN procedure. The proper reducing agent would
ensure that all of the soluble selenium present as selenate
would be reduced to selenite (Se(IV)) for reaction with DAN.
A desirable reducing agent would also be compatible with the
HNOs/HClOit digestion mixture used to oxidize any elemental
selenium that might be present in the particulate sample to
Se(IV). The utility for this purpose of a hydrochloric acid
digestion subsequent to the HN03/HC10it digestion was suggested
by an article on the Se(IV)/Se(VI) electrochemical couple.28
It was indicated in this study that the oxidation of Se(IV)
to Se(VI) could be effected in aqueous solution with chlorine
and that Se(VI) could in turn be reduced to Se(IV) by treat-
ment with concentrated hydrochloric acid. Thus, a hydro-
chloric acid digestion step was incorporated in the analysis
of known Se(VI) solutions by the DAN method. These results
are also contained in Table 11. It was concluded that the
hydrochloric acid digestion was effective in quantitatively
reducing Se(VI) to Se(IV) for the DAN analysis. The final
group of results in Table 11 indicate that the simultaneous
determination of Se(IV) and Se(VI) was successful when the
additional hydrochloric acid digestion was used but not when
only the conventional HNOa/HClO.* digestion was used. In the
latter case, only the selenium added as Se(IV) was determined
and not the Se(VI). As a result of these findings, we
included the hydrochloric acid digestion step in subsequent
analyses of atmospheric particulate samples.
32
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Table 11. EFFECT OF DIGESTION TREATMENT ON THE
DETERMINATION OF SELENIUM BY THE DAN METHOD
__ Sample
Se(IV) (control)
Se(VI)
Se(VI)
Se(VI)
Se(IV) (control)
Se(VI)
Se(VI)
Se(VI)
Se(IV) (control)
Se(IV) + Se(VI)
Se(IV) + Se(VI)
Amount of Se
taken, yg
1.00
1.00
0.75
0.50
1.00
1.00
0.75
0.50
1.00
0.5 + 0.5
0.5 + 0.5
Amount of Se
found, yg
0.97
<0.02
<0.02
<0.02
0.94
0.95
0.73
0.52
0.96
0.97
0.50
Digestion
treatment
HNOa/HClO.*
HN03/HC10.+
HNOs/HClO.*
HNOs/HClOit
HC1
HC1
HC1
HC1
HaO only
HNOa/HClOit/HCl
HN03/HCKK only
ANALYSIS OF ATMOSPHERIC PARTICULATE MATERIAL FOR Se(VI)
These findings also suggested a means of estimating the rela-
tive amount of selenium present in a particulate sample as
Se(VI). Consequently, we conducted selenium analyses of atmo-
spheric particulate samples with and without the hydrochloric
acid digestion step in an effort to determine whether Se(VI)
was present in the samples. Although a limited number of
determinations were made for this comparison, the results
with the hydrochloric acid digestion step were not signifi-
cantly different from those obtained without it; that is, the
results of both methods agreed within the experimental repro-
ducibility (2.0 ± 0.5 ng/m3). On the basis of these limited
findings, therefore, we may conclude that Se(VI) (as selenate)
is not a primary form of atmospheric selenium.
ACCIDENTAL OXIDATION OF SELENIUM IN PARTICULATE MATERIAL TO
Se(VI)
Particulate samples on glass-fiber filters that were treated
with an extended HClOij/HNOa digestion step and no hydrochloric
acid digestion step appeared to contain essentially no sele-
nium by conventional DAN analysis. However, an identical
sample treated in the same manner but with the incorporation
of the hydrochloric acid digestion step yielded the expected
amount of selenium (^1.5 ng/m3). The extended HClOu/HNOs
digestion step was characterized by the complete bleaching
and dissolution of the initially black atmospheric particulate
33
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matter by repeated heating to dense fumes of perchloric acid
and to near dryness, whereas the usual HClO^/HNOa digestion
did not always result in complete dissolution of the particu-
late material because the samples were not taken to dense
fumes of perchloric acid. It appeared that such rigorous
oxidizing conditions may have oxidized all the selenium pres-
ent in oxidation states lower than +6 to Se(VI). Subsequently,
the sample treated with the hydrochloric acid digestion step
gave the expected result because all the selenium that was
previously oxidized to Se(VI) was reduced by the hydrochloric
acid to Se(IV), the oxidation state appropriate for DAN
analysis.
These apparently low results obtained in the case of an
extended digestion with nitric and perchloric acids have been
interpreted by other workers29'30 to be due to losses of sele-
nium by volatilization. The present results, however, suggest
that the selenium was not lost at all but that it was simply
oxidized to a form inappropriate for DAN analysis. Thus, the
inclusion of a hydrochloric acid digestion step not only
allows DAN determination of Se(VI), but it also minimizes the
probability of low results due to over-oxidation in the
HClCU/HNOs digestion step.
34
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SECTION IX
CONCLUSIONS CONCERNING THE NATURE OF
ATMOSPHERIC SELENIUM
The statement is made in the description of the "Tentative
Methods of Analysis for Selenium Content of the Atmospheric
Particulate Matter" that "selenium may exist in the atmosphere
most^probably as the element, the oxide, or as the sele-
nite".11* it is also stated that hydrogen selenide is likely
to have a short lifetime because, like hydrogen sulfide, it
is rapidly oxidized in air.
A similar conclusion can be drawn from the experimental evi-
dence presented in this report. The present results indicate
that the selenium contained in particulate matter consists of
approximately equal amounts of water-soluble and water-
insoluble forms of selenium. These forms are most likely
elemental selenium as the water-insoluble form and selenium
dioxide (or selenite) as the water-soluble form. Results of
experiments designed to indicate the presence of Se(VI)
failed to establish selenate as a component of atmospheric
aerosols.
Results of experiments with the dry-selenium dioxide generator
suggested that little or no selenium dioxide would exist as a
true vapor in an ambient atmosphere. Indeed, it appears
likely that atmospheric selenium dioxide exists as, or is
associated with, particulate matter. These results also indi-
cated that conventional particulate sampling would be suffi-
cient for atmospheric selenium dioxide sampling with negligi-
ble losses due to volatilization. Experimental results also
demonstrated the greater efficiency of glass-fiber filters
relative to distilled-water bubblers for sampling the effluent
of the dry-selenium dioxide generator. These observations
and conclusions contradict statements by West as quoted in a
recent article by Pupp e_t al. 3 l West reported that gross
sampling errors would occur for selenium dioxide if only
particulate sampling was employed. Also, West suggested that
bubblers filled with water are highly efficient samplers of
selenium dioxide.
Pupp et al.3 1 also reported a few measurements on the equilib-
bium vapor concentration of selenium dioxide. The method
employed for the measurement was a weight-loss Knudsen system,
which assumes a weight loss occurs because of the effusion of
a vapor through an orifice. The values reported by Pupp
35
-------
agree, in general, with the concentrations found in the
effluent of the dry-selenium dioxide generator employed in
this study. However, in the present work, it was found that
the selenium dioxide existed almost entirely in an aerosol
form and not in the expected vapor form.
Because the burning of fossil fuels, coal in particular, has
been cited as the largest source of atmospheric selenium,4
the chemical form of selenium emitted in this process is
likely to be the predominant selenium species present in an
ambient atmospheric aerosol. Recent studies have indicated
that the selenium present in the effluent of a coal-burning
power plant is exclusively in the elemental state.32 It was
suggested in these studies that the elemental selenium
resulted from the reduction of selenium dioxide (or selenious
acid) by sulfur dioxide. Also, it was determined that greater
than 90% of the emitted selenium existed in the vapor phase.
This result was observed in the case of a coal-burning steam
plant with electrostatic precipitators that gave a fly-ash
removal efficiency in excess of 99.5%.
However, it is possible, perhaps likely, that the elemental
selenium vapor released from power plant stacks is converted
rapidly to particulate form—by condensation or adsorption,
or by some other process. This view was also presented by
Weiss et al.3 3 who studied selenium-to-sulfur ratios in dated
Greenland ice cores and found that sulfur has increased con-
siderably during recent times, whereas, selenium has remained
fairly constant. Such results suggest that atmospheric sele-
nium is particulate in nature and that input of elemental
selenium vapor into the environment should be a local effect.
The manufacture of glass has also been pointed out as a sig-
nificant source of atmospheric selenium.k At one location
where large quantities of colored structural plate glass are
produced, the stack effluent was analyzed. The stack efflu-
ent analysis showed that a large part of the metallic sele-
nium used in the batch composition was volatilized during
melting, and consequently appeared in the effluent as red,
amorphous selenium metal. The particle size was reported to
be less than 0.35 ym.1*
The possibility of organic selenium compounds being present
in the ambient atmosphere must at least be considered because
of the metabolic fate of selenium ingested by both plants and
animals. The volatile organic compound, dimethyl selenide,
is an example of a selenium compound known to be a metabolic
product expired by plants and animals.17'18 Although this
compound is one of the most probable forms of airborne organic
selenium, the contribution of dimethyl selenide or any organic
selenium compound to total atmospheric selenium in an urban
36
-------
nvironment is likely to be very small. Indeed, no evidence
r the presence of an organic selenium vapor—or any signif-
1?a^t selenium vapor, for that matter—was obtained in this
study. However, it should be pointed out that concentrations
o elemental selenium vapor could have been underestimated in
tnis investigation. Although the data of Pillay et al.21'34
suggested that approximately 50% of atmospheric selenium is
in a vapor form, bubblers used in the present study for atmo-
spheric sampling indicated in one case a maximum of 20% sele-
nium present in the vapor form.
Thus, it appears that the selenium present in the ambient
atmosphere exists predominantly as, or in association with,
particulate matter, and that atmospheric selenium is most
likely in the chemical form of the element and the dioxide
(or selenite).
37
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1. Documentation of the Threshold Limit Values for Sub-
stances in Workroom Air. Third Edition. Cincinnati,
Ohio, American Conference of Governmental Industrial
Hygienists, 1971. p. 224-225.
2. Stahl, Q. R. Air Pollution Aspects of Selenium and Its
Compounds. Litton Systems, Inc. Bethesda, Md. Con-
tract Number PH-22-68-25. Department of Health, Educa-
tion and Welfare. September 1969. 88 p.
3. Johnson, J. Determination of Selenium in Solid Waste.
Environ. Sci. Technol. 4_(K>_) : 850-853, October 1970.
4. National Inventory of Sources and Emissions: Selenium—
1969. W. E. Davis & Associates. Contract Number 68-
02-0100. Report prepared for the Environmental Protec-
tion Agency. Research Triangle Park, N. C. Publication
Number APTD-1130. April 1972. 50 p.
5. Talmi, Y., and A. W. Andren. Determination of Selenium
in Environmental Samples Using Gas Chromatography with
a Microwave Emission Spectrometric Detection System.
Anal. Chem. 4_6 :2122-2126, 1974.
6. West, P. E., and T. V. Ramakrishna. A Catalytic Method
for Determining Traces of Selenium. Anal. Chem. 40:966-
968, May 1968.
7. Shendrikar, A. D., and P. W. West. Determination of
Selenium in the Smoke from Trash Burning. Environ.
Letters. 5_U) : 29-35 , 1973.
8. West, P. W., S. L. Sachdev, and A. 0. Shendrikar. Sele-
nium in Papers, Cigarette Papers and Tobaccos. Environ.
Letters. 2_(£) : 225-238 , 1972.
9. Nakashima, S., and K. Toei. Determination of Ultramicro
Amounts of Selenium by Gas Chromatography. Talanta
15_:1475-1476, 1968.
10. Shimoishi, Y. , and K. Toei. Gas-Chromatographic Deter-
mination of Ultramicro Amounts of Selenium in Pure Sul-
furic Acid. Talanta. 17^165-168, 1970.
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11• Shimoishi, Y. Gas-Chromatographic Determination of
Ultramicro Amounts of Selenium in Pure Tellurium Metal.
Bull. Chem. Soc. Japan. £4_: 3370-3372, 1971.
12• Shimoishi, Y. The Determination of Selenium in Sea
Water by Gas Chromatography with Electron-Capture Detec-
tion. Anal. Chim. Acta. 6^:465-468, 1973.
13. Young, j. w. , and G. D. Christian. Gas-Chromatographic
Determination of Selenium. Anal. Chim. Acta. 65:127-
138, 1973.
14. Methods of Air Sampling and Analysis. Washington, D. C.
American Public Health Association, Inc., 1972. p. 316-
321.
15. Parker, C. A., and L. G. Harvey. Luminescence of Some
Piazselenols: A New Fluorimetric Reagent for Selenium.
Analyst. ^7:558-565, 1962.
16. Hodgman, C. D., Editor. Handbook of Chemistry and
Physics, 44th Edition. Cleveland, The Chemical Rubber
Publishing Company, 1961. p. 2441.
17. Martin, J. L. Selenium Compounds in Nature and Medi-
cine. B. Selenium Assimilation in Animals. In:
Organic Selenium Compounds: Their Chemistry and
Biology, Klayman, D. L. , and W. H. H. Giinther (ed. ) .
New York, John Wiley & Sons, Inc., 1973. p. 674-675.
18. Shapiro, J. R. Selenium Compounds in Nature and Medi-
cine. C. Selenium and Human Biology. In: Organic
Selenium Compounds: Their Chemistry and Biology,
Klayman, D. L. , and W. H. H. Giinther (ed.). New York,
John Wiley & Sons, Inc., 1973. p. 704-707.
19. Natusch, D. F. S., J. R. Sewell, and R. L. Turner.
Determination of Hydrogen Sulfide in Air—An Assessment
of Impregnated Paper Tape Methods. Anal. Chem. 46:410-
415, March 1974.
20. Lewis, B. G., C. M. Johnson, and C. C. Delwiche.
Release of Volatile Selenium Compounds by Plants. Col-
lection Procedures and Preliminary Observations. J.
Agr. Food Chem. 14. (6_) : 638-640 . 1966.
21. Pillay, K. K. S., C. C. Thomas, Jr., and J. A. Sondel.
Activation Analysis of Airborne Selenium as a Possible
Indicator of Atmospheric Sulfur Pollutants. Environ.
Sci. Technol. 5_U) : 74-77, January 1971.
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22. Hashiomoto, Y., and J. W. Winchester. Selenium in the
Atmosphere. Environ. Sci. Technol. 1_(4) : 338-340 ,
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23. John, W., R. Kaifer, K. Rahn, and J. J. Wesolowski.
Trace Element Concentrations in Aerosols from the San
Francisco Bay Area. Atmos. Environ. 7_: 107-118, 1973.
24. Gray, D., D. M. McKown, M. Kay, N. Eichor, and J. R.
Vogt. Determination of the Trace Element Levels in
Atmospheric Pollutants by Instrumental Neutron Activa-
tion Analysis. I.E.E.E. Trans. Nucl. Sci. 19 (1) ;194-
198, 1972.
25. Hashiomoto, Y., J. Y. Hwang, and S. Yanagisawa. Possi-
ble Source of Atmospheric Pollution of Selenium.
Environ. Sci. Technol. 4_(2_) : 158-158, February 1970.
26. Pillay, K. K. S., C. C. Thomas, Jr., and J. W.
Karminski. Neutron Activation Analysis of the Selenium
Content of Fossil Fuels. Nucl. Appl. Technol. 7.(5_) :
478-483, 1969.
27. Natusch, D. F. S., J. R. Wallace, and C. A. Evans, Jr.
Toxic Trace Elements: Preferential Concentration in
Respirable Particles. Science. 183;202-204, January
1974.
28. Sherrill, J. S., and E. F. Izard. The Reduction Poten-
tial of Selenous Acid and the Free Energy of Aqueous
Selenic Acid. J. Am. Chem. Soc. _50^1665-1675, 1928.
29. Passwater, R. A. Fluorometric Analysis of Selenium.
Fluorescence News. ]_(2) : 11-15, April 1973.
30. Lott, P. F., P. Cukor, G. Moriber, and J. Solga. 2,3-
Diaminonaphthalene as a Reagent for the Determination
of Milligram to Submicrogram Amounts of Selenium. Anal.
Chem. 35^1159-1163, August 1963.
31. Pupp, C., R. C. Lao, J. J. Murray, and R. F. Pottie.
Equilibrium Vapour Concentrations of Some Polycyclic
Aromatic Hydrocarbons, AsuOe and SeOa and the Collection
Efficiencies of These Air Pollutants. Atmos. Environ
£:915-925, 1974.
32. Andren, A. W. , Y. Talmi, D. H. Klein, and N. E. Bolton..
Physical and Chemical Characterization of Selenium in
Coal-Fired Steam Plant Emissions. Submitted for publi-
cation. September 1974.
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Weiss, H. V., M. Koide, and E. D. Goldberg. Selenium
and Sulfur in a Greenland Ice Sheet: Relation to
Fossil Fuel Combustion. Science. 172;261-263, 1971.
Pillay, K. K. S., and C. C. Thomas, Jr. Determination
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by Neutron Activation Analysis. J. Radioanal. Chem.
1:107-118, 1971.
41
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
DEPORT NO.
EPA 650/2-74-124
3. RECIPIENT'S ACCESSIOWNO.
4. TITLE AND SUBTITLE
5. REPORT
Development of a Sampling Method for Total
Atmospheric Selenium
CODE
. Barrett
Herbert C. Miller
8. PERFORMING ORGANIZATION REPORT NO.
SORI-EAS-74-353
Project 3128 - XIII
I. PERFORMING ORGANIZATION NAME AN.O ADDRESS
Engineering and Applied Sciences Department
Southern Research Institute
2000 Ninth Ave. South
Birmingham, Ala. 35205
10. PROGRAM ELEMENT NO.
1AA010
11. CONTRACT/GRANT NO.
68-02-1220
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, NERC
Research Triangle Park,
13. TYPE OF REPORT AND PERIOD COVERED
Final. June 1973/May 1974
C. 27711
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The primary purposes of this contract were to develop a collection technique
for the quantitative collection of total atmospheric selenium and to characterize
the forms in which selenium occurs in the atmosphere.
Retentive filters were used to collect particulate material containing selenium;
chemically treated filters for the collection of gaseous or vaporous selenium were
evaluated. Laboratory generators were setup for the evaluation of filter materials.
The 2,3-diaminonaphthalene (DAN) fluorometric method was established as the primary
analytical technique to determine selenium. Air particulate samples were analyzed
for selenium and procedures were studied for determining relative amounts of
selenium present in different oxidation states. Selenium aerosol and vapor
generators were set up, characterized and used to evaluate other sampling devices.
Selenium appears to be present in ambient air predominantly as or with
particulate matter; thus it was tentatively established that conventional particulate
sampling suffices to collect the bulk of atmospheric selenium. Selenium vapors
appear to make negligible contributions to total atmospheric selenium; however,
concentrations of elemental selenium could have been underestimated.
The most probable chemical forms of atmospheric selenium were determined to be
the element and the dioxide (or selenite).
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Particulate Sampling
Selenium Sampling and Analysis
Selenium - Vapor and Aerosol
Ambient Air Selenium
Fluorometry with
2,3-diaminonaphthalene
Methylene Blue Method
Gas Chromatography
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
47
!0. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
42
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